Effect of chronic sublethal exposure of major heavy metals on filtration rate, sex ratio, and gonad development of a bivalve species.

The chronic toxic effects of major heavy metals including copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd) on the filtration rate (FR), sex ratio, and gonad development of immature blood clams, Tegillarca granosa, were investigated. The FRs were significantly inhibited by Cu, Pb and Cd, with rates generally decreasing with both increasing metal concentrations and exposure time. EC50 values for FR after 28 days of exposure were 12.9, 12.7 and 14.4 μg/L for Cu, Pb and Cd, respectively. Zn exposure had no effect on FR. Sex ratios were significantly altered from controls in favor of an increased proportion of males at metal concentrations of ≥ 14.2, ≥ 86 and ≥ 110 μg/L for Cu, Pb and Cd, respectively; and at ≥ 1.68 mg/L for Zn. The gonado-somatic index was significantly reduced in clams at all metal exposures, except for the lowest concentration of Cu (7.1 μg/L).