Effects of Hypoxia on Valve-Closure Time and Bioaccumulation of 2,4,5-Trichlorophenol by the Freshwater ClamSphaerium corneum[L.]

The effects of hypoxia and 2,4,5-trichlorophenol (TCP) on the behavior of the freshwater clamSphaerium corneum(L.) and the accumulation and elimination rates of 2,4,5-trichlorophenol were studied in the laboratory at 20°C. After an initial high activity period, the shell valves were held closed for significantly longer periods in hypoxia than in normoxia. At the end of the 36-hr exposure period, the number of individuals with closed valves increased under normoxic conditions as well. The accumulation of TCP into clam tissues in normoxia was rapid and an uptake rate constant of 27.97 (±6.64) ml/g/hr was measured. An apparent steady state was achieved within 12 to 24 hr and the bioconcentration factors varied between 115 and 139. The depuration rate constant (kd) based on the accumulation data was 0.2717 (±0.07) hr−1. However, the much lowerkdof 0.0137 (±0.0019) hr−1measured over the depuration period from 24 to 120 hr suggests biphasic depuration kinetics. After a 6-hr exposure to TCP in both hypoxia and normoxia, the highest body burdens were found in clams exposed under normoxic conditions. A significant correlation was found between body burden and length of time the valves were open during the exposure. Results suggest that in short-term experiments,S. corneumcan reduce the bioaccumulation of TCP by closing their shell valves.