Increase in Metallothionein in Freshwater Mussels Anodonta grandis grandis Exposed to Cadmium in the Laboratory and the Field

Abstract

Abstract Freshwater unionid mussels, Anodonta grandis grandis, were exposed in the laboratory to nominal [Cd] of 0, 5, 10, 20 and 50 ug/L to determine: 1) whether this species produces metallothionein (MT) in response to Cd exposure, 2) which body parts are involved in the production, and 3) the dose-response relationship between (MT] in body parts and the treatment [Cd] in the laboratory compared with that in a field population exposed to Cd. Background [MT], as µg MT/g wet weight, measured in mussels freshly collected from a pristine lake were: kidney, 38.9 > visceral mass, 15.0; foot, 13.7; gill, 12.5 > mantle, 3.4. After these mussels were exposed to Cd in the laboratory for 22 days, blood [Cd] in the 5–50 µg/L Cd exposures averaged 5.1, 7.1, 9.3 and 15.8 times, respectively, the blood [Cd] in the 0 µg/L treatment. After the 22-day exposure, only [MT] in gill showed a statistically significant relationship with treatment [Cd] indicating that MT was induced in response to Cd exposure. The [MT] in gill after 22 days exposure to 50 µg/L Cd was 24.2 µg/g, 72% higher than in mussels exposed for this period to 0 µg/L Cd. In comparison, [MT] in the gill of mussels collected from a whole lake receiving experimental additions of Cd over three ice-free seasons (epilimnetic means of 0.08, 0.05 and 0.1 µg/L Cd, respectively), was 36.5 ug/g after two seasons exposure and 35.0 µg/g after three seasons, indicating a many-fold greater response to water-borne Cd in the field compared with the laboratory. The other body parts in the mussels collected after three seasons in the Cd-treated lake also contained significantly greater [MT] (kidney, 118.3 µg MT/g; visceral mass, 36.3; foot, 26.0 and mantle, 9.5) than did those from the pristine lake. The field samples thus indicate that all these body parts produce MT in response to exposure to Cd.