Analytical methods for antifouling booster biocides determination in environmental matrices: A review

Highlights

• Several methods for ABBs analysis in environmental matrices are described.

• There is no standardization of analytical methods for ABBs determination.

• The analytical methods used for biota determination are those employed in sediment analysis.

• An information update is needed to further standardize methods for ABB metabolites.

Abstract

Since the discovery of their toxicity to aquatic environments, antifouling booster biocides (ABBs) have been widely researched and detected at trace levels in diverse environmental compartments including water, sediment, and, less frequently, biota. Hence, the reliable assessment of environmental risks posed by ABBs requires the development of analytical methods sufficiently robust, accurate, and precise for the simultaneous trace-level determination of ABBs. Herein, we summarize outstanding sample preparation procedures for the analysis of main ABBs in environmental matrices, describing techniques ranging from traditional extraction methods to novel miniaturized and micro-extraction ones, which have recently received much attention due to their reduced number of steps, low operational cost, and greater respect for the environment. The main applied chromatographic-based methods coupled to different detection techniques are also addressed. Despite the recent development of numerous ABBs determination methods, this topic continues to draw attention because of the lack of standardization among methods, despite legislation set up maximum standards levels for selected ABBs, and the need to monitor ABB transformation products for a reliable ecological risk assessment.

Introduction

Biofouling involves the attachment of organisms on (semi-)submerged surfaces such as boat/ship hulls, pipes, and underwater equipment, resulting in losses due to corrosion, ship performance deterioration, and the impairment of structures and systems [1]. Hence, the development of antifouling materials and coatings to remove or prevent biofouling is a task of high practical importance [2]. Antifouling coatings have a long-standing history and, according to some sources, have already been used by the Phoenicians and Carthaginians to protect their ships during expeditions [3]. However, antifouling coatings impact the environment because of their diffuse sources, ubiquitous distribution, and toxicity to non-target organisms across coastal areas [4,5].

Biocide-containing paints have been widely used to combat biofouling. The first regularly used antifouling paints (first-generation paints) contained copper oxide and zinc oxide as biocides. However, they quickly lost popularity because of their low durability and consequent rapid decrease in effectiveness. At the beginning of the 1960s, the naval industry developed and started using organotin compound (OT)-based antifouling paints (second-generation paints), e.g., those containing tributyltin (TBT) or triphenyltin (TPhT) as biocides. These paints were widely used in the 1980s, accounting for 90 % of ship hulls in operation around the world. However, as a setback to their efficiency and durability, such paints were found to be highly toxic to the marine environment [1]. One of the best-known biological effects of these paints is the so-called imposex, which is the imposition of male sexual characteristics onto female marine gastropods exposed to TBT/TPhT. The above phenomenon has been adopted worldwide as the best biomarker for assessing areas contaminated by this type of biocides [5,6]. In the 1980s, the use of TBT and TPhT has been banned on boats less than 25 m long given the toxic effects of these biocides on non-target species [4]. Moreover, in September 2008, the International Maritime Organization banned the use of TBT-based antifouling paints on vessels less than 25 m long through the Antifouling System Convention, which is currently ratified by 81 states [7].

In response to the increasingly strict regulations on the use of OT-based paints, third-generation antifouling paints were introduced in 1987. These paints typically comprise inorganic biocides such as cuprous oxide in combination with up to four organic or organometallic biocides [5], being denoted as antifouling booster biocides (ABBs), novel antifouling biocides, booster biocides, or co-biocides. In the following, we will use the acronym ABB. At least 20 organic chemicals have been used as ABBs, namely diuron, irgarol 1051 (or simply irgarol), 4,5-dichloro-2-n-octyl-3-(2 H)-isothiazolin-3-one (DCOIT), 2-(thiocyanomethylthio)benzothiazole (TCMTB), chlorothalonil, dichlofluanid, tiram, TCMS pyridine, triphenylbornan pyridine, zinc pyrithione (ZnPT), copper pyrithione (CuPT), ziram, maneb, cuprous oxide, copper thiocyanate, and copper naphthenate [5] with some of them more widely used and more frequently reported than others. Table 1 summarizes the main physicochemical properties of the above biocides, which are considered in this review. This information helps to predict the worldwide occurrence and potential environmental behavior of these biocides, e.g., the short half-life of TCMTB and dichlofluanid in seawater indicates that the related transformation products are more readily generated than those of DCOIT and irgarol [8].

ABBs have been studied in many countries, including Spain [[9], [10], [11], [12], [13], [14]], Brazil [[15], [16], [17], [18]], Japan [[19], [20], [21]], China [22], Thailand [23], France [24], Korea [25,26], Greece [27,28], Sweden [29], United Kingdom (UK) [30], Vietnam [31], Southern England [32], Italy [33,34], Panama [35], the United States of America (U.S.A) [36], the Netherlands [37], and Iran [38], largely occurring in marinas with a large flow of vessels and poor maintenance system disposal. Therefore, the presence of these biocides in the marine ecosystem is increasing in terms of both frequency and concentration levels, as confirmed by analyses of sediments [11,14,31,[39], [40], [41]], water (including dissolved and particulate fractions) [9,13,20,35,[42], [43], [44]] and, less commonly, biota samples [20,[45], [46], [47], [48]] which poses an environmental concern. Moreover, antifouling paint particles generated during the maintenance of vessels in shipyards, marinas, and fishing villages [16], can enter the aquatic environment and act as a source of metals (i.e., Cu and Zn) and antifouling biocides [[49], [50], [51], [52]]. Furthermore, recent studies indicate that the presence of these particles constitutes a potential source of long-term ABBs [18].

Among the numerous ABBs used in antifouling paints, the ones most commonly employed, besides zinc/copper pyrithiones, zineb, and copper thiocyanate, are diuron, irgarol, chlorothalonil, dichlofluanid, DCOIT, and TCMTB. This review addresses the main sample preparation techniques and chromatographic-based analysis applied for the determination of the above contaminants in environmental matrices.

The occurrence of ABBs in environmental compartments (specifically, diuron and irgarol in water samples) has been studied starting from the 1990s [53,54]. Since then, different analytical techniques and methodologies have been developed, mostly involving steps such as pre-concentration, extraction, clean-up, and chromatographic separation and determination. In addition, previous works have dealt with historical contexts [1,5,55], toxicity effects [[56], [57], [58], [59]], worldwide occurrence and geographical distribution [[60], [61], [62]], environmental fate and behavior [63,64], and degradation [19]. However, only two studies addressed sample preparation and analysis: one of them evaluated different mass spectrometry (MS) techniques for ABBs detection in marine samples [65], whereas the other reviewed the main procedures of sample preparation [66]. Thus, the present work aims to overview the updated information on sample preparation procedures and instrumental analysis for the determination of the main biocides detected in the aquatic environment, providing a brief fundamental of the employed analytical techniques and describing the advances in traditionally used and miniaturized methods in sample treatment.