Symptoms and implications of selenium toxicity in fish: the Belews Lake case example
Belews Lake, North Carolina was contaminated by selenium in wastewater from a coal-fired power plant during the mid-1970s and toxic impacts to the resident fish community (20 species) were studied for over two decades. Symptoms of chronic selcnitun poisoning in Belews Lake fish included, (1) telangiectasia (swelling) of gill lamellae; (2) elevated lymphocytes; (3) reduced hematocrit and hemoglobin (anemia); (4) cornea1 cataracts; (5) exopthalmus (popeye); (6) pathological alterations in liver, kidney, heart, and ovary (e.g. vacuolization of parenchymal hepatocytes, intracapillary proliferative glomerulonephritis, severe pericarditis and myocarditis, necrotic and ruptured mature egg follicles); (7) reproductive failure (reduced production of viable eggs due to ovarian pathology, and post-hatch mortality due to bioaccumulation of selenium in eggs): and (8) teratogenic deformities of the spine, head, mouth, and fins. Important principles of selenium cycling and toxicity were documented in the Belews Lake studies. Selenium poisoning in fish can be `invisible', because, the primary point of impact is the egg, which receives selenium from the female's diet (whether consumed in organic or inorganic forms), and stores it until hatching, whereupon it is metabolized by the developing fish. If concentrations in eggs are great enough (about 10 µg/g or greater) biochemical functions may be disrupted and teratogenic deformity and death may occur. Adult fish can survive and appear healthy despite the fact that extensive reproductive failure is occurring -- 19 of the 20 species in Belews Lake were eliminated as a result of this insidious mode of toxicity. Bioaccumulation in aquatic food chains causes otherwise harmless concentrations of selenium to reach toxic levels, and the selenium in contaminated sediments can be cycled into food chains for decades. The lessons learned from Belews Lake provide information useful for protecting aquatic ecosystems as new selenium issues emerge.