Abiotic fate of tolylfluanid and dichlofluanid in natural waters

Abstract To prevent the growth of unwanted organisms on ship hulls, tolylfluanid (N-[dichlor(fluor)methyl]sulfanyl-N-(dimethylsulfamoyl)-4-methylaniline) and dichlofluanid (N-(dichlorfluormethylthio)-N′,N′-dimethyl-N-phenylsulfamid) are applied as antifouling biocides in paints. There are concerns over their occurrence and fate in the marine environment due to long-term immersion in water. In the present study, the hydrolysis and photolysis of these compounds were investigated. Results showed that tolylfluanid and dichlofluanid hydrolyzed completely to their respective hydrolysis products DMST (N,N-dimethyl-N′-p-tolylsulfamide) and DMSA (N,N-dimethyl-N′-phenylsulfamide) in coastal water within 24 h. Furthermore, the transformation of tolylfluanid and dichlofluanid under natural sunlight was determined in selected marine waters (coastal water and sea water) in comparison to deionized water. The experiments revealed that photodegradation rates of DMST and DMSA in coastal water were higher than in sea water or deionized water. The indirect phototransformation of the hydrolysis products with selected reactive species (triplet state organic matter, singlet oxygen, and hydroxyl radicals) concluded that DMST and DMSA mainly display triplet reactivity. The measured half-lives of the hydrolysis products in natural waters varied between 2.7 and 23 days with DMST being considerably faster transformed than DMSA. However, several direct and indirect photoproducts have been newly identified and measured. DMS (N,N-dimethylsulfamide), was identified as the major phototransformation product in natural waters. It is generated through indirect photodegradation processes and exhibits potential persistence in environments.