How changes in sample extraction and exposure techniques can affect conclusions on developmental toxicity

FETAX (Frog Embryo Teratogenesis Assay-Xenopus) is used as a developmental toxicity screening assay for complex environmental mixtures. Several times in the past environmental and other samples were assessed for developmental toxicity. Subsequently, different samples from the site were tested or new techniques emerged that allowed the reassessment of the developmental toxicity. Different results were then obtained that altered or modified an earlier conclusion. For example, Tar Creek, Oklahoma is contaminated with heavy metals. Early toxicity tests on water samples showed developmental toxicity. However, subsequent tests on extracted sediment samples showed higher toxicity than water samples. Another example of rethinking results was the toxicity of pine needle extracts. Toxins within these needles were thought to cause abortion in cattle. These extracts were also developmentally toxic in FETAX. However, toxicity was increased by co-culturing the frog embryos with the extract and a metabolic activation system employing Aroclor 1254-induced rat liver microsomes. This system simulated metabolic activation in the cattle. Lastly, the authors conducted developmental toxicity tests on surface water contaminated with crude oil and aqueous extracts of crude oil. These samples showed little toxicity. However, when crude oil was first mixed with agarose and plated onto the bottom of the dish, embryos were malformed at a high rate. Therefore, the developmental toxicity of a study site may be inaccurately assessed because of the sampling technique, testing method or the preparation of the sample for testing