Toxicity of Metal Pyrithione Photodegradation Products to Marine Organisms with Indirect Evidence for Their Presence in Seawater

We evaluated the acute toxicities of the metal pyrithiones (MePTs)—copper pyrithione (CuPT) and zinc pyrithione (ZnPT)—to four species of marine algae and a marine crustacean (Tigriopusjaponicus). We also performed acute toxicity tests using six of the main MePT photodegradation products: pyridine-N-oxide (PO); 2-mercaptopyridine (HPS); pyridine-2-sulfonic-acid (PSA); 2-mercaptopyridine-N-oxide (HPT); 2,2′-dithio-bis-pyridine ([PS]2); and 2,2′-dithio-bis-pyridine-N-oxide ([PT]2)—and three marine organisms representing three trophic levels: an alga (Skeletonemacostatum), a crustacean (T. japonicus), and a fish (Pagrusmajor). The acute toxicity values (72-h EC50) of CuPT, ZnPT, HPT, (PT)2, (PS)2, HPS, PO, and PSA for S. costatum, which was the most sensitive of the test organisms to the chemicals tested, were 1.5, 1.6, 1.1, 3.4, 65, 730, >100,000, and >100,000 μg l−1, respectively. CuPT was detected in the growth media used for S. costatum tests and in seawater containing HPT or (PT)2; the concentration of CuPT in seawater containing HPT was highly dependent on the Cu2+ concentration. These results indicate that in the presence of sufficient Cu2+, the toxicities of HPT and (PT)2 should be assessed as CuPT because in Japan MePTs are most frequently used as antifouling booster biocides in conjunction with cuprous oxide.