For Release: June 30, 2015

The U.S. Environmental Protection Agency has released its reviews of the Tier 1 screening assay results for the first 52 pesticide chemicals (active and inert ingredients) in the Endocrine Disruptor Screening Program. This is an important step in a multi-step process to protect public health and the environment by ensuring that exposure to chemicals does not result in adverse effects that can occur from the disruption of hormones. The Tier 1 screening data are the best way to determine whether a chemical has the potential to interact with the endocrine system and requires more thorough testing.

EPA currently uses a two-tiered screening program that examines chemicals to determine whether they have the potential to affect endocrine systems. The first step is Tier 1 screening, which uses a battery of 11 assays to determine whether chemicals have the potential to interact with the estrogen, androgen or thyroid hormonal pathways. For each chemical, EPA decides whether additional (Tier 2) testing is necessary. These decisions are based on weighing whether the evidence from the assay results and other scientifically relevant data, shows more potential for endocrine bioactivity than the evidence that it does not.

Tier 2 testing includes multigenerational, longer-term testing across various species (e.g., frog, fish, bird and rat) and is designed to confirm interaction with the endocrine system, identify any adverse endocrine-related effects caused by the substance and establish a quantitative relationship between the dose and that endocrine effect.

The first 52 chemicals to be screened were not selected because of their potential to interact with endocrine systems but rather for their potential for human exposure. It is important not to equate a chemical’s bioactivity with the conclusion that the chemical harms the endocrine system in humans and wildlife. Bioactivity is an indicator that a chemical has the potential to alter endocrine function, but without further testing, one cannot determine (1) whether the chemical actually alters endocrine function and (2) whether that altered function produces an adverse outcome in humans and animals.

The Tier 1 screening assays include five in vitro (cell systems) and six in vivo (live animal) systems for determining the potential of a chemical to interact with the estrogen, androgen or thyroid hormonal pathways. In determining whether a chemical interacts with those pathways, we evaluated the number and type of effects induced and the magnitude and pattern of responses observed. We also considered the conditions under which effects occur, in particular, whether or not the dose(s) at which endocrine-related responses occurred happened concurrently with general systemic toxicity.

EPA is moving toward new technologies that would substantially speed up screening of chemicals for their potential to disrupt hormones in humans and wildlife and reduce animal use in screening. Thus far, these technologies provide alternatives to the three estrogen-related screening tests but not the androgen and thyroid tests. New tests for those hormonal systems are under development. Science is evolving, and EPA will continue to incorporate new methods involving high-throughput assays and computational toxicology.

Read more information, including the screening assessment results.