Masamitsu Iwata

A study on biological monitoring of n-hexane exposure.

Summaryn-Hexane is one of the solvents widely used in industry and well known to be neurotoxic. Recently it was clearly revealed that n-hexane is metabolized in vivo and its metabolites are excreted in the urine. However, the relationship between the exposed dose of n-hexane and the metabolites in the urine has not yet been substantially determined. Therefore, in this investigation we intended to clarify the above relationship in order to establish its usefulness for biological monitoring of n-hexane exposure.The exposed dose was measured by means of a personal monitoring badge worn by workers in seven factories manufacturing vinyl sandals. The time-weighted average (TWA) concentration of n-hexane was 0.2–47.4 ppm.The n-hexane metabolites in the urine of 22 workers were measured with modified Perbellinis method [12] in the early morning (6:00–7:00 hrs) and at 17:00 hrs. 2,5-Dimethylfuran, 2,5-hexanedione and γ-valerolactone were identified by gas chromatography and mass spectrometory. At 17:00 hrs the means ± SD of the metabolites were 0.21 ± 0.11 mg/l for 2,5-dimethylfuran, 1.13 ± 0.71 mg/1 for 2,5-hexanedione, and 2.04±2.31 mg/l for γ-valerolactone. The metabolites were also found in the urine in the early morning. 2-Hexanol was not detected in the urine of any worker examined. A strong correlation between TWA concentration of n-hexane and 2,5-hexanedione in the urine was found at 17:00 hrs (r = 0.895, P < 0.001).The results suggest that the urinary metabolites of n-hexane, especially 2,5-hexanedione, could be useful indicators for biological monitoring of n-hexane exposure. Furthermore the present study offers the advantage of a better estimate of n-hexane TWA.

Changes of n-hexane metabolites in urine of rats exposed to various concentrations of n-hexane and to its mixture with toluene or MEK

SummaryIt is well known that n-hexane produces peripheral neuropathy, and 2,5-hexanedione, one of the metabolites of n-hexane, is thought to be the main causative agent. Recently, the metabolites of n-hexane in urine have been measured by gas chromatography, and 2,5-hexanedione was proved to be useful for the biological monitoring of n-hexane exposure. In the present experiment, we intended to clarify the change of n-hexane metabolites in the urine of rats exposed to various concentrations of n-hexane and to its mixture with toluene or MEK. In the first experiment, five separate groups of five rats each were exposed to 100, 500, 1000, or 3000 ppm of n-hexane, or fresh air respectively in an exposure chamber for 8 h a day. Urinary samples were gathered during exposure, 16, 24, and 40 h after exposure. Half of each sample was analyzed by gas chromatography after hydrolysis with acid and enzymes, and the other half was analyzed without hydrolysis. 2,5-Dimethylfuran, MBK, 2-hexanol, 2,5-hexanedione, and γ-valerolactone could be identified as n-hexane metabolites in the urine. The main metabolites were 2-hexanol and 2,5-hexanedione. 2-Hexanol was mostly excreted during exposure, while most of the 2,5-hexanedione was excreted after the end of exposure. The amount of metabolites in the urine correlatively increased with the concentration of n-hexane from 100 to 1000 ppm, but the amount of metabolites scarcely increased when the concentration of n-hexane increased from 1000 to 3000 ppm. The maximum concentration of the excreted metabolites in urine was delayed when the concentration of n-hexane increased. These findings may indicate that the capacity of hydroxylation in rat liver microsomes was saturated when exposed to high concentrations of n-hexane. Free (not conjugated) metabolites were also excreted in the urine in all concentrations during exposure and 16 h after exposure. In the second experiment, four separate groups of five rats each were exposed to 1000 ppm of n-hexane, 1000 ppm of n-hexane plus 1000 ppm of toluene, 1000 ppm of n-hexane plus 1000 ppm of MEK, or fresh air. The analyzing procedure was the same as that in the first experiment. Distributions of n-hexane metabolites in the mixed exposure group were almost similar to that of the n-hexane-alone group. The amount of metabolites decreased to about one-sixth of that in the n-hexane group by co-exposure with toluene and to about one-fourth by co-exposure with MEK. From these results, it can be considered that toluene decreases the neurotoxicity of n-hexane by the inhibition of n-hexane metabolism. However, the reason the neurotoxicity of n-hexane is increased by co-exposure with MEK cannot be clearly explained.

Changes of n-hexane neurotoxicity and its urinary metabolites by long-term co-exposure with MEK or toluene

SummaryIt is well known that the neurotoxicity of n-hexane may be modified upon co-exposure with other organic solvents. In order to elucidate this mechanism further, rats were exposed to 500ppm n-hexane, 500ppm n-hexane plus 500ppm methyl ethyl ketone (MEK), 500ppm n-hexane plus 500ppm toluene, or air only for 8h per day for 33 weeks. The body weight, motor nerve conduction velocity (MCV) and distal latency (DL) were determined before exposure and after 4, 8, 12, 16, 20, 24, 29, and 33 weeks of exposure. From each group one rat was histologically examined after 33 weeks of exposure. To establish a relationship between the n-hexane neurotoxicity and changes in biotransformation, urinary metabolites (2-hexanol, methyl n-butyl ketone (MBK), 2,5-hexanedione, 2,5-dimethylfuran, and γ-valerolactone) were measured by gas chromatography on the first exposure day, and after 1, 2, 4, 8, 12, 16, 20, 24, 29, and 33 weeks of exposure. The total amounts of metabolites of n-hexane in the urine significantly decreased upon co-exposure of n-hexane, with MEK as well as with toluene, in comparison with those of animals exposed to n-hexane alone. 2,5-Hexanedione, which is considered the ultimate neurotoxic metabolite of n-hexane, also decreased. Electrophysiological and histological studies did not reveal statistically significant differences between any two groups among the four groups. It is considered that the present results might explain the combined effects of n-hexane and toluene which decrease n-hexane neurotoxicity, but do not explain those of n-hexane and MEK. Therefore, other mechanisms of the combined effects of n-hexane and MEK should be studied.

Relationship between chlordane and its metabolites in blood of pest control operators and spraying conditions

SummaryChlordane has been widely used to protect soil and house foundations against termite infestation. Pest control operators (PCOs) are occupationally exposed to chlordane. The relationship between chlordane and its metabolites in blood of PCOs and spraying conditions were investigated. Chlordane and its metabolites were detected in the blood of some chlordane-exposed PCOs, but not in that of the controls. Trans-nonachlor and the metabolites oxychlordane and heptachlor epoxide were detected in the blood of PCOs. Total concentration of chlordane and its metabolites in blood (trans-nonachlor + oxychlordane + heptachlor epoxide) was less than 5.6 ppb (mean: 0.89 ppb). The concentration of chlordane and its metabolites in blood of chlordane-exposed PCOs was significantly correlated with the number of spraying days and the amount of chlordane sprayed, particularly with a large correlation coefficient (r = 0.81, P < 0.001) with the spraying days in the three months prior to the medical examination. The concentration of chlordane and its metabolites in blood is considered to be a useful indicator of biological monitoring for chlordane exposed workers (PCOs).