A Method for Evaluating the Efficacy of Antifouling Paints Using Mytilus galloprovincialis in the Laboratory in a Flow-Through System

Biocide vs. Eco-Friendly Antifoulants: Role of the Antioxidative Defence and Settlement in Mytilus galloprovincialis

Antifoulant paints were developed to prevent and reduce biofouling on surfaces immersed in seawater. The widespread use of these substances over the years has led to a significant increase of their presence in the marine environment. These compounds were identified as environmental and human threats. As a result of an international ban, research in the last decade has focused on developing a new generation of benign antifoulant paints. This review outlines the detrimental effects associated with biocide versus eco-friendly antifoulants, highlighting what are effective antifoulants and why there is a need to monitor them. We examine the effects of biocide and eco-friendly antifoulants on the antioxidative defence mechanism and settlement in a higher sessile organism, specifically the Mediterranean mussel, Mytilus galloprovincialis. These antifoulants can indirectly assess the potential of these two parameters in order to outline implementation of sustainable antifoulants.

Passive-Sampler-Based Bioavailability Assessment of PCB Congeners Associated with Aroclor-Containing Paint Chips in the Presence of Sediment

This is the first investigation of the bioavailability of PCBs associated with paint chips (PC) dispersed in sediment. Bioavailability of PCB-containing PC in sediment was measured using ex situ polyethylene passive samplers (PS) and compared to that of PCBs from field-collected sediments. PC were mixed in freshwater sediment from a relatively uncontaminated site with no known PCB contamination sources and from a contaminated site with non-paint PCB sources. PC < 0.045 mm generated concentrations in the PS over one order of magnitude higher than coarser chips. The bioavailable fraction was represented by the polymer-sediment accumulation factor (PSAF), defined as the ratio of the PCB concentrations in the PS and organic carbon normalized sediment. The PSAF was similar for both field sediments. The PSAFs for the field sediments were ~ 50-60 and ~ 5 times higher than for the relatively uncontaminated sediment amended with PC for the size fractions 0.25-0.3 mm and < 0.045 mm, respectively. These results indicate much lower bioavailability for PCBs associated with PC compared to PCBs associated with field-collected sediment. Such information is essential for risk assessment and remediation decision-making for sites where contamination from non-paint PCBs sources is co-located with PCB PC.

Leaching Rate of Polychlorinated Biphenyls (PCBs) from Marine Paint Chips

Polychlorinated biphenyls (PCBs) were added to certain marine vessel bottom paints as a plasticizer to improve the adhesion and durability of the paint. The most common PCB formulation used to amend such paints was Aroclor 1254. Fugitive Aroclor-containing paint chips generated from vessel maintenance and repair operations represent a potential source of PCB contamination to sediments. Limited published studies indicate that Aroclor-containing paint is largely inert and exhibits low PCB leaching into water; however, the rate and degree of leaching of PCBs from paint chips have not been directly studied. This laboratory-based study evaluated the rate and extent of leaching of PCBs from paint chips into freshwater. The results of this investigation demonstrate that the rate of PCB dissolution from paint chips decreased rapidly and exponentially over time. Based on this study, it is estimated that the rate of leaching of PCBs from paint chips would cease after approximately 3 years of exposure to water. When all leachable PCBs were exhausted, it is estimated that less than 1% of the mass of PCBs in the paint chips was amenable to dissolution. The results of this experiment suggest that Aroclor-containing paint chips found in sediments are likely short-term sources of dissolved-phase PCB to pore or surface waters and that the majority of the PCBs in paint chips remain in the paint matrix and unavailable for partitioning into water.

Effectiveness and Mechanisms of Recoverable Magnetic Nanoparticles on Mitigating Golden Mussel Biofouling

Mussel biofouling has become a problem in aquatic ecosystems, causing significant ecological impact and huge economic loss globally. Although several strategies have been proposed and tested, efficient and environment-friendly antifouling methods are still scarce. Here, we investigated the effects of recoverable magnetic ferroferric oxide nanoparticles (Fe₃O₄-NPs) with different sizes (10 and 100 nm), coatings (polyethylene glycol and polylysine), and concentrations (0.01 and 0.1 mg/L) on byssus adhesion-mediated biofouling by the notorious golden mussel Limnoperna fortunei. The results showed that magnetic Fe₃O₄-NPs, especially negatively charged polyethylene glycol-coated Fe₃O₄-NPs, size- and concentration-dependently reduced the byssus production, performance (breaking force and failure location), and adhesion rate. Further investigations on mechanisms showed that the down-regulation of foot protein 2 (Lffp-2) and energy-related metabolic pathways inhibited byssus production. The declined gene expression level and metal-binding ability of Lffp-2 significantly affected foot protein interactions, further reducing the plaque size and byssus performance. In addition, the change in the water redox state likely reduced byssus performance by preventing the interface interactions between the substrate and foot proteins. Our results confirm the effectiveness and underlying mechanisms of magnetic Fe₃O₄-NPs on mitigating L. fortunei biofouling, thus providing a reference for developing efficient and environment-friendly antifouling strategies against fouling mussels.

Flavonoid Glycosides with a Triazole Moiety for Marine Antifouling Applications: Synthesis and Biological Activity Evaluation

Over the last decades, antifouling coatings containing biocidal compounds as active ingredients were used to prevent biofouling, and eco-friendly alternatives are needed. Previous research from our group showed that polymethoxylated chalcones and glycosylated flavones obtained by synthesis displayed antifouling activity with low toxicity. In this work, ten new polymethoxylated flavones and chalcones were synthesized for the first time, including eight with a triazole moiety. Eight known flavones and chalcones were also synthesized and tested in order to construct a quantitative structure-activity relationship (QSAR) model for these compounds. Three different antifouling profiles were found: three compounds (1b, 11a and 11b) exhibited anti-settlement activity against a macrofouling species (Mytilus galloprovincialis), two compounds (6a and 6b) exhibited inhibitory activity against the biofilm-forming marine bacteria Roseobacter litoralis and one compound (7b) exhibited activity against both mussel larvae and microalgae Navicula sp. Hydrogen bonding acceptor ability of the molecule was the most significant descriptor contributing positively to the mussel larvae anti-settlement activity and, in fact, the triazolyl glycosylated chalcone 7b was the most potent compound against this species. The most promising compounds were not toxic to Artemia salina, highlighting the importance of pursuing the development of new synthetic antifouling agents as an ecofriendly and sustainable alternative for the marine industry.

Antifouling paints leach copper in excess - study of metal release rates and efficacy along a salinity gradient

Antifouling paints are biocidal products applied to ship and boat hulls in order to prevent the growth and settlement of marine organisms, i.e. fouling. The release of biocides from the surface of the paint film act to repel or poison potential settling organisms. Currently, the most commonly used biocide in antifouling paints is cuprous oxide. In the EU, antifouling products are regulated under the Biocidal Products Regulation (BPR), which states that the recommended dose should be the minimum necessary to achieve the desired effect. For antifouling products, the dose is measured as the release rate of biocide(s) from coating. In this study, the release rates of copper and zinc from eight different coatings for leisure boats were determined through static exposure of coated panels in four different harbors located in Swedish waters along a salinity gradient ranging from 0 to 27 PSU. The results showed the release rate of copper to increase with increasing salinity. Paints with a higher content of cuprous oxide were also found to release larger amounts of copper. The coatings' ability to prevent biofouling was also evaluated and no significant difference in efficacy between the eight tested products was observed at the brackish and marine sites. Hence, the products with high release rates of copper were equally efficient as those with 4 - 6 times lower releases. These findings suggest that current antifouling paints on the market are leaching copper in excess of the effective dose in brackish and marine waters. Additionally, the results from the freshwater site showed no benefit in applying a copper-containing paint for the purpose of fouling prevention. This indicates that the use of biocidal paints in freshwater bodies potentially results in an unnecessary release of copper. By reducing the release rates of copper from antifouling paints in marine waters and restricting the use of biocidal paints in freshwater, the load of copper to the environment could be substantially reduced.

Advanced Numerical Method for Determining the Wetted Area of Container Ships for Increased Estimation Accuracy of Copper Biocide Emissions

Research into the consequences of the accumulation of copper biocides in the marine environment has intensified since the ban on the use of organotin tributyltin (TBT) and the introduction of copper-based compounds in antifouling (AF) coatings. The specific emission of copper biocides and the surface of the wetted area of a vessel are the key parameters for the estimation of biocide emission. The estimated values of specific emissions of copper biocides should be taken with caution and their limitations and suitability for various surfaces and types of vessel should be known. Baseline limitations are also present in determining vessels’ wetted area. The available models do not provide realistic values, allowing multiple deviations. The proposed method of determining the wetted area considering container vessels and the specifics of their forms results in a set of hydrostatic diagrams that enable much more accurate estimation. The use of Automatic Identification System (AIS) is also proposed in terms of independent collection of required calculation parameters, enabling a full assessment of the total emission of copper biocides from container ships in the observed area.

Designing a Laboratory Bioassay for Evaluating the Efficacy of Antifouling Paints on Amphibalanus amphitrite Using a Flow-Through System

With the aim of establishing a protocol for evaluating the efficacy of antifouling paints on different organisms, a flow-through laboratory test using triangular boxes was developed for cyprids of the barnacle Amphibalanus (=Balanus) amphitrite. Six different formulations of antifouling paints were prepared in increasing content (0 to 40 wt.%) of Cu2O, which is the most commonly used antifouling substance, and each formulation of paint was coated on one surface of each test plate. The test plates were aged for 45 days by rotating them at a speed of 10 knots inside a cylinder drum with continuously flowing seawater. The settlement behavior of 3-day-old cyprids released inside triangular boxes made from the test plates was observed. A decreasing number of juveniles settled on surfaces of test plates that were coated with paint containing more than 30 wt.% of Cu2O. Results of the laboratory bioassays were consistent with those from the field experiments.

A new flow-through bioassay for testing low-emission antifouling coatings

Current antifouling (AF) technologies are based on the continuous release of biocides into the water, and consequently discharge into the environment. Major efforts to develop more environmentally friendly coatings require efficient testing in laboratory assays, followed by field studies. Barnacles are important fouling organisms worldwide, increasing hydrodynamic drag on ships and damaging coatings on underwater surfaces, and thus are extensively used as models in AF research, mostly in static, laboratory-based systems. Reliable flow-through test assays for the screening of biocide-containing AF paints, however, are rare. Herein, a flow-through bioassay was developed to screen for diverse low-release biocide paints, and to evaluate their effects on pre- and post-settlement traits in barnacles. The assay distinguishes between the effects from direct surface contact and bulk-water effects, which are crucial when developing low-emission AF coatings. This flow-through bioassay adds a new tool for rapid laboratory-based first-stage screening of candidate compounds and novel AF formulations.