Toxicity of cadmium to Caenorhabditis elegans (Nematoda) in whole sedimentand pore water - The ambiguous role of organic matter

A bioassay using the nematode Caenorhabditis elegans was performed with nat ural sediment that had been spiked with organic matter (36-117 g total orga nic carbon/kg dry wt) and cadmium (Cd: 10-1,200 mg/kg wet wt). Whole sedime nt and pore water were tested to study the influence of particulate organic matter (POM) and dissolved organic matter (DOM) on Cd toxicity and to comp are the toxicity of the two sediment phases. Toxicity was measured with nem atode growth as test parameter. No toxicity was observed if sediment concen trations of Cd were below concentrations of acid-volatile sulfides (AVS). A t higher Cd concentrations. toxicity in whole sediment and pore water incre ased with increasing organic content. This phenomenon was explained by an i ncrease of DOM concentrations in organically enriched treatments and a resu lting solubilization of Cd due to Cd complexation by DOM. Because DOM did n ot alter the bioavailability of Cd for the nematodes, bacteria, serving as food, might have functioned as vectors for Cd-DOM complexes, so that Cd cou ld have become available in the gut of the nematodes. A higher toxicity in whole sediment compared to in pore water in the organically enriched treatm ents indicated that POM-bound Cd may have contributed to the toxicity of Cd to C. elegans.