Exploring Coconut Husk as an Organic Matter Enrichment Alternative in Sediment Toxicity Test

The use of artificial sediment in toxicity testing is required in studies assessing the impact of chemicals on benthic communities and testing chemicals for registration, as it offers increased repeatability and enhances consistency across bioassays and laboratories. While peat is conventionally incorporated into artificial sediment formulations for toxicological testing as the source of organic matter (OM), it is not a sustainable resource due to the long time it takes to form and the environmental impact of its extraction (carbon loss equivalent to 2.1 megatons of carbon dioxide emissions annually and potential release of other elements into the environment). In a preliminary effort, the usability of coconut husk as an alternative to peat in formulating artificial sediments for toxicity testing was assessed. Post-larval American lobsters (Homarus americanus) were exposed for 15 days to test sediment prepared with either peat or coconut husk as a source of OM. Three OM levels were tested: 0.5, 2.3, and 5% of sediment. Dry sediment was mixed with an antiparasitic drug, ivermectin, to achieve 4 desired concentrations (nominal 0, 40, 100, 400 ng/g DW). Immobility and mortality were assessed every day to calculate EC50s and LC50s, as well as incipient EC50 and LC50. The test was replicated twice over two years. Although the test is preliminary and warrants further investigation, the control performances (within validity criteria in all cases) and the EC-LC50 results indicate that the presence of coconut husk does not introduce toxicity effects of the tested chemical, suggesting its suitability as a viable alternative for toxicity testing.