Evaluation of three antidotes on arsenic toxicity in the common earthworm (Lumbricus terrestris)

The common earthworm (Lumbricus terrestris) is being evaluated in our laboratories as a substitute for mice in metal toxicity studies. These two disparate species have enzymes in common, such as catalase, superoxide dismutase and glutathione-S-transferase. Also, worms respond similarly to these rodents for selenium and nickel toxicity. Worms are less sensitive, however, to metal toxicity. In this study earthworms were challenged with three different arsenic compounds: arsenite, arsenate and the vesicant phenyldichloroarsine (PDA). The median lethal dose for each arsenic compound was determined. The order of toxicity of the arsenic compounds to the worms was PDA > arsenite > arsenate (24 h LD50 values were 189.5, 191.0 and 519.4 mumol kg-1, respectively). Individual mammalian dithiol antidotes, namely the sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS), meso-dimercaptosuccinic acid (DMSA) or 2,3-dimercapto-1-propanol (BAL), were injected into the worms 5 min after various doses of the arsenic compound were administered. The decreases in acute toxicity values were recorded. All three antidotes protected the worms against arsenic toxicity with varying degrees of effectiveness. The protective action for the inorganic arsenic compounds was in the order DMPS > DMSA > BAL. For the organic arsenical, PDA, the most effective antidote was BAL.