FIELD TRANSPLANTATION OF A FRESH-WATER BIVALVE, PYGANODON GRANDIS, ACROSS A METAL CONTAMINATION GRADIENT .1. TEMPORAL CHANGES IN METALLOTHIONEIN AND METAL (CD, CU, AND ZN) CONCENTRATIONS IN SOFT-TISSUES

To test the response of the freshwater bivalve Pyganodon grandis (formerly Anodonta grandis) to increased metal exposure in the field, we transferred specimens (8 cm length; 4-6 years old) from a less to a more contaminated lake in the mining area of Rouyn-Noranda, in northwestern Quebec. The transplanted bivalves were maintained in open enclosures placed in the bottom sediments of the contaminated lake. Up to 16 individuals were removed from pairs of enclosures at times t = 0 (June 1990), 5, 14, 30, 60, 90, and 400 d; tissue concentrations of metallothionein (MT) and metals were monitored over time. Measurements on control molluscs enclosed in their lake of origin showed that enclosure per se had no apparent effect on tissue [MT] or tissue metal levels, but did decrease shell growth. Metallothionein levels in specimens transplanted to the more contaminated lake showed a slow but steady increase with time; in contrast, MT levels in the control populations showed only modest seasonal fluctuations. The increase in MT over time in the transplanted bivalves was closely correlated with a similar slow increase in soft tissue [Cd]. We conclude that MT in the freshwater bivalve P. grandis is a promising biochemical indicator of metal exposure.