L.E. Burridge

The lethality of anti-sea lice formulations Salmosan® (Azamethiphos) and Excis® (Cypermethrin) to stage IV and adult lobsters (Homarus americanus) during repeated short-term exposures

Stage IV and adult lobsters (Homarus americanus) were exposed repeatedly to one of two pesticide formulations currently in use as anti-sea lice treatments: Salmosan® (azamethiphos) and Excis® (cypermethrin). Stage IV lobsters were affected by these exposures only at the highest concentrations and longest exposure periods but no deaths occurred. Exposure to concentrations equivalent to 10 or 25% of that recommended for sea lice treatment for periods of 15 or 30 min resulted in significant mortalities in adult lobsters. Adult lobsters exposed to Excis® were affected over a wider range of concentrations and exposure times than those exposed to Salmonsan®. The No Observed Effect Concentration (NOEC) for azamethiphos and adult lobsters is 1.03 μg/l (as azamethiphos) when exposed repeatedly for 120 min. The NOEC for Excis® is 0.025 μg/l (as cypermethrin) when exposed repeatedly for 60 min.

Sublethal effects of azamethiphos on shelter use by juvenile lobsters (Homarus americanus).

The use of pesticides to treat sea lice infestations in aquaculture may have negative impacts on non-target organisms such as the American lobster (Homarus americanus). Juvenile lobsters spend most of their time in shelter to avoid predation. This study examined: (1) whether the organophosphate pesticide azamethiphos affected shelter use by juvenile lobsters; (2) whether leaving shelter was a form of azamethiphos avoidance; and (3) whether azamethiphos affected shelter re-entry. The experiments were performed on juvenile lobsters (6.5–8 mm carapace length) in individual aquaria with an artificial shelter placed on a sand substrate. Azamethiphos concentrations of 0, 100, 500 and 1000 μg l−1 were used. Ten-minute short-term pulsed exposures to azamethiphos mimicking field conditions resulted in no shelter exits or lobster deaths. Under continuous exposure to azamethiphos, all lobsters left their shelters and the time to shelter exit and death decreased with increasing azamethiphos concentration. Survival of lobsters placed in fresh seawater following shelter exit was 100% for the 100 μg l−1 treatment, 50% for the 500 μg l−1 treatment and 33% for the 1000 μg l−1 treatment. Time to re-enter the shelter following exposure to azamethiphos was significantly shorter than the control for lobsters exposed to 100 μg l−1 and significantly longer than the control for lobsters exposed to 1000 μg l−1. Shelter exit appears to be a form of avoidance behavior to high concentrations of azamethiphos. At concentrations used by the aquaculture industry (100 μg l−1 and short exposure times), azamethiphos would not affect lobster shelter use. However, if the concentration or exposure time increased, mortality could occur directly due to this pesticide or indirectly as a consequence of leaving shelter.

The influence of water temperature on induced liver EROD activity in Atlantic cod (Gadus morhua) exposed to crude oil and oil dispersants

Juvenile Atlantic cod were exposed to either the water-accommodated fraction (WAF) or the chemically enhanced water-accommodated fraction (CEWAF) of Mediterranean South American (MESA), a medium grade crude oil at three different temperatures. Two concentrations of each mixture were tested, 0.2% and 1.0% (v/v) at 2, 7 and 10°C. Corexit 9500 was the chemical dispersant tested. The liver enzyme ethoxyresorufin-O-deethylase (EROD) was measured during a 72-h exposure. The WAF of oil had significant (P<0.05) effect on enzyme activity compared to controls at only one sampling time: 48 h at 10°C. Exposure of CEWAF of oil resulted in significantly (P<0.05) elevated EROD activity compared to controls. The level of EROD induction was temperature related with higher induction being observed in cod exposed to CEWAF at higher temperatures. Total polycyclic aromatic hydrocarbon (PAH) concentrations in exposure water were significantly higher in chemically dispersed mixtures. While PAH concentrations were lower in the 2°C water compared to 7 or 10°C (8.7 vs 11.9 μg mL(-1)), the level of EROD induction was approximately 9 and 12 times lower at 2°C compared to 7 or 10°C, respectively, suggesting the metabolic rate of the cod plays a role in the enzyme response. These data suggest the risk of negative impacts associated with exposure to chemically dispersed oil may be affected by water temperature and that risk assessment of potential effects of WAF or CEWAF should consider the effects of water temperature on the physiology of the fish as well as the effectiveness of dispersants.

The lethality of the cypermethrin formulation Excis® to larval and post-larval stages of the American lobster (Homarus americanus)

The pesticide formulation Excis® (1% w/v cypermethrin) is currently registered for use in the State of Maine, USA to treat farmed salmon for infestations of the copepod parasites, Lepeophtheirus salmonis and Caligus elongatus (sea lice). In Canada, the product has yet to receive regulatory approval. We have determined the acute lethality of this product to the three larval stages and the first post-larval stage of American lobster (Homarus americanus), a species of significant economic importance in eastern Canada and the northeast United States. The 48-h LC50 (as cypermethrin) is: 0.18 μg/l for stage I, 0.12 μg/l for stage II, 0.06 μg/l for stage III, and 0.12 μg/l for stage IV (the first post-larval stage). The differences in sensitivity among the larval stages are not statistically significant. These data, when interpreted in conjunction with known physical oceanographic data and results of chemical dispersion studies, indicate that single anti-louse treatments are unlikely to result in lobster mortality. However, the sublethal effects of this product on lobsters and the consequences of repeated exposures have yet to be determined.

Uptake and excretion of organochlorine pesticides by Nereis virens under normoxic and hypoxic conditions

The marine polychaete worm, Nereis virens, is resistant to organochlorine pesticides. When exposed to each of five pesticides (endosulfan, chlordane, endrin, dieldrin, and DDT) in concentrations ranging from 0.03 mg/L (DDT) to 22.0 mg/L (chlordane), only endosulfan and chlordane killed Nereis. In comparison, the same compounds were much more toxic to another marine invertebrate, Crangon septemspinosa. The authors wondered if the resistance of N. virens to organochlorines was related to their response to hypoxia. N. virens is a sediment dweller often found in intertidal regions and consequently may experience periods of severe oxygen deprivation; varying degrees of hypoxia can initiate a switch to anaerobic energy metabolism. When N. virens encounter hypoxic conditions, they can also exhibit a compensatory ventilation response. In the present study, the authors measured the bioaccumulation of endosulfan, dieldrin, and DDT by N. virens under normoxic and hypoxic conditions.

Lethality of mexacarbate and of its formulation UCZF-19 to juvenile Atlantic salmon

Abstract Mexacarbate was less toxic to juvenile Atlantic salmon ( Salmo salar ) than its formulation, UCZF-19 (96-h LC50 - 19.5 and 3.4 mg/L, respectively). The increased lethality of the formulation is due to its volatile components (largely C3–C5 alkylbenzenes and naphthalene). The hazard indices of mexacarbate and UCZF-19 in forest spraying indicate low risk of direct mortality of juvenile Atlantic salmon.