FUNCTIONAL-RESPONSES IN LEPTOXIS-PRAEROSA TO INCREASING METAL CONCENTRATION AND EXPOSURE DURATION

The protectiveness of USEPA ambient water quality criteria for copper (Cu) and zinc (Zn) was tested using the snail Leptoxis praerosa in sho rt- and long-term artificial stream tests. Acute criteria were tested in 96-h survival tests. Chronic criteria were tested by comparing cell ulolytic enzyme activity impairment, bioconcentration, and survival in 14-, 20-, 30-, and 114-d exposures. Significant Cu bioconcentration o ccurred within 40 d at the chronic Cu criteria concentration, followed by significant cellulolytic enzyme activity impairment within 54 d. S ignificant bioconcentration and enzyme activity impairment occurred wi thin 40 and 54 d, respectively, at the chronic Zn criteria concentrati on, but survival was much higher than in Cu-exposed snails. Approximat e additive effects were seen in combination treatments of Cu and Zn. S imilar patterns of effects were seen from both increased exposure dura tion and concentration. This research concluded that criteria based on abbreviated chronic tests may be underprotective for some sensitive t axa when exposures are prolonged.