Effects of Long-term Exposure to Silver Or Copper on Growth, Bioaccumulation and Histopathology in the Blue Mussel Mytilus Edulis

Résumé du livre

The purpose of this study was to determine the long-term accumulation of either silver or copper from low concentrations in seawater by blue mussels, Mytilus edulis. Mussels raised from eggs in the laboratory to the age of 2.5 months (approximately 4.5 mm in length) were continuously exposed to 0, 1, 5 and 10 micrograms/liter of either silver (nitrate) or copper (chloride) and sampled at 12, 18 and 21 months for growth studies, measurements of metal accumulation and histopathological examination. Whole-body soft tissues were analyzed for the presence of both silver and copper, as background levels of copper in the incoming seawater averaged 2-4 micrograms/liter. Mussels exposed to silver had accumulated significant amounts of silver only at the highest test concentration (10 micrograms/liter Ag) after 12 months, but at 18 and 21 months significant levels were accumulated at all three test concentrations. Mussels exposed to copper accumulated significant amounts of copper at 5 and 10 micrograms/liter Cu after all three sampling periods, but not at 1 micrograms/liter. Silver-exposed animals also accumulated significantly greater amounts of copper than control animals. In a comparative study, field-collected juvenile mussels (approximately 16.1 mm in shell length) and adults mussels (approximately 53.4 mm in shell length) were exposed for 12 months to 0, 5, 25 and 50 micrograms/liter silver only and subsequently sampled for metal-accumulation analyses and growth measurements. Juvenile mussels accumulated significant amounts of silver at all test concentrations, with the exception of mussels exposed to 5 micrograms/liter Ag for 6 months. Copper accumulation in the silver-exposed juveniles was significant only at 50 micrograms/liter Ag after 6 months, but at all test concentrations after 12 months. Adult mussels exposed to silver accumulated significant levels of both silver and copper, but at somewhat lower levels than juveniles. In the growth study, silver had no effect on laboratory reared mussels at the highest concentration of 10 micrograms/liter tested, whereas copper at 10 micrograms/liter did appear to affect growth as early as 4 months after the start of experimental exposure. Field-collected juvenile mussels did show inhibition in growth after 6 months' exposure to 25 and 50 micrograms/liter Ag, with some growth occurring after 12 months . Adults also showed inhibition in growth after 6 months but not at 12 months. Histopathological examination of mussels exposed to either 5 or 10 micrograms/liter of copper for 18 months showed changes in the digestive diverticula, gastrointestinal tract, reproductive tract and muscle tissues. These changes were more noticeable in mussels exposed to 5 micrograms/liter Cu than in those exposed to 10 micrograms/liter. Mussels exposed to silver for 21 months showed yellowish to black particulate deposition in the basement membrane and connective tissue of the various organs and tissues. Silver deposition increased with increasing test concentration.