Ecosystems & Environment: Aquatic Effects
Assessing the aquatic effects of endocrine disrupting chemicals released into waterways presents challenges. Although contaminated waterways may be dominated by a handful of compounds, thousands of chemicals may have potential to impact the hormonal systems of fish and other aquatic animals. Standardized tests to detect each chemical and measure its concentration can take years to develop and implement and be costly to collect and analyze, which makes it nearly impossible to obtain a complete profile of all the chemicals present in water samples from lakes and rivers nationwide. Compounding this problem is the fact that endocrine disruptors can be present at very low concentrations, making detection and exact quantification difficult. Also, a profile of the chemicals present in a particular waterway does not address whether they will have an effect on the hormonal systems of aquatic species - particularly given that mixtures of chemicals can have unknown cumulative effects on animal biology. Traditional toxicology testing can assess whether an uncharacterized compound or mixture of compounds has an effect on reproduction in a whole animal such as a fish - but such tests can take years as researchers examine the effects across generations. EPA researchers are developing innovative testing tools to overcome some of these challenges.
EPA researchers have developed a battery of testing methods for endocrine disrupting chemicals and the effects on aquatic species. These tests range from tests on animals to chemical assays in a test tube. For instance, researchers have developed whole-animal tests of shorter duration, such as a 21-day test which is being used as part of the endocrine disruptor screening program's Tier one tests. This 21-day test on fathead minnows is designed to detect changes in fish morphology and spawning, as well as specific biochemical endpoints that reflect disturbances in hormonal systems. The results of this test are useful for assessing potential effects of a chemical or mixture of chemicals on aquatic organisms and in some cases human health as well, given that fish and humans have similarities in their reproductive hormonal systems. Even quicker tests on whole animals have also been developed, such as test that measures the production of vitellogenin, a component of the egg yolk, in fish. Female fish with hormone disturbances make elevated or depressed amounts of vitellogenin. In contrast, male fish normally do not make vitellogenin but can take on this female characteristic if they are exposed to an external source of estrogen. Other tests are even simpler and operate at the cellular level. For instance, one test for vitellogenin simply examines whether the DNA that makes vitellogenin is turned on in cells. Another test assesses whether cells proliferate, indicating they are stimulated by a hormone-like substance. Yet other tests simply ask if two molecules bind together, for instance whether a chemical interacts with the estrogen receptor, the molecule that carries out the hormones instructions. Dozens of such tests for various types of hormones have been developed and new ones are under evaluation.
Results and Impact
The development of innovative tools to measure potential endocrine disrupting chemicals (EDCs) has bolstered research at the EPA and other institutions. Field researchers have used these tests to assess EDCs in wastewater effluents and in runoff from animal feeding operations. Some of these tests have gone through an extensive review and validation process and will be used by the regulatory arm of the EPA in 'Tier 1' screening for the Endocrine Disruption Screening Program. Many tests for EDCs have already been adapted by the EDSP for tier 1 testing and other methods such as high-throughput screening are being used to prioritize the order in which chemicals go through 1 testing.