Lethal and sublethal toxicity of the sea lice chemotherapeutants Salmosan®, Paramove® 50, ivermectin, and Slice® to Pacific marine benthic species

The Atlantic salmon aquaculture industry uses anti-sea lice chemotherapeutant treatments to control sea lice, a damaging endemic ectoparasite. These treatments are then released into the receiving environment exposing non-target marine invertebrates. The lethal and sublethal toxic effects of Slice® (active ingredient [a.i.]: emamectin benzoate [EB]), ivermectin (IVM), Salmosan® (a.i.: azamethiphos), Paramove® 50 (a.i.: hydrogen peroxide [H2O2]) and combinations of these were determined for the Pacific marine invertebrates Alitta virens (polychaete), Eohaustorius estuarius (amphipod), and Pandalus platyceros (spot prawn). A combination of IVM and Slice® resulted in the highest 30-d sediment lethal toxicity (LC50 values ranged from 4.1 sum µg a.i./kg for E. estuarius to 890 sum µg a.i./kg for P. platyceros) and Slice® exhibiting the lowest lethality in all test species; the sensitivity of the organisms was E. estuarius > A. virens > P. platyceros. Acute pulse exposures of amphipods and polychaetes to Salmosan® did not result in mortality high enough to determine LC50 values; in addition, Paramove® 50 was not acutely toxic to amphipods. 20-d LC50 values for Paramove® 50 after 0.5-h and 1-h pulse exposures for polychaetes were 1,566 and 338 mg a.i./L, respectively. The time to reburrow in polychaetes was affected by 30-d sediment exposures at threshold values of 8 µg/kg IVM, 200 µg/kg EB, and 3/2 µg/kg IVM/EB. Reburrowing was also affected by 0.5-h and 1-h Paramove® 50 pulse exposures at concentrations of 18 and 900 mg a.i./L, respectively. 30-d exposures to IVM, Slice®, and a combination in sediment resulted in emergence responses in polychaetes at threshold concentrations of 12, 200, and 3/2 µg a.i./kg respectively, and in response to 0.5-h and 1-h pulse exposures to Paramove® 50 at 1,800 and 900 mg a.i./L respectively. These results support regulatory decision-making regarding the use of anti-sea lice chemotherapeutants.