A Study of the Relative Toxicity of Anions, with Polycelis Nigra as Test Animal

A brief review is given of existing knowledge regarding the physiological effects of anions, and literature dealing with their relative toxicity. The degree of toxicity of twenty-seven anions to Polycelis nigra (Müller) has been assessed, by determining in each case the molar concentration the animal survives for 48 hr. at 15-18° C. On this basis their order of increasing toxicity is as follows; commas separate ions of similar degree of toxicity: Cl<ClO3, acetate, Br <CO3 <tartrate <S2O3 <SO4, SO3 <I, NO3 <PO4, BO3 <BrO3 <citrate <CNS, C2O4 <AsO4 <CrO3 <IO3 <F <Fe(CN)6, Fe(CN)5NO <NO2, CN <S<OH. Generally speaking anions are very much less toxic than cations. Even the most toxic anion (OH) is far less toxic than ionic copper, silver or gold. The respiration rate of Polycelis is heavily depressed by cyanide, but the survival time is three days or longer, as long as the respiration rate is not less than about 16% of the normal value. With further depression the survival time shortens rapidly, and at 9% normal is under 4 hr. The normal respiration rate of Polycelis nigra is 0.165 c.c. O2/g./hr. This is not very much less than that of the trout. Polycelis is considerably the more resistant to cyanide. This is probably connected with its capability of surviving very many hours in water containing a very reduced supply of oxygen.