The effects of emamectin benzoate or ivermectin spiked sediment on juvenile American lobsters (Homarus americanus)

This study examined the effects of a range of ½-log concentrations of emamectin benzoate (commercially applied as SLICE^®) and ivermectin (commercially applied as IVOMEC^®) on juvenile American lobster, Homarus americanus. Phase I of the research assessed acute (up to 4 days) and chronic (30-day) toxicity of sediment dosed with the active ingredients emamectin benzoate (EMB) formulated as SLICE^® or ivermectin (IVM) formulated as IVOMEC^® at various nominal concentrations (EMB: 15, 48, 150, 475 and 1500 ng g^-1 wet sediment; IVM: 3, 9.5, 30, 95 and 300 ng g^-1 wet sediment) on juvenile Atlantic lobster (stages IV). Phase II evaluated sublethal effects (e.g., growth, moulting success) of all lobster surviving past the 30 day exposure period, over an additional 41 days. Chemical analysis of EMB and IVM in sediment samples from the exposure tanks revealed a strong linear association (R² values 0.99 and 0.98 for EMB and IVM, respectively) between nominal dose and measured concentration of compound. EMB exposure concentrations at very high levels (≥ 343.3 ng g^-1) were acutely toxic to juvenile lobster such that 100% of lobsters had died after 13 days of exposure. The maximum cumulative mortality of lobsters exposed to the highest concentrations of EMB and IVM was 100% after 10 days and 25 days, respectively. The 10-day LC₅₀ estimates (± 95% CI) for EMB and IVM were 250.23 ± 90.4 and 212.14 ± 202.64 ng g^-1, respectively. Using abnormal behaviour as an indicator, the 15-day EC₅₀ estimates (± 95% CI) for EMB and IVM were 96.19 ± 51.42 and 15.82 ± 6.93 ng g^-1, respectively. The NOEC (no observed effect concentration) for abnormal behaviour was 0.0 ng g^-1 for each product and the LOEC (lowest observed effect concentration) was 8.8 and > 3.0 ng g^-1 for EMB and IVM, respectively. Observations on sublethal effects included delayed moulting to stage VI and reduced growth at higher exposure concentrations for both therapeutants. Using failure to moult to stage V or VI as an indicator, the 15-day EC₅₀ estimates (± 95% CI) for EMB and IVM were 32.72 ± 18.26 and 14.00 ± 12.43 ng g^-1, respectively. The NOEC for failure to moult to stage V only was 343.3 and 14.7 ng g^-1 for EMB and IVM, respectively. Whereas, the LOEC was 1066.7 and > 61.0 ng g^-1 for EMB and IVM, respectively. The concentrations of EMB and IVM tested in the present study were acutely toxic to juvenile lobster exposed to the highest dosages (343.3 and 1066.7 ng EMB g^-1 and 61.0 and 300.0 ng IVM g^-1). There was significant evidence of chronic toxicity, longer exposure increased mortality with LT₅₀ values decreasing with increasing test material concentration.