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Alternative biological monitoring methods are currently being pursued to better quantify pesticide exposures. In this study, the feasibility of using saliva as a tool for measuring diazinon exposure was determined in an animal model. Male Spraque-Dawley rats were dosed with 1 or 10 mg/kg diazinon by bolus intravenous injection. Time-matched saliva and arterial blood samples were collected from 10 to 250 min post administration. Diazinon was distributed and eliminated rapidly in rats following intravenous (iv) bolus injection, according to a two-compartmental pharmacokinetic analysis. Salivary concentration of diazinon showed a strong correlation with plasma concentration of diazinon. The saliva/plasma (S/P) concentration ratio of diazinon was not affected by administered dose, sampling time, or salivary flow rate, suggesting that salivary excretion of diazinon in rats is fairly constant. Diazinon concentrations in saliva were consistently lower than those in arterial plasma. The mean S/P concentration ratios of diazinon were 0.16 and 0.13 for 1 and 10 mg/kg iv bolus doses, respectively. It is most likely that the incomplete transfer of diazinon from plasma to saliva is due to protein binding of diazinon in plasma. If the protein-unbound fraction of diazinon in plasma is used to calculate the S/P ratio, the S/P concentration ratio of diazinon is close to unity. The results from this study support the conclusion that diazinon salivary concentrations not only can be used to predict the plasma levels of diazinon in rats, but also reflect the unbound fraction of diazinon in plasma.

This analysis compares two deterministic reentry exposure models that differ in their treatment of the time dependence of dermal absorption. The first model, called the "traditional model," assumes that dermal absorption is a fixed fraction of the cumulative load on skin at the end of the workshift and that absorption is independent of residence time on the skin. The second model, called the "time-integrated model," incorporates the time dependence of both exposure and absorption by assuming that absorption begins at the outset of exposure and continues through the workshift and beyond, until an effective washing event occurs. These two models were evaluated using previously collected biological monitoring data from apple thinners exposed to azinphosmethyl. Daily doses predicted by the models were compared to doses estimated from the biological sampling results assuming pseudo steady-state excretion. The geometric mean dose estimated from the biological sampling data was 20 microg/kg/day. Corresponding geometric mean doses produced by the traditional model and the time-integrated model were 79 microg/kg/day and 24 microg/kg/day, respectively. When the doses predicted by the traditional model were plotted against those estimated from the biological measurements, the slope of the regression line was significantly greater than 1 (beta = 1.37). However, when this same analysis was conducted for the doses predicted by the time-integrated model, the confidence interval around the slope encompassed 1 (beta = 1.01). Thus, time-integrated treatment of absorption appeared to provide more realistic dose estimates than did the traditional approach.

Agricultural workers reentering fields after pesticide application to engage in hand labor activities are subject to potentially significant dermal exposures to residues on foliage and in soil. Environmental Protection Agency (EPA) guidelines for assessment of post-application exposures were originally described in the 1984 Pesticide Assessment Guidelines Subdivision K which is currently undergoing revision. A successor document will eventually appear as Series 875, Group B Postapplication Exposure Monitoring Test Guidelines. Regulatory protocols found in these documents utilize dislodgeable foliar residues, foliage-to-human-transfer coefficients, and duration of activity to estimate exposure. Dermal absorption factors are then used to estimate dose. However, the experiments from which absorption factors are derived typically involve constant or nearly constant exposures which are not consistent with assumed field exposure conditions. This can lead to inconsistent interpretation and questionable dose estimates. An AFL-CIO challenge to procedures used by EPA to estimate the dose of the fungicide captan [N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide] to strawberry harvesters, which elicited a response from EPA, provides a useful opportunity for examination of the derivation and use of absorption factors. An improved, but still relatively simple, method for dermal dose estimation featuring explicit treatment of the time dependence of absorption has been developed. A benefit of the proposed method is capability for consideration of the effect of delay in post-shift washing on dose.

Hand exposures of apple thinners to the pesticide azinphos-methyl (Guthion) were measured using three methods (glove, handwash, and wipe). Hand exposure sampling for each method was conducted following apple thinning work for a period of two hours for six to eight workers. Foliar residue samples were collected on each day of hand exposure sampling in the same orchard blocks that were thinned; foliar residues are considered to have been constant during the four-day study, which took place, on average, six days after pesticide application. Hand exposure estimates derived from each of the three methods differed significantly (ANOVA: p < 0.001). Mean measured exposure rates for the glove, handwash, and wipe methods were 6.48, 1.83, and 0.28 mg/hr, respectively. A corrected estimate of hand exposure, 2.7 mg/hr, was calculated from the handwash measurements and the handwash removal efficiency factor from a laboratory study. Comparison with this hand exposure estimate suggests that the glove method produced a 2.4-fold overestimate of exposure, whereas the wipe method produced a 10-fold underestimate. Studies that measure hand exposure to pesticides should include a careful description of sampling methods and should recognize the potential for measurement bias. Furthermore, the standardization and validation of dermal exposure assessment methods are critical to developing more comparable and more accurate pesticide exposure estimates.

The protein binding of atrazine in plasma and its effect on salivary excretion of atrazine was determined in male Sprague-Dawley rats. The degree of protein binding of atrazine was determined at 3 steady-state plasma concentrations, 50, 150, and 250 microg/L, using an ultrafiltration technique. In total, 48 arterial blood samples were collected from 18 rats; 38 of 48 blood samples had their time-matched whole saliva samples. The average protein binding of atrazine ranged from 18% to 37%; however, it was not significantly different across the 3 steady-state plasma concentrations nor among the individual rats. Overall, 26% of atrazine was bound to plasma proteins and not available for transport from blood into saliva. Protein binding of atrazine in plasma was not correlated with total atrazine plasma concentration nor with free atrazine plasma concentration, which indicates that the protein-bound fraction of atrazine is independent of plasma concentration within the range measured in this study (30-400 microg/L). The average saliva/plasma (S/P) concentration ratio of atrazine increased from 0.7 using total atrazine plasma concentration to 0.94 (S/fP) when free atrazine plasma concentrations calculated as 26% of protein binding was used. Salivary concentration was highly correlated with free atrazine plasma concentration. The results suggest that salivary concentration of atrazine not only reflects its total plasma level but accurately measures the portion of atrazine (free atrazine) in plasma, which may be of toxicological significance.

The stability of the saliva/plasma (S/P) concentration ratio of atrazine was determined under varying conditions of salivary flow rate and plasma concentration of atrazine in Sprague-Dawley rats. In the salivary flow study, whole saliva samples were collected at different salivary flow rates while the plasma concentration of atrazine was maintained at a steady-state level of approximately 150 micrograms/L. In the plasma level study, whole saliva samples were collected at two steady-state plasma concentrations of atrazine (50 and 250 micrograms/L), while salivary flow rate was maintained at a relatively constant level. In both studies, atrazine concentrations in whole saliva and arterial plasma demonstrated a consistent relationship, but salivary concentrations were always lower than those of arterial plasma. Linear regression analysis demonstrated that the S/P concentration ratio of atrazine was not significantly different for salivary flow rates ranging from 23 to 92 microL/min/kg body weight, and did not vary for atrazine plasma concentrations between 30 and 433 micrograms/L. The S/P concentration ratio of atrazine was relatively constant throughout each experimental period (0.68 +/- 0.1 and 0.70 +/- 0.11 for salivary flow and plasma level studies, respectively) and did not differ significantly between rats. When data from both studies were pooled, salivary concentrations were highly correlated with plasma concentrations (r2 = .94). It is concluded that under these experimental conditions, the stability of the S/P concentration ratio of atrazine is not affected by variations in salivary flow rate or atrazine plasma concentrations. The results from this study support the conclusion that atrazine salivary concentrations can be used to predict plasma levels of atrazine in rats.

The extensive international use of organophosphorus compounds (OP) results in numerous acute intoxications each year. OPs inhibit acetylcholinesterase, the enzyme responsible for breaking down the neurotransmitter acetylcholine. The World Health Organization recognizes cholinesterase (ChE) biomonitoring as a preventive measure against OP overexposure. The aim of this study was to determine if dermal OP contamination could interfere with current field ChE biomonitoring assays, which use a fingerstick blood sample. In this study we also sought to determine if high levels of a plasma enzyme, A-esterase, could protect ChE from inhibition by hydrolyzing environmentally generated oxons potentially present in a fingerstick sample. A heparinized venous blood sample was collected from a volunteer. Erythrocyte acetylcholinesterase (AChE) and plasma butyrylcholinesterase (PChE) activities were measured using a field-based colorimetric cholinesterase kit. ChE dose-response curves were constructed by allowing 10-microliters blood samples to contact environmentally realistic levels of OP thioate and oxon for 10 s. An inhibition threshold could not be established for PChE when exposed to oxon within the time necessary to perform a fingerstick analysis. AChE was also inhibited by trace amounts of oxon consistent with previously reported environmental levels. These findings suggest that the reliability of field-based biomonitoring results is limited if OP residues remain on a skin surface at the time of sample collection. A-esterase's role in protecting ChE activity was investigated using capillary and venous blood from 30 unexposed individuals. Baseline ChE activities were measured, as were individual A-esterase activities using paraoxon, diazoxon, and phenylacetate as substrates. Results were then compared to ChE activities measured after 10 s of contact with an environmentally realistic amount of OP, containing 1% oxon. Both ChE activities were significantly inhibited, with capillary values being significantly more inhibited than their venous counterparts. However, no protective effect could be associated between the degree of A-esterase activity and the subsequent level of ChE inhibition observed in an individual's blood. These results suggest that (1) if there is any uncertainty about OP skin contamination, venous blood would be a more appropriate specimen to employ when using field ChE biomonitoring kits--it is collected in larger volumes and has essentially no direct contact to dermal surfaces; and (2) A-esterase activity demonstrates no protective effect against ChE inhibition upon a blood droplet's brief contact with an OP residue containing traces of oxon.

Current biological monitoring techniques are often unable to provide accurate estimates of pesticide dose in exposed worker populations. This study was conducted to investigate the feasibility of pesticide biomonitoring using saliva. Atrazine [2-chloro-4-ethylamino-6-(isopropylamino)-s-triazine], a member of the triazine herbicides, was selected to investigate salivary excretion following direct gastric administration in rats. Concentrations of atrazine in whole saliva and arterial plasma samples were determined by enzyme-linked immunosorbent assay (ELISA). Atrazine reached its highest level in both arterial plasma (238 micrograms/L) and whole saliva (157 micrograms/L) 35 min after administration of 105 mg/kg of atrazine, and then decreased with time in a parallel fashion. Although saliva atrazine levels were lower than levels in arterial plasma, there was a very high correlation between whole saliva and arterial plasma atrazine concentrations (r2 = .95). In addition, pharmacokinetic analysis suggested that salivary levels of atrazine can be used to predict concentrations of atrazine in plasma. The mean whole saliva/arterial plasma atrazine concentration ratio (S/P) was 0.66 +/- 0.11 (n = 20). The S/P ratios did not vary significantly over time, and were not affected by salivary flow rate. This study demonstrates that atrazine is transported into saliva, and that a relatively constant concentration ratio between whole saliva and arterial plasma is maintained. Because the salivary concentrations of atrazine are independent of variation in salivary flow rate, salivary monitoring of atrazine in humans may prove useful and practical. Finally, this study suggests that other pesticides with chemical and physical properties similar to those of atrazine can be monitored in saliva.

The constriction of pupil dilation following dark adaptation was studied as a potentially useful biological monitor of systemic exposure to organophosphorus pesticides (OPs). Pupil dilation and blood cholinesterase levels were monitored in 4 cynomolgus monkeys following oral administration of 2.0 mg/kg parathion in corn oil. No consistent pattern of change in pupil/iris diameter ratios following exposure was found despite depressions in blood cholinesterase activities of 27-50% for red cells and 65-80% for plasma. A slight mydriasis was observed in one of the monkeys, who appeared the most affected behaviorally by the exposure. Results of this work suggest that the measurement of pupil dilation after dark adaptation is not a sensitive indicator for systemic exposure to OPs. However, in situations where direct exposure to the eyes may occur, such as during aerial or airblast pesticide applications, other studies indicate that constriction of pupil dilation can occur at exposure levels below those resulting in systemic effects.

Exposure to and absorption of Guthion 50 W.P. (azinphos-methyl) were estimated in orchardists from the Okanagan Valley in British Columbia who were involved in mixing, loading, and application with ultra-low volume air blast equipment. Air monitoring and patch techniques were used to estimate exposure, and alkyl phosphate excretion and cholinesterase inhibition were measured to estimate absorption. All workers were issued with standardized cotton shirts, trousers, and long-sleeved coveralls. All wore half-face respirators, gloves, boots, and hats. Eight wore rubberized protective clothing in addition. The indirect method of measuring urinary metabolites appeared to be the most sensitive. All workers had quantifiable levels of alkyl phosphates following exposure, and 24-h urine samples provided a more reliable estimate than first morning voids. A high correlation was observed between 48-h alkyl phosphate excretion and amount of active ingredient sprayed. A fluorescent tracer was added to the tank along with the Guthion. The finding of Guthion on patches beneath the clothing was confirmed by the presence of the tracer on the skin. With the ultralow-volume application used in this study, the rubberized clothing did not appear to be significantly more protective than the heavy coverall. There was no significant depression of either red blood cell or serum cholinesterase activity in any workers.