Molluscs in biogeochemical flows (C, N, P, Si, Al) and water self-purification: Effects of surfactants

Abstract

Effects of a cationic surfactant on the feeding rate and the pellet excretion by the molluscs Lymnaea stagnalis and freshwater mussels (Unionidae) was studied. It is shown that the molluscs Lymnaea stagnalis excret pellets of faeces at the rate of 4-7 mg (dry weight) per 1 g of the wet weight of molluscs per 72 h. Under the conditions when the food is the leaves of Nuphar lutea, the content of C in the pellets was 69,74%; N - 2,3-2,9%; P - 0,4-0,5%; Si - 1,1-1,7%, Al - 0,054-0,059%. In the presence of the cationic surfactant, tetradecyltrimethylammonium bromide (TDTMA) (2 mg/L), the feeding rate of molluscs was decreased by 27,9-70,9%. Under the effect of the cationic surfactant, TDTMA (2 mg/L), the production of pellets per g of the wet weight of molluscs was decreased by 41,7% (over the incubation period of 72 h). We also studied the content of the pellets of freshwater mussels after their feeding on the natural seston (the sample of mussels taken from the natural community). In the sample, the species and their percentages were: Unio tumidus 63,21%, U. pictorum 27,36%, Crassiana crassa 7,55% and Anodonta cygnea 1,89%. This sample of bivalves produced the pellets that had the following chemical content: C - 64,3%; N - 2,73%; P - 0,39%; Si - 1,14%; Al - 0,071%. Water filtering by the unionids was also inhibited by TDTMA and some other surfactants. Therefore it was shown that the surfactant inhibited the matter and elements transfer through this level of the trophic chain.