Recently, the United States Environmental Protection Agency (US EPA) released results of Tier 1 EDSP (Endocrine Disruptor Screening Program) testing for 52 pesticides. Through a Weight of Evidence approach, results of this first round of screening will be used to determine which chemicals should be placed through more rigorous (and animal-based) testing.
Currently, Tier 1 screening is comprised of 11 assays; five of which are in vitro and six are in vivo. The EPA is evaluating the applicability of high-throughput (HT) systems for Tier 1 EDSP assays with favourable results. Combination of data from HT screening and computational modelling using ToxCast™ data have so far led to the proposed acceptance of alternative, animal-free in vitro assays for Estrogen Receptor (ER) Binding, Estrogen Receptor Transactivation (ERTA) and Uterotrophic screening. In vitro alternatives for male and female rat pubertal, Androgen Receptor (AR) Binding, Aromatase, Steroidogenesis and the other Tier 1 assays remain under development. By the EPA’s official estimation, HT endocrine disruption testing could save as much as 90% of the cost and 75% of the time required per chemical, while entirely forgoing the need for animal testing for certain hormonal systems that may interact with chemicals.
An important component in the ongoing development of in vitro endocrine disruption screening is the Toxicology in the 21st Century (Tox21) consortium, which is made up of members from the EPA, the National Institutes of Health (NIH) and the Food and Drug Administration (FDA). As of 18 June, 2015, Tox21 had provided estrogen screening results from HT systems for 1800 chemicals, with the results of an additional 1200 expected by 2016. It is important to note, however, that these data reflect estrogen receptor pathways specifically. Development and evaluation of in vitro assays for the androgen and thyroid pathways is incomplete.
Tier 2 EDSP testing is only required for chemicals where more test data are required to fully understand their impact on the endocrine system. This testing examines life cycle and generational impacts of chemicals thought to have endocrine disruption potential. These studies look at how a compound can effect an organism over time and whether or not any observed effects manifest in offspring. Because of the longitudinal nature of Tier 2 assays, there are no viable options for in vitro alternative methods. These tests, however, provide critical insight into the long-term effects chemicals can have on the environment.