The ecotoxicology of marine tributyltin (TBT) hotspots: A review

Tributyltin-induced visceral adiposity is associated with impaired redox balance in white adipose tissue of male rats

Tributyltin (TBT) is an organotin compound that has several adverse health effects, including the development of obesity. Although obesity is strongly associated with adipose redox imbalance, there is a lack of information on whether TBT promotes a pro-oxidative environment in WAT. Thus, adult male Wistar rats were randomly exposed to either vehicle (ethanol 0.4%) or TBT (1000 ng/kg) for 30 days. Body and fat pad masses, visceral fat morphology, lipid peroxidation, protein carbonylation, redox status markers, and catalase activity were evaluated. TBT promoted increased adiposity and visceral fat, with hypertrophic adipocytes, but did not alter body mass and subcutaneous fat. ROS production and lipid peroxidation were elevated in TBT group, as well as catalase protein expression and activity, although protein oxidation and glutathione peroxidase protein expression remained unchanged. In conclusion, this is the first study to demonstrate that subacute TBT administration leads to visceral adipose redox imbalance, with increased oxidative stress. This enlights the understanding of the metabolic toxic outcomes of continuous exposure to TBT in mammals.

Biodiversity and antifouling activity of microbes associated with gorgonian corals Leptogorgia rigida and Menella kanisa from the South China Sea

Recently, coral-associated microorganisms have attracted widespread attention, and most of these studies have focused on stony and soft corals. However, our knowledge of the diversity and bioactivity of microorganisms in gorgonian corals is still limited. In this study, the biodiversity of microbes in two gorgonian corals (Leptogorgia rigida and Menella kanisa) from the South China Sea was investigated by combining traditional culture method with molecular biology technique (bacterial 16S or fungal internal transcribed spacer (ITS) rRNA gene sequences). A total of 216 bacterial and 98 fungal isolates were obtained using 4 different isolation media. These isolates were identified and belonged to 31 bacterial and 12 fungal species, suggesting an unexpectedly diverse microbial community harbored in the South China Sea gorgonian corals L. rigida and M. kanisa. Furthermore, 56% of the tested microbial isolates displayed various antifouling activities against four biofouling organisms (including two microfouling bacteria Micrococcus luteus and Shewanella onedensis, and two macrofouling organisms Bugula neritina and Balanus amphitrite). Among the microbial isolates with antifouling activity, Bacillus firmus SCAU-038 and Streptomyces parvulus SCAU-062 displayed moderate or strong antifouling activity against all tested biofouling organisms. This is the first study on the biodiversity and antifouling activity of microorganisms associated with gorgonians L. rigida and M. kanisa from the South China Sea. These results contribute to the further understanding of microorganisms associated with gorgonian corals and provide potential resources for new natural antifouling agents.

Preparation and antifouling performance of tin-free self-polishing antifouling coatings based on side-chain suspended indole derivative structural resins

Tin-free self-polishing antifouling coatings have the highest market share since organotin self-polishing antifouling coatings have been banned. However, its high dependence on cuprous oxide was found to have caused potential harm to the environment, making it necessary to improve the functionality of the resin. In this paper, a zinc acrylate resin with side chain hanging indole derivative structure was prepared by using N-(1H-5-bromoindole-3-methylene) (BIAM) with good biological activity as functional monomer. The functional resin with good antifouling performance was selected by antibacterial and algae inhibition experiments. The results showed that when the BIAM content was 9 %, the inhibition rates of the resin on E. coli and Prymnesium parvum reached 98 % and 90 %, respectively. Tin-free self-polishing antifouling coatings were prepared using the above resins as film-forming materials. The anti-protein adsorption performance and antifouling performance of the coating were tested by anti-protein adsorption experiment and real sea hanging plate experiment. The results showed that the coating containing indole derivative structure had good anti-protein adsorption performance and antifouling performance, and the higher the BIAM content, the better the anti-protein adsorption performance and marine antifouling performance.

Development of methodology for the visual identification of Tributyltin (TBT) in antifouling paint matrices

Organotin compounds (OTC), mainly tributyltin (TBT), have been used since the 1970s as biocides in the composition of antifouling paints. Due to its physical-chemical characteristics, TBT has high toxicity to the marine environment affecting non-target organisms. The present study aims to develop a method of direct visual identification of TBT in antifouling paints using the cyclopalladate complex, 4- (2-thiazolylazo) resorcinol (TAR-Pd), synthesized in our laboratory. Tests were performed in blank and in the paint matrix with the following OTC: TBT-O; TBT-Cl; TPT-Cl; DBT-Cl (tributyltin oxide, tributyltin chloride, triphenyltin chloride, dibutyltin chloride), in addition to the SnCl4 and SnCl2 compounds (tin IV chloride and tin II chloride), all at a concentration of approximately 20 g/ kg of dry paint). The test was performed by applying paint samples to test bodies and scraping a few tens of milligrams of the dry paint film. The scraped paint samples were submitted to the test, showing a different staining reaction for the TBT-Cl and SnCl4 samples concerning blank and other samples (TBT-O, TPT, DBT-Cl, and SnCl2). Solution tests were performed to characterize reaction products by spectroscopy in the visible band. The method developed has potential for application in real samples, being selective for TBT-Cl and SnCl4 in an acid medium, obtaining a limit of detection, in the range of 1-10 mg/kg dry paint.

Regional disparities and technological approaches in heavy metal remediation: A comprehensive analysis of soil contamination in Asia

Rapid industrialization and urbanization in Asia have significantly increased heavy metal emissions, leading to severe challenges in soil contamination. This review critically examines the diverse sources of heavy metal pollution, regional disparities in contamination levels, and various remediation strategies across Asia. The connections between pollution sources and the resulting heavy metal contamination are explored, with a focus on individual assessments of pollution status in East Asia, South Asia, Southeast Asia, Central Asia, and West Asia. These assessments consider human, geographical, policy, and economic factors. The advantages and limitations of physical, chemical, and biological remediation techniques, as well as their combined applications, are analyzed. Additionally, the importance of regulatory measures, sustainable practices, and public awareness is emphasized for ensuring the long-term health and sustainability of Asian soils. This review aims to contribute to the sustainable development of Asian soils by providing region-specific strategies for the effective remediation of heavy metal contamination.

Responses of zebra and quagga mussels to copper and tribytiltin exposure: Bioconcentration, metabolic and cardiac biomarkers

One of the top ecological priorities is to find sensitive indicators for pollution monitoring. This study focuses on the bioconcentration and responses (condition index, survival, oxygen consumption, heart rates, and oxidative stress and neurotoxic effect biomarkers) of mussels from the Volga River basin, Dreissena polymorpha and Dreissena bugensis, to long-term exposure to toxic chemicals such as tributyltin (TBT, 25 and 100 ng/L) and copper (Cu, 100 and 1000 μg/L). We found that TBT was present in the tissues of zebra and quagga mussels in comparable amounts, whereas the bioconcentration factor of Cu varied depending on its concentration in water. Differences in responses between the two species were revealed. When exposed to high Cu concentrations or a Cu-TBT mixture, quagga mussels had a lower survival rate and a longer heart rate recovery time than zebra mussels. TBT treatment caused neurotoxicity (decreased acetylcholinesterase activity) and oxidative stress (increased levels of thiobarbituric acid reactive substances) in both species. TBT and Cu levels in mussel tissues correlated positively with the condition index, but correlated with the level of acetylcholinesterase in the mussel gills. The principal component analysis revealed three main components: the first consists of linear combinations of 14 variables reflecting TBT water pollution, TBT and Cu levels in mussel tissues, and biochemical indicators; the second includes Cu water concentration, cardiac tolerance, and mussel size; and the third combines weight, metabolic rate, and heart rates. Quagga mussels are less tolerable to contaminants than zebra mussels, so they may be used as a sensitive indicator.

Bioaccumulation of organotin compounds in the marbled electric ray (Torpedo marmorata) in the northern Adriatic Sea

Organotin compounds (OTC), tri-, di- and monobutyl tin, were determined in the tissues of marbled electric ray (Torpedo marmorata) in the Adriatic Sea. Marbled electric ray specimens were provided by local fishermen from three localities in the northern Adriatic: area close to the shipyard in Seča, the natural protected area Strunjan Nature Reserve and along the west Istrian coast. To assess the concentration of OTC in the environment, sediment samples were also analysed. After an adequate extraction of OTC from both matrices, their concentrations were determined by GC-ICP-MS. The results indicate that the accumulation of TBT (tributyltin) and DBT (dibutyltin) in the marbled electric ray is related to the possible pollution sources, since their total concentrations were significantly higher (p < 0.001) in the area close to the shipyard (up to 69 μg Sn kg-1, w.w.) in comparison to the other two areas less affected by direct pollution (up to 7 μg Sn kg-1, w.w.). TBT concentrations ranged from 2 to 42 μg Sn kg-1, w.w., DBT concentrations were in the range from 2 to 22 μg Sn kg-1, w.w., and MBT concentrations were mostly below the detection limit with the highest up to 4 μg Sn kg-1, w.w. The proportion of the three determined congener concentrations in sediment samples indicate a temporally older pollution with these compounds, with prevailing DBT and MBT concentrations up to 30 μg Sn kg-1, w.w., and much lower TBT concentrations up to 7 μg Sn kg-1, w.w. According to our results, marbled electric ray could be considered as an ideal bioindicator of environmental pollution due to its ecological characteristics.

Microcosm study reveals the microbial and environmental effects on tributyltin degradation in an estuarine sediment

Tributyltin (TBT) is one of the most harmful contaminants ever released into the aquatic environment. Despite being banned, it is still present at many locations throughout the world. Its degradation in sediment mainly occurs through microbial biodegradation, a process that remains unclear. This study therefore aimed at better understanding TBT biodegradation in estuarine sediment and the microbial community associated with it. Microcosm experiments were set up, embracing a range of environmental control parameters. Major community shifts were recorded, mainly attributed to the change in oxygen status. The highest percentage of degradation (36,8%) occurred at 4 °C in anaerobic conditions. These results are encouraging for the in-situ bioremediation of TBT contaminated muddy sediment in temperate ports worldwide. However, with TBT able to persist in the coastal environment for decades when undisturbed in anoxic sediment, further research is needed to fully understand the mechanisms that triggered this biodegradation observed in the microcosms.

Long-term tributyltin exposure alters behavior, oocyte maturation, and histomorphology of the ovary due to oxidative stress in adult zebrafish

Tributyltin (TBT), an organotin endocrine-disrupting substance, is recognized as one of the important toxic environmental pollutants. The present study was carried out to investigate the toxic effects of TBT on behavior and the ovary of adult zebrafish with a focus on oxidative stress markers and oocyte maturation. Adult zebrafish were exposed to three different concentrations (125, 250, and 500 ng/L of water) of TBT for 28 days. TBT exposure produced a concentration-dependent negative effect on the body weight and behavior (anxiety-like symptoms) of adult zebrafish. Alterations in the activity of superoxide dismutase (SOD) and catalase (CAT), the total antioxidant capacity of ovarian tissue by the highest exposure level of TBT resulted in lipid peroxidation as indicated by increased malondialdehyde (MDA) level. The numbers of early-vitellogenic oocytes were significantly increased in zebrafish exposed to TBT as low as 125 ng/L. However, the numbers and size of fully-grown (mature) oocytes were significantly reduced in the highest exposure group only. Correlation between the MDA level and pre-vitellogenic oocytes in the 500 ng/L group indicated that lipid peroxidation prevented the maturation of pre-vitellogenic oocytes. TBT exposure produced significant histological changes in the ovary as evidenced by disturbed maturation of oocytes. In conclusion, TBT adversely affected the maturation of oocytes in zebrafish ovary through oxidative stress-mediated mechanisms.

Microplastic-antifouling paint particle contamination alters microbial communities in surrounding marine sediment

Paint used to coat surfaces in aquatic environments often contain biocides to prevent biofouling, and as these coatings degrade, antifouling paint particles (APPs) end up in aquatic, and especially marine, sediments. However, it is currently unclear what further influence APPs in the sediment have on biotic communities or processes. This study investigates how a variety of commercially-available APPs effect the marine microbial community by spiking different laboratory-manufactured APPs to sediment. Following exposure for 30 and 60 days, APPs caused a clear and consistent effect on the bacterial community composition as determined by 16S metabarcoding. This effect was strongest between 0 and 30 days, but continues to a lesser extent between 30 and 60 days. APPs appear to inhibit the highly diverse, but in general rarer, fraction of the community and/or select for specific community members to become more dominant. 71 antifouling-presence and 454 antifouling-absence indicator taxa were identified by indicator analysis. The difference in the level of classification in these two indicator groups was highly significant, with the antifouling-presence indicators having much higher percentage sequence identity to cultured taxa, while the antifouling-absence indicators appear to be made up of undescribed taxa, which may indicate that APPs act as a proxy for general anthropogenic influence or that APP contamination selects for taxa capable of being cultured. Given the clear and consistent effect APPs have on the surrounding sediment microbial community, further research into how APPs affect sediment functional processes and how such effects scale with concentration is recommended to better assess the wider consequences of these pollutants for marine biogeochemical cycles in the future. SYNOPSIS: Microplastic-paint particles are commonly found in marine sediment but little is known about how these, especially antifouling, paint particles affect sediment microbial communities. This study demonstrates that antifouling paint particles fundamentally alter sediment microbial communities.

Maternal exposure to tributyltin alters the breast milk, hormonal profile, and thyroid morphology of dams and induces sex-specific changes in neonate rat offspring

Tributyltin (TBT) is the chemical substance commonly used worldwide to prevent biofouling of vessels. Due to its ability to bioaccumulate and biomagnify, even after being banned, significant concentrations of TBT can be detected in sediment, affecting marine and human life. Although studies have shown that direct exposure to TBT alters physiological parameters in mammals, the relationship between exposure to TBT during pregnancy and lactation, considered critical windows for metabolic programming, has not been fully elucidated. Our hypothesis is that offspring whose mothers were exposed to TBT during critical stages of development may exhibit dysfunctions in endocrine-metabolic parameters. We used pregnant Wistar rats that were divided into groups and received the following treatments from gestational day 7 until the end of lactation by intragastric gavage: vehicle (ethanol 0.01%; Control), low TBT dose (100 ng/kg of body weight (bw)/day; TBT100ng) and high TBT dose (1000 ng/kg bw/day; TBT1000ng). Dams and offspring at birth and weaning (21 days old) were studied. Maternal exposure to TBT promoted dose-dependent changes in dams. The findings for adiposity, milk composition and lipid profile were more pronounced in TBT100 ng dam; however, thyroid morphology was altered in TBT1000 ng dam. Female offspring were differentially affected by the dose of exposure. At birth, females in the TBT100ng group had low body weight, lower naso-anal length (NAL), and higher plasma T4, and at weaning, females in the TBT100ng group had lower insulin and leptin levels. Females in the TBT1000ng group had lower NAL at birth and lower leptinemia and weight of white adipose tissue at weaning. Male offspring from TBT groups showed high T3 at birth, without biometric alterations at birth or weaning. Despite these findings, both sexes exhibited dose-dependent morphological changes in the thyroid gland. Thus, maternal exposure to TBT constitutes an important route of contamination for both dams and offspring.

Endocrine disruption in crustaceans: New findings and perspectives

A significant advance has been made, especially during the last two decades, in the knowledge of the effects on crustacean species of pollutants proven to be endocrine disruptors in vertebrates. Such effects have been also interpreted in the light of recent studies on crustacean endocrinology. Year after year, the increased number of reports refer to the effects of endocrine disruptors on several processes hormonally controlled. This review is aimed at summarizing and discussing the effects of several kinds of endocrine disruptors on the hormonal control of reproduction (including gonadal growth, sexual differentiation, and offspring development), molting, and intermediate metabolism of crustaceans. A final discussion about the state of the art, as well as the perspective of this toxicological research line is given.

Update on the status of the contamination by organotin compounds in sediment of Nuevo Gulf, Argentina. Insights from field and experimental studies

Organotin compounds are persistent pollutants and are considered chemicals of high environmental concern. In the present study, the distribution and degradation of tributyltin were evaluated in field sediments and through an ex situ experiment. For this, sediment samples from two locations were analysed: Luis Piedrabuena Harbour, with higher maritime traffic, and Cerro Avanzado, which receives less impact from anthropogenic activities. The results indicated that pollution levels at Luis Piedrabuena Harbour have decreased compared with studies performed 9 years ago for the same area. On the contrary, traces of organotin compounds have been found for the first time at Cerro Avanzado. Moreover, the butyltin degradation index indicated that organotin compounds undergo an advanced degradation process in the collected samples at both sites. Ex situ experiments revealed a limited capacity of sediments to retain tributyltin, and suggested an active role of bioturbation activity in the degradation of these compounds. In addition, visualisation using chemometric techniques (principal components analysis) allowed a simpler analysis of two sediment characteristics: the degree of contamination and the degradation levels of organotin compounds.

First record of microplastic in the Brazilian sea hare Aplysia brasiliana Rang, 1828 (Mollusca: Aplysiidae)

The presence of plastic debris in the marine environment has reached massive levels in the past decades. In marine environments, microplastics can exist for hundreds of years and the presence of microplastics in this environment has been reported since 1970 and since then has been considered ubiquitous. Mollusks are being used as microplastic pollution indicators, especially in coastal areas and bivalves are more often used in microplastic-monitoring studies. On the other hand, gastropods are poorly used as indicators for microplastic pollution, even though they are the most diverse group of mollusks. The sea hares of the genus Aplysia are herbivorous gastropods, important model organisms commonly used in neuroscience studies, isolating the compounds in their defensive ink. Until today, there is no previous record of the presence of MPs in Aplysia gastropods. Therefore, this study aims to investigate the presence of microplastics in tissues of A. brasiliana found in southeastern Brazil. We collected seven individuals of A. brasiliana from a beach in southeastern Brazil, dissected them to isolate the digestive tract and the gills, and digested the tissues with a solution of 10 % NaOH. In the end, 1021 microplastic particles were found, 940 in the digestive tissue, and 81 in the gills. These results represent the first record of the presence of microplastics in the Brazilian sea hare A. brasiliana.

Effects of Tributyltin-Contaminated Aquatic Environments and Remediated Water on Early Development of Sea Urchin (Hemisentrotus pulcherrimus)

In this study, gametotoxicity and embryotoxicity experiments were performed using Hemicentrotus pulcherrimus to investigate the toxic effects of tributyltin (TBT). The effects of TBT on fertilization and embryogenesis were assessed at various concentrations (0, 0.02, 0.05, 0.09, 0.16, 0.43, 0.73, 4.68, and 9.22 ppb). The fertilization rates decreased in a concentration-dependent manner, with significant reduction following treatment with TBT at 0.05 ppb. Embryos exhibited developmental impairment after TBT exposure at each tested concentration. The frequency of developmental inhibition delay that treatment with TBT delayed embryonic development in a dose-dependent manner, with 100% of embryos exhibiting developmental impairment at 4.68 ppb. During developmental recovery tests, embryos cultured in fresh media without TBT showed advanced embryonic development. Although the observed normal development after transferring the developmentally delayed embryos to fresh media without TBT offers prospects for the restoration of contaminated environments, embryonic development remained incomplete. These results suggest that TBT adversely affects the early embryonic development of H. pulcherrimus.

Ciona spp. and ascidians as bioindicator organisms for evaluating effects of endocrine disrupting chemicals: A discussion paper

In context of testing, screening and monitoring of endocrine-disrupting (ED) type of environmental pollutants, tunicates could possibly represent a particularly interesting group of bioindicator organisms. These primitive chordates are already important model organisms within developmental and genomics research due to their central position in evolution and close relationship to vertebrates. The solitary ascidians, such as the genus Ciona spp. (vase tunicates), could possibly be extra feasible as ED bioindicators. They have a free-swimming, tadpole-like larval stage that develops extremely quickly (<20 h under favorable conditions), has a short life cycle (typically 2-3 months), are relatively easy to maintain in laboratory culture, have fully sequenced genomes, and transgenic embryos with 3D course data of the embryo ontogeny are available. In this article, we discuss possible roles of Ciona spp. (and other solitary ascidians) as ecotoxicological bioindicator organisms in general but perhaps especially for effect studies of contaminants with presumed endocrine disrupting modes of action.

Biobanks, offspring fitness and the influence of developmental plasticity in conservation biology

Mitigation of the widely known threats to the world's biodiversity is difficult, despite the strategies and actions proposed by international agreements such as the United Nations Framework Convention on Climate Change (UNFCCC) and the Convention on Biological Diversity (CBD). Nevertheless, many scientists devote their time and effort to finding and implementing various solutions to the problem. One potential way forward that is gaining popularity involves the establishment of biobank programs aimed at preserving and storing germplasm from threatened species, and then using it to support the future viability and health of threatened populations. This involves developing and using assisted reproductive technologies to achieve their goals. Despite considerable advances in the effectiveness of reproductive technologies, differences between the reproductive behavior and physiology of widely differing taxonomic groups mean that this approach cannot be applied with equal success to many species. Moreover, evidence that epigenetic influences and developmental plasticity, whereby it is now understood that embryonic development, and subsequent health in later life, can be affected by peri-conceptional environmental conditions, is raising the possibility that cryopreservation methods themselves may have to be reviewed and revised when planning the biobanks. Here, I describe the benefits and problems associated with germplasm biobanking across various species, but also offer some realistic assessments of current progress and applications.

Evaluation of lipophosphoramidates-based amphiphilic compounds on the formation of biofilms of marine bacteria

The bacteriostatic and/or bactericidal properties of few phosphoramide-based amphiphilic compounds on human pathogenic bacteria were previously reported. In this study, the potential of two cationic (BSV36 and KLN47) and two zwitterionic (3 and 4) amphiphiles as inhibitors of marine bacterial growth and biofilm formation were investigated. Results showed that the four compounds have little impact on the growth of a panel of 18 selected marine bacteria at a concentration of 200 µM, and up to 700 µM for some bacterial strains. Interestingly, cationic lipid BSV36 and zwitterionic lipids 3 and 4 effectively disrupt biofilm formation of Paracoccus sp. 4M6 and Vibrio sp. D02 at 200 µM and to a lesser extent of seven other bacterial strains tested. Moreover, ecotoxicological assays on four species of microalgae highlighted that compounds 3 and 4 have little impact on microalgae growth with EC50 values of 51 µM for the more sensitive species and up to 200 µM for most of the others. Amphiphilic compounds, especially zwitterionic amphiphiles 3 and 4 seem to be promising candidates against biofilm formation by marine bacteria.

Tributyltin chloride (TBTCL) induces cell injury via dysregulation of endoplasmic reticulum stress and autophagy in Leydig cells

Tributyltin chloride (TBTCL), a commonly used antiseptic substance, is commonly found in the environment. Human exposure to TBTCL through the consumption of contaminated seafood, fish, or drinking water has aroused concern. It is well-characterized that TBTCL has multiple detrimental effects on the male reproductive system. However, the potential cellular mechanisms are not fully elucidated. Here, we characterized molecular mechanisms of TBTCL-induced cell injury in Leydig cells, a critical supporter for spermatogenesis. We showed that TBTCL induces apoptosis and cell cycle arrest in TM3 mouse Leydig cells. RNA sequencing analyses revealed that endoplasmic reticulum (ER) stress and autophagy were potentially involved in TBTCL-induced cytotoxicity. We further showed that TBTCL causes ER stress and inhibited autophagy flux. Notably, the inhibition of ER stress attenuates not only TBTCL-induces autophagy flux inhibition but also apoptosis and cell cycle arrest. Meanwhile, the activation of autophagy alleviates, and inhibition of autophagy exaggerates TBTCL-induced apoptosis and cell cycle arrest flux. These results suggest that TBTCL-induced ER stress and autophagy flux inhibition contributed to apoptosis and cell cycle arrest in Leydig cells, providing novel understanding into the mechanisms of TBTCL-induced testis toxicity.

Biochemical mechanisms of tributyltin chloride-induced cell toxicity in Sertoli cells

Tributyltin chloride (TBTCL) is a widely used fungicide and heat stabilizer in compositions of PVC. TBTCL has been detected in human bodies and potentially causes harmful effects on humans' thyroid, cardiovascular and other organs. As one of the first examples of endocrine disruptors, the toxicity effects of TBTCL on the male reproduction system have aroused concerns. However, the potential cellular mechanisms are not fully explored. In the current study, by using Sertoli cells, a critical regulator of spermatogenesis as a cell model, we showed that with 200 nM exposure for 24 h, TBTCL causes apoptosis and cell cycle arrest. RNA sequencing analyses suggested that TBTCL probably activates endoplasmic reticulum (ER) stress, and disrupts autophagy. Biochemical analysis showed that TBTCL indeed induces ER stress and the dysregulation of autophagy. Interestingly, activation of ER stress and inhibition of autophagy is responsible for TBTCL-induced apoptosis and cell cycle arrest. Our results thus uncovered a novel insight into the cellular mechanisms for TBTCL-induced toxicology in Sertoli cells.

Molecular and biochemical responses to tributyltin (TBT) exposure in the American oyster: Triggers of stress-induced oxidative DNA damage and prooxidant-antioxidant imbalance in tissues by TBT

Environmental pollution increases due to anthropogenic activities. Toxic chemicals in the environment affect the health of aquatic organisms. Tributyltin (TBT) is a toxic chemical widely used as an antifouling paint on boats, hulls, and ships. The toxic effect of TBT is well documented in aquatic organisms; however, little is known about the effects of TBT on DNA lesions in shellfish. The American oyster (Crassostrea virginica, an edible and commercially important species) is an ideal marine mollusk to examine the effects of TBT exposure on DNA lesions and oxidative/nitrative stress. In this study, we investigated the effects of TBT on 8'-hydroxy-2'-deoxyguanosine (8-OHdG, a biomarker of pro-mutagenic DNA lesion), double-stranded DNA (dsDNA), dinitrophenyl protein (DNP, a biomarker on reactive oxygen species, ROS), 3-nitrotyrosine protein (NTP, a biomarker of reactive nitrogen species, RNS), catalase (CAT, an antioxidant), and acetylcholinesterase (AChE, a cholinergic enzyme) expressions in the gills and digestive glands of oysters. We also analyzed extrapallial (EF) fluid conditions. Immunohistochemical and qRT-PCR results showed that TBT exposure significantly increased 8-OHdG, dsDNA, DNP, NTP, and CAT mRNA and/or protein expressions in the gills and digestive glands. However, AChE mRNA and protein expressions, and EP fluid pH and protein concentrations were decreased in TBT-exposed oysters. Taken together, these results suggest that antifouling biocide-induced production of ROS/RNS results in DNA damage, which may lead to decreased cellular functions in oysters. To the best of our knowledge, the present study provides the first molecular/biochemical evidence that TBT exposure results in oxidative/nitrative stress and DNA lesions in oysters.

Organotin Antifouling Compounds and Sex-Steroid Nuclear Receptor Perturbation: Some Structural Insights

Organotin compounds (OTCs) are a commercially important group of organometallic compounds of tin used globally as polyvinyl chloride stabilizers and marine antifouling biocides. Worldwide use of OTCs has resulted in their ubiquitous presence in ecosystems across all the continents. OTCs have metabolic and endocrine disrupting effects in marine and terrestrial organisms. Thus, harmful OTCs (tributyltin) have been banned by the International Convention on the Control of Harmful Antifouling Systems since 2008. However, continued manufacturing by non-member countries poses a substantial risk for animal and human health. In this study, structural binding of common commercial OTCs, tributyltin (TBT), dibutyltin (DBT), monobutyltin (MBT), triphenyltin (TPT), diphenyltin (DPT), monophenyltin (MPT), and azocyclotin (ACT) against sex-steroid nuclear receptors, androgen receptor (AR), and estrogen receptors (ERα, ERβ) was performed using molecular docking and MD simulation. TBT, DBT, DPT, and MPT bound deep within the binding sites of AR, ERα, and Erβ, showing good dock score, binding energy and dissociation constants that were comparable to bound native ligands, testosterone and estradiol. The stability of docking complex was shown by MD simulation of organotin/receptor complex with RMSD, RMSF, Rg, and SASA plots showing stable interaction, low deviation, and compactness of the complex. A high commonality (50-100%) of interacting residues of ERα and ERβ for the docked ligands and bound native ligand (estradiol) indicated that the organotin compounds bound in the same binding site of the receptor as the native ligand. The results suggested that organotins may interfere with the natural steroid/receptor binding and perturb steroid signaling.

Tributyltin exposure disrupted the locomotor activity rhythms in adult zebrafish (Danio rerio) and the mechanism involved

The fish circadian rhythm system might be an emerging target of tributyltin (TBT), however, the mechanism by which TBT interferes with the circadian rhythm is poorly understood. Therefore, in the present study, zebrafish were used to assess the effects of TBT at environmental concentrations (1 and 10 ng/L) on locomotor activity rhythm. Furthermore, we focused on the visual system to explore the potential mechanism involved. After 90 d of exposure, TBT disturbed the locomotor activity rhythms in zebrafish, which manifested as: (1) low activities and lethargy during the arousing period; (2) inability to fall asleep quickly and peacefully during the period of latency to sleep; and (3) no regular "waves" of locomotor activities during the active period. After TBT exposure, the histological structure of the eyes significantly changed, the boundary between layers became blurred, and the melanin concentrations significantly decreased. Using KEGG and GSEA pathway analyses, the differentially expressed genes in the eyes screened by transcriptomics were significantly enriched in the tyrosine metabolism pathway and retinol metabolism pathway. Furthermore, a decrease in melanin and disruption of retinoic acid were found after TBT exposure, which would affect the reception of phototransduction, and then interfere with the circadian rhythm in fish. The disruption of the circadian rhythm of fish by aquatic pollutants would decrease their ecological adaptability, which should be considered in future research.