Reproductive toxicity of metals in calanoid copepods

This study investigated the effect of exposure route on metal accumulation, tissue distribution, and toxicity in the marine copepods Acartia hudsonica and A. tonsa. Sublethal toxicity was measured as decreases in egg producti on, hatching rate, ovarian development and protein (yolk) content of the eg g. When algal food, exposed to Hg at 1 nM or Cd at 5 nM resulting in cells containing 34 and 64 nmol metal g(-1) dry weight, respectively, was ingeste d over a 4-h period by copepods, the total copepod body burden increased ni ne-fold for Hg and two-fold for Cd over background concentrations, and egg production decreased by 50%. Sublethal concentrations of metals were > 2 or ders of magnitude lower than LC50 concentrations. Hatching rate, ovarian de velopment and egg protein content all decreased following trophic exposure to metals, implying that the process of yolk accumulation (vitellogenesis) was affected. Exposure to dissolved Cd had no effect, but dissolved Hg at c oncentrations as low as 0.25 nM did affect egg production. Different toxic effects following different exposure routes were related to different metal distributions in the copepods: exposure to dissolved metal resulted in met al deposition in the exoskeleton, whereas exposure to dietary metal resulte d in metal deposition in internal tissues. These findings indicate that enr ichment of metal concentrations in internal tissues, which occurs primarily after exposure to dietary metal, affects vitellogenesis. The reproduction rate decreases by about 75% at metal concentrations only moderately higher than levels in coastal waters. Toxicity tests involving aquatic animals nee d to consider effects following uptake by different pathways, including the trophic transfer of metals.