In this study, the contamination levels and seasonal variation of 22 PFASs were investigated in coastal reef-building corals (n = 68) from the northern South China Sea (SCS) during wet and dry seasons. Perfluorohexane sulfonate (PFHxS) was the predominant PFASs in all coral samples, representing 43% of the total PFAS. Long-chain PFASs, as well as PFAS alternatives, were frequently detected above the MQL (>88%) but showed relatively low concentrations compared to short-chain PFASs in most species and seasons. Seasonal variation of PFAS concentrations were observed in branching corals, indicating that the accumulation of PFASs may be associated with coral morphological structures. Interspecies differences in PFAS levels agree well with different bioaccumulation potentials among coral species. Redundancy analysis (RDA) showed that seasonal factor and coral genus could partly influence PFAS concentrations in coral tissues. In summary, our study firstly reported the occurrence of PFASs in coral communities from the SCS and highlights the necessity for future investigations on more toxicity data for coral communities.

Microplastics (MPs) in the ocean have been widely recognized as causing global marine environmental problems. To gain a quantitative and comprehensive understanding of oceanic MP contamination, detailed numerical Lagrangian particle tracking experiments were conducted to evaluate the regional oceanic transport and dispersal of MPs in the South China Sea (SCS) derived from three major rivers, Pearl (China), Mekong (Vietnam), and Pasig (the Philippines), which are known to discharge large amounts of plastic waste into the SCS. As previous field surveys have suggested, MP contamination spreads from the surface to the deeper ocean in the water column, we thus considered three types of MPs: (1) positively buoyant (light) MPs, (2) positively buoyant (light) MPs with random walk diffusion, and (3) full 3-D tracking of non-buoyant MPs that are passively transported by ambient currents. Transport patterns of these MPs from the three rivers clearly showed the intra-annual variability associated with seasonally varying circulations driven by the Asian monsoons in the SCS. Many MPs floating during the prevailing southwest monsoon are transported to the northwest Pacific Ocean and the East China Sea through the Luzon Strait and the Taiwan Strait to form MP hotspots. Non-buoyant MPs are broadly transported from the surface layer to depths of approximately 100 m or deeper, where in situ observations are rare. In addition, the buoyant MPs drifting on the continental shelf originating from southern China tend to be pushed toward the shore and beached by northward wind-induced currents more pronouncedly than the non-buoyant MPs. Therefore, the river-derived MPs to the SCS were found to serve as sources to adjacent basins and oceans, to be distributed not only in the upper layer but also in the abyssal ocean (non-buoyant MPs), and to be transported to the shores (buoyant MPs).

The occurrence and spatial distribution of polybrominated diphenyl ethers (PBDEs) and novel brominated flame retardants (NBFRs) in seawater and surficial sediment samples (N = 19 and 45, respectively) from the South China Sea (SCS) in 2018 were investigated, and the correlation between BFRs and site parameters (total organic carbon, depth, etc.) were assessed by principal component analysis. The concentration ranges of ΣPBDEs in seawater and sediments were 0.90–4.40 ng/L and 0.52–22.67 ng/g dry weight (dw), respectively, while those of ΣNBFRs were 0.49–37.42 ng/L and 0.78–82.29 ng/g dw, respectively. BDE-209 and decabromodiphenyl ethane were the predominant BFRs, accounting for 38.65% and 36.94% in seawater and 26.71% and 68.42% in sediments, respectively. Notably, tris(2,3-dibromopropyl)isocyanurate and 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine, seldomly detected in aquatic matrices worldwide, were detected for the first time in the study area, and their relatively high levels and detection frequencies indicate the ubiquitous application of these NBFRs in the Pearl River Delta. Zhuhai and Jiangmen are the main sources of NBFRs in the SCS. Preliminary risk assessment on NBFRs using hazard quotient indicates low to medium risks to marine organisms at some sites. The occurrence of NBFRs in the SCS highlights the prioritization of more toxicological information on these compounds.

With the implementation of COVID-19 restrictions and consequent improvement in air quality due to the nationwide lockdown, ozone (O₃) pollution was generally amplified in China. However, the O₃ levels throughout the Guangxi region of South China showed a clear downward trend during the lockdown. To better understand this unusual phenomenon, we investigated the characteristics of conventional pollutants, the influence of meteorological and anthropogenic factors quantified by a multiple linear regression (MLR) model, and the impact of local sources and long-range transport based on a continuous emission monitoring system (CEMS) and the HYSPLIT model. Results show that in Guangxi, the conventional pollutants generally declined during the COVID-19 lockdown period (January 24 to February 9, 2020) compared with their concentrations during 2016–2019, while O₃ gradually increased during the resumption (10 February to April 2020) and full operation periods (May and June 2020). Focusing on Beihai, a typical Guangxi region city, the correlations between the daily O₃ concentrations and six meteorological parameters (wind speed, visibility, temperature, humidity, precipitation, and atmospheric pressure) and their corresponding regression coefficients indicate that meteorological conditions were generally conducive to O₃ pollution mitigation during the lockdown. A 7.84 μg/m³ drop in O₃ concentration was driven by meteorology, with other decreases (4.11 μg/m³) explained by reduced anthropogenic emissions of O₃ precursors. Taken together, the lower NO₂/SO₂ ratios (1.25–2.33) and consistencies between real-time monitored primary emissions and ambient concentrations suggest that, with the closure of small-scale industries, residual industrial emissions have become dominant contributors to local primary pollutants. Backward trajectory cluster analyses show that the slump of O₃ concentrations in Southern Guangxi could be partly attributed to clean air mass transfer (24–58%) from the South China Sea. Overall, the synergistic effects of the COVID-19 lockdown and meteorological factors intensified O₃ reduction in the Guangxi region of South China.

With the development of marine resources and marine transportation, oil spill accidents occur frequently which threaten the marine ecological environment and human life. In this paper, an oil spill model was established. The two-dimensional shallow water equation was discretized by the finite element weighted lumped mass method, and the time is discretized by the forward Euler scheme, then the planar two-dimensional hydrodynamic model was established. The model was verified by measure tidal level data. The oil particle drift model and oil spill weathering model were established in this paper, and it can be used to simulate the oil spill accidents on the sea area by inputting the terrain data, environmental conditions and oil spill information into the hydrodynamic model and oil spill model. The model is applied to Daya Bay, South China Sea, the oil spill behavior and destination under different residual currents were simulated and calculated, the pollution area of oil spill under clockwise residual flow is larger than that under anti-clockwise residual flow. The oil spill model is mainly used to simulate oil spill accidents on the sea surface such as ship oil spill accidents, and the simulation results can provide theoretical basis for taking effective emergency measures and risk assessment after oil spill.

Laboratory research has indicated that antibiotics had negative effects on coral growth by disturbing natural microbiota; however, no field studies have reported antibiotic contamination levels and their influence on coral growth in natural coral reef regions (CRRs). This study investigated antibiotic occurrence and sources in the surface water from CRRs that have suffered from rapid coral degradation and evaluated their risk to coral growth. These regions are in the South China Sea, including four coastal and two offshore CRRs. The results show that 13 antibiotics were detected in the coastal CRRs with concentrations ranging from 10⁻²–10⁰ ng L⁻¹, while 5 antibiotics occurred in offshore CRRs (300–950 km from the mainland), with concentrations ranging from 10⁻² to 10⁻¹ ng L⁻¹. Their concentrations decreased gradually from the coast to offshore in the transport process. However, Yongxing Island, which is approximately 300 km from the mainland, was an exception with relatively higher concentrations than the surrounding reefs because of the ever-increasing human activity on the island. The presence of anthropogenic contaminants antibiotics in CRRs may be a potential risk to coral growth.

A systematic field measurement was conducted at an island site (Wanshan Island, WSI) over the South China Sea (SCS) in autumn 2013. It was observed that mixing ratios of O₃ and its precursors (such as volatile organic compounds (VOCs), nitrogen oxides (NOₓ = NO + NO₂) and carbon monoxide (CO)) showed significant differences on non-episode days and episode days. Additional knowledge was gained when a photochemical box model incorporating the Master Chemical Mechanism (PBM-MCM) was applied to further investigate the differences/similarities of O₃ photochemistry between non-episode and episode days, in terms of O₃-precursor relationship, atmospheric photochemical reactivity and O₃ production. The simulation results revealed that, from non-O₃ episode days to episode days, 1) O₃ production changed from both VOC and NOₓ-limited (transition regime) to VOC-limited; 2) OH radicals increased and photochemical reaction cycling processes accelerated; and 3) both O₃ production and destruction rates increased significantly, resulting in an elevated net O₃ production over the SCS. The findings indicate the complexity of O₃ pollution over the SCS.

Coastal upwelling prevails in the coast of Hainan Island, the northern South China Sea (SCS) during summer. We studied the influences of the upwelling on the horizontal and vertical transport of terrigenous polycyclic aromatic hydrocarbons (PAHs). PAHs in dissolved and suspended particulate phase of water samples were determined in the upper (depth < 1 m) and water column (depth > 10 m). PAH levels decreased sharply from inshore to offshore to open sea. The results showed that terrestrial input was the main source of coastal PAHs. Perylene, an important indicator of land plant-derived PAH, showed the significant correlation with PAHs (p < 0.005). This implied that fluvial transport was the primary pathway of terrigenous PAHs into the coast of northern SCS. Variations of the concentrations, compositions and diagnostic ratios of PAHs, accompanied the partition equilibrium in the water column, could indicate the selective degradation of PAHs by the plankton affected by upwelling. Different from the “traditional” transport pathway of PAHs in the water column (surface enrichment-depth depletion distribution), the upwelling could provide the original driver to elevate the upward diffusion of sediment entrained contaminants towards the intermediate even the upper waters. It could also enhance the outward diffusion of terrigenous PAHs accompanied by the offshore transport of the upper waters. Therefore, the transport pathway of PAHs can be summarized by the coastal upwelling rising PAHs with their subsequent transport offshore and settling in the adjacent open sea.

In this study, we conducted a 14-month investigation in Daya Bay, southern China to understand the effects of oyster farming on phytoplankton community and biomass by using size-fractionated phytopigments. Results proved the filtering effects of oysters on phytoplankton biomass. During the oyster culture period, the average concentration of total chlorophyll a (sum of size-fractionated Chl a) within the farming area was approximately 60% lower than that at the reference site. Phytoplankton depletion in the aquaculture zone mainly occurred in micro-sized fractions (>20 μm) of Chl a, fucoxanthin, and peridinin. The influence of oyster filtration on nano-sized (2.7–20 μm) pigments seemed less than that on micro-sized ones. The depletion of peridinin and 19′-hex-fucoxanthin in aquaculture zone was higher than those of the other pigments, which indicated that flagellated cells might be selectively filtered by oysters and could be more easily influenced by oyster aquaculture. The pico-sized Chl a (<2.7 μm) comprised 24% of total Chl a on the average in the aquaculture zone during the cultural period compared to 6% in the reference site. Picoeukaryote abundance, which was determined via flow cytometry, was significantly higher in the aquaculture zone than in the non-aquaculture areas. The abundance of picoeukaryote is significantly and positively correlated with the concentrations of pico-sized prasinoxanthin, violaxanthin, and neoxanthin, indicating that picoeukaryote is dominated by those in prasinophyte. The results suggest that oyster aquaculture might stimulate the growth of prasinophyte, although the seasonal variations are mainly controlled by the water temperature in the study area. This research highlights the successful use of size-fractionated phytopigments to estimate size-specific phytoplankton biomass and community, which can be applied as a routine method to monitor the environmental effect and food resources of bivalve aquaculture.

Ancient eggshells over the past 700 years were extracted from an ornithogenic sediment profile on Guangjin Island, South China Sea. Based on SEM and nitrogen isotope analyses, we determined that neither post-depositional processes nor seabirds’ dietary changes had a large influence on eggshell Hg levels. The historical change of Hg in these eggshells was reconstructed. Eggshell Hg was a marker for past Hg deposition in marine environment. The eggshell Hg showed three small peaks at around 1300AD, 1600 AD and 1700–1750AD and rapid increase since 1800 AD. Before 1970 AD the Hg deposition in the Xisha area had global distribution characteristics, with increased Hg emissions due to global anthropogenic activities in industrial times. However, after 1970 AD, a further sharp increase up to present day occurred, implying that the Hg production center had gradually shifted from Europe and America to Asia.