Risk assessment of trace metals and polycyclic aromatic hydrocarbons in seawater of typical bays in the Bohai Sea

The ecological risks of trace metals (Cu, Zn, As, Cd, Pb, and Hg) and PAHs in seawater from three typical bays of the Bohai Sea (the Liaodong Bay, Bohai Bay, and Laizhou Bay) were comprehensively assessed by recompiling 637 sites. Results highlighted that scrutiny should be given to the ecological risks of Cu (3.80 μg/L) in the Bohai Bay and Hg (0.23 μg/L) in the Laizhou Bay. Conversely, the Liaodong Bay exhibited negligible ecological risks related to trace metals. The risks of ΣPAHs in the Liaodong Bay, Bohai Bay, and Laizhou Bay were moderate, with mean concentrations of 368.16 ng/L, 731.93 ng/L, and 187.58 ng/L, respectively. The source allocation of trace metals and PAHs required consideration of spatial variability and anthropogenic factors, which greatly affected the distribution and composition of these pollutants. The combined ecological risks in the Bohai Bay (6.80 %) and Laizhou Bay (5.43 %) deserved more attention.

Correlation between polycyclic aromatic hydrocarbons and total organic carbon in surface sediments of the Bohai Sea and the North Yellow Sea

The correlation between polycyclic aromatic hydrocarbons (PAHs) and organic carbon is an important indicator of the marine environment. In this paper, twenty-six surface sediment samples were collected from the Bohai Sea and the North Yellow Sea as the study area, and the contents of sixteen PAHs ranged from 71.34 ng·g-1 to 240.78 ng·g-1 with an average of 143.26 ng·g-1 by gas chromatography. The source analysis indicated the source of PAHs in the surface sediments of the study area was more complex, and the percentage of combustion sources was higher than that of petroleum sources, which might cause less negative ecological risks. The average content of total organic carbon (TOC) was 5.25%, as determined by automatic potentiometric titration, and the content of TOC was higher in the Bohai Sea than in the North Yellow Sea. TOC was significantly correlated with HWM-PAHs but was not correlated with LWM-PAHs, which proved organic matter was more effective in controlling high-molecular-weight PAHs than low-molecular-weight PAHs in the surface sediments of the Bohai Sea and the North Yellow Sea.

Missing relationship between meso- and microplastics in adjacent soils and sediments

Meso- and microplastics (MMPs) have attracted attention as globally dispersed environmental pollutants. However, little is known about the transfers of MMPs between aquatic and terrestrial systems. A large watershed-estuarine area of Bohai Sea was used as a case study, and soils and sediments were sampled adjacent to each other at a wide range of sites. MMPs were detected in all sediments (6.7-320 MMPs/kg) and soils (40-980 MMPs/kg), with the average abundance in soils double that in sediments on a dry mass basis. MMPs < 1 mm were most abundant and the dominant shape was film in both sediments and soils. Over twenty polymer types were detected and their compositions in sediments and soils were different. MMP abundance in sediments was lower in the upper catchment than the lower catchment, while the abundance of soil MMPs was the opposite. Despite the proximity of the sampling locations, no clear relationship was identified between the soil and sediment MMPs, suggesting low transfer between the two compartments and high heterogeneity of the sources. The missing associations between aquatic and terrestrial MMPs should be systematically examined in future studies, which is crucial for understanding the environmental fate and impacts of MMPs.

Trophic transfer of cyclic methyl siloxanes in the marine food web in the Bohai Sea, China

Trophic transfer of cyclic methyl siloxanes (CMS) in aquatic ecosystems is an important criterion for assessing its environmental risks. This study researched the trophic transfer of four CMS (octamethylcyclotetrasiloxane (D₄), decamethylcyclopentasiloxane (D₅), dodecamethylcyclohexasiloxane (D₆), and tetradecamethylcycloheptasiloxane (D₇)) in marine food web from zooplankton up to seabirds in the Chinese Bohai Sea. In the zooplankton-invertebrate-fish-seabird based food web, the significant trophic magnifications were found for D₄ to D₆ (D₄: R² = 0.040, p < 0.05, D₅: R² = 0.26, p < 0.0001, D₆: R² = 0.071, p < 0.001), and the significant trophic dilution was found for D₇ (R² = 0.026 and p < 0.05). The trophic magnification factors (TMF) for D₄ to D₇ were 1.7 (95% confidence interval: 1.1-2.6), 3.5 (2.5-5.0), 1.8 (1.3-2.6), and 0.63 (95% CI: 0.40-0.99) respectively. In the zooplankton-invertebrate-fish based food web, both significant trophic magnification for D₅ (R² = 0.16, p < 0.0001, TMF = 3.0) and significant trophic dilution for D₇ (R² = 0.073, p < 0.01, TMF = 0.4) were found, but for D₄ and D₆, the trophic magnifications were not significant (D₄: R² = 0.010, p = 0.23, D₆: R² = 0.010, p = 0.23). The trophic transfer of the legacy contaminant BDE-47 and BDE-99 were also conducted as the benchmark chemicals and significant positive correlation was found. As far as we know, this is the first research on the trophic transfer of CMS in the zooplankton-invertebrate-fish-bird food chain which provided new insight of these compounds in the area.

Coastline Detection with Gaofen-3 SAR Images Using an Improved FCM Method

The coastline detection is one of the main applications of the Gaofen-3 satellite in the ocean field. However, the capability of Gaofen-3 SAR image in coastline detection has not yet been validated. In this paper, two Gaofen-3 SAR images, acquired in 2016, were used to extract the coastlines of the regions of Bohai and Taihu in China, respectively. The classical Fuzzy C-means (FCM) method was used in the coastline detection, but had been improved by combining the Wavelet decomposition algorithm to better suppress the inherent speckle noises of SAR image. Coastline detection results obtained from two Sentinel-1 SAR images acquired on the same regions were compared with those of the Gaofen-3 images. By using the manually delineated coastlines as the standards in the qualitative evaluations, improvements of about 12.0%, 8.3%, 23.8%, and 9.4% can be achieved by the improved FCM method with respect to the indicators of mean, RMSE, PGSD, and P90%, respectively; demonstrating that the Gaofen-3 data is superior to the Sentinel-1 data in the detection of coastline.

Identification and quantification of shipping emissions in Bohai Rim, China

Rapid development of port and shipbuilding industry in China has badly affected the ambient air quality of coastal zone due to shipping emissions. A total of 60 ambient air samples were collected from background site of Tuoji Island in Bohai Sea strait. The air samples were analyzed for PM2.5, organic carbon (OC), element carbon (EC), inorganic elements, and water-soluble ions. The maximum concentration of PM2.5 was observed during spring (73.6 μg·m(-3)) compared to winter (39.0 μg·m(-3)) with mean of 54.6 μg·m(-3). Back trajectory air mass analysis together with temporal distribution of vanadium (V) showed that V could be the typical tracer of shipping emissions at Tuoji Island. Furthermore, the ratios of vanadium to nickel (V/Ni), vanadium to lead (V/Pb) and vanadium to zinc (V/Zn) also suggest shipping emissions at Tuoji Island. The annual average primary PM2.5 estimate of shipping emissions was 0.65 μg·m(-3) at Tuoji Island, accounting for 2.94% of the total primary PM2.5, with a maximum of 3.16% in summer and a minimum of 2.39% in autumn.