Organophosphate esters (OPEs) in corals of the South China Sea: Occurrence, distribution, and bioaccumulation.

Organophosphate esters (OPEs) have garnered significant attention in recent years. In view of the enormous ecosystem services value and severe degradation of coral reefs in the South China Sea, this study investigated the occurrence, distribution, and bioaccumulation of 11 OPEs in five coral regions: Daya Bay (DY), Weizhou Island (WZ), Sanya Luhuitou (LHT), Xisha (XS) Islands, and Nansha (NS) Islands. Although OPEs were detected at a high rate, their concentration in South China Sea seawater (1.56 ± 0.89 ng L-1) remained relatively low compared to global levels. All OPEs were identified in coral tissues, with Luhuitou (575 ± 242 ng g-1 dw) showing the highest pollution levels, attributed to intense human activities. Coral mucus, acting as a defense against environmental stresses, accumulated higher ∑11OPEs (414 ± 461 ng g-1 dw) than coral tissues (412 ± 197 ng g-1 dw) (nonparametric test, p < 0.05), and their compositional characteristics varied greatly. In the case of harsh aquatic environments, corals increase mucus secretion and then accumulate organic pollutants. Tissue-mucus partitioning varied among coral species. Most OPEs were found to be bioaccumulative (BAFs >5000 L kg-1) in a few coral tissue samples besides Triphenyl phosphate (TPHP). Mucus' role in the bioaccumulation of OPEs in coral shouldn't be ignored.

Distribution and adsorption-desorption of organophosphate esters from land to sea in the sediments of the Beibu Gulf, South China Sea: Impact of seagoing river input.

Organophosphate esters (OPEs) have been a class of emerging environmental contaminants. However, studies on their environmental behavior, specifically their adsorption-desorption behavior between sediment and seawater in estuarine and coastal areas, remain limited. To address this gap, our study focused on investigating the levels and behavior of 11 OPEs in sediment samples collected from the Beibu Gulf, South China Sea, encompassing estuaries and coastal regions. The total concentrations of 11 OPEs (Σ11OPEs) in the sediments exhibit a significant decrease in summer, both in seagoing rivers (4.67 ± 2.74 ng/g dw) and the coastal zone (5.11 ± 3.71 ng/g dw), compared to winter levels in seagoing rivers (8.26 ± 4.70 ng/g dw) and the coastal zone (7.71 ± 3.83 ng/g dw). Chlorinated OPEs dominated the sediments, constituting 63 %-76 % of the total. Particularly, port and mariculture areas showed the highest levels of OPEs. Through load estimation analysis, it was revealed that the sedimentary OPEs in Qinzhou Bay (221 ± 128 kg) had the highest load, with input from the Qin River identified as a significant source. Chlorinated OPEs showed a trend of desorption from sediments to the water column with increasing salinity, emphasizing the crucial role of land-based OPEs input through suspended particulate matter in rivers as a pathway to the ocean. The impact of strong flow in estuarine environments was highlighted, as it can scour sediments, generate suspended sediments, and release OPEs into the water bodies. Additionally, the results of the ecological risk assessment indicated that most of the OPEs posed low-risk levels. However, attention is warranted for the contamination levels of some chlorinated OPEs, emphasizing the need for ongoing monitoring and assessment.

Black Carbon in Deep-Sea Seamount Sediment Cores: Vertical Variation and Non-negligible Char Black Carbon.

Deep-sea sediments (>1000 m) are often considered to be the ultimate sink for black carbon (BC), and the long-term buried BC in these sediments is believed to potentially provide a negative feedback effect on climate warming. The burial flux of BC in marine sediments is predominantly estimated based on soot BC (SBC) in most studies, frequently ignoring the contribution of char BC (CBC). While this methodology may result in an underestimation of the BC burial flux, the precise extent of this underestimation is yet to be determined. This study used the benzene poly(carboxylic acid) (BPCA) method and chemothermal oxidation (CTO) method to analyze CBC and SBC in four deep-sea sediment cores from the Zhongnan seamount in the South China Sea, respectively. The CBC content increased from 0.026 ± 0.010% at the seamount upper part (1432 m) to 0.039 ± 0.012% at the seamount foot (4278 m), constituting approximately 25 to 42% of the SBC content. The content disparity between CBC and SBC diminishes as depth increases. In deep-sea sediments, biogeochemical factors influence the variation of CBC molecules with depth. In the seamount middle-upper part (1432 and 2465 m), highly condensed CBC gradually accumulated along the core downward profile. In the sediment core profile of the seamount middle-lower part (3497 m), benzenetricarboxylic acid and benzenetetracarboxylic acid content decreased while the BC condensation degree rose, i.e., less condensed CBC was preferentially consumed. Afterward, CBC molecules reached a relatively stable state at the seamount foot. This study reveals that CBC possesses the capacity for long-term carbon sequestration in deep-sea sediments, and its content is not negligible.

Occurrence, bioaccumulation and ecological risk of organic ultraviolet absorbers in multiple coastal and offshore coral communities of the South China Sea.

The occurrence of organic ultraviolet absorbers (OUVAs) in coral reef regions has aroused widespread concern. This study focused on the occurrence, distribution, bioaccumulation and ecological risk of ten OUVAs in both coastal and offshore coral reef regions in the South China Sea. While the Σ10OUVAs was 85 % lower in the offshore seawater (15.1 ng/L) than in the coastal seawater (102.1 ng/L), the Σ10OUVAs was 21 % lower in the offshore corals (1.82 µg/g dry weight (dw)) than in the coastal corals (2.31 µg/g dw). This difference was speculated to relate to the high intensity of human activities in the coastal regions. Moreover, the offshore corals showed higher bioaccumulative capability toward OUVAs (log bioaccumulation factors (BAFs): 1.22-5.07) than the coastal corals (log BAFs: 0.17-4.38), which was presumably the influence of varied physiological status under different environmental conditions. The results of the ecological risk assessment showed that BP-3 resulted in 73 % of coastal corals and 20 % of offshore corals at a risk of bleaching. Therefore, the usage and discharge of BP-3 should be managed and controlled by the countries adjacent to the South China Sea for the protection of coral reefs.

Organophosphate esters (OPEs) in a coral reef food web of the Xisha Islands, South China Sea: Occurrence, trophodynamic, and exposure risk.

Despite organophosphate esters (OPEs) are widely prevalent in the environment, however, limited information is available regarding their occurrence, trophodynamics, and exposure risks in coral reef ecosystems. In this study, 11 OPEs were investigated in a tropical marine food web (7 fish species and 9 benthos species) from the Xisha (XS) Islands, South China Sea (SCS). The ∑11OPEs were 1.52 ± 0.33 ng/L, 2227 ± 2062 ng/g lipid weight (lw), 1024 ± 606 ng/g lw, and 1800 ± 1344 ng/g lw in seawater, fish, molluscs, and corals, respectively. Tris (2-chloroisopropyl) phosphate (TCIPPs) were the dominant OPEs in seawater, fish, and molluscs, while tris (2-butoxyethyl) phosphate (TBOEP) predominated in coral tissues. Abiotic and biotic factors jointly affect the OPEs enrichment in marine organisms. Trophic magnification factors (TMFs) (range: 1.31-39.2) indicated the biomagnification potency of OPEs. A dietary exposure risk assessment indicated that OPEs at current levels in coral reef fish posed a low risk to human health but were not negligible. Overall, this study contributes to a further understanding of the environmental behaviors of OPEs in coral reef ecosystems.

Environmental fate and effects of PAHs in tropical mariculture ponds near the northern South China Sea: Rainfall plays a key role.

The behavior and fate of PAHs are affected by multiple meteorological factors, but the main factors driving PAHs in tropical mariculture areas are still not clearly understood. This study continuously monitored PAHs in a few tropical land-based mariculture ponds, discussed their dynamic change trend, migration among the multiple media, and the relevant affected factors. Results indicated that PAHs were widely distributed in these environmental media, and the PAHs' concentration showed an obvious attenuation trend in the mariculture cycle. Wet deposition brought overwhelming majority atmospheric PAHs (92 % ± 5.7 %) to the aqueous system, and >72 % of these PAHs came from oil combustion-related sources and biomass combustion. Compared with the natural sea areas in the same region, mariculture ponds sediment could be changed from a sink at the early stage to a secondary release source of PAHs at the late stage of the rainy season, which intensifies the bioaccumulation of PAHs and the risk of edible carcinogenesis of aquatic products. Our research revealed that rainfall drove the occurrence and environmental behavior of PAHs in the tropical mariculture areas, while land-based mariculture ponds ecosystem affected the regional environmental fate of PAHs and weakened their transmission to the marine environment from land.