Toxicity of ingested cadmium to the nematode Caenorhabditis elegans

Benthic organisms ingest dissolved and particle-bound contaminants together with their food, whereas it is not clear which fraction of the ingested suspension causes the toxic effects. In the standard toxicity test using the nematode Caenorhabditis elegans, the organisms are fed with bacteria that bind contaminants, thus influencing the bioavailability of the contaminants for the organisms. To unravel the role of food bacteria in the toxicity of contaminants in C. elegans, suspensions with varying densities of bacteria were spiked with the toxic metal cadmium (Cd), either via the water or via the bacteria. The toxicity of Cd to C. elegans was clearly related to the uptake of bacteria in the nematode's gut. An increase in the bacterial density resulted in a significant decrease in the toxicity of Cd such that toxic effects better correlated with the aqueous than with the bacterial-bound or total Cd concentrations. The results suggested that the aqueous Cd that was ingested together with the food was the best available fraction and thereby mainly caused the observed toxicity on the reproduction of C. elegans.