Heavy Metal Exposure Disrupts Electrotactic Behavior in Caenorhabditis elegans

Abstract

Environmental toxicants such as heavy metals can profoundly impact organismal physiology, yet sensitive and rapid behavioral assays to quantify such effects are limited. Here, we employed a microfluidic-based electrotaxis assay to systematically evaluate the impact of chronic exposure to metal salts on the electrotactic swimming behavior of the nematode Caenorhabditis elegans. We report that exposure to Ag, Hg, MeHg, Cu, Mn, and Pb significantly alters electrotaxis speed. Notably, Cu required higher concentrations to induce phenotypes, whereas Ag and Hg disrupted behavior at lower doses. Three other metals (Ni, Fe, and Cd) did not elicit marked electrotaxis defects. Bioaccumulation analysis of Cu, Ag, Hg, and MeHg via ICP-MS revealed that MeHg was present in highest amount in worms. Consistent with this, MeHg showed the highest toxicity. We also found dopaminergic neurodegeneration in most metal-exposed animals, correlating with behavioral impairments. Although heat shock factor-1 (HSF-1) and its downstream target hsp-16.2 were induced by some metals, their expression did not consistently correlate with electrotaxis defects. Moreover, metal-induced impairments persisted even after recovery on toxin-free media, indicating possible irreversible damage. Our findings establish electrotaxis in C. elegans as a robust, non-invasive assay to assess neurobehavioral toxicity and demonstrate its utility for detecting sub-lethal impacts of environmental metals.