Effects of DCOIT (4,5-dichloro-2-octyl-4-isothiazolin-3-one) to the haemocytes of mussels Perna perna

Enhanced antifouling and antibacterial performances of novel UV-curable polysiloxane/microcapsules/Ag composite coatings for marine applications

Marine biological fouling is a widespread phenomenon encountered by various oceanic ships and naval vessels, resulting in enormous economic losses. Herein, novel 4,5-dichloro-2-octyl-isothiazolone@sodium alginate/chitosan microcapsules (DCOIT@ALG/CS) were prepared through composite gel method using DCOIT as core materials, ALG and CS as shells, and CaCl2 as the cross-linking agent. The formed microcapsules (MCs) with Ag nanoparticles (AgNPs) were then filled in UV-curable polysiloxane (UV-PDMS), followed by UV irradiation to yield UV-PDMS/microcapsules/AgNPs (UV-PDMS/MCs/Ag) composite coatings. The constructed micro-nano dual-scale surface using the MCs and AgNPs improved the antifouling and antibacterial properties of UV-PDMS/MCs/Ag coatings. The as-obtained UV-PDMS/MCs/Ag coatings exhibited a static contact angle of about 160°, shear strength of 2.24 MPa, tensile strength of 3.32 MPa and elongation at break of 212%. The synergistic bacteriostatic effects of DCOIT and AgNPs in UV-PDMS/MCs/Ag coatings resulted in a bactericidal rate of 200 μg ml-1 towards Escherichia coli and Staphylococcus aureus with saturation at 100% within 10 min. In sum, the proposed composite coatings look promising for future marine transportation, pipeline networks and undersea facilities.

Adults of Sun Coral Tubastraea coccinea (Lesson 1829) Are Resistant to New Antifouling Biocides

Biocides used in antifouling (AF) paints, such as 4,5-dichlorine-2-n-octyl-4-isothiazole-3-one (DCOIT), can gradually leach into the environment. Some AF compounds can persist in the marine environment and cause harmful effects to non-target organisms. Nanoengineered materials, such as mesoporous silica nanocapsules (SiNCs) containing AF compounds, have been developed to control their release rate and reduce their toxicity to aquatic organisms. This study aimed to evaluate the acute toxicity of new nanoengineered materials, SiNC-DCOIT and a silver-coated form (SiNC-DCOIT-Ag), as well as the free form of DCOIT and empty nanocapsules (SiNCs), on the sun coral Tubastraea coccinea. T. coccinea is an invasive species and can be an alternative test organism for evaluating the risks to native species, as most native corals are currently threatened. The colonies were collected from the Alcatrazes Archipelago, SP, Brazil, and acclimatized to laboratory conditions. They were exposed for 96 h to different concentrations of the tested substances: 3.33, 10, 33, and 100 µg L-1 of free DCOIT; 500, 1000, 2000, and 4000 µg L-1 of SiNC; and 74.1, 222.2, 666.7, and 2000 µg L-1 of SiNC-DCOIT and SiNC-DCOIT-Ag. The test chambers consisted of 500 mL flasks containing the test solutions, and the tests were maintained under constant aeration, a constant temperature of 23 ± 2 °C, and photoperiod of 12 h:12 h (light/dark). At the end of the experiments, no lethal effect was observed; however, some sublethal effects were noticeable, such as the exposure of the skeleton in most of the concentrations and replicates, except for the controls, and embrittlement at higher concentrations. Adults of T. coccinea were considered slightly sensitive to the tested substances. This resistance may indicate a greater capacity for proliferation in the species, which is favored in substrates containing antifouling paints, to the detriment of the native species.

Antifouling coatings can reduce algal growth while preserving coral settlement

In the early stages after larval settlement, coral spat can be rapidly overgrown and outcompeted by algae, reducing overall survival for coral reef replenishment and supply for restoration programs. Here we investigated three antifouling (AF) coatings for their ability to inhibit algal fouling on coral settlement plugs, a commonly-used restoration substrate. Plugs were either fully or partially coated with the AF coatings and incubated in mesocosm systems with partial recirculation for 37 days to track fouling succession. In addition, settlement of Acropora tenuis larvae was measured to determine whether AF coatings were a settlement deterrent. Uncoated control plugs became heavily fouled, yielding only 4–8% bare substrate on upper surfaces after 37 days. During this period, an encapsulated dichlorooctylisothiazolinone (DCOIT)-coating was most effective in reducing fouling, yielding 61–63% bare substrate. Antiadhesive and cerium dioxide (CeO_2−x) nanoparticle (NP) coatings were less effective, yielding 11–17% and 2% bare substrate, respectively. Average settlement of A. tenuis larvae on the three types of AF-coated plugs did not statistically differ from settlement on uncoated controls. However, settlement on the NP-coating was generally the highest and was significantly higher than settlement found on the antiadhesive- and DCOIT-coating. Furthermore, on plugs only partially-covered with AF coatings, larval settlement on coated NP- areas was significantly higher than settlement on coated antiadhesive- and DCOIT-areas. These results demonstrate that AF coatings can reduce fouling intensity on biologically-relevant timescales while preserving robust levels of coral settlement. This represents an important step towards reducing fine-scale competition with benthic fouling organisms in coral breeding and propagation.

A preliminary study on multi-level biomarkers response of the tropical oyster Crassostrea brasiliana to exposure to the antifouling biocide DCOIT

This study investigated the sublethal effects of environmentally relevant concentrations of DCOIT on the neotropical oyster Crassostrea brasiliana. Gills and digestive glands of animals exposed to increasing concentrations of DCOIT were analyzed for biochemical, cellular, and histopathological responses. Exposure to DCOIT (0.2 to 151 μg L^-1) for 120 h triggered oxidative stress in both tissues (through the modulation of GPX, GST, GSH and GR), which led to damage of membrane lipids (increase of LPO and reduction of the NRRT). DCOIT increased histopathological pathologies in gills, such as necrosis, lymphocyte infiltration and epithelial desquamation. This study showed that short term exposure to environmental concentrations of DCOIT causes negative effects on C. brasiliana at biochemical, physiological, and histological levels. Therefore, the use of DCOIT as a booster biocide in antifouling paints should be further assessed, as it may cause environmental hazards to marine organisms.

How does the brown mussel Perna perna respond to environmental pollution? A review on pollution biomarkers

The brown mussel Perna perna (Linnaeus, 1758) is a valuable resource for aquaculture in tropical and subtropical coastal regions. It presents desirable characteristics for biomonitoring, including being sessile, widely distributed and abundant, and is a filter-feeder able to accumulate several classes of pollutants (e.g., metals, hydrocarbons, among others). Mussels' biological responses to pollution exposure can be measured as biomarkers, which include alterations ranging from molecular to physiological levels, to estimate the degree of environmental contamination and its effects on biota. This full review compiles two decades (2000-2020) of literature concerning biological effects on P. perna mussel caused by environmental pollutants (i.e., metals, hydrocarbons, and emerging pollutants), considering environmental and farm-based biomonitoring. Biochemical markers related to mussels' oxidative status were efficient for the biomonitoring of metals (i.e., antioxidant enzymes associated with oxidative damage in biomolecules). Genotoxicity and cytotoxicity indicators (i.e., comet, micronucleus, and neutral red assays) provided a depiction of hydrocarbon contamination. The neutral red assay gave a time-concentration cytotoxic response to a wide range of pollutants, including emerging pollutants (e.g., pharmaceuticals and biocides) and hydrocarbons. Perna perna hemocyte parameters provided a useful approach for biocide biomonitoring. This paper summarizes useful biomarkers from molecular to physiological levels in this mussel species used to identify and quantify the degree of coastal pollution. An integrated biomarker analysis may provide a way to overcome possible biomarker variations and assess multi-polluted sites. Nevertheless, it is necessary to investigate biomarker variations according to natural factors (e.g., season and gonad maturation stage) to standardize them for trustworthy biomonitoring.

Legacy and emerging antifouling biocide residues in a tropical estuarine system (Espirito Santo state, SE, Brazil)

The contamination by antifouling biocide residues (booster biocides - diuron, Irgarol, chlorothalonil, dichlofluanid and DCOIT; butyltin compounds-BTs (TBT, DBT and MBT); and antifouling paint particles-APPs) was appraised in sediments of Vitoria Estuarine System (VES). Even at its historical lower (ΣBTs ≤113 ng Sn g^-1 dry wt), the current environmental levels of BTs in areas with a predominance of boatyards still pose a risk to the local biota and human population. DCOIT, among booster biocides, was the most frequently detected, especially in boatyards (≤40 ng g^-1 dry wt) and Vitoria Port (64 ng g^-1 dry wt), while APPs were also detected mainly in sediments of boatyards (≤5,969 μg g^-1 dry wt). Since levels of diuron and DCOIT in APPs were as high as 1,670,000 and 899,000 ng g^-1 dry wt, respectively, they are acting as secondary sources of these antifouling biocides. Therefore, VES is threatened by antifouling biocide residues due to the multiple diffuse sources of contamination, showing the need for more efforts on public policies (including temporal trend monitoring studies).

Can Encapsulation of the Biocide DCOIT Affect the Anti-Fouling Efficacy and Toxicity on Tropical Bivalves?

The encapsulation of the biocide DCOIT in mesoporous silica nanocapsules (SiNC) has been applied to reduce the leaching rate and the associated environmental impacts of coatings containing this biocide. This research aimed to evaluate the effects of DCOIT in both free and nanostructured forms (DCOIT vs. SiNC-DCOIT, respectively) and the unloaded SiNC on different life stages of the bivalve Perna perna: (a) gametes (fertilization success), (b) embryos (larval development), and (c) juveniles mussels (byssus threads production and air survival after 72 h of aqueous exposure). The effects on fertilization success showed high toxicity of DCOIT (40 min-EC50 = 0.063 μg L−1), followed by SiNC-DCOIT (8.6 μg L−1) and SiNC (161 μg L−1). The estimated 48 h-EC50 of SiNC, DCOIT and SiNC-DCOIT on larval development were 39.8, 12.4 and 6.8 μg L−1, respectively. The estimated 72 h-EC50 for byssus thread production were 96.1 and 305.5 µg L−1, for free DCOIT and SiNC-DCOIT, respectively. Air survival was significantly reduced only for mussels exposed to free DCOIT. Compared to its free form, SiNC-DCOIT presented a balanced alternative between efficacy and toxicity, inhibiting efficiently the development of the target stage (larvae that is prone to settle) and satisfactorily preventing the juvenile attachment.