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In recent years there has been an increasing focus in environmental risk assessment on children as a potentially susceptible population. There also has been growing recognition of the need for a systematic approach for organizing, evaluating, and incorporating the available data on children's susceptibilities in risk assessments. In this article we present a conceptual framework for assessing risks to children from environmental exposures. The proposed framework builds on the problem formulation → analysis → risk characterization paradigm, identifying at each phase the questions and issues of particular importance for characterizing risks to the developing organism (from conception through organ maturation). The framework is presented and discussed from the complementary perspectives of toxicokinetics and toxicodynamics.

This report discusses the principles of developmental and reproductive toxicity (DART) testing for biopharmaceuticals. Biopharmaceuticals are large‐molecular‐weight proteins or peptides produced by modern biotechnology techniques incorporating genetic engineering and hybridoma technologies. The principles of DART testing for biopharmaceuticals are similar to those for small‐molecule pharmaceuticals and in general follow the regulatory guidance outlined in International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) document S5(R2). However, because many biopharmaceuticals are species‐specific, alternate approaches may be needed to evaluate DART potential as outlined in ICH S6. For molecules that show species‐specific cross‐reactivity restricted to non‐human primates (NHP), some aspects of DART may require NHP testing. For biopharmaceuticals that are uniquely specific and only active on intended human targets or human and chimpanzee targets, surrogate molecules that cross‐react with the more traditional rodent species may need to be developed and used for DART testing. Alternatively, genetically modified transgenic animals may also need to be considered. Surrogate molecules and transgenic animals may also be considered for DART testing even if the biopharmaceutical is active in NHPs in order to reduce the use of NHPs. Because of the unique properties of biopharmaceuticals, a case‐by‐case approach is needed for DART and general toxicity evaluation, which requires consideration of specific product attributes including biochemical and biophysical characteristics, pharmacological activity, and intended clinical indication. Birth Defects Res (Part B), 33:176–203, 2009. © 2009 Wiley‐Liss, Inc.

Chlorpyrifos (O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl)-phosphorothioate), an organophosphate insecticide, was evaluated for its potential to produce developmental and reproductive toxicity in rats following oral exposure. Pregnant Fischer 344 rats were given doses of 0 (corn oil vehicle), 0.1, 3.0, or 15 mg chlorpyrifos/kg/day, by gavage, on Gestation Days 6 through 15. Maternal effects noted at the two higher dose levels included decreased cholinesterase levels at 3.0 mg/kg/day and cholinergic signs (excessive salivation and tremors), decreased cholinesterase levels, and decreased body weight gain at 15 mg/kg/day. No maternal effects were apparent at 0.1 mg/kg/day. Although maternal toxicity was observed at these two higher exposure levels, no developmental effects were noted at any dose. In a two-generation reproduction study, Sprague-Dawley rats were maintained on diets supplying 0, 0.1, 1.0, or 5.0 mg chlorpyrifos/kg/day. Parental effects included decreased plasma and erythrocyte cholinesterase at 1.0 mg/kg/day, and decreased plasma, erythrocyte, and brain cholinesterase and histopathologic alterations of the adrenal zona fasciculata at 5.0 mg/kg/day. The histopathologic alterations of the adrenal were characterized as very slight to slight vacuolation (consistent with fatty change) in males, and very slight vacuolation and/or altered tinctorial properties in females. No effects on the reproductive or fertility indices or on the histopathology of reproductive tissues were observed at any dose level, and no neonatal effects were observed at 0.1 or 1.0 mg/kg/day in the F1 or F2 litters. Parental toxicity at the high dose was accompanied by decreased pup body weight and increased pup mortality in the F1 litters only. These data show that oral administration of chlorpyrifos to rats at parentally toxic dose levels was not embryolethal, embryo/fetotoxic, or teratogenic and did not adversely affect fertility or the function or structure of the reproductive organs. Although effects on neonatal growth and survival were observed at a maternally toxic dose level in one generation, this effect was not observed in the subsequent generation and, therefore, may not have been related to treatment.