Water residence time controls seasonal nitrous oxide budget in a semi-enclosed bay: Insights from an improvement estimation method.

This study developed an estimation method for the N2O budget using 15N stable isotope labeling techniques, a dual-layer model and a box model, which was used to elucidate the underlying dynamics of N2O accumulation in Zhanjiang Bay. The results showed that although the net input of N2O during the rainy season was 2.36 times higher than that during the dry season, the overall N2O concentration was only 66.6 % of that during the dry season due to the extended water residence time in the dry season. Our findings highlighted that water residence time was the key factor for the N2O emission, and a longer water residence time was unfavorable for the efflux of N2O through hydrodynamic processes and was more conducive to the production and accumulation of N2O within the bay. This research enhanced our comprehension of N2O dynamics and provided crucial insights for refining nitrogen management strategies and mitigation efforts.

High-throughput screening of 222 pesticides in road environments in a megacity of northern China: A new approach to urban population exposure.

A large number of pesticides have been widely manufactured and applied, and are released into the environment with negative impact on human health. Pesticides are largely used in densely populated urban environments, in green zones, along roads and on private properties. In order to characterize the potential exposure related health effects of pesticide and their occurrence in the urban environment, 222 pesticides were screened and quantified in 228 road dust and 156 green-belt soil samples in autumn and spring from Harbin, a megacity in China, using GC-MS/MS base quantitative trace analysis. The results showed that a total of 33 pesticides were detected in road dust and green-belt soil, with the total concentrations of 650 and 236 ng/g (dry weight = dw), respectively. The concentrations of pesticides in road dust were significantly higher than that in green-belt soil. Pesticides in the environment were influenced by the seasons, with the highest concentrations of insecticides in autumn and the highest levels of herbicides in spring. In road dust, the concentrations of highways in autumn and spring (with the mean values of 94.1 and 68.2 ng/g dw) were much lower than that of the other road classes (arterial roads, sub-arterial roads and branch ways). Whereas in the green-belt soil, there was no significant difference in the concentration of pesticides between the different road classes. A first risk assessment was conducted to evaluate the potential adverse health effects of the pesticides, the results showed that the highest hazard index (HI) for a single pesticide in dust and soil was 0.12, the hazard index for children was higher than that for adults, with an overall hazard index of less than 1. Our results indicated that pesticide levels do not have a significant health impact on people.

Air-sea exchange of PAHs in the Taiwan Strait: Seasonal dynamics and regulation mechanisms revealed by machine learning approach.

In this study, to understand the seasonal dynamics of air-sea exchange and its regulation mechanisms, we investigated polycyclic aromatic hydrocarbons (PAHs) at the air-sea interface in the western Taiwan Strait in combination with measurements and machine learning (ML) predictions. For 3-ring PAHs and most of 4- to 6-ring, volatilization and deposition fluxes were observed, respectively. Seasonal variations in air-sea exchange flux suggest the influence of monsoon transitions. Results of interpretable ML approach (XGBoost) indicated that volatilization of 3-ring PAHs was significantly controlled by dissolved PAH concentrations (contributed 24.0 %), and the gaseous deposition of 4- to 6-ring PAHs was related to more contaminated air masses originating from North China during the northeast monsoon. Henry's law constant emerged as a secondary factor, influencing the intensity of air-sea exchange, particularly for low molecular weight PAHs. Among environmental parameters, notably high wind speed emerges as the primary factor and biological pump's depletion of PAHs in surface seawater amplifies the gaseous deposition process. The distinct dynamics of exchanges at the air-water interface for PAHs in the western TWS can be attributed to variations in primary emission intensities, biological activity, and the inconsistent pathways of long-range atmospheric transport, particularly within the context of the monsoon transition.

Distinct anthropogenic signatures: A comparative analysis of polycyclic aromatic hydrocarbons in sediments from two southeastern Chinese bays.

Sansha and Luoyuan Bay are influenced by different industrial structure, but the sources and pollution status of polycyclic aromatic hydrocarbons (PAHs), especially alkylated PAHs, are poorly understood. We studied 25 PAHs in surface sediments from the two bays. The results showed that PAHs concentrations in Sansha and Luoyuan Bay sediment range from 6.54 to 479.28 ng/g and 118.82 to 2984.09 ng/g, respectively. Alkylated PAHs dominated in Sansha (48.86 % of Σ25PAHs), while 3-ring PAHs dominated in Luoyuan (36.32 % of ∑25PAHs). Results of sources analysis indicated oil spills as the main PAHs source in Sansha, and domestic emissions and fossil fuel combustion in Luoyuan. Ecological risk assessment of showed low sediment risk, but in Luoyuan was higher than in Sansha. Compared with Luoyuan Bay, Sansha Bay emits less industrial pollutants, so the pollution is lower than Luoyuan Bay. Increased attention to protecting Luoyuan Bay is recommended.

Occurrence, seasonal variations, and fate of household and personal care chemicals in a wastewater treatment plant with Bacillus bioreactor process.

Household and personal care chemicals (HPCCs) constitute a significant component of everyday products, with their global usage on the rise. HPCCs are eventually discharged into municipal wastewater treatment plants (WWTPs). However, the behaviors of HPCCs inside the Bacillus Bioreactor (BBR) process, including their prevalence, fate, and elimination mechanisms, remain underexplored. Addressing this gap, our study delves into samples collected from a BBR process at a significant WWTP in the northeast of China. Our results spotlight the dominance of linear alkylbenzene sulfonates (LASs) in the influent with concentrations ranging between 238 and 789 µg/L, much higher than the other HPCC concentrations, and remained dominant in the subsequent treatment units. After treatment using the BBR process, the concentrations of HPCCs in the effluent were diminished. Examination of different treatment units underscores the grit chamber removed over 60% of higher-concentration HPCCs, while the performance of the (RBC) tank needs to be improved. Except for the ultraviolet radiation (UV)-filters, seasonal variations exert minimal impact on the concentrations and removal efficiencies of other HPCCs in the BBR process. According to the mass balance analysis, the important mechanisms for HPCC removal were biodegradation and sludge adsorption. Also, the octocrylene (OCT) concerns raised by the environmental risk assessment of the HPCCs residuals in the final effluent, indicate a moderate risk to the surrounding aquatic environment (0.1 < RQ < 1), whereas other HPCCs have a lower risk level (RQ < 0.1). Overall, the research offers new perspectives on the fate and elimination mechanisms of HPCCs throughout the BBR process.

Multimedia distribution, dynamics, and seasonal variation of PAHs in Songhua wetland: Implications for ice-influenced conditions.

The knowledge of polycyclic aromatic hydrocarbons (PAHs) in wetlands remains limited. There is a research need for the dynamics between interfaces of multimedia when ice is present in this fragile ecosystem. In this study, sediment, open-water, sub-ice water, and ice samples were collected from the Songhua wetland to study the behaviors of PAHs with and without influences from ice. The concentration of all individual PAHs in sub-ice water (370-1100 ng/L) were higher than the open-water collected from non-ice-covered seasons (50-250 ng/L). Enrichment of PAHs in the ice of wetland was found, particularly for high-molecular-weight PAHs (HMW). This could be attributed to the relatively lower polarity of hydrocarbons compounds, making them more likely to remain in the ice layer during freezing. Source assessments reveal common sources for sub-ice water and ice, which differ from those in the open water in non-ice-covered seasons. This difference is primarily attributed to heating activities in the Harbin during winter. The average percentage contributions were 79% for sub-ice water and 36% for ice related to vehicle exhausts and coal combustion. Additionally, wood burning contributed 25% to sub-ice water and 62% to ice. Sediment in the wetland was found to serve as a final deposit particularly for heavier PAHs, especially those with 6 rings. Sediment also has the potential to act as a source for the secondary emission of low-molecular-weight PAHs (LMW) congeners into the water. PAHs in wetland displayed low ecological risk, while HMW PAHs with relative higher ecological risk is recommended to be further monitored.

Carbon sequestration reduced by the interference of nanoplastics on copper bioavailability.

Microplastics (MPs) have been recognized as a serious new pollutant, especially nanoplastics (NPs) pose a greater threat to marine ecosystem than larger MPs. Within these ecosystems, phytoplankton serve as the foundational primary producers, playing a critical role in carbon sequestration. Copper (Cu), a vital cofactor for both photosynthesis and respiration in phytoplankton, directly influences their capacity to regulate atmospheric carbon. Therefore, we assessed the impact of NPs on Cu bioavailability and carbon sequestration capacity. The results showed that polystyrene nanoplastics (PS-NPs) could inhibit the growth of Thalassiosira weissflogii (a commonly used model marine diatom) and Chlorella pyrenoidosa (a standard strain of green algae). The concentration of Cu uptake by algae has a significant negative correlation with COPT1 (a Cu uptake protein), but positive with P-ATPase (a Cu efflux protein). Interestingly, PS-NPs exposure could reduce Cu uptake and carbon Cu sequestration capacity of algae, i.e., when the concentration of PS-NPs increases by 1 mg/L, the concentration of fixed carbon dioxide decreases by 0.0023 ppm. This provides a new perspective to reveal the influence mechanisms of PS-NPs on the relationship between Cu biogeochemical cycling and carbon source and sink.

Does mangrove leave falling dominate the bury of polycyclic aromatic hydrocarbons in the mangrove of China?

Mangrove wetlands are vital coastal ecosystems that can absorb and accumulate pollutants. Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants that pose potential risks to ecosystems and human health. However, their source and transport fate in mangrove areas are poorly understood. This study investigates 29 PAHs pollution of water and sediment in Zhangjiangkou Mangrove Wetland, the northernmost large-scale mangrove wetland reserve in China. We examine the distribution, source, transport mechanisms and risk assessment of PAHs. The results show that the concentrations of PAHs in mangrove sediment range from 55.62 to 347.36 ng/g (DW), with 5-ring PAHs being the dominant species. While the concentrations of PAHs in surface water range from 10.61 to 46.39 ng/L, with 2-ring PAHs and alkylated PAHs being the dominant species. The PAHs concentrations in surface water and sediment of river are higher than those in mangrove area, indicating that mangrove water could receive PAHs through tidal exchange. Based on diagnostic ratios (DRs), principal component analysis (PCA), and positive matrix factorization (PMF), we infer that the leaf deposition (48.55%) could be an important pathway of PAHs in mangrove sediment except for river water transport (51.45%), while the PAHs in estuary water originate mainly from point sources such as biomass burning (50.96%) and traffic emission (49.04%). The range of toxic equivalents in surface water and sediment was 2.73-16.09 ng TEQ g-1 and 0.03-3.63 ng/L, respectively. Although the ecological risk assessment suggests that the PAHs pollution in surface water and sediment poses a low risk, we recommend more attention to the protection of the mangrove ecosystem. This study reveals that mangrove leaf falling might be a significant mechanism of PAH sequestration in the mangrove system, which deserves more attention in future research.

Seasonal distribution of water masses and their impacts on nutrient supply in the southern Beibu Gulf.

Dual water isotopes were investigated to reveal the seasonal distribution of water masses and their impacts on nutrient supply in southern Beibu Gulf. In summer and winter, the South China Sea (SCS) water (61-69%) contributed the most to the seawater in the southern Beibu Gulf, followed by the diluted water (24-34%), and the west-Guangdong coastal current (WGCC) (5-7%) had the minimum contribution. However, the major nutrient source shifted from the diluted water in summer (39-73%) to the SCS water (57-90%) in winter. The WGCC's impact on nutrient loads was relatively small (2-10% in summer, 4-34% in winter). Our results highlight the control of nutrient supply was the SCS water (winter) and diluted water (summer), with limited influence from the WGCC, providing new insights into the impact of water mass transportation and its nutrient supply in the Beibu Gulf.

Microplastics in the Taiwan Strait and adjacent sea: Spatial variations and lateral transport.

This study investigates the distribution, structural properties, and potential impacts of oceanic processes on microplastics (MPs) in the Taiwan Strait (TWS) and surrounding seas. With an average of 174 particles/m3, the MP abundance in surface seawater ranged from 84 to 389 particles/m3. MP abundance ranged from 16 to 382 particles/kg in sediments, with a median of 121 particles/kg. Fragment and fiber were the two most frequently detected shapes. These MPs were found to be composed primarily of carbon and oxygen elements at 70-90% levels using energy-dispersive X-ray spectroscopy. Additionally, several examples had trace levels of metallic components. Black was the color that MPs saw the most often out of all the hues. The two main types of polymers are polyester and rayon, and their production is influenced by home sewage discharge and synthetic fiber production. The main routes of MP transport were land source input, riverine input, and oceanic currents. This study showed that salinity affects the distribution of MPs, with high-salinity seawater serving to saturate their presence. On the other hand, upwelling raises MP concentrations by bringing nutrients from the deep to the surface. Furthermore, it has been discovered that the dilution of the Pearl River plume increases the MP prevalence in the region. The South China Sea Warm Current had the highest lateral MPs transport flux (2.1 × 1014 particles/y), which was followed by the Taiwan Strait Current area (1.0 × 1014 particles/y) and the Guangdong coastal areas (8.6 × 1013 particles/y). In sediments, the MP prevalence was inversely correlated with particle size. Flocculation processes probably made it easier for MPs to travel down the water column and deposit themselves on the aquatic substrate. Although the relationship between MPs, total organic carbon, and total organic nitrogen was not correlated, a favorable trend showed that MPs may discreetly contribute to carbon storage in coastal sediment.

Effects of polyethylene and polyvinyl alcohol on growth and protease activity of Acanthopagrus schlegelii juveniles.

Many plastic products are used in aquaculture. Studying the toxicological effects of plastics differing in water solubility on marine organisms can provide valuable information. In this study, different amounts of polyvinyl alcohol (PVA) and polyethylene (PE) films were embedded in the feed and fed to Acanthopagrus schlegelii. After 1, 2, 4, and 8 weeks, the changes in percentage weight gain (PWG), feed efficiency (FE), pepsin activity (PA), and trypsin activity (TA) were observed. Either fed to PE or PVA, PWG, and FE of the experimental group were lower than those of the control group after eight weeks. Plastics level recovered from digestive tracts, feces, and water were higher in the PE groups than in the PVA groups. PA rose with increased feeding of plastics, but TA showed the opposite trend. TA activity decreased with increased feeding of plastics. Further analysis showed that TA was positively correlated with PWG.

Heavy metals and Pb isotopes in sediment cores from the Bering and Chukchi seas: Implications for environmental changes and human activities over the past century.

The Bering Sea and the Chukchi Sea are important regions for marine ecosystems and climate change. However, the historical deposition and sources of metals in these regions are poorly understood. In this study, we utilized Pb isotopes and multi-element concentrations (Ni, Cu, Fe, Mn, Zn, Cd, Pb) coupled with Pb-210 dating to investigate the historical deposition and source identification of metals in sediment cores collected from the Bering Sea and the Chukchi Sea. Our findings reveal that the transport of organic matter was mainly transported by marine and terrestrial sources in the Bering and Chukchi Sea, respectively. Historical variations of metals were similar in both seas, showing an increasing trend of metals (excluding Mn) from the 1960s to the 1990s, followed by a gradual decrease after the 1990s, which can be attributed to the development of industrial and gasoline emission. The results of the geo-accumulation index indicated that sediment in both seas was relatively unpolluted with metals. Additionally, Pb isotopic ratios suggested that natural weathering was the primary source of Pb in the area, but the use and phase-out of gasoline were also well-reconstructed. This study provides valuable information for assessing environmental changes and human activities over the past century in the Arctic and subarctic Ocean.

Can water dating trace the transport history of HCHs in the ocean?

Long-range atmospheric and oceanic transport play a crucial role in the accumulation of persistent organic pollutants (POPs), including hexachlorocyclohexanes (HCHs), in the Arctic Ocean. Herein, transient tracers, specifically chlorofluorocarbon-12 and sulfur hexafluoride, were used to determine the ventilation time of HCHs. Results revealed that dissolved HCHs can penetrate to a depth of ~500 m in the western Arctic Ocean, corresponding to water masses with a mean age of 45 ± 14 years. The average long-range transport time for α-HCH from initial atmospheric release to entering the western Arctic Ocean was estimated to be >30 ± 5 years, indicating continued moderate to high ecological risks from HCHs in the Arctic. This study demonstrates that transient tracers serve as effective water dating tools to elucidate the transport history of stable POPs in the ocean, contributing to a better understanding of their environmental characteristics and fate.

Ocean Stratification Impacts on Dissolved Polycyclic Aromatic Hydrocarbons (PAHs): From Global Observation to Deep Learning.

Ocean stratification plays a crucial role in many biogeochemical processes of dissolved matter, but our understanding of its impact on widespread organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), remains limited. By analyzing dissolved PAHs collected from global oceans and marginal seas, we found different patterns in vertical distributions of PAHs in relation to ocean primary productivity and stratification index. Notably, a significant positive logarithmic relationship (R2 = 0.50, p < 0.05) was observed between the stratification index and the PAH stock. To further investigate the impact of ocean stratification on PAHs, we developed a deep learning neural network model. This model incorporated input variables determining the state of the seawater or the stock of PAHs. The modeled PAH stocks displayed substantial agreement with the observed values (R2 ≥ 0.92), suggesting that intensified stratification could prompt the accumulation of PAHs in the water column. Given the amplified effect of global warming, it is imperative to give more attention to increased ocean stratification and its impact on the environmental fate of organic pollutants.

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).

Vertical distribution and transport of microplastics in the urban atmosphere: New insights from field observations.

The distribution and transport of atmospheric microplastics (AMPs) have raised concerns regarding their potential effects on the environment and human health. Although previous studies have reported the presence of AMPs at ground level, there is a lack of comprehensive understanding of their vertical distribution in urban environments. To gain insight into the vertical profile of AMPs, field observations were conducted at four different heights (ground level, 118 m, 168 m and 488 m) of the Canton Tower in Guangzhou, China. Results showed that the profiles of AMPs and other air pollutants had similar layer distribution patterns, although their concentrations differed. The majority of AMPs were composed of polyethylene terephthalate and rayon fibers ranging from 30 to 50 µm. As a result of atmospheric thermodynamics, AMPs generated at ground level were only partially transported upward, leading to a decrease in their abundance with increasing altitude. The study found that the stable atmospheric stability and lower wind speed between 118 m and 168 m resulted in the formation of a fine layer where AMPs tended to accumulate instead of being transported upward. This study for the first time delineated the vertical profile of AMPs within the atmospheric boundary layer, providing valuable data for understanding the environmental fate of AMPs.

Surface structures changes and biofilm communities development of degradable plastics during aging in coastal seawater.

Biodegradable plastics (BPs) are a suitable alternative to conventional plastics. Still, their excessive or unplanned use may disrupt the abundance and community structure of the microbial population. To this end, a 58-day experiment in which biodegradable plastic objects, such as bags and boxes, were exposed to near-coastal seawater was conducted. They also assessed how they affected the diversity and organization of bacterial populations in seawater and on the surface of BPs products. It is evident that after the exposure time, both BP's bag and box products deteriorate in the ocean to varying degrees. The results of high-throughput sequencing of bacterial communities in seawater and those colonized on BPs products reveal significant differences in microbial community structures between seawater and BPs plastic samples. These suggest that the degradation of biodegradable plastics is shadowed by microorganisms and exposure time, while BP products influence the structural characteristics of microbial communities.

Enrichment and ecological risks of microplastics in mangroves of southern Hainan Island, China.

Mangroves have recently been identified as one of the most threatened ecosystems by microplastics (MPs) pollution from terrestrial and marine sources, while little is known regarding the MPs enrichment, influencing factors and associated ecological risks in mangroves. The present investigation aims to evaluate the accumulation, characteristics, and ecological risks of MPs in various environmental matrices from three mangroves of southern Hainan Island during dry and wet seasons. The results revealed the prevalence of MPs pollution in the surface seawater and sediment from all studied mangroves during two seasons, where the highest MPs abundance was observed at Sanyahe mangrove. The abundance of MPs varied considerably in surface seawater by seasons and were distinctly modulated by rhizosphere effect. The characteristics of MPs also exhibited some pronounced variations across mangroves, seasons and environmental compartments, but the detected MPs were dominated by fiber-shaped, transparent-colored, and smaller-sized (100-500 µm) MPs. The most prevalent polymer types were polypropylene, polyethylene terephthalate and polyethylene. Further analyses revealed positive correlations between MPs abundance and contents of nutrient salts in surface seawater but negative relationships between MPs abundance and water physicochemical properties, including temperature, salinity, pH and conductivity (p < 0.05). The joint use of three evaluation models indicated MPs posed varying degrees of ecological risks to all studied mangroves, whereas Sanyahe mangrove exhibited the highest ecological risk of MPs pollution. This study provided new insights into the spatial-seasonal variations, influencing factors and risk assessment of MPs in mangroves, which would be helpful for source tracing, pollution monitoring and policy formulation.

Gaseous polycyclic aromatic hydrocarbons over the South China Sea: Implications for atmospheric transport under monsoon influences.

The seasonal monsoon variations have significant impact on the atmospheric transport of semi-volatile organic pollutants over the South China Sea (SCS). We analyzed polycyclic aromatic hydrocarbons (PAHs) over the basin and island areas (Yongxing Island and Yongshu Island) in 2017. Gaseous PAHs (0.17-1.4 ng m-3) showed spatio-temporal distinctions in their composition and sources among the basin and island areas. Mixed combustion sources of PAHs were identified over the SCS, including a petroleum source near the island areas. The transport routes of PAHs were inferred by the air mass back trajectories and potential source contribution factor analysis, identifying strong biomass burning signals from the Indochina Peninsula and other Southeast Asian countries. Emissions from approximately 90 % of the combustion sources were transported to basin areas by monsoons, whereas the island areas were dominated by local emissions. This study emphasizes the main potential terrestrial source of PAHs over the SCS under monsoon influences.

The interference of marine accidental and persistent petroleum hydrocarbons pollution on primary biomass and trace elements sink.

More than 80 % of the primary biomass in marine environments is provided by phytoplankton. The primary mechanism in the trace element sink is the absorption of trace elements by phytoplankton. Because of their difficult degradability and bioaccumulation, petroleum hydrocarbons are one of the most significant and priority organic contaminants in the marine environment. This study chose Chlorella pyrenoidosa as the model alga to be exposed to short and medium-term petroleum hydrocarbons. The ecological risk of accidental and persistent petroleum hydrocarbon contamination was thoroughly assessed. The interaction and intergenerational transmission of phytoplankton physiological markers and trace element absorption were explored to reflect the change in primary biomass and trace element sink. C. pyrenoidosa could produce a large number of reactive oxygen species stimulated by the concentration and exposure time of pollutants, which activated their antioxidant activity (superoxide dismutase (SOD) activity, ß-carotene synthesis, antioxidant trace elements uptake) and peroxides production (hydroxyl radicals and malondialdehyde). The influence of the growth phase on SOD activity, copper absorption, and manganese adsorption in both persistent and accidental pollution was significant (p < 0.05, F > Fα). Adsorption of manganese and selenium positively connected with SOD, malondialdehyde, and Chlorophyl-a (p < 0.01). These findings convincingly indicate that petroleum hydrocarbon contamination can interfere with primary biomass and trace element sinks.