Urgent caution to trace organometal pollution: Occurrence, distribution and sources of methyltins, butyltins and phenyltins in sediments from South Hangzhou Bay, China

Abnormal eyes and spine development in zebrafish (Danio rerio) embryos and larvae induced by triphenyltin

Triphenyltin (TPT) is widely used in crop pest control and ship antifouling coatings, which leads to its entry into aquatic environment and poses a threat to aquatic organisms. However, the effects of TPT on the early life stages of wild fish in natural water environments remains unclear. The aim of this study was to assess the toxic effects of TPT on the early life stages of fish under two different environments: field investigation and laboratory experiment. The occurrence of deformities in wild fish embryos and larvae in the Three Gorges Reservoir (TGR) and the developmental toxicity of TPT at different concentrations (0, 0.15, 1.5 and 15 μg Sn/L) to zebrafish embryos and larvae were observed. The results showed that TPT content was higher in wild larvae, reaching 27.21 ng Sn/g w, and the malformation of wild fish larvae mainly occurred in the eyes and spine under natural water environment. Controlled experiment exposure of zebrafish larvae to TPT also resulted in eye and spinal deformities. Gene expression analysis showed that compared with the control group, the expression levels of genes related to eye development (sox2, otx2, stra6 and rx1) and spine development (sox9a and bmp2b) were significantly up-regulated in the 15 μg Sn/L exposure group, which may be the main cause of eye and spine deformity in the early development stage of fish. In addition, the molecular docking results further elucidate that the strong hydrophobic and electrostatic interactions between TPT and protein residues are the main mechanism of TPT induced abnormal gene expression. Based on these results, it can be inferred that TPT is one of the teratogenic factors of abnormal eye and spine development in the early life stage of fish in the TGR. These findings have important implications for understanding the toxicity of TPT on fish.

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.

Factors affecting the accumulation of organotins by wild fish: A case study in the Three Gorges Reservoir, China

Organotin compounds (OTs) accumulate in fish easily, however, research on their influencing factors is still limited. This study collected 25 species of fish with different diets, habitats, and age from the Three Gorges Reservoir (TGR), the largest deep-water river channel-type reservoir in China, and analyzed the accumulation characteristics of OTs in these fish. The results showed that tributyltin (TBT) and triphenyltin (TPhT) were the dominant OTs in fish from the TGR. The correlation between OTs concentration and age, body length, and body weight varied with fish species. The concentrations of TBT and TPhT in carnivorous fish (mean, 25.78 and 11.69 ng Sn/g dw, respectively) were higher than those in other diet fish (P<0.01), but there was no significant difference in fish at different habitat water layers (P>0.05). In addition, the degradation rates of TBT and TPhT in different fish species were all below 50%. In summary, the accumulation of TBT and TPhT in fish is mainly influenced by diet, and both TBT and TPhT were difficult to degrade in fish. These results reveal the pollution characteristics of OTs in fish from the TGR, and can improve our understanding of the factors influencing TBT and TPhT accumulation in freshwater fish.

Occurrence of halogenated methanesulfonic acids in water and sediment from the Hangzhou Bay, China

Halogenated methanesulfonic acids (HMSAs) are an important new class of organic compounds as they were universal in the water cycle and drinking water sources. However, no study has investigated the presence of HMSAs in surface water and sediment from China. The present study reports the occurrence and spatiotemporal distribution of seven HMSAs in water and sediment samples from Hangzhou Bay, China. Trifluoromethanesulfonic acid (TFMSA) was the main contributor to the concentrations of HMSAs in water and sediment samples from spring, summer, autumn and winter which were 30.8-541 ng/L, n. d.-86.6 ng/L, 4.22-70.9 ng/L and 8.86-192 ng/L, separately, while in sediment samples were n. d.-11.1 ng/g, n. d.-12.9 ng/g, n. d.-22.5 ng/g, n. d.-4.60 ng/g, respectively. The levels of HMSAs in water from winter and spring were higher than those in summer and autumn, and the concentrations of the target HMSAs in water presents a seasonal pattern affected by the temperature, the precipitation and river flow variations. Nevertheless, the levels of HMSAs in sediment were highest in the area near the industrial area and the confluences of rivers. Correlation analysis revealed that the concentrations of TFMSA were significantly positively correlated with total organic carbon (TOC) in water samples. Although TFMSA is regarded as low toxic based on the EC₅₀ value of acute toxicity, the potential risks to aquatic ecology should be paid more attention due to its high concentrations in the aquatic system and the environmental persistency.

Toxicity of antifouling biocides on planktonic and benthic neotropical species

Organotin-based (OTs: TBT and TPT) antifouling paints have been banned worldwide, but recent inputs have been detected in tropical coastal areas. However, there is a lack of studies evaluating the toxicity of both legacy and their substitute antifouling booster biocides (e.g., Irgarol and diuron) on neotropical species. Therefore, the acute toxicity of four antifouling biocides (TBT, TPT, Irgarol, and diuron) was investigated using the marine planktonic organisms Acartia tonsa and Mysidopsis juniae, the estuarine tanaid Monokalliapseudes schubarti (water exposure), and the burrowing amphipod Tiburonella viscana (spiked sediment exposure). Results confirmed the high toxicity of the OTs, especially to planktonic species, being about two orders of magnitude higher than Irgarol and diuron. Toxic effects of antifouling compounds were observed at levels currently found in tropical coastal zones, representing a threat to planktonic and benthic invertebrates. Furthermore, deterministic PNEC_{marine sediment} values suggest that environmental hazards in tropical regions may be higher due to the higher sensitivity of tropical organisms. Since regulations on antifouling biocides are still restricted to a few countries, more ecotoxicological studies are needed to derivate environmental quality standards based on realistic scenarios. The present study brings essential contributions regarding the ecological risks of these substances in tropical and subtropical zones.

Organotins in a food web from the Three Gorges Reservoir, China: Trophic enrichment and potential health risk

Triphenyltin (TPhT) and tributyltin (TBT) remain widely present in various aquatic environments despite restrictions on their use in many countries for many years. The biomagnification of these compounds in the aquatic food web remains controversial. This study reports the bioaccumulation of TPhT and TBT in aquatic animals in the Three Gorges Reservoir (TGR), a deep-water river channel-type reservoir and the largest reservoir in China. We measured TPhT, TBT and their metabolites in 2 invertebrates, 27 fish and the aquatic environment. The logarithmic bioaccumulation factors of TPhT and TBT were 4.37 and 3.77, respectively, indicating that TPhT and TBT were enriched in organisms of the TGR. Both TPhT and TBT concentrations were significantly and positively correlated with trophic level, with trophic magnification factors of 3.71 and 3.63, respectively, indicating that TPhT and TBT exhibited similar trophic enrichment in the freshwater food web of the TGR. The results of health risk assessment showed that although all hazard index (HI) values were <1, more attention should be paid to the health risk to children associated with consumption of aquatic products (HI = 0.67). This study provides powerful evidence of trophic enrichment of TPhT and TBT in a freshwater food web in a deep-water river channel-type reservoir and provides valuable data regarding organotins in aquatic animals in the TGR.

Pulsed distribution of organotins in the turbidity maximum zone of the Yangtze Estuary throughout a tidal cycle

This study investigated the concentration fluctuation of organotin compounds in the Turbidity Maximum Zone (TMZ) of the Yangtze Estuary within a tidal cycle. Organotin concentrations varied greatly during the tidal cycle with dissolved organotins ranged from 39 to 682 ng Sn·L^-1 and 40-1588 ng Sn·L^-1, and particulate organotins ranged from 59 to 467 ng Sn·g^-1 dw and 21-429 ng Sn·g^-1 dw in TMZ water close to Hengsha Island and Jiuduansha Island, respectively. Meanwhile, the maximum levels of organotins appeared at each period of tidal transition, suggesting the tidal-driven pulsed exposure of organotins was prevalent in the estuaries. Besides, the organic carbon-normalized partition coefficients (K_oc) of tri-organotins between suspended particulate matter (SPM) and aqueous phase were correlated with the phase distribution of natural organic matter (NOM). The dissolved tri-organotins were also associated with the properties of dissolved organic carbon (DOC) including aromaticity, hydrophobicity, and chromophoricity. Hence, pulsed exposure on organotins in the TMZ are highly dictated by the dynamic environmental conditions (i.e., SPM and NOM) with the tidal currents, which could further provide information to assess organotin ecological risks accurately in estuaries.

Mexican paradise under threat: The impact of antifouling biocides along the Yucatán Peninsula

Levels of booster biocides (Irgarol, diuron, chlorothalonil, dichlofluanid and DCOIT), organotins (TBT, DBT, MBT, TPhT, DPhT and MPhT) and antifouling paint particles (APPs) were assessed in sediments of sites under the influence of maritime activities along the coastal zone of the Yucatán Peninsula, Mexico. Imposex incidence and organotin levels were also evaluated in seven caenogastropod species. The incidence of imposex was detected in five species from sites nearby fishing harbors and marinas, including the first reports to Gemophos tinctus and Melongena bispinosa. Butyltins levels were higher than phenyltins in gastropod tissues, sediments, and APPs. Regarding booster biocides, chlorothalonil was the most frequently detected compound and DCOIT was the most abundant biocide in sediments. DCOIT levels were registered in APPs from fishing harbors and marina areas. In addition, the highest levels of TBT, Irgarol, diuron and DCOIT exceeded the threshold limits set by international sediment quality guidelines, indicating that toxic effects could be expected in some of the studied areas, thus being a potential threat to marine life. Based on such outputs, Mexico urgently needs to adopt restrictive actions aiming at conserving the rich biological heritage of the Yucatán Peninsula.

Butyltin Contamination in Fishing Port Sediments after the Ban of Tributyltin Antifouling Paint: A Case of Qianzhen Fishing Port in Taiwan

This study investigated the concentrations of monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) in the sediments of the Qianzhen Fishing Port (Taiwan) in 2020. Further, the pollution status, composition, and potential ecotoxicity of BTs were evaluated. This case study provides a reference for the benefits of the ban of TBT-based antifouling paint to date. Results showed that the total butyltin (ΣBTs, sum of TBT, DBT, and MBT) concentrations measured in the sediments of the Qianzhen Fishing Port ranged between 14.2–807 ngSn·g−1 dw, with an average of 356 ± 305 ngSn·g−1 dw. TBT was the most dominant species, with an average concentration of 303 ± 287 ngSn·g−1 dw. This average TBT concentration is about 4.3 times lower than in 2003, showing the progress of gradual degradation of TBT in the sediments. Still, the degradation is rather slow, with a half-life of about 8.09 years. An analysis of the effects of TBT on organisms in the sediments of the Qianzhen Fishing Port was carried out according to the TBT toxicity guidelines of the US Environmental Protection Agency and the assessment class criterion for imposex (ACCI) of the Oslo and Paris Commission (OSPAR). The results showed that TBT levels in 80% of the sediments may pose negative effects on sensitive gastropods, and half of the sediments may even have an impact on gastropod reproduction. These show that marine life is still affected and threatened by TBT compounds, despite the decline of TBT concentrations since the ban of TBT-containing antifouling paints on ships in 2008. Therefore, it is necessary to continue paying attention to the changes of TBT concentrations and their potential ecological risks in the marine environment, and to formulate TBT management plans and strategies to mitigate their impacts in marine ecosystems.

A mass spectrometry-based approach gives new insight into organotin-protein interactions

In this study, the combination of speciation analysis and native mass spectrometry is presented as a powerful tool to gain new insight into the diverse interactions of environmentally relevant organotin compounds (OTCs) with proteins. Analytical standards of model proteins, such as β-lactoglobulin A (LGA), were thereby incubated with different phenyl- and butyltins. For adduct identification and characterization, the incubated samples were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) and electrospray ionization-mass spectrometry (ESI-MS) in combination with size exclusion chromatography (SEC). It allowed for a mild separation, which was most crucial to preserve the acid-labile organotin-protein adducts during their analyses. The binding of triorganotin compounds, such as triphenyltin, was shown to be sulfhydryl-directed by using cysteine-specific protein labeling. However, the sole availability of reduced cysteine residues in proteins did not automatically enable adduct formation. This observation complements previous studies and indicates the necessity of a highly specific binding pocket, which was identified for the model protein LGA via enzymatic digestion experiments. In contrast to triorganotins, their natural di- and mono-substituted degradation products, such as dibutyltin, revealed to be less specific regarding their binding to several proteins. Further, it also did not depend on reduced cysteine residues within the protein. In this context, they can probably act as linker molecules, interconnecting proteins, and leading to dimers and probably to higher oligomers. Furthermore, dibutyltin was observed to induce hydrolysis of the protein's peptide backbone at a specific site. Concerning unknown long-term toxic effects, our studies emphasize the importance of future studies on di- and mono-substituted OTCs.

Effective methods for the determination of triphenyltin residues in surface water and soil samples by high-performance liquid chromatography with tandem mass spectrometry

Monitoring of triphenyltin (TPhT) in the environment, particularly to control its misuse in agriculture, is of great importance because of its high toxicity. In this work, methods for determination of TPhT residues in surface water and soil samples by liquid chromatography with tandem mass spectrometry (LC-MS/MS) were developed and validated. Different sample volumes and pH and elution solvent types and volumes were evaluated for solid phase extraction (SPE) of TPhT in surface water samples. The optimized conditions were 500 mg sorbent Strata C18-E, 100 mL of the sample, pH adjusted to 9.0 and 1 mL of methanol containing acetic acid as the eluent. For a 10 g soil sample, the extraction was established using a modified QuEChERS method with 10 mL of acidified acetonitrile followed by a clean-up step by dispersive solid phase extraction (dSPE) with C18. A full factorial 23 design of experiments was applied to optimize the sample preparation method for soil samples. Practical method limits of quantification were 0.1 μg L-1 and 10 μg kg-1 for surface water and soil samples, respectively. Satisfactory accuracy, with recoveries from 86 to 107% for surface water and 72 to 87% for soil samples, as well as good precision, with an overall relative standard deviation (RSD) from 3 to 8% was observed. The validated methods were applied to real samples and some residues of TPhT were found, especially in soil samples (30 to 190 mg kg-1), indicating the suitability for routine analysis.

Integrated thyroid endocrine disrupting effect on zebrafish (Danio rario) larvae via simultaneously repressing type II iodothyronine deiodinase and activating thyroid receptor-mediated signaling following waterborne exposure to trace azocyclotin

As a widely used organotin acaricide nowadays, azocyclotin (ACT) could induce thyroidal endocrine disruption in fishes and amphibians, but its dominant disrupting mode remains unknown. In this study, zebrafish were firstly exposed to ACT (0.18-0.36 ng/mL) from 2 hpf (hours post fertilization) to 30 dpf (days post fertilization), and a series of developmental toxicological endpoints and thyroid hormones were measured. Result showed that no developmental toxicity to zebrafish was found in 0.18 and 0.24 ng/mL groups except decreased body weight (30 dpf, 0.24 ng/mL). However, exposed to 0.36 ng/mL ACT led to reductions in heartbeat (48 hpf), hatching rate (72 hpf) and bodyweight (30 dpf). General tendencies of decreases in free T3 but increases in free T4 and reductions in ratio of free T3/T4 were also found, inferring that type II deiodinase (Dio2) was repressed. This inference was confirmed by Western analysis that Dio2 expression reduced by 42.7% after 0.36 ng/mL ACT treatment. Moreover, RNA-Seq analysis implied that exposed to 0.36 ng/mL ACT altered the genome-wide gene expression profiles of zebrafish. Totally 5660 genes (involving 3154 down-regulated and 2596 up-regulated genes) were differentially expressed, and 13 deferentially expressed genes including down-regulated dio2 were significantly enriched in thyroid hormone signaling pathway. Subsequently, an in vitro thyroid receptor-reporter gene assay using GH3 cells was performed to further explore the potential disrupting mechanism. Result showed that luciferase activity slightly increased after exposure to ACT alone or ACT combined with low level T3, but was suppressed when combined with high level T3. It indicted there probably existed a competitive relationship in some extent between ACT and T3 in vivo. Overall, the present study provided preliminary evidences that long-term exposure to trace ACT repressed Dio2 expression, declined T3 and then activated thyroid receptor-mediated signaling, thereby leading to integrated thyroid endocrine disruption in zebrafish larvae.

Combined Effect of Tides and Wind on Water Exchange in a Semi-Enclosed Shallow Sea

The Bohai Sea is a semi-enclosed shallow sea in China, where the tides and wind are the dominant factors contributing to the water exchange with the Yellow Sea. However, existing studies on this water exchange primarily consider only the effect of tidal action, neglecting the contribution of wind. In this study, numerical models were used to simulate the hydrodynamic processes and tracer transport, with the consideration of both tides and wind. Based on the models, the two time scales, age and half-life, are applied to study the water exchange in the Bohai Sea quantitatively. The results show that the age and half-life decrease significantly when wind is included in the simulation, revealing that wind is an important contributor to the water exchange in such a semi-enclosed shallow sea. Under the combined forcing of tides and wind, the water transport in the Bohai Sea becomes clockwise, in contrast with the counterclockwise transport driven by the tides only. The seasonal-varying wind leads to a fluctuation of water exchange in an annual cycle, with the stronger water exchange in the northern (Liaodong Bay) and the western (Bohai Bay) regions of the Bohai Sea in winter and in the southern part (Laizhou Bay) in summer.