Research into the environmental distribution and effects of biocides added to marine paints has, to date, been focused on the antifouling agent tributyltin (TBT). It has been estimated that in Arcachon Bay (France) alone, the use of TBT provoked a loss in revenue of 147 million U.S. dollars through reduced oyster production ( I ) . Its use has subsequently been severely restricted internationally ( I , 2) , and TBT has largely been replaced by copper-based substitutes. In addition to these biocides (which are added primarily to control aquatic animals), herbicides are also frequently added to inhibit primary colonization of hull surfaces by micro-algae and subsequent growth of seaweeds. Environmental contamination by these compounds has not, to date, been reported. 2-Methylthio-4-tert-butylamino-6-cyclopropylamino-s-triazine (trade name: IRGAROL 1051) is an effective herbicidal additive, and analytical methods were developed within our laboratory to afford quantification of this compound in environmental waters in order to investigate coastal contamination.