Human Health: Reproductive Effects
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, can be sensitive to environmental chemicals.
One class of chemicals under scrutiny by EPA is phthalates, chemicals used in consumer products ranging from vinyl to perfumes. Phthalates are known to interfere with several hormones, particularly androgens such as testosterone. Animal studies have shown phthalates to cause a range of reproductive problems in rodents, and a large human population study found an association between phthalate metabolites in pregnant women and effects on the genitalia of their offspring. Other studies show effects of phthalates on the timing of puberty. Bisphenol-A, a phenol present in the linings of cans used for food products, has also been implicated in changing reproductive development, but some of these studies are controversial and are currently under debate.
Animal studies to examine effects of endocrine disruptors can take months or years to complete. So, EPA is trying to develop better, faster testing models for these assessments.
EPA researchers are assessing the following research questions:
- How will exposure during fetal or early postnatal development affect reproductive health later in life and how can these effects be determined using molecular endpoints as early predictive tools?
- What are the most critical windows of vulnerability to these environmental chemicals and which time points during fetal life, puberty and adulthood are most susceptible?
EPA researchers are discovering biological indicators in developing animals that will help scientists predict the effects of phthalates on reproductive health. One study is examining the response of the hypothalamus, a hormone-rich region of the brain, to chemicals that shift the timing of pubertal onset.
Researchers are also performing simple tests in cells that can streamline the assessment of potential endocrine disruptors. For instance, one study is examining the response of hormone-producing brain cells to various chemicals and comparing that response with effects in the adult animal. They are working to see if the 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).
Results and Impact
Research on biological indicators in animal cells that can predict reproductive effects will increase the understanding of how endocrine disrupting chemicals can alter human health. Chemicals aside from phthlates examined by EPA researchers using such methods include alternative chemicals to phthalates, triclosan-a microbe-killing compound common in soaps, and chlorotrazine herbicides. This research will help EPA's Endocrine Disruptor Screening Program in one of its main tasks - developing ways to streamline the assessment of chemicals for potential human hazard. The research will also help answer questions such as what the potential impacts could be of puberty starting early and early prenatal exposures on later reproductive function. Answers to these research questions will help EPA inform regulators who examine the effects of endocrine disrupting chemicals on reproductive development and latent effects on offspring.