Summary
Persistent organic pollutants (POPs) are well known to accumulate in polar food webs; yet there is little ecotoxicological data available for environmental risk assessment of POPs in these extreme ecosystems. The premise of the tissue residue approach (TRA) is that xenobiotics cause toxic effects at similar tissue residues across species and geographical ranges, regardless of differences in external factors such as ambient temperature. Empirical data are however, fundamental for validation of the TRA for polar species. p,p'-DDE has been identified as a priority POP accumulating in Antarctic krill, which play a central role in the Southern Ocean ecosystem. This study evaluated the toxicological sensitivity of Antarctic krill to p,p'-DDE exposure on a body residue/effect basis. Baseline toxicity ('narcosis'), which is a commonly applied endpoint in the TRA, was used as indicator of sublethal toxicity. Several different exposure scenarios were tested: i) 96 h aqueous exposure of adult krill, ii) 1, 3 and 9 d aqueous exposure of larval krill and iii) 10 d dietary exposure of adult krill. For all exposure scenarios, krill immobility was induced at the low end of the body residue range (4 - 16 mmol/kg lipid weight (l.w.)) known to cause sublethal narcosis in temperate species (e.g. small fish, crustaceans). Internal effect concentrations (IECs) were relatively constant across tests (3.3 - 6.2 mmol/kg l.w.), although the degree of narcosis varied between tests. Adult krill reached partial immobility during 96 h aqueous exposure (IEC50partial immobility = 3.9 mmol/kg l.w.), whereas complete immobility and mortality were observed in the 10 d dietary exposure tests at similar internal concentrations (IEC50complete immobility = 3.3 mmol/kg l.w.). Complete immobilisation was observed in 20 % of larval krill after only 24 h exposure (IEC20complete immobility = 3.6 mmol/kg l.w.). The apparent variability in toxicological sensitivity between different life stages may be partly explained by differences in p,p'-DDE uptake rates. The observed differences in the narcotic response of adult krill between 4 and 10 d exposure indicate however, the possibility of delayed effects of p,p'-DDE exposure in Antarctic krill. Overall, the findings for Antarctic krill are in support of the TRA indicating that effective body residues for baseline toxicity in this polar species are comparable to those measured for temperate species.