Comparative safety of the antifouling compound butenolide and 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) to the marine medaka (Oryzias melastigma)

Biomarkers responses in the amphipod Tiburonella viscana exposed to the biocide DCOIT and CO2-induced ocean acidification

Anthropogenic carbon dioxide emissions (CO2) have led to climate change and marine acidification, with an estimated decrease in ocean surface pH of 0.3-0.4 units by the end of the current century. Chemical pollution also contributes to biodiversity loss in marine environments. This issue is particularly critical in areas under pressure from shipping activities, where the introduction of new antifouling system formulations poses a major threat to non-target species. The biocide DCOIT is the most widely used alternative to organotin compounds due to its rapid degradation in seawater. The toxicity of waterborne DCOIT to marine organisms has been documented, but sediment-bound effects are limited to apical responses and pH scenarios corresponding to current levels. In this study, we determine in a combined way, the toxicity of DCOIT under marine acidification scenarios assessing biomarker responses in the burrowing amphipod Tiburonella viscana as a parameter of sublethal effects in solid phase exposures. Environmental relevant concentrations of DCOIT caused inhibition of the enzyme glutathione S-transferases (GST), changed acetylcholinesterase-like activity (AChE), and increased DNA damage at pHs of 7.7 and 7.4. For lipid peroxidation (LPO), increased levels caused by DCOIT were found for both control (8.1) and intermediate (7.7) conditions of pH. Our data provides evidence of oxidative and genotoxic effects induced by DCOIT, with activation of detoxification and defense mechanisms in T. viscana. These results are important for ecological risk assessment and managing of antifouling paint biocides in multiple stressors scenarios.

Mechanism-Driven Design of Isothiazolinone Alternatives

The extensive application of isothiazolinones has led to widespread pollution and poses a threat to ecological health, creating a need for the development of green alternatives. With the objective of devising chemical design strategies, we initially explored the structure-activity relationship (SAR) and structure-toxicity relationship (STR) of isothiazolinones. By comparing the antimicrobial activities of commercial isothiazolinone analogues, chlorine substitutions were identified as key determinants of pathogen growth inhibition potency. The variability of reproductive endocrine-disrupting toxicity was primarily driven by the length of the alkyl carbon chain, based on interactions with molecular initiating events and disturbances in sex hormones. Inspired by the SAR and STR guidelines, two new isothiazolinones (i.e., Target 1 and Target 2) were designed and synthesized. Compared to the commercial analogue dichloro-octylisothiazolinone, Target 1, which has a shorter alkyl chain and the same chlorine count, demonstrated slightly stronger antimicrobial activity, significantly lower endocrine-disrupting toxicity, and longer environmental persistence. Meanwhile, Target 2, containing ether bonds within a shorter alkyl chain and the same chlorine count, exhibited weaker antimicrobial activity, significantly lower endocrine-disrupting toxicity, and slightly longer environmental persistence. Overall, this study proposes a mechanism-driven design strategy for isothiazolinone alternatives that successfully reduces endocrine toxicity while maintaining antimicrobial activity.

Thyroid Endocrine Disruption and Mechanism of the Marine Antifouling Pollutant 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one

The antifoulant 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) is an emerging pollutant in the marine environment, which may disrupt the thyroid endocrine system. However, DCOIT toxicity in relation to thyroid endocrine disruption and the underlying mechanisms remains largely unclear. In this study, in vivo, in silico, in vitro, and ex vivo assays were performed to clarify DCOIT's thyroid toxicity. First, marine medaka (Oryzias melastigma) were exposed to environmentally realistic concentrations of DCOIT for an entire life cycle. The results demonstrated that DCOIT exposure potently stimulated the hypothalamic-pituitary-thyroid axis, characterized by hyperthyroidism symptom induction and prevalent key gene and protein upregulation in the brain. Moreover, the in silico and in vitro results evidenced that DCOIT could bind to thyroid hormone receptor β (TRβ) and interact synergistically with triiodothyronine, thus promoting GH3 cell proliferation. The CUT&Tag experiment found that DCOIT interfered with the affinity fingerprint of TRβ to target genes implicated in thyroid hormone signaling cascade regulation. Furthermore, ex vivo, Chem-seq revealed that DCOIT directly bound to the genomic sequences of thyrotropin-releasing hormone receptor b and thyroid-stimulating hormone receptor in marine medaka brain tissues. In conclusion, the current multifaceted evidence confirmed that DCOIT has a strong potency for thyroid endocrine system disruption and provided comprehensive insights into its toxicity mechanisms.

A Chemical Toolbox to Unveil Synthetic Nature-Inspired Antifouling (NIAF) Compounds

The current scenario of antifouling (AF) strategies to prevent the natural process of marine biofouling is based in the use of antifouling paints containing different active ingredients, believed to be harmful to the marine environment. Compounds called booster biocides are being used with copper as an alternative to the traditionally used tributyltin (TBT); however, some of them were recently found to accumulate in coastal waters at levels that are deleterious for marine organisms. More ecological alternatives were pursued, some of them based on the marine organism mechanisms' production of specialized metabolites with AF activity. However, despite the investment in research on AF natural products and their synthetic analogues, many studies showed that natural AF alternatives do not perform as well as the traditional metal-based ones. In the search for AF agents with better performance and to understand which molecular motifs were responsible for the AF activity of natural compounds, synthetic analogues were produced and investigated for structure-AF activity relationship studies. This review is a comprehensive compilation of AF compounds synthesized in the last two decades with highlights on the data concerning their structure-activity relationship, providing a chemical toolbox for researchers to develop efficient nature-inspired AF agents.

Developmental cardiotoxicity of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) in marine medaka (Oryzias melastigma)

The application of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) as an antifouling biocide causes high toxicity to non-target marine organisms. To examine the developmental cardiotoxicity and mechanisms of DCOIT, we concurrently performed sub-chronic exposure and life-cycle exposure experiments using marine medaka embryos. After sub-chronic exposure to DCOIT at 1, 3, 10, and 33 μg/L, cardiac defects were caused by upregulation of cardiac gene transcriptions, decreasing heart size, and accelerating heartbeat. Hyperthyroidism in medaka larvae was identified as the cause of developmental cardiotoxicity of DCOIT sub-chronic exposure. In addition, parental life-cycle exposure to 1, 3, and 10 μg/L DCOIT led to transgenerational impairment of cardiogenesis in offspring medaka. A crossbreeding strategy discriminated a concentration-dependent mechanism of transgenerational cardiotoxicity. At 1 μg/L, the DCOIT-exposed female parent transferred a significantly higher amount of triiodothyronine (T3) hormone to offspring, corresponding to an accelerated heart rate. However, DCOIT at higher exposure concentrations modified the methylome imprinting in larval offspring, which was associated with cardiac dysfunction. Overall, the findings provide novel insights into the developmental cardiotoxicity of DCOIT. The high risks of DCOIT-even at environmentally realistic concentrations-raise concerns about its applicability as an antifoulant in a marine environment.

Isothiazolinone dysregulates the pattern of miRNA secretion: Endocrine implications for neurogenesis

Isothiazolinones are extensively used as preservatives and disinfectants in personal care products and household items. The unintended exposure of humans and animals to isothiazolinones has led to increasing concerns about their health hazards. The compound 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT), a representative isothiazolinone, can simultaneously induce endocrine disruption and neurotoxicity. However, the underlying mechanisms and linkages remain unclear. Our purpose was to elucidate the role of miRNAs as the signaling communicator during the crosstalk between endocrine and nervous systems in response to DCOIT stress. H295R cells were exposed to DCOIT, after which the alterations in intracellular miRNA composition, exosome secretory machinery, and extracellular miRNA composition were examined. Then, a PC12 cell line of neuronal differentiation potential was cultured with the extract of extracellular miRNAs from DCOIT-exposed H295R cell media to explore the functional implications in neurogenesis. The results showed that DCOIT exposure resulted in 349 differentially expressed miRNAs (DEMs) in H295R cells, which were closely related to the regulation of multiple endocrine pathways. In the media of H295R cells exposed to DCOIT, 66 DEMs were identified, showing distinct compositions compared to intracellular DEMs with only 2 common DEMs (e.g., novel-m0541-5p of inverse changes in the cell and medium). Functional annotation showed that extracellular DEMs were not only associated with sex endocrine synchronization, but were also implicated in nervous system development, morphogenesis, and tumor. Incubating PC12 cells with the extracellular exosomes (containing miRNAs) from DCOIT-exposed H295R cells significantly increased the neurite growth, promoted neuronal differentiation, and shaped the transcriptomic fingerprint, implying that miRNAs may communicate transduction of toxic information of DCOIT in endocrine system to neurons. Overall, the present findings provide novel insight into the endocrine disrupting and neural toxicity of DCOIT. The miRNAs have the potential to serve as the epigenetic mechanism of systems toxicology.

Acute Toxicity of a Novel anti-fouling Material Additive DCOIT to Marine Chlorella sp

DCOIT (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one) is the main ingredient in SeaNine-211, a new antifouling agent that replaces organotin compounds to prevent the growth of fouling organisms on board. Biocides from antifoulants can cause problems for marine ecosystems by destroying non-target algal species. This study evaluated the potential adverse effects DCOIT using the Marine Chlorella sp. The concentration of DCOIT were set according to the semi-inhibitory concentrations for acute exposure experiments, and relevant oxidative stress indicators were measured to assess the acute toxic effects. The results showed that the inhibition concentrations (IC50) of DCOIT against Marine Chlorella sp was 2.522 mg/L. The genes related to photosynthesis and antioxidant capacity showed the effect of promoting low concentration and inhibiting high concentration. In addition, based on the ultrastructural observation and the expression analysis of photosynthesis related genes, it was found that DCOIT had a significant effect on plant photosynthesis.

Acute and mutigenerational effects of environmental concentration of the antifouling agent dichlofluanid on the mysid model, Neomysis awatschensis

A broad-spectrum fungicide, dichlofluanid is widely used in antifouling paints and agricultural pesticides. In this study, the acute and chronic effects of sublethal concentrations, namely, no observable effect concentration (NOEC) and 50% lethal concentration (LC₅₀) of dichlofluanid (1/10 NOEC, NOEC, 1/10 LC₅₀, and LC₅₀) were evaluated on the marine mysid, Neomysis awatschensis. Acute toxicity test (96 h) showed higher sensitivity to dichlofluanid in juvenile mysids (LC₅₀ 3.1 μg L^-1) than adults (LC₅₀ 24.5 μg L^-1), with lower survival rate and reduction in food consumption. Exposure with dichlofluanid considerably induced oxidative imbalance, as NOEC (0.006 μg L^-1 for juveniles and 0.074 μg L^-1 for adults) and 1/10 LC₅₀ values increased intracellular concentrations of malondialdehyde and glutathione, and the enzymatic activities of catalase and superoxide dismutase, whereas exposure to LC₅₀ value decreased the values of oxidative parameters. Enzymatic activity of acetylcholinesterase decreased considerably when exposed to LC₅₀ value. In the case of chronic effects, exposure to NOEC for 4 weeks markedly decreased the juvenile survival rate, while adults showed tolerance. Multigenerational monitoring in response to NOEC showed a significant growth retardation with an increase in intermolt duration as well as a decrease in the number of newborn mysids from females of the third generation. Consistent exposure to environmentally relevant sublethal concentrations of dichlofluanid would be detrimental to mysid individuals and the survival of the mysid population.

Toxicity of innovative antifouling additives on an early life stage of the oyster Crassostrea gigas: short- and long-term exposure effects

Recent advances in nanotechnology have allowed the encapsulation of hazardous antifouling (AF) biocides in silica mesoporous nanocapsules (SiNC) reducing their short-term toxicity. However, the chronic effects of such novel nanoadditives remain understudied. The present study aimed to assess short- and long-term sub-lethal effects of soluble forms (DCOIT and Ag) and nanostructured forms (SiNC-DCOIT and SiNC-DCOIT-Ag) of two AF biocides and the "empty" nanocapsule (SiNC) on juveniles of Crassostrea gigas after 96 h and 14 days of exposure. Juvenile oysters exposed for a short period to free DCOIT and AgNO₃ presented worse physiological status comparing with those exposed to the nanostructured forms. The long-term exposure to DCOIT and Ag⁺ caused an extensive biochemical impairment comparing with the tested nanomaterials, which included oxidative damage, activation of the antioxidant defense system, and neurotransmission impairment. Despite the negative effects mostly observed on the health condition index and AChE, the encapsulation of the abovementioned AF biocides into SiNC seems to be a technological advantage towards the development of AF nanoadditives with lower long-term toxicity comparing with the soluble forms of such biocides.

Assessment of the risk posed by three antifouling biocides to Pacific oyster embryos and larvae in Hiroshima Bay, Japan

The Pacific oyster (Crassostrea gigas) is an important species in oyster farming worldwide, including in Japan. Hiroshima Bay is one of the most important oyster farming areas in Japan. We investigated the occurrence of antifouling biocides used worldwide including diuron, Irgarol 1051 (Irgarol), and 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT), which have been detected at sub-ppb levels in seawater in Japan, and estimated their no observed effect concentrations (NOECs). In recent years, the spat settlement of Pacific oysters has become poor, which presents a challenge for oyster aquaculture in Hiroshima Bay; hence, we conducted embryotoxicity and larva settlement tests using Pacific oysters. Compared to diuron and Irgarol, DCOIT exhibited a higher toxicity toward oyster embryos, and the minimum 24-h NOEC toxicity value for the oyster embryos was <3 ng/L. The highest concentrations of diuron, Irgarol, and DCOIT in the environmental seawater in the Seto Inland Sea were 27.6, 3.2, and 24 ng/L, respectively. Considering the NOECs, the environmental concentrations of these biocides suggest that the ecological risks posed by diuron and Irgarol are low, whereas those posed by DCOIT are high. However, the rate of detection of DCOIT was low because it degraded rapidly in the seawater before treatment for chemical analysis, except in the case of the treatment on the research vessel.

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.

Effects of nanostructure antifouling biocides towards a coral species in the context of global changes

Biofouling prevention is one of the biggest challenges faced by the maritime industry, but antifouling agents commonly impact marine ecosystems. Advances in antifouling technology include the use of nanomaterials. Herein we test an antifouling nano-additive based on the encapsulation of the biocide 4,5-dichloro-2-octyl-4-isothiazolin-3-one (DCOIT) in engineered silica nanocontainers (SiNC). The work aims to assess the biochemical and physiological effects on the symbiotic coral Sarcophyton cf. glaucum caused by (1) thermal stress and (2) DCOIT exposure (free or nanoencapsulated forms), in a climate change scenario. Accordingly, the following hypotheses were addressed: (H1) ocean warming can cause toxicity on S. cf. glaucum; (H2) the nanoencapsulation process decreases DCOIT toxicity towards this species; (H3) the biocide toxicity, free or encapsulated forms, can be affected by ocean warming. Coral fragments were exposed for seven days to DCOIT in both free and encapsulated forms, SiNC and negative controls, under two water temperature regimes (26 °C and 30.5 °C). Coral polyp behavior and photosynthetic efficiency were determined in the holobiont, while biochemical markers were assessed individually in the endosymbiont and coral host. Results showed transient coral polyp retraction and diminished photosynthetic efficiency in the presence of heat stress or free DCOIT, with effects being magnified in the presence of both stressors. The activity of catalase and glutathione-S-transferase were modulated by temperature in each partner of the symbiosis. The shifts in enzymatic activity were more pronounced in the presence of free DCOIT, but to a lower extent for encapsulated DCOIT. Increased levels of oxidative damage were detected under heat conditions. The findings highlight the physiological constrains elicited by the increase of seawater temperature to symbiotic corals and demonstrate that DCOIT toxicity can be minimized through encapsulation in SiNC. The presence of both stressors magnifies toxicity and confirm that ocean warming enhances the vulnerability of tropical photosynthetic corals to local stressors.

DCOIT unbalances the antioxidant defense system in juvenile and adults of the marine bivalve Amarilladesma mactroides (Mollusca: Bivalvia)

DCOIT is a co-biocide that is part of the formulation of the commercial antifouling Sea-Nine 211® and although it is "safe to use", negative effects have been reported on the antioxidant defense system of non-target organisms. Therefore, the objective of this research was to verify and compare the response of antioxidant enzymes of juveniles and adults of Amarilladesma mactroides exposed to DCOIT. The animals were exposed to solvent control (DMSO 0.01%) and DCOIT (measured concentration 0.01 mg/L and 0.13 mg/L) for 96 h, then gills, digestive gland and mantle were collected for analysis of the enzymatic activity of glutathione S-transferase (GST), superoxide dismutase (SOD) and catalase (CAT). The results revealed that adults, in relation to juveniles, have low basal activity of GST and SOD enzymes in the gills and digestive gland and high basal activity of SOD and CAT in the mantle. DCOIT did not alter GST activity in the gills of any life stage, while both concentrations decreased SOD and CAT in adults. In the digestive gland, it was observed that DCOIT (0.13 mg/L) decreased the GST activity in adults and CAT in juveniles, and both concentrations of the co-biocide decreased the SOD and CAT in adults. In the mantle, DCOIT (0.13 mg/L) increased CAT in juveniles. We conclude that juveniles have greater basal activity of antioxidant enzymes than adults and, in addition, DCOIT negatively affected the adults of A. mactroides, mainly decreasing the activity of GST, SOD and CAT in the gills and digestive gland of these organisms.

Ecological risk assessment of booster biocides in sediments of the Brazilian coastal areas

Although booster biocides (Irgarol, diuron, chlorothalonil, dichlofluanid, and DCOIT) have been detected in sediments along the Brazilian coastal areas, the risk associated to their occurrence and levels is still unknown. Thus, the ecological risk of booster biocides to sediment-dwelling organisms from the Brazilian coast was assessed using a risk characterization approach through the Risk Quotient (Measured environmental concentration (MEC)/Predicted no effect concentrations (PNECs)). Sedimentary PNECs for Irgarol, diuron, chlorothalonil and DCOIT were derived based on published ecotoxicological data from both freshwater and marine studies, while a NORMAN methodology was used to derived it for dichlofluanid. Results showed that DCOIT, diuron, Irgarol, chlorothalonil, and dichlofluanid can pose high risk on 47%, 35%, 15%, 1% and 1%, respectively, of the 113 Brazilian sites appraised. Considering the trend of expansion of navigation/maritime activities, DCOIT may worsen its impact over the coastal areas of Brazil, especially ports, but also ship/boatyards, marinas, and maritime traffic zones. The present study is an important contribution to support advance on policy formulation concerning booster biocides worldwide, particularly considering the lack of regulation on the use of antifouling biocides in Brazil.

Toxicity effects of hydrophilic algal lysates from Coolia tropicalis on marine medaka larvae (Oryzias melastigma)

Coolia tropicalis is a species of benthic and epiphytic toxic algae, which can produce phycotoxins that intoxicate marine fauna. In this study, the potential toxic effects of C. tropicalis on fish were investigated using larval marine medaka (Oryzias melastigma) as a model to evaluate fish behavior, physiological performance, and stress-induced molecular responses to exposure to two sublethal concentrations (LC₁₀ and LC₂₀) of hydrophilic algal lysates. Exposure to C. tropicalis lysates inhibited swimming activity, activated spontaneous undirected locomotion, altered nerve length ration, and induced early development abnormalities, such as shorter eye diameter, body as well as axon length. Consistent with these abnormalities, changes in the expression of genes associated with apoptosis (CASPASE-3 and BCL-2), the inflammatory response (IL-1β and COX-2), oxidative stress (SOD), and energy metabolism (ACHE and VHA), were also observed. This study advances our understanding of the mechanisms of C. tropicalis toxicity in marine fish in the early life stages and contributes to future ecological risk assessments of toxic benthic dinoflagellates.

Biomimetic surface coatings for marine antifouling: Natural antifoulants, synthetic polymers and surface microtopography

Marine biofouling is a ubiquitous problem that accompanies human marine activities and marine industries. It exerts detrimental impacts on the economy, environment, ecology, and safety. Traditionally, mainstream approaches utilize metal ions to prevent biological contamination, but this also leads to environmental pollution and damage to the ecosystem. Efficient and environmentally friendly coatings are urgently needed to prevent marine devices from biofouling. Since nature is always the best teacher for humans, it offers us delightful thoughts on the research and development of high-efficiency, broad-spectrum and eco-friendly antifouling coatings. In this work, we focus on the research frontier of marine antifouling coatings from a bionic perspective. Enlightened by three distinctive dimensions of bionics: chemical molecule bionic, physiological mechanism bionic, and physical structure bionic, the research status of three main bioinspired strategies, which are natural antifoulants, bioinspired polymeric antifouling coatings, and biomimetic surface microtopographies, respectively, are demonstrated. The antifouling mechanisms are further interpreted based on biomimetic comprehension. The main fabrication methods and antifouling performances of these coatings are presented along with their advantages and drawbacks. Finally, the challenges are summarized, and future research prospects are proposed. It is believed that biomimetic antifouling strategies will contribute to the development of nontoxic antifouling techniques with exceptional repellency and stability.

Transgenerational Effects of Hexavalent Chromium on Marine Medaka (Oryzias melastigma) Reveal Complex Transgenerational Adaptation in Offspring

Hexavalent chromium [Cr(VI)] pollution is one of most serious heavy metal pollutants in the coastal area and posed serious threats to marine organisms and human beings. Many studies have been conducted on its toxicological effects on living organisms from morphological to physiological aspects. However, there are few studies about the transgenerational toxicological of Cr(VI). In this study, we exposed adult marine medaka fishes with Cr(VI) and their offspring with Cr(VI) to examine transgenerational effects of Cr(VI). We found that there were mechanisms such as changing reproduction modes in males to compensate for impacts on the reproduction. There were differences and similarities between the parental effect and the environmental effect, with the former one causing more serious adverse effects on the offspring of Cr(VI)-exposed fish. It was noteworthy that there was an interaction between the parental and offspring treatment which leads to the attenuation of the parental effects on offspring when the offspring also underwent the same treatment. In addition, physiological adaptation has also been observed in fish to improve their fitness. Overall, effects of Cr(VI) on fish and their offspring were studied to pave a way to study the of mechanisms of adaptation.

Molecular and biochemical effects of the antifouling DCOIT in the mussel Perna perna

Biological fouling is an unwanted phenomenon that results in economic losses to the shipping industry. To prevent fouling, antifouling paints are used. DCOIT (4,5- dichloro-2-n-octyl-4-isothiazolin-3-one) is a biocide present in many antifouling paint formulations, and is toxic to a wide range of organisms. The aim of the present study was to evaluate the effects of DCOIT on oxidative stress indicators of the brown mussel, Perna perna. Molecular (SOD-like, GSTO-like and MGST-like mRNA levels) and biochemical (activities of superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST), and levels of glutathione (GSH), reactive oxygen species (ROS) and protein carbonyls (PCO)) components were evaluated. Further, levels of biomarkers were assessed in the gills and digestive glands of mussels. Bivalves were exposed to DCOIT (control, 0.1 μg/L and 10 μg/L) for up to 96 h. DCOIT exposure decreased GSH content in gills. Moreover, exposure to DCOIT also decreased CAT activity in the gills and digestive glands of mussels. GST activity increased in digestive gland after exposure for 24 h to both concentrations of DCOIT tested. SOD activity, ROS levels and PCO content were not affected by exposure to the contaminant. Regarding the molecular biomarkers evaluated, DCOIT exposure altered mRNA levels of SOD-like in both tissues after 24 and 96 h of exposure, and decreased MGST-like mRNA levels in the digestive gland after 96 h of exposure to the chemical. These findings suggested that exposure to DCOIT may alter the biochemical and molecular functioning of P. perna, which may harm the species.

Marine natural products as antifouling molecules - a mini-review (2014-2020)

In the present review, 182 antifouling (AF) natural products from marine microorganisms, algae and marine invertebrates reported from August 2014 to May 2020 are presented. Amongst these compounds, over half were isolated from marine-derived microorganisms, including 70 compounds from fungi and 31 compounds from bacteria. The structure-relationship of some of these compounds is also briefly discussed. Based on the work reported, a general workflow was drafted to refine the procedures for the commercialization of any novel AF compounds. Finally, butenolide, which is considered a potential environmentally friendly antifoulant, is used as a case study to show the procedures involved in AF compound work from the aspect of discovery, structure optimization, toxicity, stability, AF mechanism and coating incorporation, which highlight the current challenges and future perspectives in AF compound research.

Biofilm inhibition effect of an ivermectin/silyl acrylate copolymer coating and the colonization dynamics

Ivermectin is now being used as a substitute for toxic organic biocide in marine antifouling coatings due to its environmentally friendly nature and the efficacy against parasites. However, the release performance of ivermectin from the hydrolyzed acrylic-based resin into the seawater is not clear. Moreover, the efficiency and mechanism of ivermectin in preventing biofilm or slime formation have not been fully investigated. In this study, a coating was developed by mixing ivermectin with an acrylic-based resin, silyl acrylate copolymer, and a 45-day in situ antifouling test was conducted in the Yellow Sea. Direct observation and confocal microscope investigation indicated that the polymer coating with ivermectin was effective against biofilm formation. High-throughput sequencing analysis showed that ivermectin can selectively inhibit the adhesion of microorganisms. Abundances of Gammaproteobacteria and Alphaproteobacteria decreased significantly with the increased concentration of ivermectin. As for the eukaryote community, species of Stolidobranchia and unidentified_Bacillariophyceae were proved to be sensitive to ivermectin. Therefore, the ivermectin/silyl acrylate copolymer coating is a promising substitute for marine antifouling material.

Preparation of Microcapsules Coating and the Study of Their Bionic Anti-Fouling Performance

With the increasing demands to better the marine environment, environmentally friendly anti-fouling coatings have attracted attention from society. Adding hydrolyzable microcapsules without toxin to paints is a very useful and safe method to get bionic anti-fouling coatings with a micro-nano surface structure. Based on this trend, a form of environment-friendly microcapsules were prepared through mini-emulsion polymerization. The target microcapsules had a poly(urea-formaldehyde) (PUF) shell and a mixed core of silicone oil and capsaicin. Additionally, the microcapsules were introduced into zinc acrylate resin to obtain bionic anti-fouling coatings with micro-nano morphology. The effects of polyvinyl alcohol (PVA) molecular weight, stirring rate, and temperature on the morphology of the microcapsules were studied by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that spherical nanoparticles with smooth surfaces were obtained, and the mean diameter was approximately 1.38 μm when the molecular weight of PVA was 77 K, the stirring rate was 600 rpm and the temperature was 55 °C. Fourier-transform infrared spectra (FTIR) results showed that the silicone oil and capsaicin were successfully encapsulated, the core materials of the microcapsules reached 72.37% and the yield of microcapsules was 68.91% by the Soxhlet method. Furthermore, the hydrophobicity, corrosion resistance and anti-fouling performance of the coatings were evaluated by the water contact angle, electrochemical and real-sea tests. The results indicated that the anti-fouling coatings had excellent hydrophobicity and anti-fouling performance due to the micro-nano convex structure and the release of core materials. Encouragingly, the anti-fouling coatings show excellent and long-term anti-fouling performance, which is expected to be widely applied in marine anti-fouling coatings.

Combining a bio-based polymer and a natural antifoulant into an eco-friendly antifouling coating

Biodegradable polymers are promising binders and carriers for natural antifoulants. In the present study, an antifouling (AF) coating was developed by adding a non-toxic AF compound (butenolide) to a bio-based and biodegradable poly(lactic acid)-based polyurethane. Mass loss measurement showed that the polymer degraded in seawater at a rate of 0.013 mg cm^-2 day^-1. Measurements showed that butenolide was released from the coatings into seawater over a period of at least three months. Both the concentration of butenolide in the coatings and the ambient temperature determined the release rate of butenolide. The results further demonstrate that incorporating rosin into the coatings increase the self-renewal rate of the polymer and facilitated the long-term release of butenolide from the coating. The results show that poly(lactic acid)-based polyurethane is a suitable polymer for butenolide-based AF coatings.

Effect of marine antifouling paint particles waste on survival of natural Bermuda copepod communities

Marine antifouling paints (MAPs) are widely used to prevent organisms from fouling vessel hulls. When scraped from vessels as part of regular maintenance, MAP particles discharged into the seawater become a source of toxic substances, like copper (Cu), to the environment, and biocides leaching from them are known to cause toxic effects on non-target organisms. We investigated the toxicity of MAP particles collected from a Bermuda boatyard on local copepod communities using two experiments. Copepod survival, Chlorophyll a and total dissolved Cu concentrations were measured before and after MAP particles addition. In an acute toxicity test, the addition of 0.3 g/L of MAP particles resulted in 0% copepods survival within 88 h and increased dissolved Cu by 1.8 μM. A significant inverse relationship was observed between copepod survival and MAP particles quantity, highlighting the toxic effects of MAP particles from boat maintenance on copepod communities in the surrounding seawater.

Effects of sublethal concentrations of the antifouling biocide Sea-Nine on biochemical parameters of the marine polychaete Perinereis aibuhitensis

Sea-Nine™ 211 is an emerging biocide that has an adverse impact on aquatic environments. In this study, the marine polychaete Perinereis aibuhitensis was exposed to Sea-Nine (0.1, 1, and 10 μg L^-1), and acute toxicity and biochemical responses such as changes in the intracellular contents of malondialdehyde (MDA) and glutathione (GSH) and enzymatic activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST), and acetylcholinesterase (AChE) were evaluated over a period of 14 d. Determined median lethal doses, LC50 were 268 μg L^-1, 142 μg L^-1, and 55 μg L^-1 at 24 h, 96 h, and 14 d, respectively. The MDA content increased significantly in a dose- and time-dependent manner, indicative of lipid peroxidation-related oxidative damage. Significantly higher intracellular GSH levels and antioxidant defense-related enzyme (CAT, SOD, GPx, GR, and GST) activities were observed after exposure to 10 μg L^-1 Sea-Nine. In contrast, Sea-Nine treatment significantly reduced AChE activity at the highest concentration of Sea-Nine used (10 μg L^-1). Taken together, these results indicate that sublethal concentrations of Sea-Nine are toxic to marine polychaetes through potential lipid peroxidation, induction of oxidative stress, and modulation of the cholinergic system. Our results can contribute to biomonitoring of aquatic environments and ecotoxicological research through the measurements of polychaete cellular defenses against waterborne biocides.

Toxicity of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) in the marine decapod Litopenaeus vannamei

DCOIT (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one) is the main component of SeaNine-211, a new antifouling agent that replaces tributyltin to prevent the growth of undesirable organisms on ships. There have been some studies on the toxicity of DCOIT, but the mechanism of DCOIT's toxicity to crustaceans still requires elucidation. This study examined the chronic toxicity (4 weeks) of 0, 3, 15, and 30 μg/L DCOIT to the Pacific white shrimp (Litopenaeus vannamei) from the aspects of growth and physiological and histological changes in the hepatopancreas and gills. A transcriptomic analysis was performed on the hepatopancreas to reveal the underlying mechanism of DCOIT in shrimp. The exposure to 30 μg/L DCOIT significantly reduced the survival and weight gain of L. vannamei. High Na⁺/K⁺-ATPase activity and melanin deposition were found in the gills after 4 weeks of 15 μg/L or 30 μg/L DCOIT exposure. The highest concentration of DCOIT (30 μg/L) induced changes in hepatopancreatic morphology and metabolism, including high anaerobic respiration and the accumulation of triglycerides. Compared with the exposure to 3 μg/L DCOIT, shrimp exposed to 15 μg/L DCOIT showed more differentially expressed genes (DEGs) than those in the control, and these DEGs were involved in biological processes such as starch and sucrose metabolism and choline metabolism in cancer. The findings of this study indicate that L. vannamei is sensitive to the antifouling agent DCOIT and that DCOIT can induce altered gene expression at a concentration of 15 μg/L and can interfere with shrimp metabolism, growth and survival at 30 μg/L.

Dynamic surface antifouling: mechanism and systems

Marine biofouling is a global problem today. High efficiency and eco-friendly antifouling systems are in pressing need. In recent years, we have proposed the concept of dynamic surface antifouling (DSA). That is, a continuously changing surface can effectively prevent marine fouling organisms from landing and adhesion. Based on this strategy, we developed coatings with dynamic surfaces by using degradable polymers including polyester-polyurethane, modified polyester and poly(ester-co-acrylate). They exhibit tunable renewability, and excellent antifouling and mechanical performance. Moreover, the polymers can serve as carrier and controlled release systems of antifoulants so that they have long service life. This paper reviews the progress and trends in marine anti-biofouling, and presents the mechanism and systems of DSA.

Long-term exposure of xenoestrogens with environmental relevant concentrations disrupted spermatogenesis of zebrafish through altering sex hormone balance, stimulating germ cell proliferation, meiosis and enhancing apoptosis

Environmental estrogens are capable of interfering with the spermatogenesis and fertility of fish. However in natural waters, these chemicals are more likely to occur as a combination rather than a single stressor. Whether and how the mixture of xenoestrogens with environmental relevant concentrations may affect fish spermatogenesis remains largely unknown. In this study, male zebrafish adults were administered to 17alpha-ethinylestradiol (EE2) and a mixture of xenoestrogens (Mix (E2, EE2, DES, 4-t-OP, 4-NP and BPA)), with the estrogenic potency equivalent to EE2. After a 60-day exposures, elevated mRNA levels of vitellogenin 1 (vtg1) and estrogen receptor 1 (esr1) in the liver of fish in both treated groups were observed. Moreover, the plasma level of E2 declined significantly in the Mix group and the ratio of 11-KT/E2 was significantly elevated in both treated groups. Consistently, the mRNA level of P450 side-chain cleavage (scc) in the EE2 group and ovarian type aromatase (cyp19a1a) in the Mix group was significantly suppressed. In addition, decreased gonadosomatic index and sperm count in the fish of Mix group were present. Furthermore, increased number of the proliferating germ cells (such as spermatogonia and spermatocytes) was observed in the fish of both groups, suggesting a stimulated germ cell proliferation and meiosis. Accordingly, both exposures significantly up-regulated the mRNA levels of genes in mitosis (cyclinb1) and meiosis (cyp26a1 in EE2 group, aldh1a2, cyp26a1, sycp3 and spo11 in Mix). In addition, decreased number of spermatozoa and increased number of TUNEL-positive signals were present in the testis of fish in the Mix group, indicating an enhanced apoptosis. Further analyses demonstrated the significant elevated expressions of tnfrsf1a and the ratio of tnfrsf1a/tnfrsf1b in the Mix group, suggesting an elevated apoptosis in the testis of fish in the Mix group via extrinsic pathway. The present study greatly extends our understanding of the underlying mechanisms of the reproductive toxicity of xenoestrogens on fish.

Constant exposure to environmental concentrations of the antifouling biocide Sea-Nine retards growth and reduces acetylcholinesterase activity in a marine mysid

Sea-Nine (4,5-dichloro-2-n-octyl-4-isothiazoline3-one; DCOIT) antifoulant has been widely used owing to its broad spectrum of biocide activity against major fouling organisms. In this study, several physiological parameters of a marine mysid were analyzed upon exposure to sublethal environmental concentrations (1 and 100 ng L^-1) of Sea-Nine in two exposure conditions, intermittent (weekly; once per week) and constant (daily; once per 24 h) exposure, for 4 weeks. In both experimental conditions, growth retardation, acetylcholinesterase (AChE) activity, glutathione S-transferase (GST) activity, and number of newborn juveniles as second generation, together with their survival were measured. Morphometric parameters of total body, antennal scale, exopod, endopod, and telson were significantly retarded by 22%, 14%, 13%, and 24%, respectively, by daily exposure to 100 ng L^-1 Sea-Nine for 4 weeks. Significant inhibition of AChE activity was observed at week 4 in the 100 ng L^-1 daily Sea-Nine-exposed groups, whereas no significant GST activity was measured at the same experimental conditions. Inhibition of AChE activity would be associated with impairment of cholinergic system and may adversely modulate growth parameters of the mysid. The number of newly hatched juveniles from females that were exposed daily to 100 ng L^-1 Sea-Nine was significantly lower than that of the control. Although no significant differences were observed between survival percentages of newborn juveniles for 30 days, mortality (NOEC and LC50) increased in the surviving offspring from the 100 ng L^-1-exposed 1st generation of mysids. These findings suggested that constant exposure to Sea-Nine has detrimental effects on the growth parameters of marine mysids with inhibition of AChE activity.

Endoplasmic reticulum stress mediates 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT)-induced toxicity and liver lipid metabolism changes in Nile tilapia (Oreochromis niloticus)

DCOIT (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one) is the main active ingredient in an emerging water environment antifoulant, the toxicity and environmental impacts of which need to be further investigated. Thus, this study examined the toxicity of DCOIT on Nile tilapia (Oreochromis niloticus), including its effects on behavior, respiration and energy metabolism as well as the role of endoplasmic reticulum stress (ER stress) in mediating its toxicity and metabolic changes. The changes in fish behavior, respiration, neuronal signal transmission, energy metabolism, ER stress, and liver histology were examined via acute (4 days) and chronic (28 days) exposures to 0, 3, 15, 30 μg/L DCOIT in vivo. Additionally, ER stress levels were measured in 24-h periods of hepatocyte exposure to 0, 3, 15, 30 and 300 μg/L DCOIT in vitro. The hyper-locomotor activities decreased, but the respiration rate increased after a 4-day acute exposure period, indicating that DCOIT exposure altered fish energy metabolism. After acute exposure at a low DCOIT concentration, the activation of ER stress induced triglyceride accumulation in the liver. After chronic exposure for 28 days, the prolonged ER stress induced a series of pathological cellular changes. At the cellular level, exposure to a high DCOIT concentration induced ER stress in the hepatocytes. In addition, as a neurotoxin, DCOIT has the potential to disrupt the neurotransmission of the cholinergic system, resulting in motor behavior disruption. This study demonstrates that DCOIT plays a role in time- and concentration-dependent toxicity and that changes in lipid metabolism are directly related to endoplasmic reticulum function after exposure to an antifouling agent. This work advances the understanding of the toxic mechanism of DCOIT, which is necessary for its evaluation.

Reprint of: Environmental toxicology and omics: A question of sex

Molecular initiating events and downstream transcriptional/proteomic responses provide valuable information for adverse outcome pathways, which can be used predict the effects of chemicals on physiological systems. There has been a paucity of research that addresses sex-specific expression profiling in toxicology and due to cost, time, and logistic considerations, sex as a variable has not been widely considered. In response to this deficiency, federal agencies in the United States, Canada, and Europe have highlighted the importance of including sex as a variable in scientific investigations. Using case studies from both aquatic and mammalian toxicology, we report that there can be less than ~20-25% consensus in how the transcriptome and proteome of each sex responds to chemicals. Chemicals that have been shown to elicit sex-specific responses in the transcriptome or proteome include pharmaceuticals, anti-fouling agents, anticorrosive agents, and fungicides, among others. Sex-specific responses in the transcriptome and proteome are not isolated to whole animals, as investigations demonstrate that primary cell cultures isolated from each sex responds differently to toxicants. This signifies that sex is important, even in cell lines. Sex has significant implications for predictive toxicology, and both male and female data are required to improve robustness of adverse outcome pathways.

BIOLOGICAL SIGNIFICANCE

Clinical toxicology recognizes that sex is an important variable, as pharmacokinetics (ADME; absorption, distribution, metabolism, and excretion) can differ between females and males. However, few studies in toxicology have explored the implication of sex in relation to the transcriptome and proteome of whole organisms. High-throughput molecular approaches are becoming more frequently applied in toxicity screens (e.g. pre-clinical experiments, fish embryos, cell lines, synthetic tissues) and such data are expected to build upon reporter-based cell assays (e.g. receptor activation, enzyme inhibition) used in toxicant screening programs (i.e. Tox21, ToxCast, REACH). Thus, computational models can more accurately predict the diversity of adverse effects that can occur from chemical exposure within the biological system. Our studies and those synthesized from the literature suggest that the transcriptome and proteome of females and males respond quite differentially to chemicals. This has significant implications for predicting adverse effects in one sex when using molecular data generated in the other sex. While molecular initiating events are not expected to differ dramatically between females and males (i.e. an estrogen binds estrogen receptors in both sexes), it is important to acknowledge that the downstream transcriptomic and proteomic responses can differ based upon the presence/absence of co-regulators and inherent sex-specific variability in regulation of transcriptional and translational machinery. Transcriptomic and proteomic studies also reveal that cell processes affected by chemicals can differ due to sex, and this can undoubtedly lead to sex-specific physiological responses.

From TBT to booster biocides: Levels and impacts of antifouling along coastal areas of Panama

Antifouling biocides in surface sediments and gastropod tissues were assessed for the first time along coastal areas of Panama under the influence of maritime activities, including one of the world's busiest shipping zones: the Panama Canal. Imposex incidence was also evaluated in five muricid species distributed along six coastal areas of Panama. This TBT-related biological alteration was detected in three species, including the first report in Purpura panama. Levels of organotins (TBT, DBT, and MBT) in gastropod tissues and surficial sediments ranged from <5 to 104 ng Sn g^-1 and <1-149 ng Sn g^-1, respectively. In addition, fresh TBT inputs were observed in areas considered as moderate to highly contaminated mainly by inputs from fishing and leisure boats. Regarding booster biocides, TCMTB and dichlofluanid were not detected in any sample, while irgarol 1051, diuron and DCOIT levels ranged from <0.08 to 2.8 ng g^-1, <0.75-14.1 ng g^-1, and <0.38-81.6 ng g^-1, respectively. The highest level of TBT (149 ng Sn g^-1) and irgarol 1051 (2.8 ng g^-1), as well as relevant level of DCOIT (5.7 ng g^-1), were detected in a marina used by recreational boats. Additionally, relatively high diuron values (14.1 ng g^-1) were also detected in the Panama Canal associate to a commercial port. DCOIT concentrations were associated with the presence of antifouling paint particles in sediments obtained nearby shipyard or boat maintenance sites. The highest levels of TBT, irgarol 1051, and diuron exceeded international sediment quality guidelines indicating that toxic effects could be expected in coastal areas of Panama. Thus, the simultaneous impacts produced by new and old generations of antifouling paints highlight a serious environmental issue in Panamanian coastal areas.

SeaNine 211 as antifouling biocide: A coastal pollutant of emerging concern

SeaNine 211, with 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) being the biocidal ingredient, is a widely-used antifouling agent to deter the undesirable biofouling phenomenon. It is commercially promoted as an environmentally acceptable antifoulant mainly due to its claimed rapid degradation in marine environment. However, increasing researches document varying degradative kinetics in different environments, proving that SeaNine 211 is actually not degraded equally fast around the world (half-life between <1day and 13.1days). Large-scale application of SeaNine 211 in antifouling coatings has also caused global contamination of marine environment in various compartments. For example, accumulation of SeaNine 211 is detected as high as 3700ng/L in Spanish seawater and 281ng/g dry weight in Korean sediment. Considering that SeaNine 211 is highly toxic against non-target marine organisms, environmental risk assessment finds that most marine organisms are endangered by SeaNine 211 in worst-case scenario. Its endocrine disrupting and reproductive impairing effects at environmentally worst-case concentrations further constitute a long-term threat to the maintenance of population stability. Therefore, in the light of the varying degradability, environmental pollution and high toxicity, especially the endocrine disruption, SeaNine 211 as an antifouling agent is likely to cause non-negligible damages to the marine ecosystem. There is an urgency to perform a systematic ecological risk assessment of SeaNine 211 to prevent the potential impacts on the health of marine environment. A regular monitoring also becomes necessary to place the usage of antifouling biocides under control.

4,5-Dichloro-2-octyl-4-isothiazolin-3-one (DCOIT) modifies synaptic transmission in hippocampal CA3 neurons of rats

4,5-Dichloro-2-octyl-4-isothiazolin-3-one (DCOIT) is an alternative to organotin antifoulants, such as tributyltin and triphenyltin. Since DCOIT is found in harbors, bays, and coastal areas worldwide, this chemical compound may have some impacts on ecosystems. To determine whether DCOIT possesses neurotoxic activity by modifying synaptic transmission, we examined the effects of DCOIT on synaptic transmission in a 'synaptic bouton' preparation of rat brain. DCOIT at concentrations of 0.03-1 μM increased the amplitudes of evoked synaptic currents mediated by GABA and glutamate, while it reduced the amplitudes of these currents at 3-10 μM. However, the currents elicited by exogenous applications of GABA and glutamate were not affected by DCOIT. DCOIT at 1-10 μM increased the frequency of spontaneous synaptic currents mediated by GABA. It also increased the frequency of glutamate-mediated spontaneous currents at0.3-10 μM. The frequencies of miniature synaptic currents mediated by GABA and glutamate, observed in the presence of tetrodotoxin under external Ca²⁺-free conditions, were increased by 10 μM DCOIT. With the repetitive applications of DCOIT, the frequency of miniature synaptic currents mediated by glutamate was not increased by the second and third applications of DCOIT. Voltage-dependent Ca²⁺ channels were not affected by DCOIT, but DCOIT slowed the inactivation of voltage-dependent Na⁺ channels. These results suggest that DCOIT increases Ca²⁺ release from intracellular Ca²⁺ stores, resulting in the facilitation of both action potential-dependent and spontaneous neurotransmission, possibly leading to neurotoxicity.

Review on Molecular Mechanisms of Antifouling Compounds: An Update since 2012

Better understanding of the mechanisms of antifouling compounds is recognized to be of high value in establishing sensitive biomarkers, allowing the targeted optimization of antifouling compounds and guaranteeing environmental safety. Despite vigorous efforts to find new antifouling compounds, information about the mechanisms of antifouling is still scarce. This review summarizes the progress into understanding the molecular mechanisms underlying antifouling activity since 2012. Non-toxic mechanisms aimed at specific targets, including inhibitors of transmembrane transport, quorum sensing inhibitors, neurotransmission blockers, adhesive production/release inhibitors and enzyme/protein inhibitors, are put forward for natural antifouling products or shelf-stable chemicals. Several molecular targets show good potential for use as biomarkers in future mechanistic screening, such as acetylcholine esterase for neurotransmission, phenoloxidase/tyrosinase for the formation of adhesive plaques, N-acyl homoserine lactone for quorum sensing and intracellular Ca²⁺ levels as second messenger. The studies on overall responses to challenges by antifoulants can be categorized as general targets, including protein expression/metabolic activity regulators, oxidative stress inducers, neurotransmission blockers, surface modifiers, biofilm inhibitors, adhesive production/release inhibitors and toxic killing. Given the current situation and the knowledge gaps regarding the development of alternative antifoulants, a basic workflow is proposed that covers the indispensable steps, including preliminary mechanism- or bioassay-guided screening, evaluation of environmental risks, field antifouling performance, clarification of antifouling mechanisms and the establishment of sensitive biomarkers, which are combined to construct a positive feedback loop.

Identification of Molecular Targets for 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) in Teleosts: New Insight into Mechanism of Toxicity

Environmental pollutants are capable of concomitantly inducing diverse toxic effects. However, it is largely unknown which effects are directly induced and which effects are secondary, thus calling for definitive identification of the initiating molecular event for a pollutant to elucidate the mechanism of toxicity. In the present study, affinity pull-down assays were used to identify target proteins for 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT), a costal pollutant of emerging concern, in various tissues (e.g., brain, liver, plasma, and gonad) from marine medaka (Oryzias melastigma) and zebrafish (Danio rerio). Pull-down results showed that, in male and female brains from medaka and zebrafish, DCOIT had a consistently high affinity for G protein alpha subunits (Gα), suggesting the targeted effects of DCOIT on signaling transduction from G protein-coupled receptors (GPCRs) and an extrapolatable mode of action in teleost brains. Validation using recombinant proteins and molecular docking analysis confirmed that binding of DCOIT to Gα protein competitively inhibited its activation by substrate. Considering the involvement of GPCRs in the regulation of myriad biological processes, including the hypothalamus-pituitary-gonadal-liver axis, binding of DCOIT to upstream Gα proteins in the brain may provide a plausible explanation for the diversity of toxic effects resulting from DCOIT challenge, especially abnormal hormonal production through the mitogen-activated protein kinase pathway. A new mechanism of action based on GPCR signaling is thus hypothesized for endocrine disrupting chemicals and warrants further research to clearly elucidate the link between GPCR signaling and endocrine disruption.

Bioconcentration, metabolism, and biomarker responses in marine medaka (Oryzias melastigma) exposed to sulfamethazine

The antibiotic sulfamethazine (SM₂) is commonly used in agriculture and livestock for its broad-spectrum antibacterial properties. Due to its widespread application, SM₂ is frequently detected in surface water and sediments. The objective of this study was to investigate the bioconcentration, distribution and biomarker responses of SM₂ and its main metabolite, acetylated sulfamethazine (N-SM₂) in medaka (Oryzias melastigma). Two treated groups of medaka were exposed to concentrations of 40μg/L and 200μg/L of SM₂ for 24h to simulate the habitual use of those antibiotics in aquiculture activities. SM₂ and its main metabolite, N-SM₂, were measured in several tissues during the 24h uptake period by UPLC/MS/MS. The bile exhibited the highest SM₂ concentration followed by the liver, gonad, gills, and muscle and the bioconcenration factor (BCF) was 10.69-42.95 in female fish and 2.78-145.36 in male fish. N-SM₂ showed a different distribution pattern from the parent compound, accumulating mainly in the gonad, and its BCF was much higher in the male group. Gender-related differences were also observed in the bioconcentration, transform rate and biomarkers of SM₂. Biomarkers (SOD, CAT) in the liver changed significantly after 2, 12, and 24h of exposure (P<0.05), and presented a double-peak phenomenon. These results indicated that SM₂ can be absorbed and metabolized through multiple routes by fish in a short time. Interactions between biological systems and SM₂ or its metabolites may induce biochemical disturbances in fish.

Chronic Exposure of Marine Medaka (Oryzias melastigma) to 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) Reveals Its Mechanism of Action in Endocrine Disruption via the Hypothalamus-Pituitary-Gonadal-Liver (HPGL) Axis

In this study, marine medaka (Oryzias melastigma) were chronically exposed for 28 days to environmentally realistic concentrations of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) (0, 0.76, 2.45, and 9.86 μg/L), the active ingredient in commercial antifouling agent SeaNine 211. Alterations of the hypothalamus-pituitary-gonadal-liver (HPGL) axis were investigated across diverse levels of biological organization to reveal the underlying mechanisms of its endocrine disruptive effects. Gene transcription analysis showed that DCOIT had positive regulatory effects mainly in male HPGL axis with lesser extent in females. The stimulated steroidogenic activities resulted in increased concentrations of steroid hormones, including estradiol (E2), testosterone (T), and 11-KT-testosterone (11-KT), in the plasma of both sexes, leading to an imbalance in hormone homeostasis and increased E2/T ratio. The relatively estrogenic intracellular environment in both sexes induced the hepatic synthesis and increased the liver and plasma content of vitellogenin (VTG) or choriogenin. Furthermore, parental exposure to DCOIT transgenerationally impaired the viability of offspring, as supported by a decrease in hatching and swimming activity. Overall, the present results elucidated the estrogenic mechanisms along HPGL axis for the endocrine disruptive effects of DCOIT. The reproductive impairments of DCOIT at environmentally realistic concentrations highlights the need for more comprehensive investigations of its potential ecological risks.

Omics of the marine medaka (Oryzias melastigma) and its relevance to marine environmental research

In recent years, the marine medaka (Oryzias melastigma), also known as the Indian medaka or brackish medaka, has been recognized as a model fish species for ecotoxicology and environmental research in the Asian region. O. melastigma has several promising features for research, which include a short generation period (3-4 months), daily spawning, small size (3-4 cm), transparent embryos, sexual dimorphism, and ease of mass culture in the laboratory. There have been extensive transcriptome and genome studies on the marine medaka in the past decade. Such omics data can be useful in understanding the signal transduction pathways of small teleosts in response to environmental stressors. An omics-integrated approach in the study of the marine medaka is important for strengthening its role as a small fish model for marine environmental studies. In this review, we present current omics information about the marine medaka and discuss its potential applications in the study of various molecular pathways that can be targets of marine environmental stressors, such as chemical pollutants. We believe that this review will encourage the use of this small fish as a model species in marine environmental research.

Relationship between metal and polybrominated diphenyl ether (PBDE) body burden and health risks in the barnacle Balanus amphitrite

In the present study, we employed the widespread and gregarious barnacle species Balanus amphitrite in a biomonitoring program to evaluate coastal pollution around three piers (i.e., Tso Wo Hang, Sai Kung and Hebe Haven) in Hong Kong. An integrated approach was used herein, combining both the chemical determination of contaminant concentrations, including metals and polybrominated diphenyl ethers (PBDEs), and a suite of biological responses across the entire barnacle lifecycle (i.e., adult, nauplius, cyprid and juvenile). The analytical results revealed a distinct geographical distribution of metals and PBDEs. Adult physiological processes and larval behaviors varied significantly among the three piers. Furthermore, a correlation analysis demonstrated a specific suite of biological responses towards metal and PBDE exposure, likely resulting from their distinct modes of action. Overall, the results of this study indicated that the combination of chemical and biological tests provided an integrated measure for the comprehensive assessment of marine pollution.

A macroalgal germling bioassay to assess biocide concentrations in marine waters

A bioassay method using the early life stages (germlings) of macroalgae was developed to detect toxicity of anti-fouling paint biocides. A laboratory based bioassay using Ulva intestinalis and Fucus spiralis germlings was performed with 4 common anti-fouling biocides (tributyltin (TBT), Irgarol 1051, Diuron and zinc sulphate), over a range of environmentally relevant concentrations (0.0033-10 μg l(-1)). Comparison between the two species showed that germlings of U. intestinalis were better adapted for in-situ monitoring, as germlings of F. spiralis appeared to be too robust to display sufficient growth differences. The response of U. intestinalis germling growth appeared to reflect environmental biocide concentrations. Overall the developed method showed potential for the assessment of the sub-lethal effects of anti-fouling biocides on the early developmental stages of U. intestinalis.

Hepatic proteomic responses in marine medaka (Oryzias melastigma) chronically exposed to antifouling compound butenolide [5-octylfuran-2(5H)-one] or 4,5-dichloro-2-N-octyl-4-isothiazolin-3-one (DCOIT)

The pollution of antifoulant SeaNine 211, with 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) as active ingredient, in coastal environment raises concerns on its adverse effects, including endocrine disruption and impairment of reproductive function in marine organisms. In the present study, we investigated the hepatic protein expression profiles of both male and female marine medaka (Oryzias melastigma) exposed to low concentrations of DCOIT at 2.55 μg/L (0.009 μM) or butenolide, a promising antifouling agent, at 2.31 μg/L (0.012 μM) for 28 days. The results showed that proteins involved in phase I (CYP450 enzyme) metabolism, phase II (UDPGT and GST) conjugation as well as mobilization of retinoid storage, an effective nonenzymatic antioxidant, were consistently up-regulated, possibly facilitating the accelerated detoxification of butenolide. Increased synthesis of bile acid would promote the immediate excretion of butenolide metabolites. Activation of fatty acid β-oxidation and ATP synthesis were consistent with elevated energy consumption for butenolide degradation and excretion. However, DCOIT did not significantly affect the detoxification system of male medaka, but induced a marked increase of vitellogenin (VTG) by 2.3-fold in the liver of male medaka, suggesting that there is estrogenic activity of DCOIT in endocrine disruption. Overall, this study identified the molecular mechanisms and provided sensitive biomarkers characteristic of butenolide and DCOIT in the liver of marine medaka. The low concentrations of butenolide and DCOIT used in the exposure regimes highlight the needs for systematic evaluation of their environmental risk. In addition, the potent estrogenic activity of DCOIT should be considered in the continued applications of SeaNine 211.

Degradation kinetics of a potent antifouling agent, butenolide, under various environmental conditions

Here, we investigated the degradation kinetics of butenolide, a promising antifouling compound, under various environmental conditions. The active ingredient of the commercial antifoulant SeaNine 211, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT), was used as positive control. The results showed that the degradation rate increased with increasing temperature. Half-lives of butenolide at 4 °C, 25 °C and 40 °C were>64 d, 30.5 d and 3.9 d, respectively. Similar half-lives were recorded for DCOIT: >64 d at 4 °C, 27.9 d at 25 °C and 4.5d at 40 °C. Exposure to sunlight accelerated the degradation of both butenolide and DCOIT. The photolysis half-lives of butenolide and DCOIT were 5.7 d and 6.8 d, respectively, compared with 9.7 d and 14.4 d for the dark control. Biodegradation led to the fastest rate of butenolide removal from natural seawater, with a half-life of 0.5 d, while no obvious degradation was observed for DCOIT after incubation for 4 d. The biodegradative ability of natural seawater for butenolide was attributed mainly to marine bacteria. During the degradation of butenolide and DCOIT, a gradual decrease in antifouling activity was observed, as indicated by the increased settlement percentage of cypris larvae from barnacle Balanus amphitrite. Besides, increased cell growth of marine diatom Skeletonema costatum demonstrated that the toxicity of seawater decreased gradually without generation of more toxic by-products. Overall, rapid degradation of butenolide in natural seawater supported its claim as a promising candidate for commercial antifouling industry.

Proteomic changes in brain tissues of marine medaka (Oryzias melastigma) after chronic exposure to two antifouling compounds: butenolide and 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT)

SeaNine 211 with active ingredient of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) has been used as a "green" antifouling agent worldwide but has raised serious biosafety concerns in coastal environments. DCOIT has the potential to disrupt the neurotransmission in nervous system, but the underlying mechanism has not been clarified. In the present study, we used TMT six-plex labeling coupled with two-dimensional LC-MS/MS analysis to investigate the protein expression profiles in brain tissues of the marine medaka (Oryzias melastigma) after a 28-day exposure to environmentally-realistic concentration of DCOIT at 2.55 μg/L (0.009 μM) or butenolide, one promising antifouling compound, at 2.31 μg/L (0.012 μM). DCOIT and butenolide induced differential expression of 26 and 18 proteins in male brains and of 27 and 23 proteins in female brains, respectively. Distinct mechanisms of toxicity were initiated by DCOIT and butenolide in males, whereas the protein expression profiles were largely similar in females treated by these two compounds. In males, DCOIT exposure mainly led to disruption of mitogen-activated protein kinase (MAPK) signaling pathway, while butenolide affected proteins related to the cytoskeletal disorganization that is considered as a general response to toxicant stress. Furthermore, a sex-dependent protein expression profile was also noted between male and female fish, as evident by the inverse changes in the expressions of common proteins (5 proteins for butenolide- and 2 proteins for DCOIT-exposed fish). Overall, this study provided insight into the molecular mechanisms underlying the toxicity of DCOIT and butenolide. The extremely low concentrations used in this study highlighted the ecological relevance, arguing for thorough assessments of their ecological risks before the commercialization of any new antifouling compound.