Adverse effects in traditional and alternative toxicity tests

Chemical safety assessment begins with defining the lowest level of chemical that alters one or more measured endpoints. This critical effect level, along with factors to account for uncertainty, is used to derive limits for human exposure. In the absence of data regarding the specific mechanisms or biological pathways affected, non-specific endpoints such as body weight and non-target organ weight changes are used to set critical effect levels. Specific apical endpoints such as impaired reproductive function or altered neurodevelopment have also been used to set chemical safety limits; however, in test guidelines designed for specific apical effect(s), concurrently measured non-specific endpoints may be equally or more sensitive than specific endpoints. This means that rather than predicting a specific toxicological response, animal data are often used to develop protective critical effect levels, without assuming the same change would be observed in humans. This manuscript is intended to encourage a rethinking of how adverse chemical effects are interpreted: non-specific endpoints from in vivo toxicological studies data are often used to derive points of departure for use with safety assessment factors to create recommended exposure levels that are broadly protective but not necessarily target-specific.

Development of a curated Hershberger database

A systematic literature review was conducted to identify Hershberger bioassays for ∼3200 chemicals including those used to validate the OECD/US EPA guideline assay, US EPA's chemicals screened for endocrine activity, and the library of chemicals run in US EPA 's ToxCast in vitro assays. For 134 chemicals that met pre-defined criteria, experimental results were extracted into a database used to characterize uncertainty in results and evaluate the concordance of the Hershberger assay with other in vivo rodent studies that measure androgen-responsive endpoints. Of 25 chemicals tested in >1 Hershberger study, 28% had disagreements between studies (i.e. ≥1 positive and ≥1 negative study), and of the 65 chemicals tested in Hershberger studies and other in vivo studies with androgen-responsive endpoints, 43% indicated disagreements, though in some cases these may be explained by differences in study designs or physiology of the animal model. Ultimately, 49 chemicals were identified with reproducible androgen pathway responses confirmed in ≥2 in vivo rodent studies that could be considered reference chemicals useful for validating alternative methods.

Improvement of the Caenorhabditis elegans growth and reproduction test to assess the ecotoxicity of soils and complex matrices

A growth and reproduction test using the nematode Caenorhabditis elegans was recently standardized by the International Organization for Standardization (ISO). Performing the ISO 10872 protocol (2010) revealed some drawbacks when applied to soil or soil mixed with complex matrices. The authors propose some modifications to the current protocol to normalize the test conditions. An appropriate range of moisture conditions was determined as a percentage of the water-holding capacity (WHC) of the soil. According to the authors' results, C. elegans tests can be performed in the range of 60% to 100% WHC. To ensure that the modifications of the protocol did not affect the organisms' recovery, extraction ratios for the juveniles were subsequently estimated. The modified protocol was found to be as reliable as the standard one concerning recovery of juveniles (over 80%). The protocol was also applied to several chemicals to investigate their potential as reference chemicals for soil toxicity tests. Boric acid, copper chloride, and nickel sulfate showed deleterious effects in a concentration-dependent manner for the growth and reproduction of C. elegans. Finally, the modified protocol was used to assess the growth and reproduction of C. elegans in soil amended with a limed sewage sludge. The authors conclude that the C. elegans modified protocol is a promising tool for the assessment of soil toxicity as well as the toxicity of mixtures with complex matrices.