To investigate whether cadmium has an independent role in diseases associated with tobacco consumption, epidemiology data were reviewed, biomonitoring data were analyzed, and probabilistic risk assessment (PRA) was performed. Results from previous epidemiology studies have indicated that there are adverse health effects potentially in common between cadmium exposure and tobacco consumption. Analysis of publically available biomonitoring data showed that blood (B-Cd) and urine (U-Cd) cadmium were higher in cigarette smokers compared with smokeless tobacco (SLT) consumers, and B-Cd and U-Cd in SLT consumers were not significantly different than in non-consumers of tobacco. Comparison with previously established biomonitoring equivalent (BE) values indicated that B-Cd and U-Cd in the majority of these cigarette smokers and SLT consumers did not exceed the blood and urine BEs. Results of the PRA showed that the mean hazard estimate was below a generally accepted regulatory threshold for SLT consumers, but not for cigarette smokers. In total, this evaluation indicated that cadmium exposures in tobacco consumers differed by product category consumed; cadmium in tobacco may not be associated with tobacco consumption related diseases; if cadmium in tobacco contributes to tobacco consumption related diseases, differences in hazard and/or risk may exist by product category.

We attempted to develop a rodent model that exhibits characteristics of human methanol toxicities such as acidosis and visual dysfunction, which are correlated with an accumulation of formate, a toxic metabolite of methanol. Initially three groups of Long-Evans rats with different levels of liver folate were prepared and examined for formate accumulation after methanol administration (3.5 g/kg). The folate-reduced (FR) rats prepared by feeding a folate-deficient diet with 1% succinylsulfathiazole yielded blood formate levels equivalent to those found in methanol-intoxicated humans and developed signs of the visual system toxicity (a manuscript on the latter aspect is in preparation). Responses of FR rats to a variety of methanol exposure scenarios were then investigated, and the results were compared with those reported in the literature for monkeys. Formate accumulation and/or lethality were used as toxic parameters for this comparative evaluation. In FR rats dosed orally with 3 g/kg, the blood formate concentration was 9.2 mmol/L at 24 h postadministration and increased to 15.6 mmol/L at 48 h. The same dose given to monkeys yielded a plateau of 7.4 mmol/L at 12 h after methanol administration, and stayed at this level for an additional 12 h. The area under the concentration vs. time curve for blood formate in FR rats was 2.5-fold greater than that in monkeys when 2.0 g/kg methanol was administered. After a 6-h exposure to 1200 ppm and 2000 ppm methanol, the blood formate concentrations in FR rats were increased by 370% and 636% above the endogenous level, respectively. However, blood formate did not accumulate above the endogenous level when monkeys were exposed to methanol up to 2000 ppm for 6 h. Under acute inhalation exposure conditions, FR rats exposed to 3000 ppm methanol, 20 h/d, could not survive more than 4 d. On the other hand, monkeys exposed to 3000 ppm, 21 h/d, out-lived 20 d. Moreover, monkeys survived for more than 4 d even after an exposure to 10,000 ppm. Thus, these results indicate that FR rats are more sensitive to methanol challenges than monkeys, and suggest that the FR rat could be a congruous animal model for evaluating the health effects of methanol in humans.

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Methanol is a toxicant that causes systemic and ocular toxicity after acute exposure. The folate-reduced (FR) rat is an excellent animal model that mimics characteristic human methanol toxic responses. The present study examines the role of the methanol metabolites formaldehyde and formate in the initiation of methanol-induced retinal toxicity. After a single oral dose of 3.0 g/kg methanol, blood methanol concentrations were not significantly different in FR rats compared with folate-sufficient (FS) (control) rats. However, FR rats treated with 3.0 g/kg methanol displayed elevated blood (14.6 mM) and vitreous humor (19.5 mM) formate levels and abnormal electroretinograms (loss of b-wave) 48 h postdose. FR rats pretreated with disulfiram (DSF) prior to 3.0 g/kg methanol treatment failed to display these symptoms. Formaldehyde was not detected in blood or vitreous humor with or without DSF treatment, suggesting that formate is the toxic metabolite in methanol-induced retinal toxicity. Additionally, creating a blood formate profile (14.2 mM at 48 h) similar to that observed in methanol-treated rats by iv infusion of pH-buffered formate does not alter the electroretinogram as is observed with methanol treatment. These data suggest that intraretinal metabolism of methanol is necessary for the formate-mediated initiation of methanol-induced retinal toxicity.

A variety of test methods were used to study the gradation, bioaccumulation, and toxicity of nicotine. Studies included determination of the octanol-water partition coefficient, conversion to CO2 in soil and activated sludge, and evaluation of the effects on microbiological and algal inhibition as well as plant germination and root elongation. The partitioning of nicotine between octanol and water indicated that nicotine will not bioaccumulate regardless of the pH of the medium. The aqueous and soil-based biodegradation studies indicated that nicotine is readily biodegradable in both types of media. The microbiological inhibition and aquatic and terrestrial toxicity tests indicated that nicotine has low toxicity. The U.S. Environmental Protection Agency Persistence, Bioaccumulation, and Toxicity Profiler model, based on the structure of nicotine and the predictive rates of hydroxyl radical and ozone reactions, estimated an atmospheric half-life of less than 5.0 h. Using this value in the Canadian Environmental Modeling Center level III model, the half-life of nicotine was estimated as 3.0 d in water and 0.5 d in soil. This model also estimated nicotine discharge into the environment; nicotine would be expected to be found predominantly in water (93%), followed by soil (4%), air (3%), and sediment (0.4%). Using the estimated nicotine concentrations in water, soil, and sediment and the proper median effective concentrations derived from the algal growth, biomass inhibition, and buttercrunch lettuce (Lactuca sativa) seed germination and root elongation studies, hazard quotients of between 10(-7) and 10(-8) were calculated, providing further support for the conclusion that the potential for nicotine toxicity to aquatic and terrestrial species in the environment is extremely low.

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