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PhD (Occupaional Hygiene), North-West University, Potchefstroom Campus Background: Outdoor agricultural workers such as farmers and farmworkers have been identified as an occupational group that is at high risk of exposure to solar ultraviolet radiation (UVR) during their work activities. Outdoor workers’ exposure to solar UVR need to be managed to prevent negative health effects such as skin cancer and ocular diseases. Skin colour and melanin content of skin provides a measure of genetic protection against exposure to high levels of solar UVR. Photoprotective measures such as wearing long sleeve clothing, broad-brimmed hats and sunglasses have been identified as measures that can reduce an individual’s exposure to solar UVR if used correctly. The solar UVR exposure of outdoor farmworkers has not previously been investigated in South Africa. Aims and objectives: The general aim of this thesis was to quantify the differences in skin colour and melanin content of facultative and constitutive skin of farmworkers on a macadamia nut and avocado farm in the Limpopo Province of South Africa, as well assessing the existing control measures and practices of those farmworkers together with their occupational exposure to solar UVR to determine if the exposure poses a risk to their health. The specific objectives were: (i) to determine the differences in skin colour (individual typology angle, ITA°) and melanin content (melanin index, MI) between the facultative and constitutive skin of farmworkers using skin bioengineering measurements, (ii) to assess the solar UVR practices, in particular the use of ocular protective measures, of the farmworkers on the farm using questionnaires, (iii) to determine the photoprotection provided by the clothing worn by farmworkers using polysulphone (PSF) badges on the shoulder both under and on top of the clothing and (iv) to assess the personal solar UVR exposure of outdoor farmworkers on the farm during autumn, spring and summer while carrying out their different work activities through polysulphone badges placed on their arms, top of the shoulder and top of any head covering worn. Methods: Outdoor and indoor farmworkers on the farm participated in this study. The skin colour and melanin content of the skin of farmworkers were classified using both a subjective method, namely questionnaires and objective methods namely measurement of ITA°) and MI. Outdoor farmworkers’ use of ocular photoprotective measures was determined with the use of a questionnaire. The photoprotection provided by the clothing worn by farmworkers was measured by placing a PSF badge on the shoulder beneath the clothing and on the outside of clothing and classified according to the requirements of the AS/NZS 4399:2017 standard. The solar UVR exposure of outdoor and indoor farmworkers was measured by placing PSF badges on the shoulder, arm and top of the head during autumn, spring and summer during different work activities. Workers’ exposure was compared with the highest value of the International Commission of Illumination (CIE) occupational exposure limit, namely 1.3 SED (standard erythemal dose). Research ethics approval for this study was obtained from the North-West University Health Research Ethics Committee (NWU-00101-17-A1). Results: Significant differences were found between both the ITA° and MI measured on the constitutive (inner upper arm) skin and facultative (back of the hand) of farmworkers. The skin colour of the majority of farmworkers were objectively classified as falling in the Fitzpatrick Phototype V/Brown. A strong correlation was found between ITA° and MI which indicates that both objective methods are appropriate to determine the skin colour of darkly-pigmented skin. The majority of outdoor farmworkers (80%) never wore sunglasses while working outside. Although more than 70% of outdoor farmworkers wore a hat while working, they preferred to wear a cap rather than a broad-brimmed hat which provides better ocular photoprotection. Statistically significant differences were found between the solar UVR underneath and outside of clothing worn by farmworkers during autumn, spring and summer. Only 5% of clothing did not provide the minimum required photoprotection. More than 75% of farmworkers reported that they removed the long sleeve overall jacket they wear as part of their uniform at some point during the day which exposes their arms to solar UVR. Statistically significant differences were found between the solar UVR measured on the shoulder, arm and top of the head of outdoor farmworkers during spring and summer. The arm received the highest solar UVR exposure during autumn (7.8 SED) while the top of the head received the highest levels during spring (11.6 SED) and summer (13.9 SED). The solar UVR exposure of all body sites exceeded the daily CIE exposure limit for more than 80% of measurements during all three seasons. Conclusion: Skin colour and melanin content of farmworkers in this study was found to provide a high level of genetic photoprotection. It was also found that objective and subjective measurement of skin colour and can both be used to classify the skin colour of an occupational group in order to identify genetic photoprotection in workers. The use of ocular photoprotective measures by the outdoor farmworkers in this study was inadequate. The clothing worn by farmworkers in the study provided sufficient photoprotection, but removal of clothing during the day decreased its effectivity. The exposure of farmworkers to solar UVR exceeded the recommended CIE exposure limit during not only summer, but autumn and spring as well which indicates that photoprotective measures should not only be in use during summer but also during the other two seasons. The solar UVR exposure of the outdoor farmworkers included in our study was generally higher than the exposure of farmers and farmworkers in other countries. Finally, ten recommendations are made to the macadamia nut and avocado farm to reduce farmworkers’ exposure to solar UVR. Limitations of this study were also Doctoral

MHSc (Occupational Hygiene), North-West University, Potchefstroom Campus Background: During the processing and refining of platinum (Pt), workers are exposed to respiratory sensitizing platinum salts. The most toxic of these platinum salts are tetra- and hexachloroplatinate, especially when attached to potassium. Although multiple researches have associated the respiratory exposure route with the development of respiratory sensitization to platinum salts, the notion of an additional dermal route of exposure was suggested. This notion was suggested due to active dermal exposure to these platinum salts in many instances and the high sensitization occurrence during low levels of respiratory exposure. Dermal exposure has previously been associated with the development of respiratory sensitization in animal studies Subsequent in vitro studies investigated the permeation of potassium tetrachloroplatinate through intact abdominal skin and substantiated the plausibility of the dermal route of exposure contributing to platinum absorption. However, the more toxic sensitizer, potassium hexachloroplatinate has not been investigated regarding its permeation profile. Aims and objections: In vitro laboratory experiments were conducted to investigate the permeation profile of potassium hexachloroplatinate (K₂PtCl₆) through full thickness human abdominal skin. The research objectives were to quantify the permeation of potassium hexachloroplatinate by utilizing the static Franz diffusion cell method, to calculate the percentage of platinum retained in the skin, and lastly, to evaluate the effect of exposure duration on the permeation of platinum at 8-, 12- and 24-hour intervals. Methods: Intact abdominal skin from Caucasian female donors, aged between 41 and 48, were obtained after abdominoplasty procedures following ethics approval and informed consent. Utilizing the Franz diffusion compartment methodology, the permeation of 0.3 mg/mL K₂PtCl₆ was quantified at time intervals of 2-, 4-, 6-, 8-, 10-, 12-, 14-, and 24-hours after the onset of the experiment. After the 24-hour extraction, the skin was digested and analyzed by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), quantifying the penetrated platinum mass inside the skin. Whereas the permeated platinum mass in the receptor solution was quantified by the means of Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Blank cells not containing the platinum salt, were used for quality control purposes. Results: Platinum permeation, increasing with the continued duration of exposure, occurred through the intact full thickness female Caucasian abdominal skin. The influence of time on permeation was significantly indicated by the 68 % increase in dermal absorption between 8 and 12 hours, and 62 % increase between 12 and 24 hours. The dose percentage of platinum mass contained in the skin after 24-hours was calculated as 3.11 ± 0.25 % (8848.03 ± 699.02 ng). Flux and lag time were calculated as 0.32 ± 0.05 ng/cm²/h and 2.26 ± 0.31 hours, respectively. Conclusion: With the results all aims and objectives were achieved. Results indicating a considerable platinum reservoir forming in the skin together with the short lag time implicated that continuous real-world permeation may occur adding to the body burden of platinum even after removal from the source of exposure. The presence of detectable levels of platinum mass in the receptor fluid at the 2-hour interval further suggested that even short periods of exposure to potassium hexachloroplatinate presents a risk of permeation into the body. Significant increase in mean permeation between 8 and 12 hours was substantial as extended work shifts are commonly implemented. Furthermore, exposure circumstances such as the so called ‘take-home’ effect and the layering of new deposition onto previous deposition on the skin, emphasize the importance of proper decontamination protocols. Indications were made towards a shorter lag time and heightened cumulative mass parameter when utilizing potassium hexachloroplatinate compared to other PGM research. Recommendations were made based on the real-world implications of the results in occupational settings to be applied by future PGM permeation investigations. Masters

Summary Background Most studies of long-term exposure to outdoor fine particulate matter (PM2·5) and cardiovascular disease are from high-income countries with relatively low PM2·5 concentrations. It is unclear whether risks are similar in low-income and middle-income countries (LMICs) and how outdoor PM2·5 contributes to the global burden of cardiovascular disease. In our analysis of the Prospective Urban and Rural Epidemiology (PURE) study, we aimed to investigate the association between long-term exposure to PM2·5 concentrations and cardiovascular disease in a large cohort of adults from 21 high-income, middle-income, and low-income countries. Methods In this multinational, prospective cohort study, we studied 157 436 adults aged 35–70 years who were enrolled in the PURE study in countries with ambient PM2·5 estimates, for whom follow-up data were available. Cox proportional hazard frailty models were used to estimate the associations between long-term mean community outdoor PM2·5 concentrations and cardiovascular disease events (fatal and non-fatal), cardiovascular disease mortality, and other non-accidental mortality. Findings Between Jan 1, 2003, and July 14, 2018, 157 436 adults from 747 communities in 21 high-income, middle-income, and low-income countries were enrolled and followed up, of whom 140 020 participants resided in LMICs. During a median follow-up period of 9·3 years (IQR 7·8–10·8; corresponding to 1·4 million person-years), we documented 9996 non-accidental deaths, of which 3219 were attributed to cardiovascular disease. 9152 (5·8%) of 157 436 participants had cardiovascular disease events (fatal and non-fatal incident cardiovascular disease), including 4083 myocardial infarctions and 4139 strokes. Mean 3-year PM2·5 at cohort baseline was 47·5 μg/m3 (range 6–140). In models adjusted for individual, household, and geographical factors, a 10 μg/m3 increase in PM2·5 was associated with increased risk for cardiovascular disease events (hazard ratio 1·05 [95% CI 1·03–1·07]), myocardial infarction (1·03 [1·00–1·05]), stroke (1·07 [1·04–1·10]), and cardiovascular disease mortality (1·03 [1·00–1·05]). Results were similar for LMICs and communities with high PM2·5 concentrations (>35 μg/m3). The population attributable fraction for PM2·5 in the PURE cohort was 13·9% (95% CI 8·8–18·6) for cardiovascular disease events, 8·4% (0·0–15·4) for myocardial infarction, 19·6% (13·0–25·8) for stroke, and 8·3% (0·0–15·2) for cardiovascular disease mortality. We identified no consistent associations between PM2·5 and risk for non-cardiovascular disease deaths. Interpretation Long-term outdoor PM2·5 concentrations were associated with increased risks of cardiovascular disease in adults aged 35–70 years. Air pollution is an important global risk factor for cardiovascular disease and a need exists to reduce air pollution concentrations, especially in LMICs, where air pollution levels are highest. Funding Full funding sources are listed at the end of the paper (see Acknowledgments).

MHSc (Occupational Hygiene), North-West University, Potchefstroom Campus Background: South Africa is the world’s most prominent supplier of platinum group metals. The refining of platinum group metals consists of three main processes namely: smelting, base metal refining and precious metals refining. Dermal exposure to both arsenic and lead has been found to occur during the smelting process of precious metals (Gorman Ng et al., 2017). It is therefore anticipated that exposure to arsenic and lead could also possibly occur during base metals refining (BMR). Objectives: To quantify and compare the dermal exposure of refinery workers to arsenic and lead in the various sampling areas with each other, to compare the exposure on the various anatomical areas with each other and to quantify arsenic and lead workplace surface contamination in order to identify potential sources of exposure. Method: Wipe samples (GhostwipesTM) were collected from the palm, wrist and forehead of workers at various times during the working shift, in one administrative and two production areas within the refinery. In the administration area two workers gave consent to participate in this study. In each of the production areas, six workers gave their consent to participate in this study. Ten wipe samples were collected from each worker per day in the administrative area, only eight wipe samples were collected per worker per day in production area A and B. Additionally, surface wipes were collected to identify potential sources of contamination. A total of 132 wipe samples (112 dermal, 14 surface, 3 media blank and 3 field blanks) were collected during sampling. The collected samples were analysed using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) by a South African National Accreditation System accredited laboratory for arsenic and lead. Results: The analytical method used had a detection limit of 1 µg for arsenic and lead. None of the wipe samples contained arsenic at a detectable concentration. Additionally, 14% of the collected wipe samples contained lead at a detectable concentration. The palm received the highest exposure concentration (0.318 µg/cm²) followed by the wrist and lastly by the forehead. Nine of the wipe samples collected from the palm of workers contained lead above the detection limit. Only one of the wrist and forehead wipes collected contained lead above the detection limit. Workers in production area A received higher lead exposure than those in production area B. Surface wipes collected in the administrative area, dirty change house and from the personal protective equipment used by the workers, was contaminated with lead. Conclusion: During the refining process of base metals, workers were not exposed to an arsenic concentration above 1 µg and only six of the workers experienced lead exposure above 1µg. The palm of workers received the highest exposure to lead in both the production areas, which suggests that the palm is the primary area of exposure for the refinery workers. Surface and skin wipe samples indicated that surfaces can act as a source of additional exposure to lead. The control measures already implemented by the refinery prevents workers direct contact with these hazardous substances, which reduces workers’ dermal exposure. Masters

M Health Sciences (Occupational Hygiene), North-West University, Potchefstroom Campus Background: There is limited but growing information available regarding the health hazards associated with additive manufacturing (AM). The study presented in this mini-dissertation is significant considering that no other studies have explored particle emissions or the personal exposure of AM operators to hazardous chemical substances (HCS), such as poly methyl methacrylate (PMMA) powder particles, acetone and methyl methacrylate (MMA), during binder jetting utilising PMMA and acetone. Aims and objectives: To determine the physical characteristics and chemical composition of PMMA powder. Assess particle emissions associated with binder jetting utilising PMMA powder. Evaluate ambient workplace concentrations as well as personal respiratory exposure concentrations of the AM operator, for particles and volatile organic compounds (VOCs) (such as acetone and MMA) when PMMA powder is utilised during binder jetting AM. Methods: Physical and chemical characterisation of virgin and used PMMA powder samples included particle size distribution (PSD), particle shape analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD) as well as X-ray fluorescence (XRF). Direct reading particle counting instruments were used to measure particle emissions and emission rates during each phase of the binder jetting process. Internationally recognised methods were used to monitor HCSs in the ambient workplace environment and personal respiratory exposure of the AM operator, during the entire binder jetting process. Results: There were no noteworthy size differences found between median of the PSD of virgin (58.32 ± 0.52 μm) and used (58.40 ± 0.11 μm) PMMA. From SEM images, the presence of < 10 μm, and a few < 4 μm, sized particles were observed in both the virgin and used powders. PMMA powders comprised mainly of amorphous elements (> 99.23% for virgin powder). In the presence of high background ambient particle number concentrations particle emission rates as high as 3.33 × 1012 particles/min for 0.01 ~ 1.00 μm sized particles were measured during the processing phase. However, no significant differences between the AM phases were observed. Ambient 8-hour Time Weighted Average (TWA) concentrations were measured at 3.83 ± 2.12 mg/m3 for inhalable particles, 0.77 ± 0.20 mg/m3 for respirable particles, 15.32 ± 2.62 mg/m3 for acetone, 0.19 ± 0.08 mg/m3 for pentane and 0.30 ± 0.03 mg/m3 for toluene. Personal TWA concentrations were measured at 6.22 ± 4.72 mg/m3 for inhalable particles, 1.15 ± 0.33 mg/m3 for respirable particles, 2.02 ± 0.58 mg/m3 for acetone, 0.16 ± 0.07 mg/m3 for pentane and 0.16 ± 0.05 mg/m3 for toluene. Conclusions: In this study, a comprehensive analysis was performed in order to determine the particle emissions and respiratory hazards, and the extent thereof, to which AM operators of PMMA binder jetting are exposed. Particles sized 0.01 ~ 1.00 μm were the most prevalent sizes emitted. Inhalable, and respirable particles, acetone, pentane and toluene were detected in the workplace atmosphere. All 8-hour TWA personal exposures were below the respective TWA Occupational Exposure Limit Recommended Limit (TWA-OEL-RL), with the exception of exposure to inhalable particles, where exposure exceeded the 10 mg/m3 TWA-OEL-RL once and averaged above 50% of the OEL. Recommendations for elimination, substitution, engineering, administrative and personal protective equipment control measures were made to reduce exposure to inhalable particles, which could also be applied to other AM facilities making use of the same AM technology and PMMA powders. Study limitations and future studies were also discussed. Masters

MSc (Occupational Hygiene), North-West University, Potchefstroom Campus Background: Additive manufacturing (AM) utilising metal powder is associated with the emission of airborne particles of various sizes, which may result in respiratory exposure of the AM operator to this powder. Research involving platinum in AM is non-existent and the aim of this pilot study was to provide an initial understanding of the characteristics of platinum powder particles and emissions during the different process phases of AM as well as personal exposure of the AM operator to metal powders. Methods: This study was conducted over two print cycles of powder bed fusion (PBF) with platinum powder as feedstock at an AM facility. Particle size selective counting instruments were used to investigate the emissions of airborne particulates during the different phases of PBF AM in the workplace atmosphere. The particle number concentrations were used to calculate the particle emission rate during the AM process. Personal exposure to inhalable, respirable and < 300 nm sized particulates was measured and analysed using inductively coupled plasma-mass spectrometry to investigate possible metal exposure during AM. Results: In this pilot study the highest concentration of 0.01 > 1 μm sized particles was emitted during the pre-processing phase, followed by the post-processing phase and lastly the processing phase. Particles of 0.3 μm in size had the highest peak particle number concentration of 7.71 x107p/m3 during the first print cycle and 3.02 x108 p/m3 in the second print cycle, followed by 0.5 μm and 1 μm sized particles. Emission rates indicated that during pre-processing, the highest concentrations of particles were emitted (7.95 x106 p/min) followed by the processing phase and lastly the post-processing phase. Personal exposure concentrations for inhalable and < 300 nm sized platinum particles were below that of the detection limit for platinum metal analysis. However, operators were exposed to inhalable sized metals such as arsenic, cobalt, copper, lead and nickel among which cobalt, copper and nickel exceeded occupational exposure limits. Conclusion: Concentrations of particles ranging from 0.01 to 10 μm were emitted during all three AM phases. The highest emission concentration was in the pre-processing phases of print cycle 1 and print cycle 2. Emission rates were highest in the pre-processing phase over both print cycles. This pilot study indicates that future studies should focus on particle emissions rather than on personal exposure of the AM operators to platinum metal powders. Personal respiratory exposure to platinum metal powder was below the detection limit but attention should be directed to other detected insoluble metals such as arsenic, cobalt and copper of which the presence was likely engendered by workplace cross-contamination. It is the duty of the AM employer at the facility to educate AM operators to any risks that may be associated with the PBF AM process or any other workplace risk. These employers further need to implement control measures, to eliminate or reduce the risk to an acceptable level. Masters

This study aimed to analyze historical soluble nickel exposure data from a South African base metal refinery and to identify trends in the soluble nickel exposure from 1981 until 2014 in the electrowinning department. Exposure data were presented in an exposure matrix, which described exposure profiles for both area and personal exposures inside two tankhouses. Exposure data were standardized by converting total nickel aerosol concentrations to inhalable nickel concentrations (correction factor 3.0). One-way analyses of variances (ANOVA) were conducted to identify significant differences in log-transformed area and personal exposures from 1982 until 2014, and the trends were assessed with linear regression. Differences were evaluated in area exposure between sections inside the tankhouses, i.e., East, West, and Center bays and in personal exposure between occupations, i.e., cell workers, crane drivers, and supervisors. Area exposure in Tankhouse 1 declined significantly (p ≤ 0.0001) between 1982 and 1986 with a factor of 29. However, after 1986 no significant downward trend in area exposure was evident in Tankhouse 1. Personal exposures in Tankhouse 1 significantly (p ≤ 0.0001) decreased with a factor of three between 1991 and 2014. No significant trends were evident in area and personal exposure in Tankhouse 2. Downward exposure trends were evident in Tankhouse 1 and may be ascribed to the implementation of various control measures and process changes, e.g., increasing polypropylene bead load. Limited data were available for Tankhouse 2, therefore, no trend in exposure could be established. Retrospective analyses may be used to identify trends and anomalies in exposure which might not have been identified during daily exposure monitoring.

Spectrophotometry is used to estimate melanin density (MD) in Caucasians1 but applicability of the calculation to people with pigmented skin, who also experience sun sensitivity, is not known. Here, we directly compared biopsy melanin concentration (MC) with Melanin Index (MI), Individual Typology Angle (ITA) values,2 calculated Melanin Density (MD) and Self‐Reported Sun Sensitivity (SRSS), with an aim to identify a non‐invasive, reliable melanin assessment technique for deeply pigmented skin

Background Farmworkers in the Limpopo Province, South Africa, are at risk of excessive exposure to solar ultraviolet radiation (sUVR) due to both their work and the sUVR environment in the geographic area. However, the natural protection provided by this group's skin against sUVR has not been quantified. The aim of this study was to evaluate the subjective and objective skin colour of a group of farmworkers in order to classify the natural photoprotection provided by melanin and to evaluate the different measurement methods. Materials and methods Skin colour was established by using the subjective Fitzpatrick skin phototype system (FST) questionnaire and two objective methods, namely the individual typology angle (ITA°) and melanin index (MI). A total of 71 farmworkers participated in the study. Results Black Africans tended to perceive their skin to be lighter than objectively measured, potentially due to cultural factors. The constitutive skin colour of most farmworkers was objectively classified in the FST V/brown group. Significant differences were found between the ITA° and MI of sun-exposed (constitutive) and non-sun-exposed (facultative) skin in Black African and White farmworkers. A strong correlation was found between ITA° and MI on different anatomical positions indicating both methods are appropriate to determine skin colour in deeply pigmented skin. Conclusion The evaluation of skin colour with the use of both subjective and objective methods may be used to design an effective photoprotection programme for farmworkers in the Limpopo Province.

Summary: Background: The associations between the extent of forced expiratory volume in 1 s (FEV1) impairment and mortality, incident cardiovascular disease, and respiratory hospitalisations are unclear, and how these associations might vary across populations is unknown. Methods: In this international, community-based cohort study, we prospectively enrolled adults aged 35–70 years who had no intention of moving residences for 4 years from rural and urban communities across 17 countries. A portable spirometer was used to assess FEV1. FEV1 values were standardised within countries for height, age, and sex, and expressed as a percentage of the country-specific predicted FEV1 value (FEV1%). FEV1% was categorised as no impairment (FEV1% ≥0 SD from country-specific mean), mild impairment (FEV1%

Background: Household air pollution (HAP) from solid fuel use for cooking affects 2.5 billion individuals globally and may contribute substantially to disease burden. However, few prospective studies have assessed the impact of HAP on mortality and cardiorespiratory disease. Objectives: Our goal was to evaluate associations between HAP and mortality, cardiovascular disease (CVD), and respiratory disease in the prospective urban and rural epidemiology (PURE) study. Methods: We studied 91,350 adults 35–70 y of age from 467 urban and rural communities in 11 countries (Bangladesh, Brazil, Chile, China, Colombia, India, Pakistan, Philippines, South Africa, Tanzania, and Zimbabwe). After a median follow-up period of 9.1 y, we recorded 6,595 deaths, 5,472 incident cases of CVD (CVD death or nonfatal myocardial infarction, stroke, or heart failure), and 2,436 incident cases of respiratory disease (respiratory death or nonfatal chronic obstructive pulmonary disease, pulmonary tuberculosis, pneumonia, or lung cancer). We used Cox proportional hazards models adjusted for individual, household, and community-level characteristics to compare events for individuals living in households that used solid fuels for cooking to those using electricity or gas. Results: We found that 41.8% of participants lived in households using solid fuels as their primary cooking fuel. Compared with electricity or gas, solid fuel use was associated with fully adjusted hazard ratios of 1.12 (95% CI: 1.04, 1.21) for all-cause mortality, 1.08 (95% CI: 0.99, 1.17) for fatal or nonfatal CVD, 1.14 (95% CI: 1.00, 1.30) for fatal or nonfatal respiratory disease, and 1.12 (95% CI: 1.06, 1.19) for mortality from any cause or the first incidence of a nonfatal cardiorespiratory outcome. Associations persisted in extensive sensitivity analyses, but small differences were observed across study regions and across individual and household characteristics. Discussion: Use of solid fuels for cooking is a risk factor for mortality and cardiorespiratory disease. Continued efforts to replace solid fuels with cleaner alternatives are needed to reduce premature mortality and morbidity in developing countries. https://doi.org/10.1289/EHP3915

PhD (Occupational Hygiene), North-West University, Potchefstroom Campus Background: Additive Manufacturing (AM) is the process of joining feedstock materials one layer at a time in order to produce objects from a three dimensional (3D) computer aided design (CAD). Powder bed fusion (PBF) and direct energy deposition (DED) are two widely applied powder based metal AM processes used commercially in the South African AM industry. A number of studies have investigated small desktop polymer material extrusion fused deposition modelling (FDMTM) 3D printers and found that these printers are high emitters of particulate matter and volatile organic compounds. Chamber studies have been of value by contributing to a better understanding of emissions from FDMTM desktop printers. However, despite the numerous studies on particulate matter emissions from desktop FDMTM printers there is an unbridged gap to identify the hazardous chemical substance emissions from and the respiratory exposure of AM operators when utilising metal powders in AM. AM processes takes place in three distinct phases, namely the pre-processing, processing and post-processing phases, and occupational exposure may occur during each of these three phases since most tasks are manually performed by the AM operator. To date only one study has investigated particle emissions from and exposure to metals during PBF while there is no published literature on emissions or exposure from DED. PBF and DED are applied in South Africa and therefore, the investigation of particle emissions from and personal exposure of AM operators to hazardous chemical substances (metals) is needed. Aims and objectives: The general research aim of this thesis was to assess the emissions of and occupational exposure to hazardous chemical substances (particles and metals) associated with two metal powder based AM process categories (powder bed fusion and direct energy deposition) at three South African institutions utilising AM. The specific objectives were: (i) to establish the physico-chemical characteristics (particle size, shape and elemental composition) of virgin and used metal powders, used during powder bed fusion and direct energy deposition, and the relevance thereof to AM operators’ health. (ii) to assess particle emissions and respiratory metal exposure of AM operators when using three titanium powders and maraging steel during the pre- processing, processing and post-processing phases of AM at three AM facilities utilising PBF. (iii) to assess particle emissions and respiratory metal exposure of AM operators when using two stainless steel powders during DED at an AM facility. Methods: Samples of virgin and used (recycled) titanium and maraging steel as well as used stainless steel powders, along with their respective safety data sheets (SDSs) were collected from three AM facilities in South Africa utilising PBF and DED. Powder samples were characterised in terms of particle size distribution (PSD), particle shape and elemental composition. Real time monitoring devices, namely a Condensation Particle Counter (0.01 to > 1 μm) and an Airborne Particle Counter (0.30 to 10.00 μm) were used to investigate particle emissions [particle number concentrations (p/m3)] during PBF and DED process phases. The concentration of metals in the workplace air was established by means of static area monitoring according to the National Institute for Occupational Safety and Health (NIOSH) 7300 method using a closed-faced cassette (CFC). Personal (AM operator) respiratory exposure to metals used the same NIOSH method. Ethics approval for this study was obtained from the Health Research Ethics Committee of the North-West University (NWU-00004-16-A1). Researchers followed well know occupational hygiene methods, and other state of the art methods nor currently used in occupational hygiene compliance monitoring. Personal exposure to metals < 300 nm in size was assessed by using a nanoparticle respiratory deposition sampler. Results: Only one of the three titanium powers PSD was in accordance with the SDS. From the SEM images, thoracic sized (< 10 μm) and respirable sized (< 4 μm) particles were observed in powders from all three facilities. The elemental composition analysis (XRD analysis) of the investigated powders differed from the composition stated in the respective SDSs. Particles ≤ 1 μm were present in the workplace air. Increases in particle number concentrations were observed during specific pre- and post-processing tasks such as cleaning and powder sieving which led to an increase in particle emissions with the highest particle number concentration of 6.12 x 1010 p/m3 (0.01 to > 1 μm) measured during the post-processing phase of PBF with titanium. Tasks such as unloading of the AM machines led to particle concentrations (0.01 to > 1 μm) as high as 5.98 x 1010 p/m3 during PBF with maraging steel and 5.75 x 1010 p/m3 during DED of stainless steel. Static area monitoring indicated low concentrations of metals in the work place atmosphere during PBF and DED. During both PBF and DED, AM operators were exposed to detectable concentrations of metals including aluminium, chromium, copper, iron, nickel, titanium and vanadium, including metals < 300 nm in size. Full shift metal exposure was calculated for comparisons with occupational exposure limits (OELs) of all detected metals. AM operators’ personal respiratory exposure was < 1.04% of the time weighted average OELs (TWA-OELs) when using titanium powders, and < 3.60% of the respective TWA-OELs and < 9.01% of threshold limit value (TLVs®) during the use of maraging steel. Exposure to Ni, a human carcinogen, was the highest. Conclusion: There is a shortage of studies reporting particle emissions from and AM operators’ respiratory exposure to metals resulting from use of titanium and metals powders used in PBF and DED. Inadequate information in the SDSs may mislead employers and AM operators’ regarding the protection of AM operator health, and therefore, powder characterisation should form an integral part of risk assessments at each facility. During the pre-and post-processing phases of PBF and DED, particles were emitted during phase specific tasks such as cleaning, sieving, and unloading of the AM machine. When particle number concentrations during the processing phase from PBF and DED were compared to FDM™ printers, it was found that particle number concentrations emitted from FDMs™ were approximately five to nine times higher. The maximum particle number concentrations emitted from DED were 3% lower than that of PBF. Low concentrations of metals were present in the workplace atmosphere throughout the use of titanium, maraging steel and stainless steel powders. Although no OELs were exceeded, AM operators were exposed to detectable concentrations of metals, including metals < 300 nm in size. The findings of this study serve as a starting point to create awareness of AM operator exposure associated with metal AM, and to assist industrial AM facilities in identifying hazards and implementing phase and task specific control measures during PBF and DED using titanium powders and metal powders. Eleven recommendations are made for the attention of all role players including AM powder manufacturers/suppliers, employers (AM facilities) and AM operators/employees in an effort to reduce particle emissions from and AM operator’s respiratory exposure to metals. Along with the recommendations, specific limitations experienced during the study were also identified along with recommendations for future studies. Doctoral

Background: The skin provides a permeable barrier which may be impaired in oc‐ cupational settings. Transepidermal water loss (TEWL), stratum corneum hydration (SCH) and skin surface pH (SSpH) have been used in occupational settings to predict early onset of occupational skin diseases, to measure the effectiveness of prevention strategies for occupational skin diseases, and to assess skin condition during expo‐ sure. The aim was to compare the findings, identify shortcomings in the methodology and data reporting and furthermore, to make recommendations for future studies. Materials and Methods: A literature study was conducted on studies published be‐ fore December 2018 to provide a review on the measurement of TEWL, SCH and SSpH in occupational settings. Results: TEWL, SCH and SSpH were previously measured in a wide variety of indus‐ tries. Results between studies were highly variable, due to different study designs and different anatomical positions measured. Not all of the measurement conditions were reported and variations in study objectives led to data being reported and in‐ terpreted differently for most studies. Conclusion: Incomplete reporting of methodology hinders comparison of bioen‐ gineering measurements. No bioengineering method has been proven useful as a predictive tool for occupational skin diseases, however, it is useful in the acute as‐ sessment of skin condition. It is recommended that future studies on TEWL, SCH and SSpH adhere to guidelines for occupational settings as far as possible to enable comparison between studies

There is a paucity of data on additive manufacturing process emissions and personal exposures in real-world workplaces. Hence, we evaluated atmospheres in four workplaces utilizing desktop “3-dimensional” (3-d) printers [fused filament fabrication (FFF) and sheer] for production, prototyping, or research. Airborne particle diameter and number concentration and total volatile organic compound concentrations were measured using real-time instruments. Airborne particles and volatile organic compounds were collected using time-integrated sampling techniques for off-line analysis. Personal exposures for metals and volatile organic compounds were measured in the breathing zone of operators. All 3-d printers that were monitored released ultrafine and fine particles and organic vapors into workplace air. Particle number-based emission rates (#/min) ranged from 9.4 × 10(9) to 4.4 × 10(11) (n = 9samples) for FFF3-d printers and from 1.9 to 3.8 × 10(9) (n = 2 samples) for a sheer 3-d printer. The large variability in emission rate values reflected variability from the printers as well as differences in printer design, operating conditions, and feedstock materials among printers. A custom-built ventilated enclosure evaluated at one facility was capable of reducing particle number and total organic chemical concentrations by 99.7% and 53.2%, respectively. Carbonyl compounds were detected in room air; however, none were specifically attributed to the 3-d printing process. Personal exposure to metals (aluminum, iron) and 12 different organic chemicals were all below applicable NIOSH Recommended Exposure Limit values, but results are not reflective of all possible exposure scenarios. More research is needed to understand 3-d printer emissions, exposures, and efficacy of engineering controls in occupational settings.

At the 8th conference of Occupational and Environmental Exposure of the Skin to Chemicals (OEESC) (16–18 September 2019) in Dublin, Ireland, several researchers performing skin permeation assays convened to discuss in vitro skin permeability experiments. We, along with other colleagues, all of us hands-on skin permeation researchers, present here the results from our discussions on the available OECD guidelines. The discussions were especially focused on three OECD skin absorption documents, including a recent revision of one: i) OECD Guidance Document 28 (GD28) for the conduct of skin absorption studies (OECD, 2004), ii) Test Guideline 428 (TGD428) for measuring skin absorption of chemical in vitro (OECD, 2004), and iii) OECD Guidance Notes 156 (GN156) on dermal absorption issued in 2011 (OECD, 2011). GN156 (OECD, 2019) is currently under review but not finalized. A mutual concern was that these guidance documents do not comprehensively address methodological issues or the performance of the test, which might be partially due to the years needed to finalize and update OECD documents with new skin research evidence. Here, we summarize the numerous factors that can influence skin permeation and its measurement, and where guidance on several of these are omitted and often not discussed in published articles. We propose several improvements of these guidelines, which would contribute in harmonizing future in vitro skin permeation experiments.

Adverse respiratory and skin health effects have been associated with occupational exposure to soluble platinum (Pt). However, the relationship between skin exposure and urinary Pt excretion has not yet been investigated. In this study we examined the relationship between skin and respiratory exposure to soluble Pt and urinary Pt excretion at two South African precious metals refineries. The skin and respiratory exposure to soluble Pt as well as the urinary Pt excretion of forty precious metals refinery workers was assessed simultaneously using Ghostwipes™, Methods for the Determination of Hazardous Substances method 46/2 and spot urine tests, respectively. The geometric mean for skin exposure to soluble Pt on four anatomical positions (palm, wrist, neck and forehead) was 0.008 μg/cm2 [95% confidence interval (CI): 0.005-0.013 μg/cm2], while the geometric mean for respiratory exposure was 0.301 μg/m3 (95%CI: 0.151-0.601 μg/m3) and the geometric mean for urinary Pt excretion was 0.212 μg/g creatinine (95%CI: 0.169-0.265 μg/g creatinine). Partial correlations identified significant positive correlations between skin exposure, respiratory exposure and urinary Pt excretion (r = 0.580 to 0.754). Skin and respiratory exposures to soluble Pt were both positively correlated with urinary Pt excretion, and both exposure routes should be considered when investigating occupational exposure to soluble Pt.

PhD (Occupational Hygiene), North-West University, Potchefstroom Campus Background: South Africa is the largest producer of platinum in the world. During the refining of platinum, complex intermediary compounds are formed, many of which are potent sensitisers. Occupational exposure to soluble platinum has been associated with the development of soluble platinum sensitisation, which is characterised by adverse effects of the respiratory system and the skin. Urinary platinum excretion has been shown to be an effective biomarker for occupational exposure to platinum and has been positively correlated with respiratory exposure. Inhalation is seen as the primary route of exposure to soluble platinum. However, the possible role of dermal exposure in the development of respiratory sensitisation has received an increasing amount of attention recently. Dermal exposure to soluble platinum and its possible correlation with platinum body burden have not previously been investigated. Aims and objectives: The research aim of this thesis was to evaluate occupational exposure to soluble platinum of South African precious metals refinery workers and to examine the contribution of the dermal and respiratory exposure routes to the platinum body burden of workers. The specific objectives for the thesis were: (i) to conduct a critical review of the available published scientific literature on respiratory exposure to platinum group metals (PGMs) in occupational settings; (ii) to assess the platinum body burden of precious metals refinery workers through analysis of their urinary platinum excretion; (iii) to assess the respiratory exposure of precious metals refinery workers to soluble platinum using established methodology; (iv) to assess the dermal exposure of precious metals refinery workers to soluble platinum by making use of a commercially available wipe; (v) to examine the relationship between respiratory and dermal exposure to soluble platinum, and urinary platinum excretion in order to establish the contribution of each route of exposure to the platinum body burden; and (vi) to assess the effectiveness of disposable coveralls in reducing dermal exposure to soluble platinum. Methods: Forty workers from two South African precious metals refineries participated in this study. Dermal and respiratory exposure to soluble platinum as well as the urinary platinum excretion of workers was measured concurrently over two consecutive working days. Dermal exposure was assessed using Ghostwipes™ on four anatomical areas (palm of hand, wrist, neck and forehead) and respiratory exposure was assessed using the Methods for the Determination of Hazardous Substances (MHDS) 46/2 method. For biological monitoring, three spot urine samples were collected from each worker. The first was collected prior to the start of the first day of exposure monitoring, the second prior to the second day of exposure monitoring and the third prior to the start of the following day's shift. Additionally surface wipe samples were also collected to examine soluble platinum surface contamination. All samples were analysed for soluble platinum according to a method based on MDHS 46/2 that uses Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Ethics approval for the study was obtained from the Health Research Ethics Committee of the North-West University (NWU-00128-14-A1). Results: A number of published research articles have reported occupational respiratory exposure to platinum compounds. However, the manner in which results are reported vary, which makes the comparison of results between different studies challenging. Authors often only report the number of measurements that exceeded the occupational exposure limit (OEL) of 2 μg/m3 and do not report more detailed descriptive statistics or whether the soluble or total fraction was analysed. Analysis of the available data showed that the highest concentrations of airborne soluble platinum were reported in precious metals refineries. The degree of exposure is the greatest risk factor for the development of soluble platinum sensitisation and is influenced by a worker's area of work, the tasks performed and the fraction of soluble platinum in the workplace air. The OEL of 2 μg/m3 has been in use since 1970. A number of studies have questioned its relevance, since sensitisation has been shown to occur at exposure below 2 μg/m3. Furthermore, very few research articles have reported respiratory exposure to PGMs other than platinum (palladium, rhodium, iridium, ruthenium and osmium). The results obtained from the biological and exposure monitoring studies indicated that quantifiable concentrations of soluble platinum were present in the urine of precious metals refinery workers and that workers were exposed to soluble platinum via the dermal and respiratory exposure routes. The geometric mean of the urinary platinum excretion was 0.212 μg/g creatinine [95% confidence interval (CI): 0.169-0.265 μg/g creatinine] and ranged from < 0.1 to 3.0 μg/g creatinine. The results from the three spot urine samples did not differ significantly. Significantly higher urinary platinum excretion was found for workers directly exposed to platinum compounds during production activities compared to that of non-production workers who were indirectly exposed (p = 0.007). The geometric mean of the average dermal exposure experienced on all four anatomical areas was 0.008 μg/cm2 (95% CI: 0.005-0.013 μg/cm2). The geometric mean of the respiratory exposure was 0.301 μg/m3 (95%CI: 0.151-0.601 μg/m3). Directly exposed workers experienced significantly higher dermal (p = 0.002) and respiratory (p = 0.002) exposure to soluble platinum. The urinary platinum excretion of workers correlated positively and significantly with their dermal exposure (r = 0.754) and respiratory exposure (r = 0.580) to soluble platinum. Detectable concentrations of soluble platinum were found on a variety of surfaces in production and non-production areas. The use of disposable coveralls and the adherence to usage procedures by workers who were directly exposed to platinum compounds significantly reduced their dermal exposure to soluble platinum (p = 0.018). Conclusions: According to the literature, the highest concentrations of airborne soluble platinum are reported in precious metals refineries. Limitations in the published body of literature investigating occupational exposure to PGMs were identified. It was clear that no standardised approach is followed for reporting respiratory exposure results which makes the comparison of studies difficult. Recommendations are made for the standardisation of the reporting methods in order to facilitate the comparison of occupational respiratory PGM exposure results from different studies in future. The urinary platinum excretion of South African precious metals refinery workers reported in this study is comparable to that of other studies conducted in precious metals refineries in the United Kingdom, Europe and the United States of America. The urinary platinum excretion of workers showed low variability and spot urine tests can, therefore, be used to evaluate the platinum body burden of precious metals refinery workers. South African precious metals refinery workers are exposed to soluble platinum via the dermal and respiratory exposure routes and both these routes are positively correlated with the platinum body burden, as determined by urinary platinum excretion. The dermal and respiratory exposure routes should therefore be considered when investigating occupational exposure to platinum. Disposable coveralls and strict usage procedures are effective in reducing the dermal exposure of workers to soluble platinum. Finally, 19 recommendations are made to the specific precious metals refineries included in this study as well as precious metals refineries in general to reduce dermal and respiratory exposure to soluble platinum. Some limitations experienced during the study are also identified along with recommendations for future studies. Doctoral

Purpose This paper aims to measure exposures to airborne contaminants during three-dimensional (3-D) printing and post-processing tasks in an industrial workplace. Design/methodology/approach Contaminant concentrations were assessed using real-time particle number (0.007 to 1 µm) and total volatile organic compound (TVOC) monitors and thermal desorption tubes during various tasks at a manufacturing facility using fused deposition modeling (FDMTM) 3-D printers. Personal exposures were measured for two workers using nanoparticle respiratory deposition samplers for metals and passive badges for specific VOCs. Findings Opening industrial-scale FDMTM 3-D printer doors after printing, removing desktop FDMTM 3-D printer covers during printing, acetone vapor polishing (AVP) and chloroform vapor polishing (CVP) tasks all resulted in transient increases in levels of submicrometer-scale particles and/or organic vapors, a portion of which enter the workers’ breathing zone, resulting in exposure. Personal exposure to quantifiable levels of metals in particles 3 for aluminum, chromium, copper, iron and titanium during FDMTM printing. Personal exposures were 0.38 to 6.47 mg/m3 for acetone during AVP and 0.18 mg/m3 for chloroform during CVP. Originality/value Characterization of tasks provided insights on factors that influenced contaminant levels, and in turn exposures to various particles, metals < 300 nm and organic vapors. These concentration and exposure factors data are useful for identifying tasks and work processes to consider for implementation of new or improved control technologies to mitigate exposures in manufacturing facilities using FDMTM 3-D printers.

The acidic nature of the skin surface was recognised more than a century ago and has been measured since 1928. Several non-invasive methods for measuring skin surface pH have been developed ever since and have contributed to our understanding of healthy and diseased skin. This chapter summarises the endogenous physiological, exogenous and environmental factors that influence skin surface pH and its measurement as well as the different measurement methods for skin surface pH, with specific emphasis on the classic planar glass electrode method. Also, practical guidance for measurement of skin surface pH using the planar glass electrode method is provided. Adherence to practical skin surface pH measurement (method) guidelines with due consideration and practicable control of all factors that may affect skin surface pH will ensure credible pH measurement results in our continuous pursuit of understanding especially diseased skin.

The majority of the South African workforce are Africans, therefore potential racial differences should be considered in risk and exposure assessments in the workplace. Literature suggests African skin to be a superior barrier against permeation and irritants. Previous in vitro studies on metals only included skin from Caucasian donors, whereas this study compared the permeation of platinum through African and Caucasian skin. A donor solution of 0.3 mg/ml of potassium tetrachloroplatinate (K2PtCl4) dissolved in synthetic sweat was applied to the vertical Franz diffusion cells with full thickness abdominal skin. Skin from three female African and three female Caucasian donors were included (n = 21). The receptor solution was removed at various intervals during the 24 h experiment, and analysed with high resolution inductively coupled plasma-mass spectrometry (ICP-MS). Skin was digested and analysed by inductively coupled plasma-optical emission spectrometry (ICP-OES). Significantly higher permeation of platinum through intact African skin (p = 0.044), as well as a significantly higher mass of platinum retention in African skin in comparison with Caucasian skin (p = 0.002) occurred. Significant inter-donor variation was found in both racial groups (p < 0.02). Results indicate that African workers have increased risk of dermal permeation and therefore possible sensitisation caused by dermal exposure to platinum salts. These results are contradictory to limited literature suggesting a superior barrier in African skin and further investigation is necessary to explain the higher permeation through African skin National Research Foundation of South Africa (Thuthuka Programme) for the grant No. 80635 and the South African Medical Research Council

BackgroundUrinary platinum (Pt) excretion is a reliable biomarker for occupational Pt exposure and has been previously reported for precious metals refinery workers in Europe but not for South Africa, the world’s largest producer of Pt.ObjectiveThis study aimed to quantify the urinary Pt excretion of South African precious metals refinery workers.MethodsSpot urine samples were collected from 40 workers (directly and indirectly exposed to Pt) at two South African precious metals refineries on three consecutive mornings prior to their shifts. Urine samples were analysed for Pt using inductively coupled plasma-mass spectrometry and were corrected for creatinine content.ResultsThe urinary Pt excretion of workers did not differ significantly between sampling days. Urinary Pt excretions ranged from 2=0.567) and the number of years workers were employed at the refineries (P=0.003; η2=0.261) influenced their urinary Pt excretion according to effect size analyses. Directly exposed workers had significantly higher urinary Pt excretion compared with indirectly exposed workers (P=0.007).ConclusionThe urinary Pt excretion of South African precious metals refinery workers reported in this study is comparable with that of seven other studies conducted in precious metals refineries and automotive catalyst plants in Europe. The Pt body burden of workers is predominantly determined by their work area, years of employment in the refineries and whether they are directly or indirectly exposed to Pt.

Platinum group metals (PGMs) is a group of metals that include platinum, palladium, rhodium, ruthenium, iridium, and osmium. Occupational respiratory exposure to platinum has been reported since 1945, but studies investigating occupational exposure to palladium, rhodium, ruthenium, iridium, and osmium are scarce. This review provides a summation of the information available on the respiratory exposure to PGMs in various industrial settings, methods used to assess exposure, and the possible adverse health effects resulting from occupational exposure to PGMs. Of these effects, respiratory sensitization caused by soluble PGMs is of most importance. Metallic PGMs have not been shown to cause allergic reactions. This review reiterates that occupational respiratory exposure to PGMs is dependent on the type of industry where exposure takes place, the chemical form (soluble or insoluble) of the PGMs present in the workplace air, and the tasks performed by workers in the specific work areas. Sensitization to soluble platinum is associated with the degree of exposure to soluble platinum compounds, and the highest concentrations of soluble PGMs in workplace air have been reported for precious metals refineries where personal exposures frequently exceed the occupational exposure limit for soluble platinum (2 μg/m3). Additionally, this review emphasizes that personal exposure monitoring is preferred over area monitoring when assessing workers’ exposure to PGMs. The legislation applicable to occupational exposure to PGMs is also discussed, and it is highlighted that the occupational exposure limit for soluble platinum has remained unchanged, in most countries, since 1970 and that too few countries have classified PGM compounds as respiratory or skin sensitizers. Finally, recommendations are made to ensure that future investigations are comparable in terms of the type of exposure monitoring (personal or area) conducted, the type of tasks included in the exposure monitoring program, and the format in which results are reported

Background: Occupational solar ultraviolet radiation (UVR) exposure is a skin cancer risk factor. Outdoor workers have long exposure hours and are in need of photoprotection against solar UVR, a Group 1-defined carcinogen. In South Africa, skin cancers account for one third of all histologically-diagnosed cancers. Physiological presentation of non-melanoma skin cancers (NMSC) is most common on the head in all population groups. It is expected that occupational exposure plays a role in NMSC aetiology in South Africa, although such data are presently lacking. Recognising solar UVR-inflicted skin cancer as an occupational disease occurs in some countries. We consider the experience of other countries in including NMSC as an occupational disease to draw on lessons learnt, and consider a similar approach for South Africa. Methods: We sourced articles in English on NMSC as an occupational disease. We also sent an open-ended e-mail information request to nine international academic experts from different developed countries. Data on background, legislation, reporting, notification and occupational sectors of concern were analysed. Results: Several countries, e.g. Denmark, include NMSC as an occupational disease. Despite this, under-reporting is still significant. Agriculture, construction and public service sectors report most commonly, compared to other sectors. National awareness campaigns, careful legal management and improved health care services for patients are key. Conclusions: Outdoor workers run an increased risk of developing NMSC. For South Africa to register NMSC as a reportable occupational disease, significant efforts relating to local epidemiology, exposure assessment, legal and insurance management, and policy-making, need to be considered

The skin functions as a physical barrier preventing loss of body fluids and penetration of substances (chemicals) or infectious agents (1–3). This physical, permeability barrier resides primarily in the stratum corneum (SC) (4–6). Transepidermal water loss (TEWL) and skin hydration have been widely used as indices in evaluating skin barrier function (1, 4, 7–11). TEWL represents the diffusion of condensed water through the SC (7, 12), while skin hydration reflects the water content of the SC (4, 13). An altered skin barrier function is marked by an elevated TEWL and has been observed in a number of skin diseases (e.g. atopic dermatitis and psoriasis) and experimental perturbation studies (e.g. applications of solvents and detergents) (3, 11). Furthermore, elevated TEWL values in a disturbed skin barrier are frequently correlated with low hydration of the SC (3). Several lines of evidence suggest that a disturbed, compromised skin barrier may increase dermal absorption of chemicals and other large substances (e.g. particulate), which cannot penetrate the intact skin (14, 15). In the workplace, damage to the skin and a compromised skin barrier due to physical and mechanical irritation and chemical insults commonly occur (14). Scrubbing, friction, or abrasion may partially or completely remove the SC and thus disrupt the skin barrier by exposing the viable and water-rich epidermis to the environment (14, 16). It is suggested that organic solvents increase skin permeability by extracting and altering the structure of intercellular lipids from the SC, while desmosomes may also be damaged (14). Surfactants (detergents) interact with skin lipids and proteins leading to disorganization of extracellular lipids, reducing corneocyte cohesion and decreasing skin hydration (14, 17). Occlusion created by prolonged wearing of protective clothing, most notably protective gloves, prevents evaporation of water leading to accumulation of water in intercellular spaces across the SC and swelling of corneocytes (1). A limited number of studies have been published in which changes in skin barrier function in workplaces have been investigated. Coenraads et al. (18) measured skin vapor loss (SVL) from the skin of metal industry workers during exposure to water-soluble oils and mineral oil. Over the 12-week study, four workers exposed to mineral oil developed contact dermatitis, with a marked increase in SVL. The SVL of other 50 workers remained normal, although SVL levels in workers exposed to water-soluble oils were slightly but not significantly higher than that of the control group. Goh and Gan (19) measured changes in TEWL in newly employed machinists exposed to cutting oils. Smit et al. (20) measured TEWL in apprentice hairdressers and nurses and results implied that hairdressers had an increased risk of hand dermatitis at TEWL >15 g/m2/h in the hand, but the increased risk was not statistically significant. No relationship was observed for nurses. In a study conducted by Berndt et al. (21), the validity of skin bioengineering methods (including skin hydration and TEWL) as predictive measures for the development of hand eczema, was investigated in a follow-up study of metalworker trainees. They concluded that no single biophysical method can be considered as a valid screening test. However, a combination of short irritation tests and skin hydration permits identification of individuals at high risk for hand dermatitis with a high sensitivity, but with low specificity. Chou et al. (22) measured TEWL in rayon manufacturing workers exposed predominantly to carbon disulfide and sulfuric acid. Significant differences in basal TEWL levels between exposed Chinese workers and a control group were reported. Chou et al. (23) measured TEWL and skin hydration changes among manufacturing workers employed in ultra-low humidity. Both TEWL and skin hydration decreased within 2 weeks of exposure to ultra-low humidity. The maximum change in TEWL occurred after 0.5–1 month and for skin hydration after 2 weeks. In another study by Chou et al. (24), TEWL was measured in cement workers exposed to chromium. They reported a significant increase in TEWL for workers exposed to high levels of chromium. More recently, du Plessis et al. (25) measured TEWL and skin hydration in base metal refinery workers. Results indicated a significant decrease in skin hydration during an 8 h work shift, which recovered to baseline (before shift) levels at the end of the shift. A significant increase was reported between TEWL measured prior to and after the work shift. Changes in skin barrier function were most probably due to exposure to sulfuric acid used in the electrowinning (refining) of nickel. Furthermore, Kutting et al. (26) measured TEWL in metal-workers and reported a slightly but significantly lower TEWL in a group of workers using barrier cream after a 1 year follow-up. However, no other significant difference in TEWL were reported for other sub-groups investigating skin care, skin protection, or both. Most evident from these studies are: (i) the variation in ambient measurement conditions [e.g. temperature and relative humidity (RH)] under which skin barrier function was measured; (ii) the range of different anatomical positions (locations) that were measured; (iii) the frequent lack of information regarding the exact methodology of measurements (e.g. acclimatization time, calibration of instruments and number of measurements for each anatomical position); and (iv) the manner in which collected data were represented and interpreted. Guidelines exist for the measurement of TEWL and skin hydration in highly controlled clinical settings (7, 27, 28); however, measurement conditions in non-clinical settings, such as workplaces, may be more variable as a result of numerous factors that are often beyond the control of investigators. Workplaces represent ‘worst-case’ environments for in vivo measurement of skin properties. Hence, there is a need to develop guidelines on non-clinical (e.g. workplace) measurement of TEWL and skin hydration to establish best practices for data collection and reporting. In response to this need, an expert workshop was convened as part of the 5th International Conference on Occupational and Environmental Exposure of the Skin to Chemicals (OEESC) held in Toronto, Canada in June 2011. This paper presents a consensus summary of workshop participants to develop guidelines and best practices for measuring TEWL and skin hydration in non-clinical settings such as the workplace.

During the last few decades, the interest in skin permeation of, specifically, metals has increased with the in vitro method utilizing diffusion cells as the prominent method of investigating permeability. This review provides a systematic synopsis focused on an in vitro diffusion cell method utilizing human skin and examines the differences in experimental design as this could influence the results obtained. The permeation of metals such as chromium, cobalt, copper, gold, lead, mercury, nickel, palladium, platinum, rhodium, silver, titanium, and zinc are discussed. The metals included in this review, except for titanium and zinc, can permeate through intact human skin under physiological conditions. On the basis of flux values, the order of permeability could be summarized as Cu > Pb > Cr > Ni > Co > Pt > Hg > Rh (excluding nanoparticles). Permeability of metals through human skin is highly variable with the different methodologies as a contributing factor. Furthermore, metals are retained in the skin which could lead to reservoir (depot) formation and extended exposure even after the removal thereof from the outer surface of the skin. Finally, recommendations are provided on the standardization of experimental design and format of data reporting to enable the comparison of results from future in vitro metal permeation studies National Research Foundation of South Africa (Thuthuka Programme) with grant no. 80635 and the South African Medical Research Council