Chiral Memory in Silylium Ions.

The configurational stability of the chiral silicon center in Lewis base-stabilized silyliums has been studied. Complete retention of configuration at silicon is observed at low temperature in silylium ions stabilized by lone-pair interactions. In contrast, loss of chiral memory is observed with systems involving π-interactions. Epimerization of the silicon center was observed by simply allowing equilibration of the diastereomeric silyliums at RT or by adding a catalytic amount of a chelating solvent. Conditions for the transfer of axial chirality to Si-centered chirality were shown to rely on the strength of the Lewis base-silylium ion interaction.

Biological monitoring of exposure to di(2-ethylhexyl) phthalate in six French factories: a field study.

OBJECTIVE: The aim of this study was to assess, by biological monitoring, workers' exposure to di(2-ethylhexyl) phthalate (DEHP) in the flexible-PVC industry in France to provide additional occupational exposure data, which are particularly scarce. METHOD: Over 5 days of pre-and post-shift sampling, three urinary metabolites of DEHP, mono (2-ethylhexyl) phthalate (MEHP), mono (5-carboxy-2-ethylpentyl) phthalate (5cx-MEPP) and 2-ethylhexanoic acid (2-EHA) were quantified in 62 workers and 29 controls from six factories. Analyses were performed by high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) after on-line extraction. RESULTS: Median concentrations of the pre- and post-shift urinary samples in the exposed workers were 12.6 and 28.7 µg/l for MEHP, 38.6 and 84.4 µg/l for 5cx-MEPP and 20.4 and 70.6 µg/l for 2-EHA, respectively. In the controls, the corresponding values were 4.8 and 4.7 µg/l for MEHP, 15.1 and 12.4 µg/l for 5cx-MEPP and 21.8 and 20.5 µg/l for 2-EHA, respectively. There was a significant increase (Mann-Whitney U-test, P < 0.05) of post-shift excretion in the exposed workers versus the unexposed controls and in the post-shift versus pre-shift concentrations only in the exposed workers. Values of 250 and 500 µg/l (100 and 280 µ/g creatinine) for MEHP and 5cx-MEPP, respectively, are proposed as guidance values. CONCLUSION: There is clear evidence of occupational exposure of workers in these factories. The guideline values proposed should prevent high exposures in the soft PVC industry, particularly in factories where DEHP compounds or plastisols are employed. An epidemiological survey is needed to complete the DEHP risk assessment.

Biological monitoring of occupational exposure to di(2-ethylhexyl) phthalate: survey of workers exposed to plastisols.

OBJECTIVE: The aim of this study was to perform a biological monitoring survey of workers exposed to di(2-ethylhexyl)phthalate (DEHP) in a factory using polyvinyl chloride plastisols and to contribute additional occupational data of exposure particularly sparse in the industrial sectors where this plasticizer is used. METHOD: Three urinary metabolites of DEHP, mono(2-ethylhexyl)phthalate (MEHP), mono(5-carboxy-2-ethylpentyl)phthalate (MCEPP) and 2-ethylhexanoic acid (2-EHA) were quantified in five workers using a plastisol (containing 33% of DEHP) and in five unexposed workers (controls), during 5 days with pre- and post-shift sampling. Analyses were performed by high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) with on-line extraction. RESULTS: Median concentrations of pre- and post-shift urinary samples in the exposed workers (n = 25) were 16.1 and 55.9 microg/l for MEHP, 37.6 and 103.7 microg/l for MCEPP and 46.3 and 72.1 microg/l for 2-EHA, respectively. In the controls (n = 19), the corresponding values were 12.0 and 10.4 microg/l for MEHP, 38.1 and 11.4 microg/l for MCEPP and 31.9 and 46.0 microg/l for 2-EHA, respectively. There is a significant increase (Mann-Whitney U-test, P < 0.05) of post-shift excretion in the exposed workers versus unexposed controls and in post-shift versus pre-shift concentrations only in the exposed workers. CONCLUSION: MEHP and MCEPP are shown to be suitable biomarkers to assess DEHP exposure while 2-EHA, less specific but classified in the category 3 of the European Union (EU) reproductive toxicants, is also an interesting biomarker. There is clear evidence of occupational exposure of workers in this factory.

Toluene toxicokinetics and metabolism parameters in the rat and guinea pig.

Cochlear disruptions induced by toluene were shown in the rat but not in the guinea pig. To better understand the differences between species, three investigations were carried out to study (1) the blood affinity and the pulmonary uptake of the solvent, (2) its clearance and (3) its urinary elimination in both species. The blood affinity of toluene was +44% higher in the rat than in the guinea pig (14.4µg/g versus 10µg/g). Similarly, the pulmonary uptake of toluene was approximately 46.5% more efficient in the rat than in the guinea pig (75.4µg/g versus 40.3µg/g) after 3h inhalation of 1500ppm toluene. Therefore, the physicochemical composition of the blood could explain the difference in the uptake performances between rats and guinea pigs. The clearance of the toluene showed that 10min after an intravenous administration of 400µL of vehicle containing 28µL (43mgkg(-1)) of toluene, the solvent concentration was approximately threefold higher in the rat than in the guinea pig blood. The last experiment was carried out to compare the concentrations of the urinary metabolites. The concentrations of o-cresol, hippuric and benzyl mercapturic acids measured in the urines were different before and after the toluene injection. These data give evidence for large differences of toluene uptake and metabolism between rat and guinea pig. Therefore, it seems reasonable to claim that guinea pigs cochleas are not susceptible to toluene as the blood burden of solvent does not reach the concentration required to induce permanent damages.

Guinea pig pulmonary response to sensitization by five preformed monoisocyanate-ovalbumin conjugates.

The ability of 5 dissimilar monoisocyanates conjugated to ovalbumin (OA) as a carrier protein to induce pulmonary hypersensitivity towards the hapten specific component was assessed by using a previously described method based on the determination of a respiratory index (RI) in the guinea pig. The test chemicals included the commercially available p-tolyl and hexyl monoisocyanates (TMI and HMI), with 4-isocyanoto-4'-diphenylmethane (IDM), 4-isocyanoato-4'-methyldiphenylmethane (IMDM) and 1-isocyanato-methyl-1,3,3-trimethylcyclohexane (IMTC) as synthetized monoisocyanates. Guinea pigs were exposed daily to an aerosol of the OA conjugate of each monoisocyanate up to day 15. Increases in respiratory rate and/or respiratory collapse occurred in the guinea pigs exposed to TMI-OA and HMI-OA conjugates by days 9 and 15, with RI values of 155 and 177, respectively, being recorded. The greatest mean RI values in guinea pigs exposed to IDM-OA, IMDM-OA and IMTC-OA conjugates up to day 15 were 20, 25 and 22, respectively, and were not indicative of any pulmonary reaction. Guinea pigs exposed in parallel to each test conjugate did not exhibit any pulmonary reaction when they were exposed to OA on the challenge days. All these findings evidence pulmonary hypersensitivity as the result of exposure to TMI-OA and HMI-OA conjugates and suggest a high degree of conjugation and strong linkage of all the monoisocyanates with OA.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of the interaction of benzene and toluene on the urinary excretion of t,t-muconic acid in rats.

The influence of simultaneous exposure to benzene and toluene on the urine excretion of t,t-muconic acid (t,t-MA) was examined in rats. t,t-MA was measured from 24-h urine of rats subjected to a single 4-h exposure to 5 or 20 ppm benzene and/or 50, 100, 200 or 1000 ppm toluene. Coexposure lowered t,t-MA excretion in a concentration-dependent manner, especially in the 20 ppm benzene group where the decrease averaged 28, 44 and 85% after exposure to 100, 200 and 1000 ppm toluene, respectively, as compared to benzene-exposed groups alone. The data confirm the sensitivity of t,t-MA as an indicator of benzene exposure and point out that measurement of t,t-MA may underestimate the exposure to benzene in the presence of toluene.

Biological monitoring of exposure to solvents using the chemical itself in urine: application to toluene.

OBJECTIVE: Biomonitoring of solvents using the unchanged substance in urine as exposure indicator is still relatively scarce due to some discrepancies between the results reported in the literature. Based on the assessment of toluene exposure, the aim of this work was to evaluate the effects of some steps likely to bias the results and to measure urinary toluene both in volunteers experimentally exposed and in workers of rotogravure factories. METHODS: Static headspace was used for toluene analysis. o-Cresol was also measured for comparison. Urine collection, storage and conservation conditions were studied to evaluate possible loss or contamination of toluene in controlled situations applied to six volunteers in an exposure chamber according to four scenarios with exposure at stable levels from 10 to 50 ppm. Kinetics of elimination of toluene were determined over 24 h. A field study was then carried out in a total of 29 workers from two rotogravure printing facilities. RESULTS: Potential contamination during urine collection in the field is confirmed to be a real problem but technical precautions for sampling, storage and analysis can be easily followed to control the situation. In the volunteers at rest, urinary toluene showed a rapid increase after 2 h with a steady level after about 3 h. At 47.1 ppm the mean cumulated excretion was about 0.005% of the amount of the toluene ventilated. Correlation between the toluene levels in air and in end of exposure urinary sample was excellent (r = 0.965). In the field study, the median personal exposure to toluene was 32 ppm (range 3.6-148). According to the correlations between environmental and biological monitoring data, the post-shift urinary toluene (r = 0.921) and o-cresol (r = 0.873) concentrations were, respectively, 75.6 microg/l and 0.76 mg/g creatinine for 50 ppm toluene personal exposure. The corresponding urinary toluene concentration before the next shift was 11 microg/l (r = 0.883). CONCLUSION: Urinary toluene was shown once more time a very interesting surrogate to o-cresol and could be recommended as a biomarker of choice for solvent exposure.

Biological monitoring of workers exposed to 4,4'-methylenediphenyl diisocyanate (MDI) in 19 French polyurethane industries.

OBJECTIVES: To study the range of urinary levels of 4,4'-methylenedianiline (MDA), a metabolite of methylenediphenyl diisocyanate (MDI), across factories in the polyurethane industries and to evaluate the validity of this biomarker to assess MDI occupational exposure. METHODS: Workers exposed to MDI, as well as non-occupationally exposed subjects, were studied and pre- and post-shift urine samples were collected from 169 workers of 19 French factories and 120 controls. Details on work activities and practices were collected by a questionnaire and workers were classified into three job categories. The identification and quantification of the total urinary MDA were performed by high-performance liquid chromatography with electrochemical detection (HPLC/EC). RESULTS: For all the factories, MDA was detectable in 73% of the post-shift urine samples. These post-shift values, in the range of <0.10 (detection limit)-23.60 microg/l, were significantly higher than those of the pre-shift samples. Urinary MDA levels in the control group were in the range of < 0.10-0.80 microg/l. The degree of automation of the mixing operation (polyols and MDI) appears as a determinant in the extent of exposure levels. The highest amounts of MDA in urine were found in the spraying or hot processes. The excretion levels of the workers directly exposed to the hardener containing the MDI monomer were significantly higher than those of the other workers. In addition, skin exposure to MDI monomer or to polyurethane resin during the curing step were always associated with significant MDA levels in urine. CONCLUSIONS: Total MDA in post-shift urine samples is a reliable biomarker to assess occupational exposure to MDI in various industrial applications and to help factories to improve their manufacturing processes and working practices. A biological guiding value not exceeding 7 microg/l (5 microg/g creatinine) could be proposed in France.

N-nitrosodiethanolamine urinary excretion in workers exposed to aqueous metalworking fluids.

OBJECTIVE: This work was intended to clarify the extent of exposure of workers occupationally exposed to N-nitrosodiethanolamine (NDELA), a carcinogenic nitrosamine, while working with aqueous metalworking fluids (MWFs) formulated with ("nitrite-formulated") or without ("nitrite-free") nitrite and to study the relationships between the nitrite and NDELA content of the MWFs as well as between the concentration of NDELA in MWFs and in urine. METHOD: Pre-shift and post-shift urine samples from 100 workers directly exposed to MWFs in 15 factories were analysed for NDELA with chemiluminescent detection (TEA) according to a previously described analytical procedure. The method was also applied to eight indirectly exposed workers and to 48 unexposed subjects. The NDELA and concentrations in 84 fluids used by the workers were also determined. RESULTS: No detectable NDELA could be observed in the control group. The mean post-shift NDELA excretion in workers exposed to "nitrite-formulated" and "nitrite-free" MWFs were 44.6 and 0.4 microg/l, with maxima of 277 and 2.7 microg/l, respectively. According to the correlation between the nitrite and NDELA concentrations in "nitrite-free" MWFs, there is a low probability of fluids exceeding 5 mg/l NDELA when the nitrite content does not exceed 20 mg/l. The NDELA concentrations in the fluids and urine were found to be highly correlated, particularly after correction for creatinine (r=0.917 in post-shift samples). Cutaneous contact probably contributes, at least in part, to the overall body uptake of NDELA: CONCLUSION: Due to clear evidence of urinary NDELA excretion in workers exposed to contaminated MWFs, and despite a lack of knowledge of the human risk following NDELA exposure, levels of NDELA in MWFs should be kept as low as possible. NDELA fluid concentrations of less than 1 mg/l must be considered as the objective to be attained, even if the limit of 5 mg/l is temporarily satisfactory and consistent with a nitrite limit of 20 mg/l that is easy to verify with inexpensive colorimetric tests. "Nitrite-formulated" fluids, still sometimes used, should be prohibited. Meanwhile, the material safety data sheets (MSDS) of commercially available products should be clearly labelled to indicate their nitrite content.

Assessment of occupational exposure to 4,4'-methylene-bis-(2-chloroaniline) "MOCA" by a new sensitive method for biological monitoring.

A new specific and sensitive method for the urinary determination of 4,4'-methylene-bis-(2-chloroaniline) ("MOCA"), a known carcinogen in rats, mice and dogs, has been developed. After a brief study on rats to determine some peculiarities in "MOCA" urinary excretion, this method was used to assess occupational exposure in French industrial firms. Both the manufacture of "MOCA" and its use as a curing agent in the production of polyurethane elastomers were surveyed. "MOCA" excretion levels were distributed from non-detectable (less than 0.5 microgram/l) up to 1600 microgram/l. Concentrations of N-acetyl metabolites, when present, were largely lower than "MOCA" levels. The results seemed to reflect workers' overall exposure fairly. Preventive measures following analytical determinations often led to an obvious lowering of excretion levels.

N-nitrosodiethanolamine in antifreeze.

Carcinogenic N-nitrosodiethanolamine has been found at concentrations varying from 15 to 5700 mg/liter in several leading French brands of antifreeze. Moreover, mixtures of antifreezes which, separately, are innocuous, can form this nitrosamine which appears to arise from interaction of triethanolamine derivatives with sodium nitrite. It is recommended that sodium nitrite be abandoned as an anticorrosion additive.

Determination of urinary 4,4'-methylenedianiline and its acetylated metabolites by solid-phase extraction and HPLC analysis with UV and electrochemical detection.

An analytical procedure based on solid-phase extraction and high-performance liquid chromatography using both ultraviolet and electrochemical detection was developed to determine, without derivatization, stable urinary forms of 4,4'-methylenedianiline (MDA) and of its acetylated metabolites at the micrograms/l level, in post-shift urine from 63 exposed workers. The determination of MDA, N-acetyl MDA (MAMDA) and N,N'-diacetyl MDA (DAMDA) was achieved on the non-hydrolysed urine samples, and that of total MDA on urine samples after alkaline hydrolysis. It was necessary to protect urine samples with sulfamic acid in order to stabilize amines and to improve the precision and accuracy of the analyses. Under these conditions, unstable labile conjugates were determined as their parent stable amine. The distribution of total MDA, MDA, MAMDA and DAMDA was assessed in 116 urine samples. Their relative concentrations (arithmetic means) were found to be in the following order: total MDA > MAMDA > MDA > DAMDA. While MAMDA represented more than 50% of total MDA, MDA and DAMDA were lower than 15% and 3% respectively. Acetylation of MDA, described as a possible pathway of detoxication, is confirmed to be an important metabolization route in humans, essentially through the monoacetylated metabolite. However, the individual ratio MAMDA/total MDA was found to vary widely (roughly from 0% to 100%).

Determination of N-nitrosodiethanolamine in urine by gas chromatography thermal energy analysis: application in workers exposed to aqueous metalworking fluids.

OBJECTIVE: The aim of this study was to describe a detailed and validated methodology designed for the analysis of carcinogenic N-nitrosodiethanolamine (NDELA) down to sub-microgram/l levels in urine and its application to a number of workers exposed to NDELA-contaminated aqueous metalworking fluids (MWF). METHODS: Following a work-up procedure based on solid-phase extraction of NDELA, the urinary extracts were analysed without derivatization by gas chromatography on a polar wide-bore column with chemiluminescent detection using a thermal energy analyser (TEA). N-Nitroso-(2-hydroxypropyl)amine was used as an internal standard. The method was applied to 12 workers using "nitrite-free" or "nitrite-formulated" MWF and to 15 unexposed subjects. The NDELA content of the MWF was also determined using a similar, but simpler method able to easily quantify NDELA down to at least 0.1 mg/l. RESULTS: Contamination by NDELA traces of some chemicals used for the sample preparation, particularly ethyl formate, must be carefully checked since it can give rise to false-positive results of up to 1 or 2 micrograms/l. The response was linear in the range of 0-500 micrograms/l. Between 0.5 and 10 micrograms/l, the recovery rate was close to 95%, while repeatability ranged from 12.5 to 6.4% (n = 5). The detection limit was 0.3 microgram/l (Signal/noise = 3). No detectable NDELA could be observed in the control workers. There was no significant increase in NDELA levels at the end of shift spot samples from an exposed worker over 1 week. Higher NDELA concentrations were found in two workers (4.3 and 10.7 micrograms/l) exposed to "nitrite-formulated" fluids (contaminated with 65 and 18 mg NDELA per 1, respectively) than in nine workers (range, 0.4-1.3 micrograms/l exposed to "nitrite-free" fluids with lower levels of NDELA (range, 0.5-6.6 mg/l). CONCLUSION: The detailed methodology described in this work and applied to a limited industrial situation was found to be suitable for monitoring NDELA in the urine of workers exposed to aqueous MWF. A much larger screening has been undertaken with the aim of obtaining better information on the real exposure of workers sometimes exposed to "nitrite-formulated" fluids that are still used.

Biological monitoring of workers exposed to 4,4'-methylene-bis-(2-orthochloroaniline) (MOCA). I. A new and easy determination of "free" and "total" MOCA in urine.

OBJECTIVE: The objective of the study was to validate a new and simple method to determine MOCA in the urine of exposed workers. METHODS: The separation, identification and quantification of urinary MOCA were performed in spiked urines by a sensitive and practical high-performance liquid chromatography (HPLC) method and applied to urine samples of 11 workers occupationally exposed to MOCA; the postshift urinary levels of MOCA in their urine samples with and without hydrolysis, "total" and "free" MOCA respectively, were determined. In addition, we investigated the use of citric or sulfamic acid as preservatives of urine samples. RESULTS: The "total" and "free" MOCA were extracted with isooctane from hydrolysed and nonhydrolysed 20-ml urine samples respectively. After evaporation, the residue was dissolved in 4 ml of 2.10(-2) M aqueous hydrochloric acid and analysed by an isocratic HPLC system using both ultraviolet (UV) detection at 244 nm and electrochemical detection working in oxidation mode (0.9 V) with an Ag/AgCl reference electrode. Mobile phase (50% acetonitrile in water containing 0.4% acetate buffer solution pH = 4.6) was used to complete the 20-min analysis. "Free" and "total" MOCA were chromatographed on a reversed-phase C8 column (5 microns, 250 mm x 4 mm). The standard curve of MOCA was linear over the range 5-500 micrograms/l in human urine. The detection limit was 1 microgram/l for a 20-microliter injection volume; the repeatability ranged from 5.6 to 1.3% (n = 6) for spiked urines at 5 and 500 micrograms/l, with a percentage recovery of 94 +/- 3%. The reproducibility of the method was 7.3% (n = 4) for spiked urine at 10 micrograms/l. The use of sulfamic acid as a preservative of urine samples is important to improve the precision and accuracy of the analysis. CONCLUSION: The results indicate that these analytical procedures using conventional apparatus may be used routinely and reliably with large numbers of urine samples for biological monitoring of the exposure to MOCA. The occupational exposure to MOCA in some factories in France is studied in the second part of this work.

Biological monitoring of workers exposed to 4,4'-methylene-bis-(2-orthochloroaniline) (MOCA). II. Comparative interest of "free" and "total" MOCA in the urine of exposed workers.

OBJECTIVES: The objectives of the study were to investigate the best urinary marker of exposure to MOCA in urine samples of exposed workers and to study its applicability in exposure evaluation in polyurethane resin production plants. In addition, our intention was to contribute to the question of biological target value in order to reduce exposure levels. METHODS: Urinary MOCA markers were measured in urine samples collected at the end of the workshifts. 40 workers from four factories were observed for three consecutive days in the same week. "Free" MOCA in non-acid-stabilized urines, "total" MOCA in urines after alkaline hydrolysis, "acid-labile" MOCA in sulfamic or citric acid-protected urines were measured in all urine samples. MOCA liberated by heating the non-acid-stabilized urines ("heat-labile" MOCA) was also measured in 17 urine samples of exposed workers. RESULTS: The median value of "free" MOCA was lower than that of "sulfamic acid-labile" MOCA: 6.0 and 12.5 micrograms/l respectively. The difference between "free" and "total" MOCA was statistically significant (Mann-Whitney test, P = 0.023) for the urine samples collected without acid. Correlations between urinary MOCA concentrations in hydrolysed and non-hydrolysed urine samples were high (r = 0.984, 0.966 and 0.950; P < 0.001) for urine samples with sulfamic acid, with citric acid and without acid respectively. For all the factories, the postshift urinary MOCA concentrations ranged between 1 microgram/l (detection limit) and 570 micrograms/l; 25% of "sulfamic acid-labile" MOCA concentrations exceeded 50 micrograms/l. Workers handling crystallized MOCA excreted the highest amounts of MOCA in urine. The urinary MOCA concentrations (median) were: 84.0 micrograms/l (mixer), 15.5 micrograms/l (moulder). 59.0 micrograms/l (maintenance) and 3.0 micrograms/l (others). CONCLUSIONS: MOCA measured in sulfamic acid-protected urine samples without hydrolysis provides a more practical and reliable biomarker than "total" MOCA (after hydrolysis) or "free" MOCA. A biological guiding value of 20 micrograms/l expressed as "sulfamic acid-labile" MOCA is proposed.

Improvement in HPLC analysis of urinary trans,trans-muconic acid, a promising substitute for phenol in the assessment of benzene exposure.

Urinary trans,trans-muconic acid (t,t-MA), a minor metabolite of benzene, is a potential candidate for biological monitoring of benzene. A clean-up procedure using SPE extraction cartridges was applied to urinary samples in order to improve the reliability of t,t-MA determinations by HPLC-UV greatly and to carry out convenient analyses on a routine scale, particularly at low levels of t,t-MA concentrations. The detection limit of the method is low enough to measure urinary t,t-MA at a concentration of 0.05-0.1 mg/l. The recovery rates and relative standard deviations from spiked urines (1 mg/l to 20 mg/l) were about 90% and 5%, respectively. t,t-MA was found to be rapidly excreted by rats and humans. In rats the background range never exceeded 0.5 mg/l with a mean concentration around 0.3 mg/l. In 49 human blank urines, t,t-MA average and median-value were respectively around 0.2 and less than 0.1 mg/l with a range of less than 0.1 to 0.5 mg/l. Experimental exposure of rats for 1 h to 10.2 ppm of benzene induced urinary excretion of 13 mg/l of t,t-MA during a 6-h post-exposure period while occupational exposures to 2.6 ppm (mean exposure level during 5 d-8 h) and 7 ppm (4 h) of benzene resulted in urinary excretion of 2.1 (mean excretion level) and 6.5 mg/l respectively at the end of the exposure. In humans, t,t-MA has a similar half-time as phenol. Analysis of urinary t,t-MA seems to be a better indicator than phenol for the assessment of exposure to low levels of benzene. Ingestion of 200 mg of sorbic acid, the only other known precursor of t,t-MA, interfered minimally with the background excretion of t,t-MA.