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 (form erly Anodonta grandis) to increased metal exposure in the field, we tr ansferred specimens (8 cm length; 4-6 years old) from a less to a more contaminated lake in the mining area of Rouyn-Noranda, in northwester n Quebec. The transplanted bivalves were maintained in open enclosures placed in the bottom sediments of the contaminated lake. Up to 16 ind ividuals were removed from pairs of enclosures at times t = 0 (June 19 90), 5, 14, 30, 60, 90, and 400 d; tissue concentrations of metallothi onein (MT) and metals were monitored over time. Measurements on contro l molluscs enclosed in their lake of origin showed that enclosure per se had no apparent effect on tissue [MT] or tissue metal levels, but d id decrease shell growth. Metallothionein levels in specimens transpla nted to the more contaminated lake showed a slow but steady increase w ith time; in contrast, MT levels in the control populations showed onl y modest seasonal fluctuations. The increase in MT over time in the tr ansplanted bivalves was closely correlated with a similar slow increas e in soft tissue [Cd]. We conclude that MT in the freshwater bivalve P . grandis is a promising biochemical indicator of metal exposure.