Chronic toxicity of tributyltin to development and reproduction of the European freshwater snail Lymnaea stagnalis (L.)

Abstract Chronic toxicity, growth and reproduction were measured in the freshwater gastropod Lymnaea stagnalis exposed to waterborne bis(tri- n -butyltin) oxide (TBTO) over a range of four nominal concentrations (0–10 μg TBT l −1 ). Egg development was completely inhibited at 10 μg TBT l −1 , whilst abnormal embryonic development was observed at 1 μg TBT l −1 . For the solvent control and the 0.01 μg TBT l −1 treatment group, normal development of L. stagnalis was observed. Survivorship of hatchlings was significantly reduced by TBT at 1 μg l −1 while inhibition of shell growth of L. stagnalis was also observed at this concentration. The data were used to determine intrinsic growth rates ( r ) using two theoretical approaches (the Euler–Lotka equation and a Leslie Matrix). Both approaches showed that survival, fecundity and population growth rate were reduced at 1 μg TBT l −1 . Interestingly, at 0.01 μg TBT l −1 snails showed a higher fecundity and growth rate than in the solvent control. The TBT concentration at which the r would equal zero (EC r 0 ) and the population NOEC (No Observed Effect Concentration) were estimated. The population NOEC was defined as either the lower 95% confidence or lower 95% pointwise percentile limit of the EC r 0 . Values obtained using the two different approaches were similar and thus a geometric mean was calculated to obtain a final representative population NOEC value for L. stagnalis of 2745 ng TBT l −1 . The present data together with chronic toxicity TBT data for freshwater organisms, obtained from peer-reviewed literature, were used to construct a species sensitivity distribution (SSD). A predicted no effect concentration was then derived from the SSD (hazardous concentration at 5%, i.e., HC5 or 95% protection level). This SSD was compared with the SSD derived from saltwater species datasets. The HC5 value for saltwater species (3.55 ng TBT l −1 ; lower confidence limit: 1.93 ng TBT l −1 ) was significantly lower than that for freshwater species (30.13 ng TBT l −1 ; lower confidence limit: 9.23 ng TBT l −1 ), indicating that saltwater species are probably more susceptible to TBT than their freshwater counterparts.