Role of food and clay particles in toxicity of copper and diazinon using Daphnia magna

Toxicity changes in copper and diazinon were investigated in the presence of food, clay, and their mixture by using Daphnia magna. In sorption equilibrium experiments, copper was significantly attracted (>34% sorbed) to food, clay, and food-clay mixture due to their negative zeta potential, while diazinon was less sorbed (<11%). In the exposure test with food and clay particles, it was revealed that copper was remarkably reduced in the presence of clay particles indicating the change in bioavailability of copper by sorption to clay. This was considered as the primary mechanism for toxicity reduction whereas diazinon toxicity was food dependent in the analysis of toxicity using toxicity change index (TCI). It was also shown that certain foods could not only act as a sorbent to copper and diazinon, but also as a material of energy source to alleviate the toxic damage. Meanwhile, clay can be considered as a prominent sorbent to copper but not to diazinon and can inhibit the sorption interaction between foodstuffs and toxicants through the aggregation and sedimentation processes. Furthermore, clay particles, as shown in TCI analysis, may be a potentially risky material as a physiological stressor or a toxicant carrier in contaminated environments. (C) 2009 Elsevier Inc. All rights reserved.