The action of heavy metals on the gametes of the marine mussel, Mytilus edulis (L.)-II. Uptake of copper and zinc and their effect on respiration in the sperm and unfertilized egg

The addition of stock copper and zinc nitrate solutions to filtered seawater (pH 7·91) resulted in a large pH shift which was more pronounced with copper. The pH shift was minimized by increasing the buffering capacity of seawater using 10 mm Tris-Tes pH 7·91. Subsequent experimentation was carried out in both unbuffered and buffered seawater.In unbuffered seawater, both copper and zinc had a pronounced inhibitory effect on Mytilus edulis sperm respiration with 50% inhibition occurring at 0.65 mm (41·3 ppm) copper and 1.0 mm (65·4 ppm) zinc. Egg respiration was also inhibited by copper with 50% inhibition occurring at 0.9 mm (57·2 ppm) whereas zinc inhibited egg respiration by only 30% at 1·5 mM (98·1 ppm).In buffered seawater, both copper and zinc produced an inhibitory effect on sperm respiration. However, with copper the inhibition was much reduced whereas zinc had tthe same inhibitory effect as in unbuffered seawater. In contrast to unbuffered seawater, egg respiration was stimulated by copper but zinc produced a comparable respiratory inhibition. The uptake of both copper and zinc in sperm and egg in buffered seawater increased with increasing metal concentration. Metal ion uptake, when expressed as ng ions μl cell volume^?1, was approximately 3-fold greater in the sperm than in the eggs and in both cases zinc uptake exceeded copper uptake.At a seawater pH of < 7·5, in the absence of copper or zinc, the respiration of both egg and sperm was inhibited. The maximum levels of inhibition at pH 5·4 were 15% and 30% for sperm and egg, respectively.The differing actions of copper on egg respiration in buffered and unbuffered seawater appear to be due to enhanced copper uptake in unbuffered seawater.