Toxicity of Ammonia to Benthic Amphipod Grandidierella bonnieroides: Potential as Confounding Factor in Sediment Bioasssy

Toxicity of ammonia was evaluated using amphipod Grandidierella bonnieroides to describe its role as confounding factor in sediment quality assessment. Ammonia is a toxic compound that is found naturally in seawater and sediment. High ammonia content in the pore water sediment can be potentially toxic to benthic biota, so that it will interfere with the results of sediment toxicity tests. Laboratory production amphipod was used in this ammonia toxicity test. Water-only toxicity tests was conducted to produce new toxicity data of ammonia, and is expressed as LC50, LOEC and NOEC for benthic amphipod G.bonnieroides. The study resulted the 96-h median lethal concentration (LC50) of ammonia for G. bonnioerides was 65.5 mg.L^-1. While the value LOEC (low observed effect concentration) is 56 mg.L^-1 and NOEC value (no observed effect concentration) was 32 mg.L^-1 . This shows that ammonia has a relatively low toxicity to amphipod and ammonia does not act as a confounding factor in the sediment toxicity test, because the ammonia content in sediment does not pose any significant effect on amphipod survival. It can be concluded that the amphipod has a potential useful as test organism in sediment bioassay for assessing the quality of marine sediment. Moreover, the high dependence of total ammonia toxicity indicates that it is necessary to measure the total ammonia and pH of the medium when testing environmental samples.