Identification of a new degradation product of the antifouling agent Irgarol 1051 in natural samples

Abstract

A main degradation product of Irgarol [2-(methylthio)-4-(tert-butylamino)-6-(cyclopropylamino)-s-triazine], one of the most widely used compounds in antifouling paints, was detected at trace levels in seawater and sediment samples collected from several marinas on the Mediterranean coast. This degradation product was identified as 2-methylthio-4-tert-butylamino-s-triazine. The unequivocal identification of this compound in seawater samples was carried out by solid-phase extraction (SPE) coupled on-line with liquid chromatography–atmospheric pressure chemical ionization-mass spectrometry (LC–APCI-MS). SPE was carried out by passing 150 ml of seawater sample through a cartridge containing a polymeric phase (PLRP-s), with recoveries ranging from 92 to 108% (n=5). Using LC–MS detection in positive ion mode, useful structural information was obtained by increasing the fragmentor voltage, thus permitting the unequivocal identification of this compound in natural samples. Method detection limits were in the range of 0.002 to 0.005 μg/l. Overall, the combination of on-line SPE and LC–APCI-MS represents an important advance in environmental analysis of herbicide degradation products in seawater, since it demonstrates that trace amounts of new polar metabolites may be determined rapidly. This paper reports the LC–MS identification of the main degradation product of Irgarol in seawater and sediment samples.

Introduction

The herbicide 2-(methylthio)-4-(tert-butylamino)-6-(cyclopropylamino)-s-triazine (trade name Irgarol 1051) is used in antifouling paints as a biocide agent in substitution to the tributyltin (TBT) and copper-based agents. This compound is used in tin-free antifouling paint formulations that are mainly based on copper and zinc metal oxides. The herbicide is added in order to inhibit the primary growth of copper-resistant fouling organisms such as algal slimes and the growth of seaweeds. Few data concerning Irgarol 1051 contamination of the aquatic environment are available. For example, important coastal concentrations of Irgarol have been found in areas of high yachting activity, particularly in marinas and sport harbors [1], [2], [3], [4]. Recently, concentrations of Irgarol and diuron in the ppt level were detected in a pilot monitoring study carried out in the coastal Mediterranean area of Catalonia during 1996–1997 [5], [6].

The degradation of contaminants in water is an area of research interest and, in this sense, sunlight photoalteration processes are known to play an important role. The study of the photochemical behavior of a contaminant is a key issue in environmental studies in order to assess its degradation and the formation of toxic transformation products. Irgarol degradation studies have been reported in the literature, such as the biodegradation work of Liu et al. [7]. Photodegradation studies of this compound have been recently reported by Okamura et al. [8]. Since degradation studies are difficult to carry out under real conditions, natural sunlight photodegradation processes are usually compared with those obtained under controlled conditions, generally using xenon arc lamp [8], [9], [10], [11]. In these studies [7], [8] the formation of the 2-methylthio-4-tert-butylamino-s-triazine degradation product was observed and the environmental detection of this compound in seawater samples was reported [8]. Information on degradation products is necessary to understand the environmental fate of pesticides and to establish important degradation pathways, which will allow us to get a better knowledge of the transformation of target compounds in the environment. For these reasons, continued development of reliable and sensitive methods of analysis for metabolites are important for studies of water quality. Moreover, the toxicity of Irgarol and its degradation products should be taken into account. One study from Okamura et al. reported the phytoxicity of Irgarol and its degradation product [12].

The objectives of this work were: (i) to develop a sensitive methodology for the detection of Irgarol and its main degradation product in seawater samples; (ii) to carry out a monitoring study evaluating the presence of the degradation products of Irgarol in environmental seawater samples from the Mediterranean coast; and (iii) to analyze sediments from a sport marina to assess the fate of Irgarol and degradation products. To our knowledge this work represents the first identification of the degradation product of the antifouling agent Irgarol in natural samples by liquid chromatography–atmospheric pressure chemical ionization-mass spectrometry (LC–APCI-MS).