River algal blooms have become a newly emerging global environmental issue in recent decades. Compared with water eutrophication in lakes and reservoirs, algal blooms in large river systems can cause more severe consequences to watershed ecosystems at the watershed scale. However, reveal the causes of river algal blooms remains challenging in the interdisciplinary of hydrological-ecological-environmental research, due to its complex interaction mechanisms impacted by multiple factors. In addition, there were still considerable uncertainties on the characteristics, impacts, driving factors, as well as the applicable water system models for river algal blooms. In this paper, we reviewed existing literature to elaborate the definition and negative effects of river algal blooms. We analyzed sensitive factors including nutrient, hydrological and climatic elements. We also discussed the application of ecohydrological models under complicated hydrological conditions. Finally, we explored the essence of the river algal bloom by the interaction effects of physical and biogeochemical process impacted by of climate change and human activities. The model-data integration accounting for multi-factor effects was expected to provide scientific guidance for the prevent and control of algal blooms in large river systems.

Hardpans are massively indurated layers formed at the top layer of sulfidic tailings dams, which develop cementation structures and result in heavy metal immobilization. However, the micro-structural and complex forms of the cementing materials are not fully understood, as well as the mechanisms by which Zn and Pb are stabilized in the hardpans. The present study deployed synchrotron-based X-ray fluorescence microscopy (XFM) to have characterized the cementing structures, examined the distribution of Fe, Zn and Pb, and obtained laterally-resolved speciation of Zn within the hardpans using fluorescence X-ray absorption near-edge structure (XANES) imaging. The XFM analyses revealed that the Fe-rich cement layers consisted of Fe (oxyhydr)oxides coupled with amorphous Si materials, immobilizing Zn and Pb. Through laterally-resolved XANES imaging analyses, Zn-ferrihydrite-like precipitates were predicted to account for >76% of the total Zn within the Fe-rich cement layers. In contrast, outside of the cement layers, 9–63% of the Zn was estimated as labile ZnSO4.7H2O, with the remainder in the form of Zn-sulfide. These findings demonstrated that the Fe-rich cement layers were critical in immobilizing Zn and Pb within hardpans via mineral passivation and encapsulation, as the basis for long-term geochemical stability in the hardpan layer of sulfidic mine tailings.

Glufosinate-ammonium (GLA) is a spectrum herbicide that is widely used in agriculture. The toxic effects of GLA on plants and mammals have been extensively studied; however, little is known about its effects on reptiles. In this study, male lizards (Eremias argus) were exposed to GLA contaminated soil for 60 days. Physical conditions, organ coefficients, antioxidant enzyme activity, tissue distribution, histopathological damage, steroid hormones levels, and related gene expression of sex steroids were evaluated. In contrast to unexposed control lizards, the body mass index of the GLA group was decreased, which elucidated that GLA adversely affected the physical condition of E. argus. Changes in antioxidant enzyme activities in response to elevated malondialdehyde levels in lizard testis indicated that testes were strongly affected by oxidative damage, and the increased testis index was associated with severe testis lesions. Moreover, alterations of plasma sex hormone levels and related gene expression levels of sex steroids were also observed, and the mechanism underlying the induction of reproductive toxicity was clarified. The activity of glutamine synthetase was severely inhibited in the liver of the GLA exposure group. Based on the results of liver index and histopathology examinations, the hepatotoxicity effect of GLA was confirmed.

Rare earth elements (REEs) are typically present as mixtures in the environment, but a quantitative understanding of mixture toxicity and interactions of REEs is still lacking. Here, we examined the toxicity to wheat (Triticum aestivum L.) of Y, La, and Ce when applied individually and in combination. Both concentration addition (CA) and independent action (IA) reference models were used for mixture toxicity analysis because the toxicity mechanisms of REEs remain obscure. Upon single exposure, the EC50s of Y, La, and Ce, expressed as dissolved concentrations, were 1.73 ± 0.24 μM, 2.59 ± 0.23 μM, and 1.50 ± 0.22 μM, respectively. The toxicity measured with relative root elongation followed La < Y ≈ Ce, irrespective of the dose descriptors. The use of CA and IA provided similar estimates of REE mixture interactions and toxicity. When expressed as dissolved metal concentrations, nearly additive effects were observed in Y-La and La-Ce mixtures, while antagonistic interactions were seen in Y-Ce mixtures. When expressed as free metal activities, antagonistic interactions were found for all three binary mixtures. This can be explained by a competitive effect of REEs ions for binding to the active sites of plant roots. The application of a more elaborate MIXTOX model in conjunction with the free ion activities, which incorporates the non-additive interactions and bioavailability-modifying factors, well predicted the mixture toxicity (with >92% of toxicity variations explained). Our results highlighted the importance of considering mixture interactions and subsequent bioavailability in assessing the joint toxicity of REEs.

Densely populated cities with a compact urban built environment have concerns over health risks derived from high levels of airborne particulate matter (PM) exposure. Understanding the association between PM and reactive oxygen species (ROS) is an important step towards unravelling the mechanisms behind. This study investigated the role of time-integrated PM sampling on cellular toxicity mechanism on a diurnal scale. The sampling took place in a highly urbanized part of Hong Kong at two contrast roadside and background sites, with simultaneous solid-PM and semi-volatile-PM (SV-PM) collection in both summer and winter seasons. A sampling day consisted three sampling intervals of 6 h each – 04:00–10:00, 12:00–18:00 and 20:00–02:00 h, representing morning rush hours, afternoon and night periods, respectively. Water and organic extracts of PM were prepared, with and without filtration, and exposed to RAW264.7 and A549 cell lines on a dose and time-dependent manner. Solid-PM and SV-PM contribution to total PM₂.₅ mass concentration was 9:1, with much higher SV-PM fraction at roadside over urban background (p < 0.001, n = 36). Also, the SV-PM mass concentration increased by 10–20% during 20:00–02:00 h compared to morning and afternoon sampling periods. Organic PM extract was observed to cause 23–29% higher cell death compared to water-soluble PM, which is complemented with increased ROS production in both cell lines. The cellular damage caused by oxidative stress, determined from increased HO-1 and TNF-α expression in RAW264.7 was higher compared to the A549, which demonstrated the greater induction of toxicity from organic PM extract over soluble PM. Similarly, the SV-PM induced greater than 2-fold cellular ROS generation on PM mass basis compared to solid-PM. Lack of phagocytic action in A549 compared to RAW264.7 suggested novel toxicity routes for water-soluble and organic PM that can be expected to occur during human PM inhalation-bronchi-alveolar exposure.

High resolution sediment records in the Yangtze Delta front were constructed to reveal recent environmental changes in response to river basin human activities. Increases in nutrient and organic C influxes that began in the 1950s, together with elevated primary productivity and increased chemical fertilizer application, suggested a shift toward anthropogenic-predominated environmental changes during this period. The depletion of total organic C (TOC), total N (TN), and biogenic Si (BSi), along with the decline in sedimentation rate and coarsening of sediment coincided with the development of hydrological engineering in the river basin from the 1980s. Reservoir Si retention substantially altered river mouth primary productivity community composition from diatoms to non-diatoms, thereby changing the BSi/TOC molar ratio in the sediment profile. Estimation of biogenic component burial fluxes was conducted to assess the variation and potential impacts. A recent dramatic decline in biogenic component burial in the delta area suggested a low nutrient removal efficiency in this region, due to the decrease in sediment discharge. Consequently, more nutrients have been further transported to the inner shelf and open waters instead of being buried in the delta sediment, thereby increasing the environmental pressure in the Yangtze Delta and adjoining coastal area.

One attraction of using hydrochar (HC) and biochar (BC) in soil is their intrinsic affinity for organic contaminants. Oxidative ageing is likely to induce changes in physicochemical properties and functionality. To explore the long-term potential trajectories for corn stalk HC and BC to adsorb organic pollutants, we employed HC and BC exposure in 5% H2O2 to simulate oxidative ageing and get insights into mechanisms of atrazine adsorption on fresh and artificially aged materials. The physicochemical properties of fresh and aged materials were systematically compared using elemental analysis, SSA, FTIR, XPS and SEM-EDS, alongside K2Cr2O7/H2SO4 treatment to assess chemical oxidation stability. Atrazine is a typical herbicide chemical and hydrophobic organic pollutant. Adsorption isotherms of atrazine were used to reveal differences in mechanisms of sorption to BC and HC, by assessment before and ageing. BC freshly produced at 650 °C displayed higher capacity for atrazine sorption than BC produced at 500 °C, with a dominant role for π-π EDA interactions. The sorption capacity of HC freshly produced at 250 °C was higher than for HC produced at 200 °C HC, owing to higher C content and atrazine partitioning into the organic phase. Ageing increased the surface abundance of oxygenated functional groups for BC and HC and diminished bulk aromaticity. After ageing, atrazine sorption by high temperature BC was lower, but for HC it was increased. Such divergent effects must be considered when developing strategies to co-manage contaminants and carbon through the addition of carbonized materials to land.

A comparative study was conducted to (1) assess the potential of raw sewage used for urban agriculture to disseminate bacterial resistance in two cities of different size in Cameroon (Central Africa) and (2) compare the outcome with data obtained in Burkina Faso (West Africa). In each city, raw sewage samples were sampled from open-air canals in three neighbourhoods. After DNA extraction, the microbial population structure and function, presence of pathogens, antibiotic resistance genes and Enterobacteriaceae plasmids replicons were analysed using whole genome shotgun sequencing and bioinformatics. Forty-three pathogen-specific virulenc e factor genes were detected in the sewage. Eighteen different incompatibility groups of Enterobacteriaceae plasmid replicon types (ColE, A/C, B/O/K/Z, FIA, FIB, FIC, FII, H, I, N, P, Q, R, T, U, W, X, and Y) implicated in the spread of drug-resistance genes were present in the sewage samples. One hundred thirty-six antibiotic resistance genes commonly associated with MDR plasmid carriage were identified in both cities. Enterobacteriaceae plasmid replicons and ARGs found in Burkina Faso wastewaters were also present in Cameroon waters. The abundance of Enterobacteriaceae, plasmid replicons and antibiotic resistance genes was greater in Yaounde, the city with the greater population.In conclusion, the clinically relevant environmental resistome found in raw sewage used for urban agriculture is common in West and Central Africa. The size of the city impacts on the abundance of drug-resistant genes in the raw sewage while ESBL gene abundance is related to the prevalence of Enterobacteriaceae along with plasmid Enterobacteriaceae abundance associated to faecal pollution.

Triclocarban (TCC) is used as a broad-spectrum antimicrobial agent, the intensive detection of TCC in aquatic environments and its potential risks to aquatic organisms are concerned worldwide. In this study, 8 Chinese resident aquatic organisms from 3 phyla and 8 families were used for the toxicity tests, and four methods were employed to derive the aquatic life criteria (ALC). A criterion maximum concentration (CMC) of 1.46 μg/L and a criterion continuous concentration (CCC) of 0.21 μg/L were derived according to the USEPA guidelines. The acute predicted no effect concentrations (PNECs) derived by species sensitivity distribution (SSD) methods based on log-normal, log-logistic and Burr Type Ⅲ models were 2.64, 1.88 and 3.09 μg/L, respectively. The comparisons of ALCs derived with resident and non-resident species showed that the CMC and CCC of TCC derived with Chinese resident species could provide a sufficient protection for non-resident species. The higher toxicity of TCC on aquatic organisms was found compared with other antimicrobial agents (except for Clotrimazole) in aquatic environment. The strong positive linear correlation was observed between the TCC and TCS concentrations in aquatic environment with a correlation coefficient (R²) of 0.8104, it is of great significance in environmental monitoring and risk assessment for TCC and TCS. Finally, the ecological risk assessment showed that the TCC in Yellow River basin and Pearl River basin had higher risk with the mean potential affected fractions (PAFs) of 9.27% and 7.09%, and 22.10% and 15.00% waters may pose potential risk for 5% aquatic organisms, respectively. In general, the risk of TCC in Asian waters was higher than that in Europe and North America.

Dietary arsenic (As) intake from food is of great concern, and developing a reliable model capable of predicting As concentrations in plant edible parts is desirable. In this study, pot experiments were performed with 16 Chinese upland soils spiked with arsenate [As(V)] to develop a predictive model for As concentrations in pepper fruits (Capsicum annum L.). Our results showed that after three months’ aging, concentrations of bioavailable As (extracted by 0.05 M NH₄H₂PO₄) in various soils varied widely, depending on soil total As concentrations and soil properties such as soil pH and amorphous iron (Fe) contents. Furthermore, both the bioconcentration factor (BCF, denoted as the ratio of fruit As to soil As) and total As concentrations in pepper fruits were largely determined by concentrations of bioavailable As, which explained 27% and 69% variations in the BCF and fruit As concentrations, respectively. Apart from bioavailable As, soil pH and Fe contents were another two important factors influencing As accumulation in pepper fruits. Taking the three factors into account, concentrations of fruit As can be well predicted using a stepwise multiple linear regression (SMLR) analysis (R² = 0.80, RMSE = 0.17). Arsenic species in soils and edible parts were also analyzed. Although As(V) predominated in soils (>96%), As in pepper fruits presented as As(V) (46%) and arsenite [As(III)] (39%) with small amount of methylated As (<15%). Aggregated boosted tree (ABT) analysis revealed that inorganic As concentrations in pepper fruits were determined by concentrations of bioavailable As, phosphorus (P) and Fe in soils. In contrast to inorganic As, methylated As concentrations were not correlated with those factors in soils. Taken together, this study established an empirical model for predicting As concentrations in pepper fruits. The predictive model can be used for establishing the As threshold in fruit vegetable farming soils.