Recent progress in understanding the causes of endocrine disruption related to pulp and paper mill effluents

Reproductive impairment in fishes exposed to pulp and paper effluent has been observed in the wild for three decades. Despite intense research, identification of causative agents, if indeed the changes are strictly chemically mediated, has yet to be achieved. This review examines the body of research developed over the last six years that was directed at understanding the mechanisms of reproductive dysfunction in fishes associated with pulp mill effluent exposures. Research has continued to show diminishing effects of effluent exposure on fish reproductive physiology. Observations of exposure to androgens and estrogens continue to be observed and new evidence suggests that antiestrogens may be present. The presence of androgenic steroids remains a consistent observation, and those androgens appear to be native to wood. Recent studies have also suggested a number of alternate mechanisms beyond androgens or estrogens. One such possibility is that neuroactive substances are interfering with endocrine balance critical to reproduction. A second possibility is that some reproductive effects in the field may be due to nutritional factors, and thus reproductive impacts are caused by indirect effects of pulp mill effluent exposure. Ongoing mechanistic studies, particularly with paired field-lab components, are required to make further progress.