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3B - Marine toxicity evaluation: current practice and applications (MOP/162) Long-term effects of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOI), the active ingredient of Sea-Nine 211, on phytoplankton in submerged pelagic enclosures. Grönvall, Frederick1, Blanck, Hans1, Arrhenius, Åsa1, Eriksson, Martin1, Gustavson, Kim2, Dahllöf, Ingela3, Pedersen, Sanne3, Henriksen, Peter3, Martinez, Karell4, 1 Botanical Institute, Göteborg University, Göteborg, N/A, Sweden2 Danish Hydrological Institute, Hörsholm, N/A, Denmark3 National Environmental Research Institute, Roskilde, N/A, Denmark4 CID-CSIC, Barcelona, N/A, Spain ABSTRACT- Sea-Nine 211, with the active ingredient 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOI), is claimed to be an environmentally friendlier antifouling agent since it is rapidly degraded, losing its toxicity when released to the aquatic environment although the information on community effects is scarce. Submerged pelagic enclosures were used to assess the effects of DCOI on marine plankton with focus on the phytoplankton community in this study carried out in August 2000 on the Swedish west-coast. Results show that effects could still be detected after seven days at an initial nominal concentration as low as 0.032 nM. The enclosure system consisted of plastic containers suspended at a depth of appr. four meters, filled with natural seawater and its indigenous phytoplankton community. Sea-Nine was added once, at the beginning of the study giving nominal concentrations in the enclosures between 0.032 and 32 nM. Species composition, pigment composition and photosynthetic activity were measured at Day one and Day seven after addition of Sea-Nine to the enclosures. At Day seven short-term toxicity tests were also performed in search of Pollution-Induced Community Tolerance (PICT). Phytoplankton photosynthesis showed a strong increase in tolerance to Sea-Nine at concentrations above 0.76 nM. However, signs of earlier tolerance induction was evident. According to the PICT concept this increased community tolerance reflects alterations in the community structure which was confirmed by the species composition analysis. Photosynthetic activity measurements made with in vivo PAM fluorometry on phytoplankton community samples from the enclosures showed a distinct lowering of the effect level for both variable photosystem II fluorescense and photosystem II quantum yield. The NEC for quantum yield is lowered by a hundredfold from Day one to Day seven, variable photosystem II fluorescense NEC showed a similarly lowered effect concentration. Photosynthetic yield was found to be the most sensitive parameter , showing effects already at a nominal concentration of 0.032 nM . The observed effect threshold for the phytoplankton community of 0.032 nM is in contrast with the previously reported toxicity data based mainly on single species tests. We conclude Sea-Nine toxicity has been severely underestimated. Key words: DCOI, SeaNine 211, Mesocosm |
