MOLLUSCAN CELLULOLYTIC ACTIVITY RESPONSES TO ZINC EXPOSURE IN LABORATORY AND FIELD STREAM COMPARISONS

Changes in cellulolytic activity of Asiatic clams (Corbicula fluminea) and snails (Mudalia dilatata) were monitored throughout 30-d exposure s to constant additions (0.0, 0.025, 0.05, 0.50, and 1.0 mg l-1) of zi nc (Zn). All exposures of 0.05 mg Zn l-1 or greater significantly redu ced enzyme activity (exo- and endocellulase) in both molluscs as early as 10 d following exposures in outdoor laboratory streams incorporati ng New River water as diluent. More sterile laboratory stream exposure s were less consistent in yielding quantifiable differences that could be attributed to metal induced stress apart from effects of nutrition al stress. Tests conducted under natural field conditions during all s easons did not differ significantly with respect to changes in annual energetics of either clams or snails. However, evidence of differing u ptake routes, with respect to two ecologically and physiologically dis tinct molluscs, was apparent in bioaccumulation, growth, and enzyme ac tivity throughout exposure and following 60-d recovery.