Toxicity of ammonia to surf clam () larvae in saltwater and sediment elutriates

International audience; Ammonia is a natural component of sediments and has been identified as a common contributor to toxicity in marine sediment, elutriate and porewater testing. In our study, the role of ammonia as a possible toxicant in sediment toxicity tests was evaluated using larvae of the surf clam, . Elutriates were prepared and tested using six baseline sediment samples. Ammonia was then purged from aliquots of the baseline sediment samples prior to elutriate preparation. Finally, ammonia was spiked into aliquots of the purged elutriates to mimic ammonia concentrations measured in the baseline elutriates. Toxicity was present in all of the baseline samples and was removed in the ammonia purged samples. In most cases, toxicity was comparable in the ammonia spiked samples to levels measured in the baseline samples. Water only toxicity tests revealed that larvae of the surf clam are one of the more ammonia sensitive marine species. The LC50 for survival was 10.6 mg/L total ammonia (0.53 mg/L unionized ammonia) and the EC50 for shell development was 2.35 mg/L total ammonia (0.12 mg/L unionized ammonia). Toxicity endpoints calculated from the water only ammonia toxicity test were good predictors of effects observed in the sediment elutriate tests.