Bioaccumulation models are used to describe chemical uptake and clearances by organisms. Averaged input parameter values are traditionally used and yield point estimates of model outputs. Hence, the uncertainty and variability of model predictions are ignored. Probabilistic modeling approaches, such as Monte Carlo simulation and the Bayesian method, have been recommended by the U.S. Environmental Protection Agency to provide a quantitative description of the degree of uncertainty and/or variability in risk estimates in ecological hazards and human health effects. In this study, a Bayesian analysis was conducted to account for the combined uncertainty and variability of model parameters in a crayfish bioaccumulation model. After a 5-d exposure in the LaBranche Wetlands (LA, USA), crayfish were analyzed for polycyclic aromatic hydrocarbon concentrations and lipid fractions. The posterior distribution of model parameters were derived from the joint posterior parameter distributions using a Markov chain Monte Carlo approach and the experimental data. The results were then used to predict the distribution of chrysene concentration versus time in the crayfish to compare the predicted ranges at the different study sites.

Chlorpyrifos is an extensively used organophosphate insecticide having many urban and agricultural crop pest control uses. Studies conducted in indoor environments after termiticide, crack-and-crevice, broadcast, or fogger applications have shown that chlorpyrifos exposure can occur via inhalation of residual air concentrations, dermal or oral exposure from residues on floors and carpets, children toys, food, and dust. Not long ago the weight of scientific evidence supported safe indoor use, but recent studies support the possibility that when pregnant female rats are given the pesticide, chlorpyrifos causes brain damage in fetal rats. Moreover, the exposure of young rats to chlorpyrifos impairs early nervous system development. After finding that chlorpyrifos is an exposure risk especially to children, in June 2000 the United States Environmental Protection Agency and manufacturers agreed to voluntary measures that will reduce the exposure of children to chlorpyrifos-containing products. This action implies a search for less harmful new products to replace it and/or safer ways to control pests through basic hygiene. Whichever pest control method is selected, one should keep in mind that preventing environmental pesticide exposure in children is always better than treating the resulting disease.

A commonly used indicator of sublethal stress in fish is impaired swimming performance. Analysis of performance data usually employs a simple comparison, in which the mean of a stressed group of fish is compared to that of a control group. Although such a comparison is satisfactory in many cases, a comparison emphasizing individual variation in performance can yield valuable information unattainable by a means comparison. In this experiment, we determined critical swimming speeds of subadult male fathead minnows before and after exposure to contaminated sediments from Devil's Swamp, Louisiana, USA. The data were then analyzed using a means comparison and an individual approach to illustrate the differences in explanatory power between the two approaches.

Biotransformation is an important parameter in assessing the environmental impact and fate of pesticides since metabolites produced may be either more or less toxic than the parent compound. Sodium arsenate (+5 inorganic), the wood preservative and insecticide, may be converted to both inorganic (+3) and organic compounds (-3) by microorganisms in soil, sediment and water bodies. Biotransformation of sodium arsenate was studied in pure cultures of 5 bacterial species using a mineral salt and limited carbon source medium. Arsenate concentrations were 10 microgram/ml and 100 microgram/ml of arsenic respectively. The rate of biodegradation of the parent compound was described by a first order composite exponential equation of the form Ct = C1e-k1t+C2e-k2t. Rates of production of metabolites (arsenite, monomethylarsine, dimethylarsine and trimethylarsine) were described by a first order exponential equation of the form Ct = Co (1-e-kt).

Abstract:Research in our laboratory has demonstrated that a trivalent form of arsenic such as arsenic trioxide (AT) has the ability to cause significant cytotoxicity, and induction of a significant number of stress genes in human liver carcinoma cells (HepG 2 ). However, the literature also indicates that the toxicity of arsenic depends on its chemical form. To test this hypothesis, we further evaluated the cellular and molecular responses of HepG 2 cells following exposure to monosodium acid methanearsonate (MSMA), a pentavalent and organic form of arsenic. Cytotoxicity was evaluated using the MTT-assay for cell viability, while the gene profile assay was performed to measure the degree of gene induction in 13 different recombinant cell lines generated from a parental HepG 2 cell line. Cytotoxicity experiments yielded LC 50 values of 11.9 + 2.6 µg/mL for AT, and 257.3 + 51.4µg/mL for MSMA; indicating that AT was about 20 times more toxic than MSMA. Exposure of HepG 2 cells to MSMA also resulted in a significant reduction (p < 0.05) in the number of stress genes induced, compared to AT. Upon MSMA exposure, only 2 (HMTIIA and HSP70) out of the 13 constructs evaluated yielded inductions to statistically significant levels (p < 0.05), compared to 11 (GSTYa, XRE, HMTIIA, c-fos, NF-kBRE, HSP70, p53RE, GADD153, GADD45, and GRP78) for AT. These results greatly support the hypothesis that the toxicity of arsenic compounds highly depends on their chemical forms; with the inorganic forms being more potent than the organic ones.