Application of Bayesian population physiologically based pharmacokinetic (PBPK) modeling and Markov chain Monte Carlo simulations to pesticide kinetics studies in protected marine mammals: DDT, DDE, and DDD in harbor porpoises.

Physiologically based pharmacokinetic (PBPK) modeling in marine mammals is a challenge because of the lack of parameter information and the ban on exposure experiments. To minimize uncertainty and variability, parameter estimation methods are required for the development of reliable PBPK models. The present study is the first to develop PBPK models for the lifetime bioaccumulation of p,p'-DDT, p,p'-DDE, and p,p'-DDD in harbor porpoises. In addition, this study is also the first to apply the Bayesian approach executed with Markov chain Monte Carlo simulations using two data sets of harbor porpoises from the Black and North Seas. Parameters from the literature were used as priors for the first "model update" using the Black Sea data set, the resulting posterior parameters were then used as priors for the second "model update" using the North Sea data set. As such, PBPK models with parameters specific for harbor porpoises could be strengthened with more robust probability distributions. As the science and biomonitoring effort progress in this area, more data sets will become available to further strengthen and update the parameters in the PBPK models for harbor porpoises as a species anywhere in the world. Further, such an approach could very well be extended to other protected marine mammals.

DDTs in rice frogs (Rana limnocharis) from an agricultural site, South China: tissue distribution, biomagnification, and potential toxic effects assessment.

Contamination with agricultural pesticides such as dichlorodiphenyltrichloroethane (DDT) and its metabolites, dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD), is among several proposed stressors contributing to the global declines in amphibian populations and species biodiversity. These chemicals were examined in insects and in the muscle, liver, and eggs of rice frogs (Rana limnocharis) from the paddy fields of an agricultural site in South China. The ΣDDT (sum of DDT, DDE, and DDD) concentrations ranged from 154 to 915, 195 to 1,400, and 165 to 1,930 ng/g lipid weight in the muscle, liver, and eggs, respectively. All the DDTs (DDT, DDE, and DDD) showed higher affinity for the liver relative to muscle tissue and can be maternally transferred to eggs in female frogs. The average biomagnification factors for DDTs ranged from 1.6 to 1.9 and 1.5 to 2.9 in female and male frogs, respectively, providing clear evidence of their biomagnification from insects to frogs. Compared with the reported DDT levels demonstrated to have toxic effects on frogs, DDTs in the present frogs are unlikely to constitute an immediate health risk. However, the adverse impacts of high DDT residues in eggs on the hatching success and their potential toxicity to the newly metamorphosed larval frogs should be assessed further.

Use of the juvenile clam, Mercenaria mercenaria, as a sensitive indicator of aqueous and sediment toxicity.

The hard clam is an economically important bivalve and is abundant along the East Coast of the US. The goal of this research was to evaluate the sensitivity of this test species as compared to that of other benthic and epibenthic organisms. Toxic effects of cadmium (inorganic metal), DDT (organochlorine pesticide), and fluoranthene (polycyclic aromatic hydrocarbon) exposure in sediments (10-day) and seawater (24-h) on juvenile (212-350-microm) hard clams Mercenaria mercenaria were determined. The aqueous 24-h LC(50) values were 0.42 mg/L cadmium (95% CL=0.35-0.45 mg/L), 0.61 mg/L DDT (95% CL=0.40-0.95 mg/L), and 0.65 mg/L fluoranthene (95% CL=0.44-1.23 mg/L). Results of sediment toxicity tests indicated that the 10-day LC(50) values were 1.66 mg/kg cadmium (95% CL=1.21-2.28 mg/kg), 5.8 mg/kg DDT (95% CL=4.8-8.3mg/kg), and 1.75 mg/kg fluoranthene (95% CL=1.38-2.09 mg/kg). Based on comparisons to toxicity data for other marine species, these findings suggest that the juvenile clam is one of the more sensitive species to a variety of contaminants and may be a valuable indicator for potential sediment toxicity.

Persistent organochlorine residues in human breast milk from Hanoi and Hochiminh City, Vietnam: contamination, accumulation kinetics and risk assessment for infants.

Despite the ban on persistent organochlorines (OCs) in most of the developed nations, their usage continued until recently in many Asian developing countries including Vietnam, for agricultural purposes and vector-borne disease eradication programs. In this study, we collected human breast milk samples from the two big cities in Vietnam: Hanoi (n=42) and Hochiminh (n=44) and determined the concentrations of persistent OCs such as PCBs, DDT and its metabolites (DDTs), hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB), chlordane compounds (CHLs) and tris-4-chlorophenyl-methane (TCPMe). The contamination pattern of OCs was in the order of DDTs > PCBs > HCHs > CHLs approximately HCB approximately TCPMe. Compilation of available data indicated that DDT residue levels in human breast milk from Vietnam were among the highest values reported for Asian developing countries as well as developed nations. This result suggests recent usage of DDTs in both north and south Vietnam. Interestingly, in both cities, the p,p'-DDT portion was higher in multiparas than those in primiparas. Considering the fact that the interval between the first and the second child of a mother in Vietnam is usually short, this result probably indicates continuous intake of DDTs in the population. Analysis of infant exposure to DDTs via breast milk suggested that the daily intake rates for number of individuals are close to or above the threshold for adverse effects which may raise concern on children health.

Comparative assessment of endocrine modulators with oestrogenic activity. II. Persistent organochlorine pollutants.

Risk assessments of synthetic chemicals with oestrogen-like activity must take into account the high dietary levels of natural endocrine modulators in food. In view of current regulations of the European Union, a hygiene-based margin of safety (HBMOS) for xeno-oestrogens was defined as a quotient of estimated human daily intakes weighted by relative rodent in vivo potencies of the compounds. Such comparisons of intakes and potencies of natural isoflavones, with short half-lives, with those of polychlorinated organic pollutants (POP) displaying significant toxicokinetic accumulation, deserves the special consideration of toxicokinetics. For slowly accumulating compounds such comparison is much more favourable when based on comparative blood and tissue levels, not on scenarios of daily exposures. Observing these principles, the present communication extends the HBMOS concept to POP, using o,p'-DDT, the oestrogenic component of DDT mixtures, as a prototype. An HBMOS of 137 is derived for o,p'-DDT indicative of a sufficient margin of safety to ensure the absence of risk to human health due to its hormonal action, under exposure conditions now prevailing in Western countries.

Assessment of location-specific human exposure to dichloro-diphenyl trichloroethane and benzenehexachloride in Gujarat state, India.

On the basis of the use of insecticides in agriculture and vector control programmes, two locations were selected in Gujarat state, India. In location 1 the insecticides are used in both agriculture and vector control programmes while in location 2 they are used only in agriculture. Raw food commodities, water, soil and blood samples were collected from the people residing in these locations, and analysed for total dichloro-diphenyl trichloroethane and total benzenehexachloride residues. Residue levels were significantly lower in location 2 than in location 1.