Environmental fate of the antifouling compound zinc pyrithione in seawater

To perform a thorough risk assessment of the new antifouling compound zinc pyrithione (ZnPT 2 ), additional information regarding the fate of the compound is needed. The present study examined the recovery and transchelation of ZnPT 2 in controlled laboratory experiments, photodegradation experiments, and a fate study in a large‐scale field experiment. Chemical analyses were performed using a newly developed method for simultaneous analyses of ZnPT 2 and copper pyrithione (CuPT 2 ). Furthermore, two antifouling paints containing ZnPT 2 were examined for the fate of leaching biocide. Naturally occurring ligands and metals in seawater influence the stability of ZnPT 2 . The presence of free Cu 2+ , which is present naturally in the seawater or is released from copper‐containing paints, results in a partial transchelation of ZnPT 2 into CuPT 2 . A complete transchelation of ZnPT 2 into CuPT 2 was observed when Cu 2+ was present at an equimolar concentration in the absence of interfering ligands. When ZnPT 2 was leached from antifouling paints containing both ZnPT 2 and Cu 2 O, CuPT 2 was found, with no trace of ZnPT 2 . Photodegradation was low in natural waters and absent from 1 m or more below the surface. The results show that ZnPT 2 has a low persistence in seawater when leached from antifouling paints. However, the more stable and toxic transchelation product CuPT 2 is formed, which has the potential to accumulate in the sediments and, therefore, should be included in both chemical analysis and risk assessment of ZPT 2 .