Significance of the great protection of the Yangtze River: Riverine input contributes primarily to the presence of PAHs and HMs in its estuary and the adjacent sea

Reducing baseline toxicity in fishery product-related sediments from land to sea: Region-specific solutions are required

Eastern China is a major producer of fishery products (including inland aquaculture, coastal mariculture, and coastal fishing products). The quality of the products is affected by hydrophobic organic contaminants (HOCs) in the sediments. Based on in-vitro luminescent bacterial assay, the baseline toxicity (BEQBio) of 56 common HOCs were assessed in the present study. Specifically, the BEQBio of sediments declined from land (31-400 mg/kg) to sea (9.1-270 mg/kg). However, the toxicity contribution explained by the HOCs increased gradually from land (0.70 %) to sea (10 %) using Iceberg Modeling. In the inland pond, current use HOCs (pyrethroid pesticide (PEs), organic tin (OTCs), and antibiotic) exhibited considerable concentrations, although their toxicity contribution was very small (0.076 %), thus more regulations on the use of HOCs should be proposed and further screening is needed to confirm the major toxicants. In coastal mariculture area, the toxicity contribution of current use HOCs further declined (0.010 %), whereas environmental background HOCs, such as polycyclic aromatic hydrocarbons (PAHs), became increasingly significant, with the contribution ratio increasing from 0.37 % to 2.4 %. To minimize the negative impacts of PAHs, optimization of energy structure in transportation and coastal industry is required. In the coastal fishing area, the phased-out persistent organic pollutants (POPs) remained a major concern, in terms of both concentration and toxicity contribution. The phased-out POPs explained 7.0 % of the toxic effects of the sediments from the coastal fishing area, due to historical residue, industrial emissions, and their high toxicities. For this reason, it is critical to improve the relevant emission regulations and standards, so as to eventually reduce the unintentional discharges of POPs.

Microplastics in different tissues of historical and live samples of endangered mega-fish (Acipenser sinensis) and their potential relevance to exposure pathways

The Chinese sturgeon (Acipenser sinensis) is an endangered freshwater mega-fish (IUCN-red listed) that survives in the Yangtze River Basin, but the population of which has declined significantly in response to environmental pressures generated by human activities. In order to evaluate the interaction between Chinese sturgeon and microplastics (MPs) for the first time, we examined the gut and gills of historical samples (n = 27), in conjunction with the blood and mucus of live samples (n = 10), to explore the potential pathways involved in MP uptake. We detected MPs in 62.9 % of the field fish, with no significant difference between guts (mean=0.9 items/individual) and gills (mean=0.8 items/individual). The abundance of MPs in fish from 2017 was significantly higher than that from 2015 to 2016 with regards to both gills and gut samples. The size of MPs in gills was significantly smaller than those in guts, yet both contained mostly fibers (90.2 %). No MPs were confirmed in blood, however 62.5 % of mucus samples contained MPs. The MPs in mucus indicated the possibility of MPs entering Chinese sturgeons if their skins were damaged. The body size of Chinese sturgeons affected their MPs uptake by ingestion and inhalation, as less MPs were detected in the gut and gills of smaller individuals. Combining the evidence from historical and live samples, we revealed the presence of MPs in different tissues of Chinese sturgeon and their potential relevance to exposure pathways. Our work expands the understanding of multiple exposure pathways between MPs and long-lived mega-fish, while emphasizing the potential risks of long-term exposure in the field.

Ecological risk assessment of dissolved heavy metals in the Yangtze River Estuary and Zhejiang coastal waters, China

The study applied a tiered ecological risk assessment method to evaluate the long-term status and trend of the ecological risks of dissolved heavy metals from 2011 to 2019 in the Yangtze River Estuary and Zhejiang coastal waters, China. The results for spring, summer, and autumn of 2019 indicated that Pb, Cd, and Zn posed no adverse ecological risk, Cu posed a potential ecological risk, and As posed an ecological risk. The annual results from 2011 to 2019 suggested that Pb, Cd, and Zn posed no adverse ecological risks, and As and Cu posed an ecological risk. The trend analysis in the nine years showed that the ecological risk of Cu is gradually decreasing, while that of As is still a concern. The overall trend is attributed to the environmental protection policies that reduced these contaminants' terrestrial sources and atmospheric sources.

Seasonal and interannual changes (2005-2021) of lake water quality and the implications for sustainable management in a rapidly growing metropolitan region, central China

A series of restoration measures such as municipal wastewater treatment and aquaculture closures have been implemented in Wuhan City during recent years. In order to explore the impact of restoration measures and climate change on lake water quality, long-term (2005-2021) water quality data of 47 lakes were explored to reveal spatiotemporal changes in lake water quality. Percentages of polluted lakes were calculated according to six water-quality parameters, including total phosphorus (TP), ammonia nitrogen (NH3-N), chemical oxygen demand (COD), biological oxygen demand (BOD), chemical oxygen demand using potassium permanganate as oxidant (CODMn) and petroleum contamination (PET), at interannual and monthly timescales. At the interannual timescale, percentages of COD, BOD, CODMn and PET pollution decreased significantly, suggestive of water quality improvement during recent years. At the monthly timescale, low percentages of NH3-N and BOD pollution in March 2020 probably resulted from the sharp reduction in human activities during the COVID-19 lockdown. At the monthly timescale, temperature was positively correlated with percentage of CODMn pollution, but negatively correlated with percentage of NH3-N pollution; precipitation was negatively correlated with percentage of BOD pollution. The similarity of water-quality parameters generally decreased with an increase in geographical distance between each pair of lakes. However, the regression coefficients between the similarity of lake water quality and the geographical distance decreased with time, probably resulting from enhanced similarity of water quality parameters among all lakes with rapid urbanization. Our results highlight the importance of active restoration measures for sustainable management of lakes in Wuhan City, as well as in similar developing regions.

Determination of high-risk factors and related spatially influencing variables of heavy metals in groundwater

Identifying high-risk factors (heavy metals (HMs) and pollution sources) by coupling receptor models and health risk assessment model (HRA) is a novel approach within the field of risk assessment. However, this coupled model ignores the contribution of spatial differentiation to high-risk factors, resulting in the assessment being subjective. Taking Dongting Plain (DTP) as an example, a coupling framework by jointly using the positive matrix factorization model (PMF), HRA, Monte Carlo simulation, and geo-detector was developed, aiming to identify high-risk factors in groundwater, and further explore key environmental variables influencing the spatial heterogeneity of high-risk factors. The results showed that at least 82.86 % of non-carcinogenic risks and 97.41 % of carcinogenic risks were unacceptable for people of all ages, especially infants and children. According to the relationships among HMs, pollution sources, and health risks, As and natural sources were defined as high-risk HMs and sources, respectively. The interactions among Holocene thickness, oxidation-reduction potential, and dissolved organic carbon emerged as the primary drivers of spatial variability in high-risk factors, with their combined explanatory power reaching up to 74%. This proposed framework provides a scientific reference for future studies and a practical reference for environmental authorities in developing effective pollution management measures.

Estuarine environmental flow assessment based on the flow-ecological health index relation model: a case study in Yangtze River Estuary, China

Environmental flow (e-flow) is the water demand of one given ecosystem, which can become the flow regulation target for protection and restoration of river or estuarine ecosystems. In this study, an e-flow assessment based on the flow-ecological health index (EHI) relation model was conducted to improve ecosystem health of the Yangtze River Estuary (YRE). Monitoring data of hydrology, biology, and water environment in the last decades were used for the model establishment. For the description of the YRE ecosystem, an EHI system was developed by cumulative frequency distribution curves and adaption of national standards. After preprocessing original flow values into proportional flow values, the generalized additive model and Monte Carlo random sampling were used for the establishment of the flow-EHI relation model. From the model calculation, the e-flow assessment results were that, in proportional flow values, the suitable flow range was 1.05-1.35, and the optimum flow range was 1.15-1.25 (flows in Yangtze River Datong Station). For flow regulation in two crucial periods, flows of 42,630-65,545 m3/s or over 14,675 m3/s are needed for the suitable flow of YRE in summer (June-August) or January, respectively. An adaptive management framework of ecological health-based estuarine e-flow assessment for YRE was contrived due to the limitation of current established model when facing the extreme drought in summer, 2022. The methodology and framework in this study are expected to provide valuable management and data support for the sustainable development of estuarine ecosystems and to bring inspiration for further studies at even continental or global levels.

Spatiotemporal variation, partitioning, and ecological risk assessment of benzothiazoles, benzotriazoles, and benzotriazole UV absorbers in the Yangtze River Estuary and its adjacent area

The distributions and toxicities of the pollutants benzothiazoles (BTHs), benzotriazoles (BTRs), and benzotriazole ultraviolet stabilizers (BUVs) have attracted much attention, but most research has focused on freshwater environments and few have examined their levels in marine environments. This study, for the first time, investigated the spatial and temporal variability and ecological risks of BTHs, BTRs and BUVs in the Yangtze River estuary and its adjacent area, and further elucidated how environmental factors influence the transport of these contaminants. The concentrations of BTHs, BTRs, and BUVs in seawater showed significant seasonal variability, with the highest concentrations in summer, followed by autumn, and then winter-spring. The spatiotemporal variability in BTHs, BTRs and BUVs in the seawater and sediments samples showed decreasing trends from nearshore to offshore, reflecting the influence of river discharge. Marine debris and continuous discharge from cities were responsible for the high detection frequency of these contaminants in the YRE and its adjacent area. Furthermore, the moderate risk from the presence of BTHs, BTRs, and BUVs as they accumulate in sediments should not be ignored. Our study provides new insights into the fate and ecological risk of BTHs, BTRs, and BUVs in the estuary.

Preliminary manifestation of the Yangtze River Protection Strategy in improving the carbon sink function of estuary wetlands

In 2016, the Yangtze River Protection Strategy was proposed and a series of measures were applied to restore the health and function of the Yangtze River ecosystem. However, the impact of these measures on the carbon (C) sink capacity of the Yangtze River estuary wetlands has not been exhaustively studied. In this work, the effects of these measures on the C sink capacity of Yangtze River estuary wetlands were examined through the long-term monitoring of C fluxes, soil respiration, plant growth and water quality. The C flux of the Yangtze River estuary wetlands has become increasingly negative after the implementation of these measures, mainly owing to reduction in soil CO2 emission. The decrease in the chemical fertilizer release and returning farmland to wetland had led to the improvement of water quality in the estuary area, which further reduced soil heterotrophic microbial activity, and ultimately decreasing soil CO2 emissions of estuary wetlands.

Implications on freshwater lake-river ecosystem protection suggested by organic micropollutant (OMP) priority list

Lake-river complex systems represent interconnected ecosystems wherein inflow rivers significantly influence the migration of terrigenous contaminants, particularly organic micropollutants (OMPs), into lakes. Given the extensive array of OMPs, screening for those with the highest potential hazard is crucial for safeguarding freshwater lake-river ecosystems. In this study, an optimized multi-criteria scoring method was applied to prioritize OMPs. Flux estimation was then performed to identify the contamination load contributed by the Le'an River to Poyang Lake. Higher concentrations of phthalate esters (PAEs) were detected in the lake-river system, ranging from 1154.5 to 22,732.8 ng/L, followed by antibiotics and polycyclic aromatic hydrocarbons (PAHs), while historical pollutant residues were comparably lower. Based on the prioritization methodology, 27 compounds, encompassing eight PAEs, six organochlorine pesticides (OCPs), six polychlorinated biphenyls (PCBs), five PAHs and two antibiotics, emerged as priority pollutants. Multiple risk assessments revealed that priority PAEs posed relatively high ecological and human health risks; concurrently, the annual fluxes of individual priority PAEs into the lake all exceeded 1000 kg, with DBP, DEHP and BBP fluxes reaching 18,352, 10,429, and 7825 kg, respectively. This research offers valuable insights stemming from OMP prioritization to aid in the conservation of freshwater lake ecosystems, particularly concerning lake-river system integrity.

Resource utilization of rice straw to prepare biochar as peroxymonosulfate activator for naphthalene removal: Performances, mechanisms, environmental impact and applicability in groundwater

Herein, biochar was prepared using rice straw, and it served as the peroxymonosulfate (PMS) activator to degrade naphthalene (NAP). The results showed that pyrolysis temperature has played an important role in regulating biochar structure and properties. The biochar prepared at 900°C (BC900) had the best activation capacity and could remove NAP in a wide range of initial pH (5-11). In the system of BC900/PMS, multi-reactive species were produced, in which 1O2 and electron transfer mainly contributed to NAP degradation. In addition, the interference of complex groundwater components on the NAP removal rate must get attention. Cl- had a significant promotional effect but risked the formation of chlorinated disinfection by-products. HCO3-, CO32-, and humic acid (HA) had an inhibitory effect; surfactants had compatibility problems with the BC900/PMS system, which could lead to unproductive consumption of PMS. Significantly, the BC900/PMS system showed satisfactory remediation performance in spiked natural groundwater and soil, and it could solve the problem of persistent groundwater contamination caused by NAP desorption from the soil. Besides, the degradation pathway of NAP was proposed, and the BC900/PMS system could degrade NAP into low or nontoxic products. These suggest that the BC900/PMS system has promising applications in in-situ groundwater remediation.

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.