Assessing the importance of dietborne cadmium and particle characteristics on bioavailability and bioaccumulation in the nematode Caenorhabditis elegans.

To investigate the impact of multiple cadmium exposure pathways on bioavailability and bioaccumulation, Caenorhabditis elegans were exposed to either dissolved cadmium or to both particulate (dietborne) and dissolved cadmium. The dietborne metal exposure scenarios included evaluations of two bacteria species (Escherichia coli and Arthrobacter globiformis), varying bacteria concentrations, artificial particles (with different surface functional groups or coated with lipopolysaccharides), as well as a mixture of both bacteria and artificial particles. Total cadmium concentration in the nematodes was used as a proxy for total metal accumulation. Internal cadmium availability was determined using the cadmium-responsive gene-1 (cdr-1) transcript level, as quantified by real-time polymerase chain reaction. Particle-associated exposure was the predominant contributor to cadmium bioavailability and bioaccumulation; however, no clear relationship between cdr-1 expression and cadmium body burden was observed. The quality and quantity of particles, rather than the total particle-associated metal load, was of primary importance in regulating cadmium uptake and accumulation. Nematodes exposed to cadmium-contaminated bacteria displayed significantly higher levels of cdr-1 expression relative to artificial particles. Furthermore, C. elegans displayed a statistically significant difference in cadmium accumulation patterns between the biotic diet, abiotic particles, and aqueous phase. Waterborne exposure caused an increase in total cadmium body burden following inhibition of the P-glycoprotein transport system in nematodes. This may suggest that cadmium taken up by the aqueous phase is detoxified preferentially by excretion.