Endocrine Disruption: Human Health Research
- Reproductive Effects of Endocrine Disrupting Chemicals
- Effects on Neurological Development by Endocrine Disrupting Chemicals
Research on the Reproductive Effects of Endocrine Disrupting Chemicals
Reproductive hormones exert their effects at many life stages. During embryo and fetus development in the womb, these hormones direct formation of sex organs and the cells that give rise to sperm and eggs. They also determine the start of puberty, labor and lactation.
Reproductive hormones, including steroids (such as estrogens and androgens) and other regulatory hormones produced by the brain and pituitary gland, can be sensitive to environmental chemicals. EPA researchers conduct studies to determine how exposure during fetal or early postnatal development affects reproductive health later in life. Researchers are also working to figure out how these effects can be determined using molecular endpoints as early predictive tools.
In developing animals, EPA researchers are discovering biological indicators that will help scientists predict the effects of chemicals on reproductive health. One study examines the response of the hypothalamus, a hormone-rich region of the brain, to chemicals that shift the timing of the beginning of puberty. Researchers are also performing simple tests in cells that can streamline the assessment of potential endocrine disruptors.
Another study examines the response of hormone-producing brain cells to various chemicals and compares that response with effects in the adult animal. Researchers are working to see if chemicals change how hormones are produced and whether those changes result in adverse health outcomes. Other studies are examining how maternal stress (both chemically induced and non-chemically induced) and other prenatal exposures can impact the developing offspring (long-term effects).
Research on the Effects on Neurological Development by Endocrine Disrupting Chemicals
Endocrine disrupting chemicals can affect multiple systems in the body, including the brain and nervous system. One way chemicals affect the brain is through disrupting the levels of thyroid hormones - one of the main hormone systems that interests EPA's Endocrine Disruptor Screening Program.
These hormones help control the development and maturation of the central nervous system. EPA scientists have found reductions in thyroid hormones in rats exposed in utero to ammonium perchlorate, a component of rocket fuel and an environmental contaminant. The quantitative relationship between reductions in thyroid hormones and neurological effects has yet to be precisely defined.
EPA scientists are currently researching:
- the degree to which thyroid hormones must be reduced before neurological effects begin to emerge,
- the timing and duration over which exposure must occur to induce them, and
- the most sensitive endpoints for detection.
EPA scientists have found neuronal effects in offspring of pregnant rats who experienced reductions in serum hormone of less than 25 percent.
Scientists also identified new methods to assess effects on the nervous system, which could reduce the reliance on behavioral assessments of neuro development. These new methods include:
- imaging techniques to determine the effects on the brain,
- identifying subtle abnormalities in brain structure, and
- examining the disruption of thyroid-sensitive genes in the brain.
Measurements generated from these methods may be more readily translated into computational models that can be used to make predictions about the neurological effects of chemicals. The research will help EPA prioritize which chemicals need animal testing and which tests are most appropriate for different types of chemicals