Acute toxicity of two hydroxylated hydrocarbons to the prosobranch gastropod Littorina littorea

The main purpose of this work is to study the mortality of the periwinkle Littorina littorea (L.) exposed to different concentrations of two hydroxylated hydrocarbons, picric acid (Trinitrophenol) and l-naphthol, and to calculate the 96h-LC50 and the asymptotic LC50 values. The selected concentrations for picric acid were 0, 20, 85, 375, and 1600 mg l-1. Due to the relatively low solubility of l-naphthol in seawater, the concentrations in the test-containers were determined by fluorometry. According to these measures, the concentrations of l-naphthol used in the assay were 0,2.075 ± 0.1, 6.22 ± 0.32, 18.68 ± 0.96, and 56.06 ± 2.89 mg l-1. The tests were conducted in replicated series and 20 winkles were placed in each test container (1 l). Tanks were continously aerated and winkles were maintained unfed during the whole assay (10 days). Bioassay data were analysed in order to obtain the response surface for both toxicants after multiple regression analysis. Hyperbolic curves LC50 vs. time were obtained from such surfaces and their asymptotes, which correspond to the so-called asymptotic LC50 values, calculated. The results show that l-naphthol is much more toxic than picric acid to L. littorea, as could be expected from the structure of both toxicants. A noticeable decrease in l-naphthol concentration during exposure was observed, being most pronounced in the beakers containing test organisms; possibly due to bioaccumulation and/or to degradation by the periwinkles.