Model studies for evaluating the neurobehavioral effects of complex hydrocarbon solvents III. PBPK modeling of white spirit constituents as a tool for integrating animal and human test data.

As part of a project designed to develop a framework for extrapolating acute central nervous system (CNS) effects of hydrocarbon solvents in animals to humans, experimental studies were conducted in rats and human volunteers in which acute CNS effects were measured and toxicokinetic data were collected. A complex hydrocarbon solvent, white spirit (WS) was used as a model solvent and two marker compounds for WS, 1,2,4-trimethyl benzene (TMB) and n-decane (NDEC), were analyzed to characterize internal exposure after WS inhalation. Toxicokinetic data on blood and brain concentrations of the two marker compounds in the rat, together with in vitro partition coefficients were used to develop physiologically based pharmacokinetic (PBPK) models for TMB and NDEC. The rat models were then allometrically scaled to obtain models for inhalatory exposure for man. The human models were validated with blood and alveolar air kinetics of TMB and NDEC, measured in human volunteers. Using these models, it was predicted that external exposures to WS in the range of 344-771mg/m(3) would produce brain concentrations similar to those in rats exposed to 600mg/m(3) WS, the no effect level (NOEL) for acute CNS effects. Assuming similar brain concentration-effect relations for humans and rats, the NOEL for acute CNS effects in humans should be in this range. The prediction was consistent with data from a human volunteer study in which the only statistically significant finding was a small change in the simple reaction time test following 4h exposure to approximately 570mg/m(3) WS. Thus, the data indicated that the results of animal studies could be used to predict a no effect level for acute CNS depression in humans, consistent with the framework described above.

Determination of methyl 5-hydroxy-2-benzimidazole carbamate in urine by high-performance liquid chromatography with electrochemical detection.

A high-performance liquid chromatographic (HPLC) assay for methyl 5-hydroxy-2-benzimidazole carbamate (5-HBC) in urine was developed in order to assess the exposure of workers to the pesticide carbendazim. 5-HBC is measured in urine after hydrolysis, sample clean-up through a strong cation-exchange (SCX) column and extraction with ethyl acetate. HPLC with electrochemical detection provides selective and sensitive determination of 5-HBC with a detection limit of 5 micrograms/l. A C18 reversed-phase column was used with 0.06 M ammonium acetate solution (pH 8)-methanol (73:27) as mobile phase. The method was validated with respect to hydrolysis of urine samples, analytical recovery of spiked 5-HBC, stability of 5-HBC conjugates, limit of detection, background and precision. The overall analytical recovery from urine was better than 60%. 5-HBC, excreted in urine as a conjugate, was stable for at least one year when stored at -20 degrees C. A background of ca. 5 micrograms/l was detected in urine from some non-occupationally exposed persons. Between-day coefficients of variation as calculated from the results of the stability test were 7, 4 and 4% for concentrations of 61, 244 and 295 micrograms/l 5-HBC, respectively (n = 16).

Determination of 2-isopropoxyphenol in urine by capillary gas chromatography and mass-selective detection.

An analytical method for the assessment of the exposure of workers to the pesticide propoxur through biological monitoring has been developed. This study was part of a survey of occupational exposure to pesticides used in greenhouses for the growing of ornamental plants. In order to assess the actual absorbed amount of propoxur in the body, an analytical method for its metabolite 2-isopropoxyphenol in urine was required. This led to the development of a gas chromatographic-mass spectrometric assay involving hydrolysis and solvent extraction. A mass-selective detector, operated in single-ion mode, provides a selective and sensitive quantification of 2-isopropoxyphenol with a detection limit of 6 micrograms/l. The method has been validated with respect to the hydrolysis of urine samples, analytical recovery of 2-isopropoxyphenol, stability of its conjugates, limit of detection, background and precision. The analytical recovery from spiked urine was over 95%. 2-Isopropoxyphenol was excreted in urine as a conjugate and was stable for at least seven months when stored at -20 degrees C. It was not detected in urine from non-exposed persons. Between-day coefficients of variation were 20, 10, 7 and 4% for concentrations of 15, 29, 150 and 213 micrograms/l, respectively. Measured as 2-isopropoxyphenol, ca. 80% of an orally administered dose of propoxur was excreted in urine within 10 h.

Gas chromatographic determination of the pesticide dodemorph for assessment of occupational exposure.

As part of a health hazard survey of occupational exposure to pesticides in greenhouse growing of ornamentals, analytical methods are developed and validated for measurement of exposure of workers to the fungicide dodemorph. A gas chromatographic method is developed using on-column injection and nitrogen-phosphorus detection for quantification. Methods for the determination of (potential) dermal exposure by the analysis of foliar dislodgeable residues and cotton gloves are validated with respect to background, analytical recovery, stability, limit of detection, and between-day coefficients of variation. Analytical recovery from 'foliar dislodgeable residue solutions' and cotton gloves is more than 95%. Dodemorph in 'foliar dislodgeable residue solutions' and on cotton gloves is stable for at least five and six months, respectively, when stored in the refrigerator. Between-day coefficients of variation are 6% for both matrices. The limit of detection is 3 micrograms per leaf sample and 150 micrograms per pair of gloves. Institute of Occupational Medicine (IOM) samplers, designed for the collection of a defined inspirable fraction of aerosols, are tested for sampling air-borne dodemorph. IOM samplers equipped with glass-fiber or cellulose filters appear unsuitable for reliable sampling of the fungicide because of breakthrough or breakdown during sampling.

Assessment of dermal exposure of greenhouse workers to the pesticide bupirimate.

An HPLC method was developed for estimation of dermal exposure of greenhouse workers to the pesticide bupirimate. Chromatography was performed on a cyano-modified silica column with methanol-water (6:4 by volume) containing 5 g/L ammonium sulfate as eluent. UV detection at 310 nm was used for quantitation. Dermal exposure was assessed by letting the workers wear cotton gloves and by measuring foliar dislodgable residues in the greenhouses as potential exposure. The analytical procedure was validated for measurement of bupirimate on cotton gloves and in solutions used for the estimation of foliar dislodgable residues. Gloves were extracted with methanol. Recovery of bupirimate from fortified gloves was complete. Methanol extracts with one volume of water added and solutions containing dislodgable residues were injected directly onto the HPLC system. The limit of detection was 30 micrograms/L. Between-day coefficients of variation were 7 and 4% at concentrations of 0.6 and 28 mg/L, respectively.

High-performance liquid chromatographic method for the determination of occupational exposure to the pesticide abamectin.

As part of a survey of occupational exposure to pesticides in greenhouses for growing ornamentals, analytical methods were developed and validated for the measurement of exposure of workers to the pesticide abamectin. Abamectin consists of a mixture of avermectin-B1a and avermectin-B1b, which are members of a class of fermentation products of the soil microorganism Streptomyces Avermitilis. Because of the high molecular weight of the avermectins (greater than 800 daltons), high-performance liquid chromatography (HPLC) was the analytical method of choice. Previously described HPLC methods that used fluorescence detection were adapted and validated for the determination of dermal exposure by the analysis of cotton gloves and foliar dislodgeable residue. IOM samplers (developed at the Institute of Occupational Medicine, Edinburgh, U.K.) for collecting the inspirable fraction of dust or aerosols were tested for the determination of airborne abamectin concentrations in greenhouses. An analytical procedure considerably simpler than published methods appeared suitable for the determination of abamectin residues on cotton gloves and on greenhouse foliage. Analytical recovery from cotton gloves, solutions of foliar dislodgeable residues, and air-sampling filters was essentially complete. However, air concentrations of abamectin could not be reliably measured by using the IOM sampling device because of breakdown during sampling. Between-day coefficients of variation for solutions of dislodgeable residue and cotton glove extracts were between 3% and 6% for abamectin concentrations between 5 and 140 micrograms/L.

Determination of the pesticide chlorothalonil by HPLC and UV detection for occupational exposure assessment in greenhouse carnation culture.

An HPLC method was developed for application in the measurement of occupational exposure to the pesticide chlorothalonil. In addition, sampling methods were validated for the determination of exposure to chlorothalonil in the greenhouse culturing of carnations. Procedures for sampling of the inspirable fraction of aerosols, for the determination of hand contamination by hand rinse and the use of cotton gloves, and for the determination of dislodgable chlorothalonil residues on carnation leaves were validated. Normal phase HPLC with hexane-dioxane as the eluent and UV detection at either 254 or 325 nm appeared suitable for the determination of chlorothalonil in the described matrices. The limit of detection, after concentration on SepPak C18 cartridges was approximately 0.5 micrograms/L. Linear calibration curves were obtained in concentration ranges from 0.5 microgram/L to 100 mg/L. In general, no interferences were noticed in the analysis of the matrices. However, cotton gloves for determination of hand contamination had to be washed before use because they contained interfering material, and in the case of air sampling, glass fiber filters for air sampling appeared to degrade chlorothalonil very rapidly. Therefore, cellulose filters were used for collection of the inspirable fraction of aerosols containing chlorothalonil.