The usefulness of Lymnaea stagnalis L. as a biological indicator in toxicological bio-assays (model substance α-HCH)

Short- and long-term studies with α-hexachlorocyclohexane (α-HCH) were carried out on the pond snail (Lymnaea stagnalis L.), to test the usefulness of this organism as a biological indicator of pollutants in surface water.Based on mortality and immobilization in the short-term study (2 days) an ec₅₀-value of 1200 μg α-HCH 1⁻¹ could be determined.In the long-term study (70 days) an inverse time-independent relation was found between egg production rate (= number of eggs produced per unit of time) and the α-HCH concentration in the water. Based on this egg production inhibition an EC⁵⁰ of 250 μg α-HCH 1⁻¹ could be determined. The percentage of fertilized eggs per capsule was not affected. No morphological abnormalities were noticed during the embryonic development, although a significantly dose-related delay occurred with respect to the hatching of the eggs. Based on the number of eggs which did not hatch, a lc₅₀ of 230 μg α-HCH 1⁻¹ could be determined. The combination of (1) the inhibition of the egg-production of the adult snails (caused by a significant prolongation of the oviposition interval and by a significant decrease of the number of eggs per capsule) and (2) the mortality of the young during their development caused a 50° reduction of the overall reproductivity at 65 μg α-HCH 1⁻¹. The heart-rate of newborn snails was slowed significantly by α-HCH. Replacing the snails into an α-HCH-free medium for 16 days, after a 40-day exposure to α-HCH, did not result in the disappearance of the effects mentioned above.The susceptibility of Lymnaea stagnalis to α-HCH did not differ much from that of Daphnia magna (a crustacean). This organism proved to be the most sensitive one of all tested organisms (Chlorella, Daphnia, Lebistes, Salmo) in previous studies with α-HCH. Therefore Lymnaea stagnalis might be useful as a test organism in future environmental toxicity studies, although these kinds of experiments have to be considered as very laborious and costly.