Expert Report

Each report is produced by a committee of experts selected by the Academy to address a particular statement of task and is subject to a rigorous, independent peer review; while the reports represent views of the committee, they also are endorsed by the Academy. Learn more on our expert consensus reports.

Key Messages

  • A recent study reported an association between dieldrin and breast cancer; additional epidemiologic and laboratory studies are needed to help confirm or refute this possible relationship.
  • Determining the risk of environmental HAAs to humans and wildlife is difficult because exposure to these agents has not been routinely monitored, and effects that might be attributed to background concentrations could be complicated by endogenous hormones, pharmacologic estrogens (e.g., hormonal contraceptives), and naturally occurring HAAs (e.g., phytoestrogens) that are ubiquitous in the environment.
  • Environmental HAAs probably have contributed to declines in some wildlife populations, including fish and birds of the Great Lakes and juvenile alligators of Lake Apopka, and possibly to diseases and deformities in mink in the United States, river otters in Europe, and marine mammals in European waters.
  • For most associations reported between HAAs and various biologic outcomes, the specific mechanism of action is not well understood.
  • In humans, data on the immunologic effects of HAAs are inadequate to support any definitive conclusions.
  • In humans, results of cognitive and neurobehavioral studies of mother-infant cohorts accidently exposed to high concentrations of PCBs and PCDFs and of mother-infant cohorts eating contaminated fish and other food products containing mixtures of PCBs, dioxin, and pesticides (such as DDE, dieldrin, and lindane) provide evidence that prenatal exposure to these HAAs can affect the developing nervous system.
  • Laboratory experiments with specific HAAs found in those effluents and polluted waters have produced effects consistent with those wildlife observations.
  • Reproductive and developmental abnormalities have also been observed in several populations of fish exposed to effluents from sewage treatment plants and paper mills and polluted waters of the Great Lakes. Effects observed include intersexes in trout exposed to sewage-treatment-plant effluent (STPE); increased egg and fry mortality in Great Lakes trout and salmon; thyroid enlargement in Great Lakes salmon; and changes in plasma sex-steroid concentrations, decreased egg and gonad size, and delayed sexual maturity in white suckers exposed to effluents from paper mills along Lake Superior.
  • Studies indicate that prenatal exposure to PCBs can cause lower birth weight and shorter gestation and have been correlated with deficits in IQ and memory as well as delayed neuromuscular development.
  • There are important differences among species and between adult and developing organisms in their responses to HAAs.
  • There are no generally accepted, adequately validated methods for routine identification or monitoring of exposures to HAAs. In addition, most in vitro and in vivo screening assays do not address the full range of putative actions of HAAs.
  • There is evidence of suppression of the immune system by exposure to organochlorines (predominantly PCBs) in birds in the Great Lakes region. There is also evidence of suppression of innate and acquired immune responses in seals fed fish from the PCB-contaminated Baltic Sea.
  • Understanding the relationships between exposure, absorption, disposition, metabolism, excretion, and response is important for predicting whether exposure to an agent will be harmful.
  • With the exception of several bioassays in which mice were exposed to DDT during fetal life, during lactation, and after weaning without apparent adverse effects, perinatal exposure to environmental HAAs has not been assessed with respect to carcinogenesis in laboratory animals or humans, nor have transgenerational effects been investigated.