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Hydrogen peroxide (H 2 O 2) is used as anti-parasitic veterinary medicine in salmon farms worldwide. In the period from 2009 to 2018 a total of 135 million kg of H 2 O 2 was used in Norway, the world's largest producer of Atlantic salmon. Since the treatment water is discharged to the sea, concerns have been raised about effects of H 2 O 2 on the coastal ecosystem. In the present study, Northern shrimp (Pandalus borealis) have been exposed to short pulses of H 2 O 2 in the PARAMOVE® formulation, followed by a recovery period in clean seawater. The exposure concentrations represented 100, 1000 and 10 000 times dilutions of the prescribed treatment concentration for salmon; 15 mg/L, 1.5 mg/L and 0.15 mg/L H 2 O 2. Significantly increased mortality was observed after 2 h exposure to 15 mg/L H 2 O 2 (50%) and after 2 h exposure to 1.5 mg/L H 2 O 2 on 3 consecutive days (33%), but no mortality was observed after 2 h exposure to 0.15 mg/L. The mortality occurred 2–4 days after the first pulse of exposure. The patterns of acute effects (immobility and death) could be captured with a toxicokinetic-toxicodynamic model (GUTS), which allows extrapolations to LC50s for constant exposure, or thresholds for effects given untested exposure profiles. Effects of H 2 O 2 were also detected in shrimp that survived until the end of the recovery period. The feeding rate was 66% lower than in the control after 12 days of recovery for the three-pulse 1.5 mg/L exposure. Furthermore, dose dependent tissue damage was detected in the gills and evidence of lipid peroxidation in the hepatopancreas in shrimp exposed for 1 h to 1.5 mg/L and 15 mg/L and kept in recovery for 8 days. Fluorescence intensity in the hepatopancreas of treated shrimp increased 47% and 157% at 1.5 mg/L and 15 mg/L, respectively, compared to the control. Local hydrodynamic conditions will determine how fast the concentration of H 2 O 2 will be diluted and how far it will be transported horizontally and vertically. Results from dispersion modelling (literature data) together with the current experiments indicate that treatment water with toxic concentrations of H 2 O 2 (1.5 mg/L) could reach P. borealis living more than 1 km from a treated salmon farm. Image 1 • The anti-parasitic hydrogen peroxide product PARAMOVE® negatively affected shrimp. • Negative effects at 1000 times diluted salmon treatment concentration of PARAMOVE®. • Gill damage after 1 h exposure to 1.5 mg/L hydrogen peroxide. • Mortality after 2 h exposure to 1.5 mg/L hydrogen peroxide for 3 consecutive days. • A toxicokinetic-toxicodynamic model was used to explain the dynamic mortality pattern. [ABSTRACT FROM AUTHOR]

Knowledge of key species sensitivity for oil spill response (OSR) options is needed to support decision-making and mitigate impact on sensitive life stages of keystone species. Here, Northern shrimp (Pandalus borealis) larvae were exposed for 24 h to a gradient (H-High, M-Medium: 10 times dilution and L-Low: 100 times dilution) of mechanically- (MDO) (H < 6 mg/L total hydrocarbon content) and chemically- (CDO) dispersed oil (Slickgone NS, H < 20 mg/L total hydrocarbon content), followed by a recovery period. Larval mortality, feeding rate and development were evaluated. Overall, the results show that 24 h exposure to field-realistic concentrations of CDO lead to lower survival, reduced feeding rate and slower larval development in P. borealis larvae compared to MDO. These effects persisted during recovery, indicating a higher vulnerability with dispersant use and the need for longer observation periods post-exposure to fully evaluate the consequences for sensitive life-stages from OSR. • 24 h oil exposure with dispersant (CDO) is more detrimental to northern shrimp larvae than oil only (MDO). • Mortality in high CDO at exposure, and in all concentrations of CDO during recovery • Reduced feeding and delayed development predominant in CDO • Inclusion of recovery warranted in environmental risk analysis from oil spill clean-up • Study relevant for prioritization of oil spill response decisions [ABSTRACT FROM AUTHOR]

The application of chemical dispersants is one option of oil spill response (OSR). Here, Northern shrimp (Pandalus borealis) larvae were experimentally exposed for short periods (6 h and 1 h) to a realistic concentration of chemically dispersed oil (CDO) (~10 mg L−1 THC), mechanically dispersed oil (MDO) (~7 mg L−1 THC), and dispersant only (D). A control (C) with seawater served as reference. Short-term effects on survival and feeding were examined right after exposure and longer-term consequences on survival, feeding, growth and development following 30 days of recovery. Both exposure durations provoked long lasting effects on larval fitness, with 1 h exposure leading to minor effects on most of the selected endpoints. The 6 h exposure affected all endpoints with more adverse impacts after exposure to CDO. This study provides important data for assessing the best OSR option relevant to NEBA (Net Environmental Benefit Analysis). • Short- and long-term effects of oil spill response on shrimp larvae • Field-realistic concentrations of oil and chemical dispersant • Long lasting effects of short exposure (6 h and 1 h) on larvae fitness parameters • Addition of chemical dispersant increases short- and long-term adverse effects of oil. • Contribution to NEBA decision-frameworks for reaction and mitigation [ABSTRACT FROM AUTHOR]