Significant methane ebullition from large shallow eutrophic lakes of the semi-arid region of northern China

Eutrophic lakes are a major source of the atmospheric greenhouse gas methane (CH4), and CH4 ebullition emissions from inland lakes have important implications for the carbon cycle. However, the spatio-temporal heterogeneity of CH4 ebullition emission and its influencing factors in shallow eutrophic lakes of arid and semi-arid regions remain unclear. This study aimed to determine the mechanism of CH4 emission via eutrophication in Lake Ulansuhai, a large shallow eutrophic lake in a semi-arid region of China.To this end, monthly field surveys were conducted from May to October 2021, and gas chromatography was applied using the headspace equilibrium technique with an inverted funnel arrangement. The total CH4 fluxes ranged from 0.102 mmol m-2 d-1 to 59.296 mmol m-2 d-1 with an average value of 4.984 ± 1.82 mmol m-2 d-1. CH4 ebullition emissions showed significant temporal and spatial variations. The highest CH4 ebullition emission was observed in July with a grand mean of 9.299 mmol m-2 d-1, and the lowest CH4 ebullition emissions occurred in October with an average of 0.235 mmol m-2 d-1. Among seven sites (S1-S7), the maximum (3.657 mmol m-2 d-1) and minimum (1.297 mmol m-2 d-1). CH4 ebullition emissions were observed at S2 and S7, respectively. As the main route of CH4 emission to the atmosphere in Lake Ulansuhai, the CH4 ebullition flux during May to October accounted for 69% of the total CH4 flux. Statistical analysis showed that CH4 ebullition was positively correlated with temperature (R = 0.391, P < 0.01) and negatively correlated with air pressure (R = 0.286, P < 0.00). Temperature and air pressure were found to strongly regulate the production and oxidation of CH4. Moreover, nutritional status indicators such as TP and NH4+-N significantly affect CH4 ebullition emissions (R = 0.232, P < 0.01; R = -0.241, P < 0.01). This study reveals the influencing factors of CH4 ebullition emission in Lake Ulansuhai, and provides theoretical reference and data support for carbon emission from eutrophic lakes. Nevertheless, research on eutrophic shallow lakes needs to be further strengthened. Future research should incorporate improved flux measurement techniques with process-based models to improve the accuracy from regional to large-scale estimation of CH4 emissions and clarify the carbon budget of aquatic ecosystems. In this manner, the understanding and predictability of CH4 ebullition emission from shallow lakes can be improved.

Quantitative analysis and risk assessment to full-size microplastics pollution in the coastal marine waters of Hong Kong

Given the potential risk to the ecosystem, attention has increased in recent decades to the contamination of the aquatic environment by microplastics (MPs). Due to the limitations of conventional analysis methods of MPs, little is known about the size distribution and abundance of a full-size MPs from 1 μm to 5 mm. The present study quantified MPs with size ranges of 50 μm - 5 mm and 1-50 μm in the coastal marine waters from twelve locations in Hong Kong using fluorescence microscopy and flow cytometry respectively, during the end of wet (September 2021) and dry (March 2022) seasons. The average abundance of MPs with size ranges of 50 μm - 5 mm and 1-50 μm from twelve sampling locations marine surface waters were found ranging from 27 to 104 particles L^-1 and 43,675-387,901 particles L^-1 in the wet season respectively, and 13-36 particles L^-1 and 23,178-338,604 particles L^-1 in the dry season respectively. Significant temporal and spatial variations of small MPs abundance might be observed at the sampling locations, which were contributed by the influences of the estuary of Pearl River, sewage discharge points, land structure, and other anthropogenic activities. Based on the MPs abundance information, ecological risk assessment was conducted and revealed that the small MPs (< 10 μm) in coastal marine surface waters may pose potential health risks to aquatic organisms. Additional risk assessments are needed in order to determine whether or not the MPs exposure would cause health risks to the public.

Ten years of investigations of Fukushima radionuclides in the environment: A review on process studies in environmental compartments

In March 2011, severe nuclear accident happened at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) after the gigantic earthquake and following huge tsunami wave. A lot of investigations to assess environmental and radiological impacts of released radionuclides have been conducted by domestic and international organizations. Environmental radioactivity research related to the FDNPP accident has spread widely over different scientific fields due to specific features of the accident, and specifically its impact on the marine environment. The present paper summarizes major lessons learned from the environmental investigations of the FDNPP accident. Environmental radioactivity studies have typical interdisciplinary character; especially physics and chemistry are fundamental as a base of process studies in the environment. In this sight, we review chemical aspects regarding FDNPP-derived radiocesium transfer within and between compartments (atmosphere, ocean and land). We also discuss future trends in investigations of behavior of anthropogenic radionuclides in the environment, important not only for a better understanding of impacts of the FDNPP accident on the environment, but also for improving our general knowledge of the total environment in the Anthropocene era and its protection for the future.

The quantification of the influencing factors for spatial and temporal variations in surface water quality in recent ten years of the Huaihe River Basin, China

Temporal and spatial variations in river water quality and the factors influencing such variations are important basis and prerequisites for identifying pollution sources and improving river water environment. Monthly data for 22 indicators at 485 surface water quality (SWQ) monitoring sites (46,560 groups) in the Huaihe River Basin (HRB) from 2011 to 2018 were analyzed. This paper assessed temporal and spatial changes in SWQ in the HRB and identified the main factors influencing the changes and each factor's contribution to the changes. The five-day biological oxygen demand, permanganate index, fluoride, ammonium nitrogen, and total phosphorus were the main pollutants. Spatial cluster analysis indicated that the HRB could be divided by SWQ into areas I-IV from light to heavy pollution. Areas I and IV were nitrogen and phosphorus nutrients pollution, and areas II and III were heavy metals and organic pollution. Area IV (poor SWQ) locates mainly north of the Huaihe mainstream with annual average rainfall ≤ 640 mm. SWQ in the HRB has been improving for two decades, with an inflection point in 2015 between 2011 and 2018, and rainfall change is an important factor for the inflection point. The urbanization rate, industrial water consumption, and rainfall were the key factors influencing SWQ changes in the watershed with significant hydrological zonation, with urbanization rate and rainfall increased, industrial water consumption decreased, the SWQ was gradually improved. The key factors contributing to SWQ changes in the future will be the sewage treatment rate and rainfall changes caused by natural variations.

Temporal and spatial variations of surface water quality in the Nile River of Damietta Region, Egypt

Temporal/spatial variations of surface water quality were examined for the Nile River in the Damietta region where it serves as the major source of water for the inhabitants of Damietta Governorate. A total of 32 water quality parameters were monitored at six sampling sites for 12 months from February 2016 to January 2017. Higher values of chemical oxygen demand (COD), biological oxygen demand (BOD), heavy metals, and nutrients were observed upstream. About ~ 70% of the total variance in observations was explained by five main influences using factor analysis. The first factor (24.6% of the variance) was indicative of the mixed sources of natural and anthropogenic inputs. The second (nutritional) and the third (organic) factors were mainly controlled by the discharges from agricultural and domestic sources, respectively. Human activities and natural processes controlled the fourth and fifth factors. Only 11 parameters (K, temperature, COD, HPC, total hardness, DO, NO₂, Na, TDS, Cl, and EC) were necessary for distinguishing temporal variations according to Discriminant analysis (DA). Seven parameters (BOD, PO₄, SiO₃, Al, Turbidity, Fe, and Chlorophyll-a) were the most important variables responsible for spatial variations. Using the results we developed a water quality index (WQI) using only those parameters identified as important. All water quality parameters were below the permissible limits except for turbidity according to the World Health Organization standards, BOD and COD according to the Egyptian regulations. The calculated WQI values ranged between 12.73 and 33.73. According to these values, the Nile River Damietta branch represents a good to an excellent source of drinking water for entering secondary treatment.

Status of chromium accumulation in agricultural soils across China (1989-2016)

The first national-scale assessment of chromium (Cr) contamination in China's agricultural soils was performed based on 1625 sites analysed with 1799 previously published papers. Spatial and temporal variations were assessed, and the ecological risk was estimated. The range of Cr concentrations in farmland soil is 1.48-820.24 mg/kg. At approximately 4.31% and 0.12% of the sampling sites, Cr concentrations exceeded the screening value (150 mg/kg) and the control value (800 mg/kg), respectively (GB15618-2018). Cr concentrations decreased in the following order: Southwest > Northwest > East > South > Northeast > Central > North China. Moreover, the Cr accumulation rate in agricultural soils may have decreased during 2011-2016, possibly due to government-led changes in China's industrial structure and policies limiting the discharge of polluted industrial wastes. Linear correlations were observed between the application amounts of fertilizers and Cr concentrations in the soil, indicating that the application of nitrogen, phosphorus and potassium fertilizers is an important contributor of Cr in agricultural soils. Additionally, geoaccumulation index (I_geo) values for Cr showed that more than 83.4% of the sampling sites were uncontaminated, with high I_geo values distributed in some areas, especially those with mining and electroplating industries. Overall, this study details the Cr contamination status of agricultural soils in China and provides insights for policymakers enacting measures to prevent pollution.

Status of copper accumulation in agricultural soils across China (1985-2016)

The first national-scale assessment of Cu contamination of agricultural soils covering 1731 sites in China was performed based on 1837 published papers. The temporal and spatial variations from 1985 to 2016 in the Cu concentrations and the ecological and health risks associated with Cu exposure were analyzed. Approximately, 21.02% of the sampling sites revealed Cu concentrations that exceeded the screening value (50.00 mg/kg; GB15618-2018). The Cu concentrations differed among five geographical regions in the decreasing order of South China > West China > East China > Northeast China > North China. Notably, concentration of Cu in agricultural soils have begun to diminish since 2011 due to reduced heavy metal inputs. Cu mainly originated from anthropogenic activities such as mining and agricultural activities. Linear correlations were observed between the amounts of fungicides and fertilizers applied and the Cu concentrations in the soils, which suggested that the application of fungicides and fertilizers is an important contributor to the accumulation of Cu in soils. Additionally, the geoaccumulation index (I_geo) and ecological risk index (E_fⁱ) values implied that pollution and ecological risk resulting from soil Cu concentration were in low levels. The hazard index (HI) values were higher for children than for adults. Therefore, children should be prioritized for protection from heavy metal pollution. Overall, this study details the status of Cu contamination of agricultural soils in China, and thus provides insights for policymakers regarding the preventive measures.

Occurrence, geochemical fractionation, and environmental risk assessment of major and trace elements in sewage sludge

Industrialization and accelerated population growth have created a huge amount of sewage sludge. Many studies have reported the sewage sludge as a sink of major and trace elements, but less is known about their geochemical fractionations. In order to assess the mobility, the distribution, bioavailability, and toxicity of those elements in sludge, we collected the sewage sludge samples from all the seven wastewater treatment plants in Xiamen City, China. Results revealed a strong spatial variation and the occurrence of 48 elements with concentrations ranging from 1.00×10^-2 mg kg^-1 (Re) to 9.03×10¹ g kg^-1 (Fe) on the basis of dry sludge weight. Sequential extraction procedure showed that residual and oxidizable fractions were the main geochemical fractions of most studied elements. However, Ca, Mn, Sr, and Ni were mainly bound to acid-exchangeable fractions, while Fe, Zn, Cd, Cr, Co, and V were mainly distributed in the reducible fractions. The contamination factor and risk assessment code indicated that Ni, Cu, Zn, Cd, Cr, Co, Sr, Ca, Mn, Mo, Re, and W were highly mobile with less retention time and exerted high environmental risks through sludge land application. The sludge disposal strategy should consider not only the total concentrations of a broad range of elements but also their bioavailability.

Status of cadmium accumulation in agricultural soils across China (1975-2016): From temporal and spatial variations to risk assessment

Based on 1186 published studies, the first national-scale assessment of cadmium (Cd) contamination in agricultural soils across China was conducted. Cd concentrations, temporal and spatial variations, and ecological and health risks resulted from Cd exposure were analyzed. A small part of sampling sites with Cd concentration surpass the screening value and the control value (GB15618-2018), respectively. Soil Cd concentrations in South China were higher than other regions. Ecological risks resulting from Cd contamination were low. Soil Cd concentrations accumulated gradually from 1981 to 2016. Cd mainly came from anthropogenic activities, such as mining, smelting, sewage irrigation, and fertilization. Linear correlations were observed between application amounts of fertilizers and Cd concentrations in soil, indicating that the application of nitrogen, phosphorus, potassium, and compound fertilizers is an important contributor of Cd in soils. This study details the overall Cd contamination status of agricultural soils in China, thus can provide insights for policymakers regarding contamination prevention measures.

A seriously sand storm mixed air-polluted area in the margin of Tarim Basin: Temporal-spatial distribution and potential sources

In order to analyze the temporal-spatial distribution characteristics of PM_2.5, PM₁₀, SO₂, NO₂, CO and O₃ in five cities and the potential sources of PM₁₀ in southern Xinjiang during 2016, we collected one year officially released data for analysis. The average PM₁₀, PM_2.5, SO₂, NO₂, O₃ and CO concentrations were 289 ± 363, 99 ± 106, 17 ± 9, 29 ± 11, 65 ± 25 μg m^-3 and 1.3 ± 0.6 mg m^-3 in southern Xinjiang in 2016, respectively. The air pollutants presented distinct seasonal and spatial distribution characteristics. During sandstorm process, the particulate matters (PM) concentrations increased abruptly, with the PM₁₀ and PM_2.5 maximum concentrations exceeding 1000 and 500 μg m^-3 in each city. The backward trajectory results showed that the air masses in Akesu, Kurla, Hotan, Kashi and Atushi were mainly from the Bayingol Mongolian Autonomous Prefecture, Kyrgyzstan, Kizilesu Kirgiz Autonomous Prefecture and Taklimakan Desert (TD). In addition, TD was the main potential contributor to ambient PM₁₀ in five cities during the dust season (DS), with a weighted potential source contribution function (WPSCF) > 0.9. While the trajectories of air masses from TD, Bayingol Mongolian Autonomous Prefecture, Urumqi-Changji Area and local emission were potential sources contributing to PM_2.5 in these five cities during DS, with a WPSCF > 0.7. Moreover, the high weighted concentration weighted trajectory (WCWT) values were distributed in the Tarim basin, with PM₁₀ > 700 μg m^-3, however, the local emission and long distance transport contributed to the PM_2.5 > 160 μg m^-3 for five cities. This study comprehensively analyzes the pollution characteristics of air pollutants in five important cities in the southern margin of the Tarim Basin for the first time, and will provide an important reference basis for the prevention and control of air pollution in southern Xinjiang.

Lead contamination in sediments in the past 20 years: A challenge for China

Lead (Pb) contamination was recognized in China early in the 1920s. However, the response of Pb contamination in sediments to China's rapid economic and social development remains uncertain to date. We conducted a literature review of over 1000 articles from 1990 to 2016 and the first national-scale survey of Pb contamination in China. A literature review showed that available research in China focused on the economically highly developed river basins, including the Pearl River Basin (PRB), Yellow River Basin (YRB), and Yangtze River Basin (YtRB), whereas those in the less developed southeastern, southwestern, and northwestern river basins received limited attention. The YtRB and YRB had higher Pb contamination levels than other basins, corresponding with the rapid economic development in those regions. However, the less economically developed river basins in the southeastern and northwestern regions of China were also contaminated by Pb. Analysis of 146 studies in the PRB, YRB, and YtRB revealed that Pb contamination in PRB sediments showed a tendency to improve over time, whereas that from the YtRB exhibited a tendency to worsen. For the YRB, there was a slight increase from 1990 to 2006 and a decreasing trend from 2007 to 2014. The overall temporal trend in Pb levels in PRB and YRB sediments corresponded with that of the Pb discharged in wastewater in the surrounding cities, indicating that industrial wastewater discharge was possibly one of the main anthropogenic sources of Pb in those sediments. For the YtRB, the increasing trend in Pb concentrations was related to the considerably high atmospheric Pb emissions in the surrounding cities and its geographical characteristics. These findings suggested that China should develop systematic and consistent approaches for monitoring Pb contents in sediments and adopt a regional economic development policy focusing on pollution prevention.

Dynamics of major air pollutants from crop residue burning in mainland China, 2000-2014

Based on satellite image data and China's Statistical Yearbooks (2000 to 2014), we estimated the total mass of crop residue burned, and the proportion of residue burned in the field vs. indoors as domestic fuel. The total emissions of various pollutants from the burning of crop residue were estimated for 2000-2014 using the emission factor method. The results indicate that the total amount of crop residue and average burned mass were 8690.9Tg and 4914.6Tg, respectively. The total amount of emitted pollutants including CO₂, CO, NOx, VOCs, PM_2.5, OC (organic carbon), EC (element carbon) and TC (total carbon) were 4212.4-8440.9Tg, 192.8-579.4Tg, 4.8-19.4Tg, 18.6-61.3Tg, 18.8-49.7Tg, 6.7-31.3Tg, 2.3-4.7Tg, and 8.5-34.1Tg, respectively. The emissions of pollutants released from crop residue burning were found to be spatially variable, with the burning of crop residue mainly occurring in Northeast, North and South China. In addition, pollutant emissions per unit area (10 km × 10 km) were mostly concentrated in the central and eastern regions of China. Emissions of CO₂, NOx, VOCs, OC and TC were mainly from rice straw burning, while burning of corn and wheat residues contributed most to emissions of CO, PM_2.5 and EC. The increased ratio of PM_2.5 emissions from crop residue burning to the total emitted from industry during the study period is attributed to the implementation of strict emissions management policies in Chinese industry. This study also provides baseline data for assessment of the regional atmospheric environment.

Monitoring, mass balance and fate of pharmaceuticals and personal care products in seven wastewater treatment plants in Xiamen City, China

The occurrence and fate of pharmaceuticals and personal care products (PPCPs) was investigated in seven wastewater treatment plants (WWTPs) in Xiamen City, China. Special emphasis was placed on their co-occurrence and the mass balances of both dissolved and adsorbed PPCPs in influent, effluent, and sludge samples. Results showed that PPCPs were widely detected and their co-occurrence was observed both in the wastewater and sludge that can be attributed to either their similar usage or similar physicochemical properties. These results further emphasize that some specific PPCPs have the potential as indicators or surrogate compounds to reduce the number of targeted PPCPs. The occurrence and distribution of PPCPs also showed strong spatial variations, as the PPCP mass loads per inhabitant were positively correlated with the urbanization levels. Both the removal efficiencies of dissolved PPCPs from the aqueous phase and mass loss proportion of the total PPCPs were evaluated and compared. Overall, a measured total amount of 8500 g PPCPs entered the seven WWTPs daily via influent with 6640 g in the dissolved form, while 3450 g left the WWTPs. The large mass loads of antibiotics in the sludge and effluents indicated their potential adverse effects to the receiving environment.