Degradation of Alternative Biocides in the Aquatic Environment

The ideal antifouling biocide, from a marine conservation perspective, should be degraded to compounds of lower toxicity in the environment to avoid impact on non-targed organisms. On the other hand, an effective biocide needs to have high toxicity to prevent fouling. These two suppositions are, to an extent, mutually exclusive. Nevertheless, some antifouling biocides released to the marine environment undergo hydrolysis, whilst others are degraded by sunlight in the photic zone.

Furthermore, a number of antifouling biocides are degraded by the many species of bacteria which inhabit water and sediment. Stable antifouling biocides are transported widely and can accumulate in sediment or are concentrated in aquatic organisms. Thus, in order to reduce the threat of magnification of residues, an ideal biocide should be degraded easily and rapidly to substances of lower toxicity, following their released into the aquatic environment. Information about their possible degradation mechanisms in the environment, whether by hydrolysis, sunlight or bacteria, is an important requirement in order to estimate the persistence of these compounds and to identify the factors that influence their behaviour. In this chapter, the degradation pathways and rated of representative alternative biocides in aquatic environment are reviewed.