Modeling cholinesterase activity for human dietary risk assessment of carbamate insecticides.

This article demonstrates statistical models to quantify the interaction between a carbamate insecticide and acetylcholinesterase. Carbamates are a class of chemicals that inhibit the activity of acetylcholinesterase in humans, an enzyme involved in the regulation of the neurotransmitter acetylcholine. Following exposure to a carbamate insecticide, we specifically address (1) if acetylcholinesterase activity recovers to its level of preexposure activity; (2) the level of inhibition of acetylcholinesterase activity; (3) the recovery time of acetylcholinesterase activity to its preexposure level for a typical individual; and (4) the upper percentiles of the recovery time of acetylcholinesterase activity across individuals. A nonlinear mixed-effects model is fitted to data from a repeated measures experiment conducted with human volunteers randomly assigned to a control and four dose groups. Repeated measurements were taken prior to exposure and at 1, 2, 4, 6, 8, and 21 hours after exposure to the carbamate aldicarb. It was found that full recovery did occur. Inhibition at 1 hour was estimated with maximum inhibition most likely occurring prior to 1-hour postexposure. In addition, recovery was rapid even for sensitive individuals. Given this information, the potential effect from exposure to a carbamate consumed in the diet during a day can be quantitatively assessed.

A survey of airborne and skin exposures to chemicals in footwear and equipment factories in Thailand.

This research reports on a pilot industrial hygiene study that was performed at four footwear factories and two equipment factories in Thailand. Workers in these factories were exposed through inhalation and dermal contact to a large number of organic vapors from solvents and cements that were hand applied. In addition, these workers were exposed to highly toxic isocyanates primarily through the dermal route. A total of 286 personal air samples were obtained at the four footwear factories using organic vapor monitors; individual job tasks were monitored using a real-time MIRAN Spectrometer. A total of 64 surface, tool, or hand samples were monitored for isocyanates using surface contamination detectors. Real-time measurements were also obtained for organic vapors in two equipment factories. From 8% to 21% of the workers sampled in each footwear factory were overexposed to mixtures of chemicals from solvents and cements. Up to 100% of the workers performing specific job tasks were overexposed to mixtures of chemicals. From 39% to 69% of the surface samples were positive for unreacted isocyanates. Many of the real-time measurements obtained in the equipment factories exceeded occupational exposure limits. Personal protective equipment and engineering controls were inadequate in all of the factories.