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Chemical transport models (CTM) can have large biases and errors when simulating pollutant concentrations. To improve the characterization of fine particulate matter (PM2.5) over complex terrain fo...

Construction activities have long been recognized as a pertinent source of PM2.5 though limited information exists regarding chemical characteristics of aerosols generated during building demolition/construction. A comprehensive investigation was carried out to assess the physical (SEM analysis) and chemical (ICP MS analysis) properties of PM2.5 in a building demolition and construction site and compared with background. Average concentrations of PM2.5 at both the sites exceeded the National Ambient Air Quality Standards (NAAQS). Overall trend of the total metal concentrations of PM2.5 followed the order of (Na, Ca, Al, Mg, Fe, Zn) > (Ti, Sr, Cd, Ba, Pb, V, Cr, Mn, Co, Ni, Cu) in both the sites. Sr, Ba, Mg, Zn, Ti, Cd, Al, Cr, Fe, Co, Mn, V, Ni, Ca, and Zn showed a ∼1.3-3.0 fold increase, and Pb showed the highest increase of almost >3.5 times when compared to the background concentrations. Health risk estimates based on the bio-available concentration of metals indicated that hazard quotient (HQ) values for non-carcinogenic metals were within the prescribed limit (HQ ≤ 1). However, the excess lifetime cancer risk (ELCR) for the carcinogenic metals Pb, Ni, Cd, and Cr(VI) were higher than the guideline limits of USEPA.

Surface sediment samples were collected at 104 stations in 34 different locations in seasonal periods in 2013–2014 on the southeastern coasts of the Black Sea. Nickel concentrations were measured with ICP-MS after microwave digestion and were higher in two seperate region than that of others. Relatively high Ni concentrations were found in Bafra (148 ± 18 mg/kg), Derekoy (147 ± 24 mg/kg), Canik (95 ± 35 mg/kg), Caltiburnu (129 ± 13 mg/kg), Carsamba (127 ± 4 mg/kg), Terme/Unye (94 ± 28 mg/kg), Akcaabat (95 ± 13 mg/kg), Carsibasi (77 ± 14 mg/kg), Vakfikebir (64 ± 5 mg/kg) and Gorele (53 ± 15 mg/kg). Nickel concentrations were higher than Effects Range-Medium (ERM) limits in the western and middle part of the region. Ni enrichment levels in sediments were calculated from both core data and earth crust values as a background. It was determined that the enrichment factors found by using earth crust values produced quite misleading results due to the geological variation of the region. It is also concluded that Ni concentrations in marine sediments of the southeastern coasts of the Black Sea are related to terrestrial geological structure.

This study was done to evaluate heavy metal concentrations in street dust samples, to compare measured concentrations in samples to background concentrations in order to make evaluations for pollut...

With utility-scale photovoltaic (PV) projects increasingly developed in dry and dust-prone geographies with high solar insolation, there is a critical need to analyze the impacts of PV installations on the resulting particulate matter (PM) concentrations, which have environmental and health impacts. This study is the first to quantify the impact of a utility-scale PV plant on PM concentrations downwind of the project site. Background, construction, and post-construction PM2.5 and PM10 (PM with aerodynamic diameters

This article summarizes the results from a survey of polycyclic aromatic hydrocarbon (PAH) and metal concentrations measured in surface and subsurface soil samples that were collected from background locations throughout Manhattan, New York, between August 2005 and May 2006. The 95th percentile total 16 US EPA Priority Pollutant PAH concentrations in surface and subsurface soils were 24.8 and 53.1 mg/kg, respectively. Diagnostic PAH source ratios for surface and subsurface soils are presented, which provide plausible bounds for where these ratios would and would not be able to confidently differentiate background soils from soil samples that are impacted by PAH contamination. The 95th percentile concentrations for lead in surface and subsurface soils were 891 and 2,540 mg/kg, respectively, and the 95th percentile concentrations for mercury in surface and subsurface soils were 1.9 and 2.7 mg/kg, respectively. A not-unexpected finding of the study was that most surface soils and all subsurface soils...

The distribution of Mn and Ni in soils of one of the most famous winegrowing regions of Spain, Rioja D.O.Ca (Denomination of origin, Spain's top category), was studied in detail according to its geographical location. There were background concentrations of 288.81 mg kg−1 total Mn in the surface horizon and 296.06 mg kg−1 in the subsoil; and a total Ni content of 17.89 mg kg−1 in the surface horizon and 24.76 mg kg−1 in the subsoil. The amounts of Mn bio- or phytoavailable were 5.28 mg kg−1 in the upper horizon and 4.70 mg kg−1 in the subsurface horizon; and for Ni bio- or phytoavailable, the amounts were 0.14 mg kg−1 in the upper horizon and 0.13 mg kg−1 in the deeper horizon. Spatial distribution patterns were established using GIS contour maps for the two elements, showing significant variations within and between the sites. The local contamination is generally associated with the quantities that are added to the soil or water from man-made sources such as industrial discharge and volatile emissions, s...

An ultra-performance liquid chromatography method using a triple quadrupole mass spectrometer was developed and validated for the determination of steroid oestrogens in wastewater matrices. To date, analytical methods established in the literature for 17α-ethinylestradiol have been unable to achieve the proposed predicted no effect concentration of 0.1 ng l−1. The extensive sample pretreatment and analytical methodology proposed herein enable 17α-ethinylestradiol to be determined at very low background concentrations with a theoretical method detection limit of 0.06 ng l−1 which has been applied in real environmental matrices. During the validation process, a trickling filter wastewater treatment works was monitored to demonstrate the method's application. Oestrogen removal across the filters demonstrated good removals of natural free oestrogens (≥62.0%) with lower removals of the synthetic oestrogen 17α-ethinylestradiol (29.2%) from wastewaters at 10°C. The method's application illustrates its capability...

In order to calculate total concentrations for comparison to ambient air quality standards, monitored background concentrations are often combined with model predicted concentrations. Models have low skill in predicting the locations or time series of observed concentrations. Further, adding fixed points on the probability distributions of monitored and predicted concentrations is very conservative and not mathematically correct. Simply adding the 99th percentile predicted to the 99th percentile background will not yield the 99th percentile of the combined distributions. Instead, an appropriate distribution can be created by calculating all possible pairwise combinations of the 1-hr daily maximum observed background and daily maximum predicted concentration, from which a 99th percentile total value can be obtained. This paper reviews some techniques commonly used for determining background concentrations and combining modeled and background concentrations. The paper proposes an approach to determine the joint probabilities of occurrence of modeled and background concentrations. The pairwise combinations approach yields a more realistic prediction of total concentrations than the US. Environmental Protection Agency's (EPA) guidance approach and agrees with the probabilistic form of the National Ambient Air Quality Standards.EPA's current approaches to determining background concentrations for compliance modeling purposes often lead to "double counting" of background concentrations and actual plume impacts and thus lead to overpredictions of total impacts. Further, the current Tier 1 approach of simply adding the top ends of the background and model predicted concentrations (e.g., adding the 99th percentiles of these distributions together) results in design value concentrations at probabilities in excess of the form of the National Ambient Air Quality Standards.

We conduct a retrospective study of ozone formation in the Lower Fraser Valley (LFV), using numerical models, observations, and emission inventories in order to understand relationships between reductions in local precursor emissions and episodic ozone concentrations. Because there appears to be little or no impact from precursor emissions upwind of the LFV during ozone episodes and because background concentrations of ozone and its precursors are generally from the North Pacific Ocean and quite low, summertime ozone formation in the LFV is mostly caused by local emissions. The observed change in behaviour of ozone formation must, therefore, arise from reductions in local precursor emissions. We exploit the observed changing precursor emission–ozone concentration relationship to perform a dynamical model evaluation. Complicating the analyses are an observed shift in the population patterns within the valley over the last 25 years and a small but documented change in the tropospheric background concentrati...

The present review summarizes the available data on the concentration of trace elements (TEs) in soils and their availability to plants with a view to reflect the quality and safety of food and fodder crops. Most soils in western Balkan countries are not contaminated. However, soils around industrial centers and historical mining sites do create concern for food and feed safety. Also high concentrations of TEs are related to their geochemical original. For example, ultrabasic rocks and serpentinites in western Serbia and western Bosnia are very rich in chromium, nickel, magnesium, iron (Fe), and cobalt, and cover an area of 5200 km2. High TE concentrations caused by anthropogenic activities are also reported. In vineyard soils in Croatia, concentrations of cadmium, copper (Cu), and zinc (Zn) were much higher than their background concentrations. On the other hand, TE deficiency in plants is also prevalent in the regions. For example, Zn and Fe deficiencies in eastern parts of Croatia and northern...

Total mercury (Hg) was measured in 150 infant formula products (as sold) and oral electrolyte solutions purchased in Canada in 2003. Results less than the limit of detection (LOD) were reported as the numeric value of the LOD. Electrolytes contained the lowest concentrations, averaging 0.026 ng/g. Average levels in milk-based ready-to-use, concentrated liquid and powdered concentrate were 0.028, 0.069 and 0.212 ng/g, respectively. In soy-based formulae, the respective mean concentrations were 0.049, 0.101 and 0.237 ng/g. These concentrations cannot be considered on an absolute basis because 76% of sample concentrations fell below the limit of detection. Despite the inability to measure many of the actual background concentrations, the method was sufficiently sensitive to identify clear cases of low-level Hg contamination (up to 1.5 ng/g) of individual lots of powdered formula. Also, all the different lots of one brand of concentrated liquid infant formulae had significantly higher concentrations of Hg than those of all other concentrated liquid products. After dilution with preparation water, the Hg concentrations in all products would be lower than the Canadian Drinking Water Guideline for Hg of 1 ng/mL and too low to impact on health.

The ability to predict hypolimnetic dissolved oxygen concentrations in lakes and to track changes in concentrations over time in response to known environmental stressors is critical for effective lake management. The background concentrations of deepwater oxygen, in particular, provide important management benchmarks for assessing the impact of current and future shoreline residential development on water quality. Background can be defined as the conditions that exist in the absence of, or prior to, human influence. We compare 2 models commonly used to predict end-of-summer, volume-weighted hypolimnetic oxygen (VWHO) concentrations in Canadian Shield lakes. The paleoecological and empirical models are evaluated in their ability to predict present-day VWHO concentrations, and then compared in their predictions of background VWHO concentrations and in predictions of changes in VWHO from background to present-day conditions. The predictive power of the 59-lake paleoecological model (jackknifed r2 =...

The National Ambient Air Quality Standard (NAAQS) for ground-level ozone, previously set as an 8-hr average of 0.08 parts per million (ppm), has been revised by the U.S. Environmental Protection Agency (EPA). Historically, background concentrations originating from non-local sources were not considered to be a major constituent of ground-level ozone. However, previous research has shown that background ozone concentrations often exceed the new 8-hr NAAQS of 0.075 ppm, and that high background concentrations are particularly troublesome in the mid-latitudes. This study measured ozone at ground level and at 210 m above ground level in Tulsa, OK (36 degrees N, 96 degrees W), from June 1 to November 30, 2005. Background ozone concentrations as high as 0.05 ppm were recorded, and substantial variability was observed in conjunction with the polar jet stream and the seasonal influence of large-scale subtropical high pressure at the study location. Additionally, the highest observed background concentrations coincided with maximum photochemical generation at ground level. On the basis of the magnitude and variability of background ozone, a more stringent 8-hr ozone standard will be difficult for local or regional regulatory agencies to meet. A clear understanding of the impacts of background ozone will be required to make and meet new State Implementation Plans (SIPs).

Using information from a variety of published studies, a data set was assembled with approximately 200 surface soil samples collected from urban locations across New York State (NYS) not directly influenced by known sources of contamination. Statistical characteristics for 17 polycyclic aromatic hydrocarbon (PAH) compounds were examined and compared with draft NYS soil cleanup objectives that had been developed using risk-based and rural background considerations. For the carcinogenic PAH compounds, approximately 12–40% of samples exceeded cleanup objectives proposed for residential land use, but few samples exceeded the less stringent standards proposed for commercial and industrial properties. Qualitative comparisons with a recent study of NYS rural soils indicated substantial differences in background PAH levels between urban and rural locations. These findings motivate further research into the best manner for incorporating background information into soil cleanup objectives for urban areas.

Farmed mussels have been collected on a monthly basis since 1999 from a remote site on the west coast of Scotland for polycyclic aromatic hydrocarbon (PAHs) analysis with the aim of establishing background concentrations as a benchmark against which to assess any environmental incident. Total PAH (2- to 6-ring parent and alkylated) concentrations ranged from 12.5 to 151.2 μg kg−1 wet weight. Seasonal trends were evident with concentrations being significantly higher for samples collected between November and March compared to those collected between April and October. By taking the median of medians for each of these time periods two background concentrations are suggested for the total PAH concentrations (2- to 6-ring PAHs parent and alkylated); for April to October: 31.2 μg kg−1 wet weight and for November to March: 62.9 μg kg−1 wet weight. Individual PAH concentrations were mainly below the OSPAR Background Assessment Concentrations (BACs), where they are specified, and were only exceeded for the heavi...

SF6 and PFC are being used as state-of-the-art tracers in tracer-technology programmes aimed at efficient oil recovery in the North Sea. This study aimed at specifying sources of leakage and quantifying emission levels of such gases and at evaluating their effect on global warming. To satisfy these goals, quantification of SF6 and PFC combustion by-products under different realistic flame/temperature conditions (turbine, refinery, power plant, households and car engine) has been performed. The PFC compounds studied were PMCP (CF3C5F9), PMCH (CF3C6F11) and 1, 2-PDMCH ((CF3)2C6F10). Three-dimensional transport atmospheric modelling has been carried out using UAM-AERO for four different tracers' emissions scenarios (Base scenario, one including maximum emissions of tracers and two scenarios including overestimated emissions during loading processes and distribution over the land of Norway). The results showed a significant increase in the background concentrations of SF6 and PFC in the last two ment...

A comprehensive field study was conducted to determine the background concentrations of benzo [a] pyrene (B[a]P) in soil samples collected at different points on a grid covering most of the northern and middle parts of the Kingdom of Bahrain. The average B[a]P concentration was 108.4 ng g−1 in winter and 73.0 ng g−1 in summer. The capital city, Manama, and the industrial areas of the country showed the highest levels of B[a]P.

In preparation for a study of the relative oral bioavailability of polychlorinated dibenzo-p -dioxins and dibenzofurans (PCDD/Fs) in soils (typically containing less than 1 ppb 2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD] toxic equivalents [TEQ]), the background concentrations of PCDD/Fs and selected polychlorinated biphenyls (PCBs) were measured in liver and adipose tissue from female Sprague-Dawley rats and juvenile swine after 30 d of ingesting laboratory chow. The measured concentrations of TCDD and other PCDD/Fs in rat livers were severalfold less than previously reported in the literature for control (unexposed) laboratory rodents. The concentrations of PCDD/Fs and selected PCBs in livers of swine were three- to fourfold lower than those reported for rats. The lower concentrations found in this study compared to previous findings may be due to inadvertent laboratory contamination in previous studies or to declining levels of PCDD/Fs in laboratory feed, which parallel the declines in emissions, general...

To further our understanding of the groundwater-to-indoor-air exposure pathway, a database of 270 paired groundwater and indoor air measurements of volatile organic compounds (VOCs) from 31 sites has been compiled and analyzed. Using regression analyses, these data have been analyzed to (1) detect evidence of indoor air impacts from dissolved petroleum hydrocarbons or chlorinated solvents in underlying groundwater, (2) estimate the true attenuation factor for volatilization from groundwater to indoor air, and (3) assess the utility of popular groundwater-to-indoor-air transport models for evaluating this exposure pathway. Key findings include the following: (1) > 95% of the indoor air concentrations fall within or below the range of national background indoor air values; (2) there is no correlation between petroleum constituent concentrations measured in groundwater and the concentrations of these VOCs in indoor air of overlying structures; and (3) for chlorinated solvent cases, a correlation between grou...

This paper discusses general approaches for evaluating the utility and manner of conducting background analyses in soil for ecological risk assessments. The types and sources of background data are discussed, and advantages and disadvantages of using literature-based versus site-specific background data are presented. The value of background evaluations is discussed with regard to the goals and objectives for a project. A comparison of literature-based ecological soil screening levels with generic metal background concentrations is presented to illustrate a typical problem in incorporating background data in ecological risk assessments, which is that many generic background concentrations are higher than ecological screening levels. This brings into question both the relevance of ecological screening levels and generic background levels. These issues are discussed along with cost-benefit considerations in an attempt to provide recommendations for determining the most appropriate type of background evaluat...

Background concentrations of soil arsenic have been used as an alternative soil cleanup criterion in many states in the U.S. This research addresses issues related to the interpretation of background concentrations of arsenic in near pristine soils in Florida. Total arsenic was measured in 448 taxonomic and geographic representative surface soil samples using USEPA Method 3052 (HCl-HNO 3 -HF, microwave digestion) and graphite furnace atomic absorption spectrophotometry analysis procedure. Values were log-normally distributed, with geometric mean and baseline concentration (defined as 95% of the expected range of background concentrations) providing the most satisfactory statistical results. An upper baseline concentration of 6.21 mg As/kg was estimated for undisturbed soils (n=267) compared to 7.63 mg As/kg for disturbed soils (n=181). Temporal trend of total soil arsenic concentrations from 1967 to 1989 paralleled decreased usage of arsenic in U.S. agriculture. Soil arsenic background concentrations were...

An approach for defining the quality of surface sediments of limited areas in terms of heavy metal contents is proposed. Sediments were taken on a bi‐dimensional mapping, for checking possible different sources of pollution in the case study, a harbour zone. Non residual metals were determined by ICP‐AES in cold diluted hydrochloric acid leachates of sediments. An “enrichment factor”;, r, can be computed for each metal: metals with r values exceeding unity can be considered as indicators of metal pollution. A “total enrichment factor”;, R, was proposed in order to assess the degree of pollution of sediments for each site. R is an adimensional value that accounts for the presence of metals that exceed threshold values determined by background concentrations.

Trace metals such as zinc play an important role in the normal metabolic functioning of all organisms. However, metals can become toxic if background concentrations are exceeded in the environment. This study investigated the sublethal effects of zinc on the haematology of Oreochromis mossambicus at different water temperatures. Fish were exposed to sublethal zinc (Zn) concentrations of 40μg/l (mean Zn concentration measured from the Mhlathuze River) for a period of 96h at different water temperatures representing the seasonal temperatures in the Mhlathuze River (18°C, 24°C, 28°C and 32°C). Exposure to zinc at 28°C and 32°C resulted in the most pronounced haematological changes in O. mossambicus. The erythrocytotic conditions found following exposure to Zn could be attributed to damage to the gill surface. The ensuing hypoxic conditions are alleviated through the release of large amounts of immature RBC into the circulatory system. The leucocytotic conditions support the findings of damage to the gill sur...

Data on the toxicokinetics of urinary 1-hydroxypyrene (OHP) elimination in workers exposed to PAHs were critically examined and led to the conclusions that half-lives from on-site studies are actually shorter (6–9 h) than the generally reported values. It is demonstrated that the renal elimination and excretion kinetics of OHP and urinary creatinine follow a similar pattern. The findings set the sound bases for adjustment of OHP concentrations to creatinine and therefore justify the corrections which have been applied. Additionally, urinary OHP determinations were used to evaluate the efficiency of respiratory protective equipments. In workers equipped with Airstream® helmets, the excretion levels of OHP are clearly in the background concentrations compared with levels in those without any protection when the skin penetration route were inhibited. The efficiency of the helmets may be higher than 95%. In practice, the notion of protection factor is preferred as the efficiency is also dependent on ...

An accurate measure of "background" airborne Cr(VI) concentrations will be necessary to derive site-specific health-based Cr(VI) soil concentrations at sites containing chromite ore processing residues (COPR) in Hudson County, NJ. To date, no such data have been collected in New Jersey. This paper describes an air sampling program designed to measure background concentrations of Cr(VI) in Hudson County and compare those concentrations with the air sampling results obtained previously at 30 COPR sites in Hudson County. Background airborne Cr(VI) concentrations ranged from 0.2 to 3.8 ng/m3 with an arithmetic mean of 1.2 ng/m3. Comparisons of the airborne Cr(VI) concentrations previously measured at 30 COPR sites indicated that more than two-thirds of the sites had mean airborne Cr(VI) concentrations that were not statistically significantly greater than background. Our findings suggest that, in general, vehicle disturbance is required for significant soil suspension to occur at these sites. Since airborne Cr(VI) concentrations at many of these sites are close to background, it is critical that background airborne Cr(VI) levels be considered when deriving health-based soil standards at the COPR sites.

This paper evaluates anthropogenic sources of mercury and dioxin, surveys background concentrations, and estimates the extent and pathways of human exposure to these chemicals in the United States for the purpose of determining the greatest sources of mercury and dioxin in the environment, and proposing best estimates of background concentrations. In addition, we estimate average daily intake using a terrestrial food chain model, described in detail elsewhere{sup 7}.

The Pliofilm cohort is the most intensely studied group of workers chronically exposed to benzene. Information on this cohort has been the basis for regulations and/or guidelines for occupational and environmental exposure to benzene. Rinsky et al. (1986, 1987) and Crump and Allen (1984) developed different approaches for reconstructing the exposure history of each member of the group. The predicted levels of exposure, combined with the data on the incidence of disease, have been used to estimate benzene's carcinogenic potency. In this paper, recent information from worker interviews and historical records from the National Archives and elsewhere were used to evaluate the accuracy of prior exposure estimates and to develop better ones for the cohort. The following factors were accounted for: (1) uptake of benzene due to short-term, high-level exposure to vapors, (2) uptake due to background concentrations in the manufacturing building, (3) uptake due to contact with the skin, (4) morbidity and mortality data on workers in the Pliofilm process, (5) the installation of industrial hygiene engineering controls, (6) extraordinarily long work weeks during the 1940s, (7) data indicating that airborne concentrations of benzene were underestimated due to inaccurate monitoring devices and the lack of adequate field calibration mated due to inaccurate monitoring devices and the lack of adequate field calibration of these devices, and (8) likely effectiveness of respirators and gloves. Our estimates suggest that Crump and Allen (1984) overestimated the exposure of workers in some job classifications and underestimated others, and that Rinsky et al. (1981, 1986) almost certainly underestimated the exposure of nearly all workers. Airborne concentrations of benzene at the St. Marys facility during the years of its operation were found (on average) to be about half those of the two Akron facilities. Our analysis indicates that short-term, high-level exposure to benzene vapors and dermal exposure significantly increased (by about 25-50%) the total absorbed dose of benzene for some workers. One of the key findings was that, unlike prior analyses, the three facilities probably had significantly different airborne concentrations of benzene, especially during the 1940s and 1950s.

Vertical concentration profiles of organic‐C, Mn, Cu, Pb and Zn have been determined in the sediments of six lakes in northwest England. The heavy metals Cu, Pb and Zn are greatly enriched in sediments deposited since the mid‐nineteenth century compared to background concentrations. Several indirect lines of evidence indicate that the enrichments result primarily from enhanced atmospheric deposition associated with industrial development throughout the region.

Soybeans (Glycine max var. Dare) were exposed to hydrogen fluoride at 2.0 μg HF m‐3‐ 16.1 μg HF m‐3 during continuous and interrupted exposures of 109 days and 53 days, respectively, following development of the seventh trifoliates. Resulting patterns of accumulation and loss suggest that leaf fluoride is exchanged with the atmosphere through a catenary two compartment system. The fluoride literature was reviewed with respect to site of fluoride entry, transport, and accumulation and used to define the boundaries and exchange relationships of the compartments. The experimental data suggest that leaf injury plays an important role in accumulation by limiting the surface available for exchange. Measurement of the rate of fluoride disappearance following intermittent exposure suggests that the distribution of excretable fluoride in the leaf changes with time and leaf necrosis. Fluoride levels in leaves, fruit and seeds showed significant increases over background concentrations, with highest levels ...

A chemiluminescence effect was found during oxidation of disulfitomercurate complex in aqueous solutions with KMnO4 under acid conditions. By employing a filter technique for air sampling the chemiluminescence method is applied to the detection of atmospheric sulfur dioxide. The quality of the complete procedure is demonstrated by comparative calibrations from the liquid and gas phase and comparative measurements with several other SO2 sensitive methods. The detection limit is shown to be (10±1) pptv SO2. Some measurements of atmospheric SO2 background concentrations are shown in order to demonstrate the potential of the whole procedure in its application to atmospheric SO2 measurements.

This paper is concerned with the estimation of air pollutant concentrations by solving the advection-diffusion equation using the Galerkin finite element method. The physical properties denoting the transport arid diffusion of the air pollution are assumed to be expressed by the two-dimensional advection-diffusion equation where the height of the stack is low and the vertical diffusion is small. The distributions of wind velocities and background concentrations are estimated using an interpolation method based on the observed data at monitoring stations. The Galerkin finite element method estimates the temporal and spatial distributions of air pollutant concentrations by solving the advection-diffusion equation. The estimation experiment of sulphur dioxide concentrations is carried out over the industrial area of Tokushima Prefecture, Japan, and the numerical results indicate the effectiveness of the proposed, method.

The background concentrations of some volatile organic compounds in urban and rural English locations have been analysed by gas chromatography after concentration on active carbon. A similar pattern of concentrations was measured at all locations. The results show broad agreement with those of similar analyses of Paris, Zurich, and Houston, but are at variance with those reported for Leningrad.

Sources contributing to human exposure to chloroform have been identified in the environment. A general approach has been followed to compare hemispheric background concentrations to those .in a co...

The mercury content of sediments and water in the Wairua (Wairoa) River, Northland, and of molluscs from the estuary of the river was determined to establish the extent of natural dispersion of mercury from deposits at the source of the river at Puhipuhi. The mercury content per gram wet weight of cockles, Chione stutchburyi, (0.032 ppm); rock oysters, Crassostrea glomerata, (0.081 ppm); pipi Paphies australe, (0.019 ppm); and green‐lipped mussels, Perna canaliculus, (0.017 ppm) was compared with that of specimens of the same species from other areas where presumably only background concentrations exist. Mercury could be detected in sediments at least 35 km from the deposits, but in water only up to about 8 km. Normal background levels were established for the soft parts and individual organs of the four species of mollusc investigated; of the molluscs found in the estuary of the Wairua River, only C. glomerata had anomalous amounts of mercury, but whether this indicates abnormally high mercury l...