Reproductive health in humans and wildlife: are adverse trends associated with environmental chemical exposure?

Abstract

In recent years, evidence from disparate observations has indicated adverse changes in the reproductive health and fecundity of animals and humans. In humans, there is strong evidence for such trends in the incidences of testicular and female breast cancer, and concern has also been expressed regarding semen quality, cryptorchidism, hypospadias and polycystic ovaries. Laboratory studies have indicated that some chemicals in the environment, both natural and synthetic, have the potential to disrupt the endocrine system and that these could, at least theoretically, be partly responsible for the observed changes. Chemicals thus identified include the naturally occurring steroid hormones, phyto- and myco-estrogens, and anthropogenic chemicals such as synthetic hormones, organotins, organochlorine pesticides, polychlorinated biphenyls, dioxins, alkylphenol polyethoxylates, phthalates and bisphenol-A. While there is no direct evidence from human studies to confirm a causal link between exposure and effect, concern exists and is strengthened by reports of adverse reproductive and developmental effects in wildlife, possibly mediated via endocrine disruptive pathways. The development of imposex in neogastropod molluscs exposed to tributyltin has been attributed to such a mechanism and in wild populations of fish, alligators and birds, instances of masculinisation or feminisation in polluted areas have been noted. Among mammals, disturbed fertility of Florida panthers and some marine species has also been reported. A concentrated research and monitoring programme is required to clarify the nature and extent of effects on reproductive health in humans and wildlife, and to assess human and wildlife exposure to relevant naturally occurring or anthropogenic endocrine disrupting substances. This will enable a more robust evaluation of the contribution that environmental chemical exposure may have on adverse trends in the reproductive health of humans and wildlife.