Spatial distribution characteristics of perfluoroalkyl substances in bulk and grain size fractionated sediments in Shenzhen Bay.

Understanding Perfluoroalkyl substances (PFASs) spatial distribution in natural environments is crucial due to their environmental persistence and potential bioaccumulation. However, limited research has investigated PFASs spatial distribution at a high resolution, especially in the Guangdong-Hong Kong-Macao Greater Bay Area. Here, we examined the composition and concentration of PFASs in 36 bulk surface sediments and grain-size fractionated sediments from 9 representative sites to determine the spatial distribution characteristics in Shenzhen Bay. We found that ΣPFASs decreased gradually from nearshore area to offshore area (0.680 and 0.297 ng g-1 dw, respectively). Furthermore, PFASs are easily adsorbed on fine-grained sediments, likely due to their chain length and hydrophobicity. We argue that the lateral movement of sediments may transport fine-grained sediments associated with ΣPFASs out of the bay, resulting in the spatial difference in ΣPFASs in Shenzhen Bay. Our findings provide important insights into explore the mechanisms associated with preservation and transport of PFASs.

Temporal variation of per- and polyfluoroalkyl substances (PFASs) abundances in Shenzhen Bay sediments over past 65 years.

We examined the vertical distribution of per- and polyfluoroalkyl substances (PFASs) and total organic carbon in sediment cores located in Shenzhen Bay area. We investigated the 210Pbex specific activity of the sediments and calculated the flux of PFASs to understand the temporal variation of PFASs in the past 65 years. The results showed that the concentrations of PFASs generally decreased with depth, ranging from 13 to 251 pg/g dw. The highest PFASs detected were perfluorobutanesulfonic acid, perfluorooctanoic acid, and perfluorohexanoic acid, which correspond to raw materials used in fire-fighting foam and food packaging industries. The flux of PFASs in Shenzhen Bay showed varying growth after 1978 when China's GDP entered a rapid growth stage. Our findings suggest that the vertical distribution of PFASs in Shenzhen Bay is fluctuating with the changes in industrial types and economic development, with implications for studying the fate of other persistent pollutants in the oceans.

Heavy metals and Pb isotopes in a marine sediment core record environmental changes and anthropogenic activities in the Pearl River Delta over a century.

Heavy metal accumulation in marine sediments is associated with changes in both the natural environment and human activities. This study used heavy metals and Pb isotopes in a precisely dated (by 210Pb and 137Cs) sediment core from the Macao Sea to reconstruct the historical changes in anthropogenic activities and the environment in the western Pearl River Estuary (PRE). The distribution of heavy metals in the sediment core could be divided into four stages (pre-1950, 1950-1976, 1976-2000, and post-2000), which corresponded to the changes in anthropogenic activities and environment of the Pearl River Delta during the past 100 years. The contribution of anthropogenic metals (Pb and Zn) in the sediments increased gradually over time. However, the concentrations, enrichment factors, and fluxes of heavy metals in the sediments all displayed a downward trend since 2010, revealing a decline in metal pollutant input due to strict emission reduction policies implemented in the last decade. The Pb isotopes in the sediments showed a similar trajectory to the heavy metals, reflecting the changes in Pb sources in the sediments at different stages. Based on a binary Pb isotope mixing model, the calculated proportions of anthropogenic and natural Pb in the sediments were 0-50.9% (mean 15.9%) and 49.1-100% (mean 84.1%), respectively, suggesting that the Pb in the PRE sediments is mainly controlled by natural sources.

Distribution, Risk Assessment, and Sources of Trace Metals in Surface Sediments from the Sea Area of Macao, South China.

Due to rapid economic development in the Pearl River Delta, South China, trace metals pose a significant threat to the coastal ecosystems. In this study, we investigated the spatial distribution, contamination status, ecological risk, and possible sources of trace metals in 150 surface sediment samples from the Macao sea area. The results showed that concentrations of Ag, Pb, Cu, Zn, and Cd were highest in the Inner Harbour, whereas Cr, Co, As, and Ni were mainly accumulated in the downstream area of the Maliuzhou Waterway and the eastern area of Macao International Airport. Sediment grain composition, organic matter, total phosphorus, and hydrological regime were key factors influencing the spatial distribution patterns of trace metals. According to the environmental contamination indices of the enrichment factor, geo-accumulation index, and contamination factor, moderate contamination of trace metals occurs in the study area, while Ag and Pb contribute significantly to the contamination. Based on the potential ecological risk index, trace metals in surface sediments pose a low ecological risk. Correlation analysis and principal component analysis indicated that Cr, Co, Ni, and As were mainly derived from natural sources, whereas Ag, Pb, Cu, Zn, and Cd were mainly associated with anthropogenic sources.

Distribution, sources and ecological risks of organochlorine compounds (DDTs, HCHs and PCBs) in surface sediments from the Pearl River Estuary, China.

The Pearl River Estuary is an important sink of organochlorine compounds (OCs), and OC pollution levels in surface sediments remain largely unknown at present. We collected and analysed residual DDTs, HCHs and PCBs of 45 surface sediments from the Pearl River Estuary in 2017. The values of DDTs (1.83 to 6.98 ng·g-1) and HCHs (0.43 to 2.14 ng·g-1) were higher in the Humen outlet, and the values of PCBs (4.6 to 187.4 ng·g-1) were higher in the coastal areas of Shenzhen. The DDTs and HCHs have generally decreased while the PCBs have been rapidly increasing in recent decades. The DDTs might originate from technical DDT and dicofol. The major source of HCHs was lindane. The main potential sources of PCBs were increased industrial products, ship painting, E-waste disassembly, maricultural and agricultural pollution. The total PCBs and DDTs had medium ecological risks according to the sediment quality guidelines.

Ecological risk assessment of trace metals and comprehensive contamination indicators in the coastal waters of Macao, South China Sea.

Few systematic and scientific assessments have been conducted on marine environmental quality in the coastal waters of Macao, a major city in the Pearl River Delta, China. In this study, we investigated the spatial distribution of trace metals (TMs) and comprehensive contamination indicators of marine water in Macao and evaluated their ecological risks. The total amount of typical TMs (∑TMs) in surface water ranged from 2.71 µg/L to 201 µg/L. ∑TMs (Hg, As, and Cd) in sediments ranged from 0.34 mg/kg to 54.8 mg/kg. TM contamination in surface water was influenced by spatial position and tidal current direction. The spatial distribution and correlation analysis of TMs and comprehensive contamination indicators were assessed, and ecological risk assessment indicated that the surface water and sediments in coastal waters of Macao are of relatively good quality, although high sulfide levels could be detected in surface water.

Remobilization mechanism and release characteristics of phosphorus in saline sediments from the Pearl River Estuary (PRE), South China, based on high-resolution measurements.

The internal loading of phosphorus (P) is commonly considered an essential factor contributing to eutrophication in freshwater bodies. However, investigation of the lability and remobilization characteristics of P in estuarine saline sediments has been limited. In this study, a sequential chemical extraction procedure and high-resolution measurement using the diffusive gradients in thin film (DGT) technique were employed to explore the lability, potential remobilization mechanism and release characteristics of sediment P in the Pearl River Estuary (PRE), South China. The P accumulated significantly in sediments along the west coast of the PRE due to the combined effects of terrestrial P inputs and specific hydrological conditions. The geochemical fractions of sediment P followed the order of organic P (Org-P) (mean: 58.6%) > iron-bound P (Fe-P) (23.4%) > calcium-bound P (Ca-P) (17.4%) > loosely bound P (LS-P) (0.63%). Synchronous vertical variations in DGT-labile Fe and P in the upper and middle parts of the sediment profiles confirmed that Fe-coupled P mobilization occurred in saline sediments. In contrast, sulfate reduction in bottom sediments supposed to decouple the Fe-P cycling relationship. Additionally, the formation of an "iron curtain" (Fe oxyhydroxides) in the oxic surface sediments efficiently prevented upward diffusion of P, leading to relatively low effluxes of P (0.098-6.59 ng cm-2 d-1) across the sediment-water interface.

Risk assessment of trace metal-polluted coastal sediments on Hainan Island: A full-scale set of 474 geographical locations covering the entire island.

Hainan Island is the second largest island and one of the most famous tourist destinations in China, but sediment contamination by trace metals in coastal areas is a major issue. However, full-scale risk assessments of trace metal-polluted coastal sediments are lacking. In this study, coastal surface sediments from 474 geographical locations covering almost the entire island were collected to identify risk-related variables. Controlling factors and possible sources of trace metals were identified, and the toxicity effects were carefully evaluated. Our results suggest that trace-metal pollution in coastal sediments, which was mainly caused by Pb, Zn and Cu emissions, has primarily resulted from industrial sewage and shipping activities and has threatened the offshore ecosystem of Hainan Island and warrants extensive consideration. This is the first study that has systematically investigated trace metal-polluted coastal sediments throughout the entirety of Hainan Island and provides solid evidence for sustainable marine management in the region.

[Distribution Characteristics, Sources and Pollution Assessment of Trace Elements in Surficial Sediments of the Coastal Wetlands, Northeastern Hainan Island].

Totally 128 surficial sediments samples were collected from the coastal wetlands, northeastern Hainan Island and analyzed for their concentrations of 14 elements including Al2O3, Fe2O3, MnO, Cu, Ni, Sr, Zn, V, Pb, Cr, Zr, As, Cd and Hg, TOC and grain sizes. The mean concentrations of trace metals V, Cr, Ni, Cu, Zn, As, Pb, Cd and Hg were (40.13 +/- 32.65), (35.92 +/- 26.90), (13.03 +/- 11.46), (11.56 +/- 10.27)-, (48.75 +/- 27.00), (5.48 +/- 1.60), ( 18.70 +/- 8.66), (0.054 +/- 0.045 ), (0.050 +/- 0.050) microg x g(-1), respectively, which were much lower than those in Pearl River Estuary, Yangzi River Estuary, Bohai Bay, upper crust and average shale. The average concentrations of Sr and Zr were much higher, reaching up to (1253.60 +/- 1649.58) microg x g(-1) and (372.40 +/- 516.49) microg x g(-1), respectively. The spatial distribution patterns of Al2O3, Fe2O3, MnO, Cu, Ni, Zn, V, Pb, Cr, Cd and Hg concentrations were the same as each other except for those of As, Sr and Zr. Generally, relatively high concentrations of these elements only appeared in the Haikou Bay, Nandu estuary, Dongzhai Harbor, Qinglan Harbor and Xiaohai in study area. The factor analysis revealed that the trace elements Al2O3 Fe2O3, MnO, Cu, Ni, Zn, V, Pb, Cr and part of Hg were mainly originated from the rock material by natural weathering processes, while the Cd and a part of Hg were from the biological source controlled by TOC. As and part of MnO were influenced by anthropogenic source, especially by aquacultures. Zr and some MnO were derived from heavy minerals dominated by the coarse grain of sediments. In contrast to the ERL, ERM and the results of enrichment factors (EF) , the environment of study area was good in general and the degree of contamination by trace elements was low on the whole. However, there are still some places where anthropogenic input have caused serious enrichments of trace elements and the occasional adverse effect on benthic organism induced by Ni could probably occur in 22% areas of all the sampling stations.

Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM-AVS analysis.

Surface sediments from the coastal area of the Leizhou Peninsula in the South China Sea were collected and analyzed and the potential ecological risks in the area were assessed based on acid-volatile sulfide (AVS) model. The AVS levels are between 0.109 and 55.6 µmol g(-1), with the average at 4.45 µmol g(-1). The high AVS-concentration zones include the aquaculture areas of Liusha Bay and the densely populated areas of Zhanjiang Bay. The simultaneously extracted metals (SEM) range from 0.026 µmol g(-1) to 8.61 µmol g(-1), with the average at 0.843 µmol g(-1). Most of high SEM-concentration stations were located in ports or aquaculture zones. Most of the coastal surface sediments of the Leizhou Peninsula (90%) had no adverse biological effects according to the criterion proposed by USEPA (2005); while adverse effects were uncertain in some stations (8%); even in 2 stations (2%) adverse biological effects may be expected.

Natural and human influences on nutrient transport through a small subtropical Chinese estuary.

Global understanding of land-ocean nutrient fluxes increasingly recognizes the disproportionate importance of small rivers. We studied nutrient fluxes from a small catchment in fast developing southern China to uncover effects of land-use. Water was sampled in the macro-tidal estuary of Nanliu River and adjacent Lianzhou Bay in spring and summer of investigate spatial and temporal variations of dissolved nutrients. High riverine concentrations of nitrate (NO3; up to 220 µM) and phosphate (PO4; up to 3.7 µM) mainly originated from agricultural fertilizer input. Riverine dissolved silica (Si; up to 47 µM) increased in the oligosaline part of the estuary through human disturbance of bottom sediments. Dissolved organic nitrogen (DON; up to 194 µM) and ammonium (NH4; up to 40 µM) concentrations increased within the estuary due to inputs from livestock and mussel beds, respectively. Aquaculture ponds contained high concentrations of NH4 (up to 355 µM) and DON (up to 151 µM) but are not an important source to the estuary due to rare wastewater discharge and low absolute nutrient amounts relative to river export. Nutrient concentrations in Lianzhou Bay were low because tidal currents disperse land-derived nutrients offshore into the adjacent Beibu Gulf. A high proportion of regenerated nitrogen in the bay suggests that primary production is sustained by rapid in situ nutrient cycling between primary producers and benthic consumers. High nutrient export makes the Nanliu River an important nutrient source for the north-western South China Sea, despite its proportionately small size. Macro-tide induced short-term concentration changes exceed variability on seasonal and sub-seasonal scales. All nutrients vary inter-annually and between seasons, depending on precipitation-driven river runoff. Total nutrient export to Beibu Gulf coastal waters is stronger during the high discharge period in summer and autumn. In recent years changing nitrogen to phosphorus ratios have alleviated phosphorus limitation in Lianzhou Bay, permitting increased primary productivity.

Selected trace metals (As, Cd and Hg) distribution and contamination in the coastal wetland sediment of the northern Beibu Gulf, South China Sea.

Contamination with As, Cd and Hg, their spatial and temporal distribution are reported from the coastal wetland sediments of the northern Beibu Gulf, South China Sea. The content of As, Cd, Hg and TOC in surface sediments is 8.1±5.8 µg g⁻¹, 0.08±0.14µg g⁻¹, 0.034±0.028 µg g⁻¹ and 0.45±0.39%, respectively. The mean sedimentation rates are 0.93-1.37 cm year⁻¹ during 1920s to 2008 determined by ²¹°Pb and ¹³7Cs dating in three cores. The vertical profiles of As, Cd and Hg content in the cores retrieved from Qin and Nanliu River estuaries show increasing trends during 1985-2008 due to anthropogenic impact caused by local economic development. Locally the surface sediments have potential ecological risk of As to benthos according to the NOAA sediment quality guidelines.

Quality characterization and impact assessment of highway runoff in urban and rural area of Guangzhou, China.

Accurate knowledge of the quality and environmental impact of the highway runoff in Pear River Delta, South China is required to assess this important non-point pollution source. This paper presents the quality characterization and environmental impact assessment of rainfall runoff from highways in urban and rural area of Guangzhou, the largest city of Pear River Delta over 1 year's investigation. Multiple regression and Pearson correlation analysis were used to determine influence of the rainfall characteristics on water quality and correlations among the constituents in highway runoff. The results and analysis indicates that the runoff water is nearly neutral with low biodegradability. Oil and grease (O&G), suspended solids (SS) and heavy metals are the dominant pollutants in contrast to the low level of nutrient constituents in runoff. Quality of highway runoff at rural site is better than that of at urban site for most constituents. Depth and antecedent dry period are the main rainfall factors influencing quality of highway runoff. The correlation patterns among constituents in highway runoff at urban site are consistent with their dominant phases in water. Strong correlations (r > or = 0.80) are found among chemical oxygen demand (COD), total phosphorus, Cu and Zn as well as conductivity, nitrate nitrogen and total nitrogen. O&G, COD, SS and Pb in highway runoff at urban site substantially exceed their concentrations in receiving water of Pear River. The soil directly discharged by highway runoff at rural site has contaminated seriously by heavy metals in surface layer accompanying with pH conversion from original acidic to alkaline at present.