Environmentally-relevant hydrogen peroxide exposure induces DNA damage and elevates coelomocyte concentrations in the sea urchin Paracentrotus lividus

Hydrogen peroxide (H₂O₂) is an antiparasitic sea lice treatment in Atlantic salmon aquaculture and considered to be environmentally-friendly due to its rapid degradation. However, degradation rates have not been widely tested in seawater. The objectives of this study were to determine the degradation rates of different H₂O₂ stocks in aquarium-filtered seawater and assess its impact on adult sea urchins (Paracentrotus lividus). H₂O₂ stocks (stabilised, pure, and industry-sourced EndoSan50) combined degradation rate was 1.92 %/day, and the half-life was 26.4 days. Environmentally-relevant concentrations of H₂O₂ (50 and 500 µM) were selected for testing. Adult sea urchins were exposed to H₂O₂ for 3 and 24 h. Total coelomocyte and red cell concentrations increased by 50 ± 22 % and 122 ± 48 %, respectively, after 3 h, and by 59 ± 21 % and 88 ± 44 % after 24 h. DNA damage was analysed by the modified fast micromethod for quantification of strand breaks, oxidised purines (FPG), and oxidised pyrimidines (EndoIII). DNA damage in coelomocytes was increased to 0.05 ± 0.02 strand scission factor (SSF) in sea urchins exposed to 500 µM for 1 h. This study indicates presence of DNA damage in sea urchins from environmentally-relevant concentration of H₂O₂. Further testing of degradation rates of H₂O₂ in different sources of natural sea water is required to fully assess and model wider ecosystem exposure and ecological impacts of H₂O₂ release into coastal marine waters.