Novel antifouling agent- Zinc pyrithione: Short- and long-term effects on survival and reproduction of the marine polychaete Dinophilus gyrociliatus

The recent ban on TBT in boat antifouling paints has resulted in a large employment of the biocide zinc pyrithione (ZnPT) as substitute. Despite concerns of environmental toxicity at ultra-trace concentrations, ZnPT has received little attention, as it was assumed to photo-degrade easily. On the contrary, recent evidence has suggested that ZnPT only partially degrades, and rather, persists in the marine environment, especially where the influence of light is limited, such as in harbours.Short-term acute toxicity tests and life table response experiments (LTREs) were performed to evaluate the effects of ZnPT on the polychaete Dinophilus gyrociliatus at both individual and population level. The 96h-LC50 values for ZnPT on D. gyrociliatus were 7.8 and 11.5 nM under dark and 12h light/12h dark conditions, respectively. In LTREs, laboratory cultured cohorts of D. gyrociliatus were exposed to sublethal concentrations of ZnPT (0.5 and 1 nM) and compared to a control cohort. The survival among individuals exposed to the highest concentration decreased already during the 2nd week of life with respect to the control. The effects of the biocide on fecundity were even more evident: ZnPT caused a considerable reduction in both the exposed groups. The demographic approach here applied succeeded in identifying ZnPT effects both on the biological cycle and on the growth potential of polychaete D. gyrociliatus. The net growth rate (R0) appeared the demographic parameter most sensitive to ZnPT, as the biocide determined a sharp decline of R0 in both the 0.5 and the 1 nM groups (-41% and -63% respectively) in comparison to the control cohort. The population growth rate l (often used as an index of population fitness) and the life expectancy e0 were also significantly reduced, while ZnPT exposure did not affect the generation time T.These results highlight the potential ecological threat posed by the biocide ZnPT, even at the very low tested concentrations, which are already detectable in some European marinas.