Phase partitioning effects on seasonal compositions and distributions of terrigenous polycyclic aromatic hydrocarbons along the South China Sea and East China Sea

A review of the pollution signatures of polycyclic aromatic hydrocarbons in the sediments of the East China Sea

Marine sediments serve as crucial reservoirs for polycyclic aromatic hydrocarbons (PAHs), and their PAH signatures offer valuable historical pollution records. This article provides a comprehensive review of the pollution status of 16 priority PAHs in more than 1000 sediments from the East China Sea (ECS). It focuses on the PAH sources, spatiotemporal distributions, driving factors, and ecological risks, with information derived from peer-reviewed papers published between 2003 and 2023. The results revealed that vehicular emissions, mixed combustion sources of coal, biomass, and coke, as well as petrogenic sources, were the primary contributors to PAH pollution in the ECS sediments, accounting for 50%, 34%, and 16%, respectively. Human activities, hydrodynamic mechanisms, and environmental variables such as particle size and organic matter, collectively influenced the distribution of PAHs. Additionally, the population size and economic development played a key role in the temporal distribution of PAHs in the ECS sediments. The ecotoxicity assessment of PAHs in sediments indicated a low risk level. These outcomes are expected to provide environmentalists with detailed and up-to-date insights into sedimentary PAHs in the ECS, helping to develop suitable monitoring plans and strategies for promoting better management of ECS environment.

Simulation and parameter determination of the net sorption of phenanthrene by sediment particles

The distribution of polycyclic aromatic hydrocarbons (PAHs) in the ocean is affected by the sorption-desorption process of sediment particles. This process is determined by the concentration of PAHs in seawater, water temperature, and organic matter content of sediment particles. Quantitative relationships between the net sorption rates (=the difference of sorption and desorption rates) and these factors have not been established yet and used in PAH transport models. In this study, phenanthrene was chosen as the representative of PAHs. Three groups of experimental data were collected to address the dependence of the net sorption processes on the initial concentration, water temperature, and organic carbon content representing organic matter content. One-site and two-compartment mass-transfer models were tested to represent the experimental data using various parameters. The results showed that the two-compartment mass-transfer model performed better than the one-site mass-transfer model. The parameters of the two-compartment mass-transfer model include the sorption rate coefficients kafand kas (L g-1 min-1), and the desorption rate coefficients kdf and kds (min-1). The parameters at different temperatures and organic carbon contents were obtained by numerical simulations. Linear relationships were obtained between the parameters and water temperature, as well as organic carbon content. kaf, kas and kdf decreased linearly, while kds increased linearly with temperature. kaf, kas and kdf increased linearly, while kds decreased linearly with organic carbon content. The r2 values between the simulation results based on the relationships and the experimental results reached 0.96-0.99, which supports the application of the model to simulate sorption-desorption processes at different water temperatures and organic carbon contents in a realistic ocean.

The assessment of bioavailability and environmental risk of dissolved and particulate polycyclic aromatic hydrocarbons in the seawater of typical bays

The pollution of dissolved and particulate polycyclic aromatic hydrocarbons (PAHs) in coastal waters has been increasing in recent decades. However, limited research has been conducted on the characteristics of dissolved and particulate PAHs in seawater and their associated risk assessment. Here, we focused on the bioavailability and environmental risk of PAHs in four typical bays of Shandong Province, China, and used scallop Chlamys farreri and clam Mactra veneriformis as sentinel species. The results revealed that dissolved PAHs tended to bioaccumulate in scallop C. farreri, and their ecological risk exhibited a significant correlation with the health risk of bioaccumulated PAHs and the bioeffect of screened biomarkers in scallop. Conversely, particulate PAHs demonstrated a higher bioaccumulation potential in the clam M. veneriformis, showing a stronger correlation between their ecological risk, health risk, and bioeffect in clams. This study provides the first elucidation of the connection between the ecological risk, health risk, and bioeffect of PAHs. Furthermore, based on the better correlation of health risk and bioeffect caused by PAHs with total PAHs in seawater, we propose that the clam M. veneriformis is a more suitable sentinel species for assessing environmental risk in typical bays of Shandong Province.

Upwelling impact and lateral transport of dissolved PAHs in the Taiwan Strait and adjacent South China Sea

The spatial distribution and depth profile of dissolved polycyclic aromatic hydrocarbons (PAHs) were investigated in the western Taiwan Strait (TWS) and northeastern South China Sea (SCS) during the southwest monsoon for a comprehensive study of spatial distribution, potential sources, upwelling, and lateral PAHs transport flux to assess the impacts of oceanic processes. The concentrations of ∑14PAHs were 33 ± 14 ng L-1 and 23 ± 11 ng L-1 in western TWS and northeastern SCS, respectively. A minor difference in potential sources in different areas was shown in principle component analysis results, which illustrated mixed sources (petrogenic and pyrogenic) in western TWS and petrogenic sources in northeastern SCS. An "enrichment in surface or deep but depletion in medium water" distribution pattern of PAHs depth profile during summertime was observed in Taiwan Bank, which was potentially influenced by the upwelling. The greatest lateral ∑14PAHs transport flux was found along the Taiwan Strait Current area (43.51 g s-1), followed by those along South China Sea Warm Current and Guangdong Coastal Current areas. Though the oceanic response to PAHs varied relatively slowly, the ocean current was a less-dominant pathway for PAHs exchange between the SCS and the East China Sea (ECS).

Spatiotemporal distribution and particle-water partitioning of polycyclic aromatic hydrocarbons in Bohai Sea, China

The Bohai Sea is one of the most polluted marine areas in China with polycyclic aromatic hydrocarbons (PAHs) due to its unique hydrological and geographical environment. To investigate differences in PAH concentrations, composition, and particle-water partitioning before and after the rainy reason, water samples were collected during two surveying voyages covering most of the area of the Bohai Sea. Total and dissolved PAH concentrations were higher during the June voyage (total PAHs: 32.29 ± 15.18 ng/L, dissolved PAHs: 31.25 ± 15.26 ng/L) than the August voyage (total PAHs: 15.98 ± 6.39 ng/L, dissolved PAHs: 11.21 ± 5.59 ng/L). The opposite trend was observed for particulate PAHs (June: 1.04 ± 1.01 ng/L, August: 4.78 ± 2.96 ng/L). Among particulate PAHs, an unusually high proportion (65.07%) of low-molecular-weight (LMW) PAHs was observed during the August voyage, which was significantly higher than the proportion during the June voyage (21.86%). This high proportion was inconsistent with the general distribution of PAHs in the aquatic environment according to their physicochemical properties. The excess LMW PAHs adsorbed on suspended particulate matter arose mainly from soil affected by the petrochemical industry of the Bohai Economic Rim, and were carried with particles on runoff into the Bohai Sea during the rainy season. An estimated 5.49 t of LMW PAHs transitioned from the particulate phase to the dissolved phase during the rainy season. This transfer of LMW PAHs from coastal soil to the water column may be an important source of PAHs in the Bohai Sea.

PAHs in the monsoonal open ocean: Homogeneous spatial pattern and wind-driven significant seasonal variations

PAHs enter the ocean via surface runoff and atmospheric transport pathways, and the distribution of PAHs is highly variable in coastal seas due to the influence of direct human activities, inputs of surface runoff, and strong biological activities. However, highly temporal variability of PAHs has also been widely observed in the open oligotrophic tropical and subtropical oceans without the influence of three types of factors mentioned above. This study developed a method to quantify the variability of oceanic PAHs based on wind frequency and wind-speed-weighted wind frequency using in-situ survey data from three cruises in the Philippine Sea, and tested the validity of this method using publicly available data from other monsoonal open oceans. The result showed that the wind frequency could better explain the variation of dissolved PAHs and particulate PAHs in the surface ocean, while the wind-speed-weighted wind frequency could better explain the variation of particulate PAHs. This study suggests that the influence of seasonal atmospheric transport cannot be ignored when describing and interpreting the distribution patterns of PAHs in the monsoon-influenced low and mid-latitude open oceans and also provides a reference method for a better understanding of the global-scale distribution patterns of PAHs in the ocean.

Considering zooplankton as a black box in determining PAH concentrations could result in misjudging their bioaccumulation

Zooplankton play an important role in energy transfer in the marine food web and form the dietary basis for the size of important fish stocks and the maintenance of their resources. Although zooplankton include numerous taxa with significantly different ecological characteristics and the interspecific differences in optimum body size and taxonomic specificity in fish feeding on zooplankton are remarkable, they are always considered as a whole (like a "black box") in current studies about the transport of persistent organic pollutants through the food chain. This approach might result in misjudgment of their bioaccumulation. In this study, the distribution properties of each taxa of zooplankton community were discerned using data from two cruise surveys conducted in the northern South China Sea. Twelve groups of zooplankton were identified, all of which had distinct ecological and functional characteristics. The carbon-based community structure of zooplankton could explain their variability with respect to polycyclic aromatic hydrocarbons (PAHs). Smaller-sized zooplankton (smaller calanoids and cyclopoids) were more likely to accumulate low molecular weight PAHs (LMW-PAHs), while larger-sized zooplankton (larger calanoids) were more likely to accumulate high molecular weight PAHs (HMW-PAHs). The bioaccumulation capacity of the zooplankton community for LMW-PAHs was negatively correlated with the proportion of omnivores and carnivores, while the opposite was true for HMW-PAHs. These results suggested that the effects of complex community structure within plankton communities should be taken into account when assessing the transfer and bioaccumulation effects of PAHs in the marine food chain.

Distribution, Source Apportionment and Risk Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) in Surface Sediments at the Basin Scale: A Case Study in Taihu Basin, China

As a systematic research at basin scale, this study investigated the spatial distribution, source apportionment and ecological risks of eighteen polycyclic aromatic hydrocarbons (PAHs) in surface sediments at different functional regions (rivers, lakes and reservoirs) from Taihu basin. Results showed that the mean values of 18 PAHs (defined as ∑₁₈PAHs) in river sediments (1277 ng/g) was much higher than those observed in lake sediments (243 ng/g) and reservoir sediments (134 ng/g). The accumulation of PAHs in river sediments was largely impacted by the local social-economic development and energy consumption. The positive matrix factorization (PMF) and isomer ratios analysis of PAHs suggest that relative contributions to PAHs in sediments were 15% for gasoline and heavy oil combustion, 9% for oil spills, 30% for coal combustion, 23% for traffic source, and 23% for diagenetic source. Ecological risk assessment based upon risk quotient (RQ) method indicated that sediments at Taihu basin have suffered moderate risk of PAHs.

An Advanced PMF Model Based on Degradation Process for Pollutant Apportionment in Coastal Areas

With increasing stress posed to the marine ecosystem and coastal communities, prevention and control of coastal pollution becomes urgent and important, in which the identification of pollution sources is essential. Currently, the pollutant source apportionment in coastal areas is mainly based on receptor models, such as the positive matrix factorization (PMF) model. Nevertheless, these models still lack consideration of the changes of pollutant behaviors (e.g., the degradation of pollutants) which cause the differences in pollutant compositions. Subsequently, the source apportionment via receptor models only based on the monitoring data may not be consistent with the one in pollution sources. To fill this gap, a pollutant degradation model was firstly developed in this study. Accordingly, the degradation model was inversed to estimate the pollutant concentrations at their emitting sources, based on the monitoring concentration in the coastal area. Finally, the estimated concentrations were fed to the PMF model for pollutant source apportionment, advancing the PMF model with degradation process. To demonstrate the feasibility and accuracy of the developed model, a case study of source appointment was carried out based on the polycyclic aromatic hydrocarbons (PAHs) in the sediments of the Pearl River Estuary. The results indicated the same types of emission source identified by the original and advanced PMF models, which were oil spill, biomass and coal combustion, and traffic emission. Nevertheless, the contributions of sources were significantly varied between the two models. According to the analyses based on emission inventory, the offsets of the results from the original PMF model were −55.4%, 22.7%, and 42.2% for the emission sources of oil spill, biomass and coal combustion, and traffic emission, respectively. Comparatively, the offsets for the advanced PMF model narrowed down to −27.5%, 18.4%, and −4.4%. Therefore, the advanced PMF model is able to provide satisfactory source apportionment for organic pollutants in coastal areas, and thus further provide a scientific basis for marine pollution prevention and control.