Contaminant effects on the teleost fish thyroid.
Numerous environmentally relevant chemicals, including polychlorinated hydrocarbons, polycyclic aromatic hydrocarbons, organochlorine pesticides, chlorinated paraffins, organophosphorous pesticides, carbamate pesticides, cyanide compounds, methyl bromide, phenols, ammonia, metals, acid loads, sex steroids, and pharmaceuticals, exert acute or chronic effects on the thyroid cascade in the approximately 40 teleost fish species tested to date. Thyroid endpoints, therefore, serve as biomarkers of exposure to environmental pollutants. However, the mechanisms underlying thyroid changes and their physiological consequences are poorly understood because the thyroid cascade may respond indirectly and it has considerable capacity to compensate for abuses that otherwise would disrupt thyroid hormone homeostasis. Indeed, a xenobiotic-induced change in fish thyroid function has yet to be conclusively causally linked to decreased fitness or survival. Other complications in interpretation arise from the diversity of test conditions employed and the often indiscriminate use of numerous thyroid endpoints. Future work should be directed toward standardizing test conditions and thyroid endpoints and investigating causal links between thyroid changes and fish growth, reproduction, and development. Development may be particularly susceptible to thyroid disruption, and thyroid endpoints appropriate for early life stages need to be applied.
Brown
Scott B
SB
Environment Canada, P.O. Box 5050, Burlington, Ontario L7R 4A6, Canada. scott.brown@ec.gc.ca
Adams
Bruce A
BA
Cyr
Daniel G
DG
Eales
J Geoffrey
JG
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects* / Q000502:physiology; D015415:Biomarkers / Q000032:analysis; D004785:Environmental Pollutants / Q000633:toxicity*; D005399:Fishes; D006846:Hydrocarbons, Halogenated / Q000737:chemistry / Q000633:toxicity; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry / Q000633:toxicity; D013959:Thyroid Diseases / Q000139:chemically induced / Q000662:veterinary; D013961:Thyroid Gland / Q000187:drug effects* / Q000378:metabolism; D013974:Thyroxine / Q000737:chemistry / Q000378:metabolism; D015262:Xenobiotics / Q000009:adverse effects
D015415:Biomarkers; D004785:Environmental Pollutants; D006846:Hydrocarbons, Halogenated; D011084:Polycyclic Aromatic Hydrocarbons; D015262:Xenobiotics; D013974:Thyroxine