The effects of the chemotherapeutants hydrogen peroxide, deltamethrin and azamethiphos on non-target crustaceans

Abstract

I present new knowledge on the toxicity of three major bath treatment chemotherapeutants used in Norway. Previously, regarding the toxicity studies of hydrogen peroxide (H2O2) alone, a total of twelve non-target crustaceans have been examined across the globe, but only five species were relevant for the Norwegian marine ecosystem. The present study applied laboratory experiments to assess the toxicity of this chemotherapeutant to three non-target crustacean species that play a crucial role in the Norwegian marine ecosystem, bringing a better understanding of the risk posed by H2O2. Hydrogen peroxide has long been labeled as the most environmentally friendly bath treatment in use for the salmonid industry. It has also been considered that it poses little to no threat in terms of lethality to non-target crustaceans such as lobster, shrimps or crabs (Burridge et al., 2014; Gebauer et al., 2017). However, papers I, II and III show that the recommended H2O2 concentrations used by the salmonid industry across the globe are lethal to non-target crustaceans. Through the creation of species sensitivity distribution curves (SSD), this thesis identified the Northern krill (Meganyctiphanes norvegica) as the crustacean species that is most sensitive to H2O2 of those that have been tested so far. By including the sensitivity of six phyla other than the arthropods, this thesis takes a broader perspective on the impact of H2O2 on the marine environment. The hazardous concentration of H2O2 for 5% of the species (HC5) derived from the available toxicity data for marine species is 5.11 (1.52 – 16.15) mg/L. As SSD curves are a central tool for ecological risk assessments, showing the different sensitivities and variations between species, it is crucial that this tool continues to be used for the risk assessment of the other chemotherapeutants.

Deltamethrin and azamethiphos have a detrimental effect on European lobster larvae (Homarus gammarus) in laboratory experiments (Paper IV). One-hour exposure to deltamethrin proved to be more toxic than H2O2 and azamethiphos to both stage I and stage II H. gammarus larvae. By examining the toxicity of all three chemotherapeutants to a single species this thesis, in combination with the results from previous studies, proposes a ranking of the toxicity of deltamethrin, H2O2 and azamethiphos based on the difference between the median lethal concentrations LC50 (Papers II & IV). With the available data from other studies, the toxicity ranking for Norwegian relevant species is: deltamethrin > H2O2 > azamethiphos.

This thesis has also shown the importance of coupling sub-lethal studies with more conventional toxicity studies (Papers I & II). It was shown that behavior parameters linked with the predator avoidance and escape response of the European lobster juveniles and the copepod Calanus spp. were affected following short-term (1 h) exposures at concentrations ≤85 mg/L H2O2 (i.e. 5% of the recommended treatment). All three chemotherapeutants induced immobility at concentrations considerably lower than the reported lethal values. Furthermore, in paper IV the calculated effective median concentration EC50 values for both deltamethrin and azamethiphos were considerably lower than the reported LC50 values based on mortality.

The results from the hydrodynamic model presented in paper IV plus the lethality findings from papers I, II and III coupled with both field studies and models should be considered by regulatory authorities in Norway and can be an important tool for other salmonid producer nations when carrying out future environmental risk assessments of H2O2, deltamethrin and azamethiphos. These results should thus be used to evaluate the potential risks associated with the expansion of salmonid aquaculture into new locations. To have a better understanding of the risks of these chemotherapeutants in the Norwegian marine environment, further studies should evaluate their broader impact by assessing chronic or pulse-like exposures that are certainly closer to real life delousing scenarios where multiple pens are treated over a cumulative period of time. Likewise, data from the flushing of well-boats should also be included in new hydrodynamic models, as this bath treatment method dilutes the effluent of waste treatments and thus reduces its environmental impact (Ernst et al., 2014).

Overall, this study has shown that the recommended H2O2, deltamethrin and azamethiphos concentrations used by the salmonid industry have a detrimental effect in the survival of the non-target crustaceans Calanus spp., H. gammarus and M. norvegica.