Lakes in arid regions are experiencing mercury pollution via air deposition and surface runoff, posing a threat to ecosystem safety and human health. Furthermore, salinity and organic matter input could influence the mercury cycle and composition of bacterial communities in the sediment. In this study, the effects of salinity and algae biomass as an important organic matter on the genes (merA and hgcA) involved in the mercury cycle under mercury contamination were investigated. Archaeal merA and hgcA were not detected in sediments of lake microcosms, indicating that bacteria rather than archaea played a crucial role in mercury reduction and methylation. The high content of mercury (300 ng g⁻¹) could reduce the abundance of both merA and hgcA. The effects of salinity and algae biomass on mercury cycling genes depended on the gene type and dose. A higher input of algae biomass (250 mg L⁻¹) led to an increase of merA abundance, but a decrease of hgcA abundance. All high inputs of mercury, salinity, and algae biomass decreased the richness and diversity of bacterial communities in sediment. Further analysis indicated that higher mercury (300 ng g⁻¹) led to an increased relative abundance of mercury methylators, such as Ruminococcaceae, Bacteroidaceae, and Veillonellaceae. Under saline conditions (10 and 30 g L⁻¹), the richness of specific bacteria associated with mercury reduction (Halomonadaceae) and methylation (Syntrophomonadaceae) increased compared to the control. The input of algae biomass led to an increase in the specific bacterial communities associated with the mercury cycle and the richness of bacteria involved in the decomposition of organic matter. These results provide insight into mercury cycle-related genes and bacterial communities in the sediments of lakes in arid regions.

Partitioning between nitrate reduction pathways, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) determines the fate of nitrate removal and thus it is of great ecological importance. Sulfide (S²⁻) is a potentially important factor that influences the role of denitrification and DNRA. However, information on the impact of microbial mechanisms for S²⁻ on the partitioning of nitrate reduction pathways in freshwater environments is still lacking. This study investigated the effects of long-term (108 d) S²⁻ addition on nitrate reduction pathways and microbial communities in the sediments of two different freshwater lakes. The results show that the increasing S²⁻ addition enhanced the coupling of S²⁻ oxidation with denitrification instead of DNRA. The sulfide-oxidizing denitrifier, Thiobacillus, was significantly enriched in the incubations of both lake samples with S²⁻ addition, which indicates that it may be the key genus driving sulfide-oxidizing denitrification in the lake sediments. During S²⁻ incubation of the Hongze Lake sample, which had lower inherent organic carbon (C) and sulfate (SO₄²⁻), Thiobacillus was more enriched and played a dominant role in the microbial community; while during that of the Nansi Lake sample, which had higher inherent organic C and SO₄²⁻, Thiobacillus was less enriched, but increasing abundances of sulfate reducing bacteria (Desulfomicrobium, Desulfatitalea and Geothermobacter) were observed. Moreover, sulfide-oxidizing denitrifiers and sulfate reducers were enriched in the Nansi Lake control treatment without external S²⁻ input, which suggests that internal sulfate release may promote the cooperation between sulfide-oxidizing denitrifiers and sulfate reducers. This study highlights the importance of sulfide-driven denitrification and the close coupling between the N and S cycles in freshwater environments, which are factors that have often been overlooked.

The crop-livestock system is responsible for a large proportion of global reactive nitrogen (Nr) losses, especially from China. There are diverse livestock systems with contrasting differences in feed, livestock and manure management. However, it is not yet well understood which factors greatly impact on the nitrogen (N) budgets and losses of each system. In this study, we systematically evaluated the N budgets of the crop-livestock production system from 1980 to 2050 in China by identifying the differences of 20 distinct livestock systems. During 1980 to 2010, the total N flow through the crop-livestock system increased from 21.4 to 49.7 Tg, with large variations in different input/output pathways, due to the strong livestock transitions of production towards to a monogastric and landless industrial system. Different systems contributed differently to the total N budgets in 2010. For example, the landless industrial system contributed 67% of livestock product N output, but accounted for 80% of total mineral N fertilizer use and feed N imports by the whole crop-livestock system. The mixed system had the highest rate of N use efficiency at system level due to high dependence on recycled N. N losses were diversely distributed by different systems, with the mixed ruminant system responsible for the majority of NH₃–N emission in livestock production, and the grazing ruminant system dominant in NO₃–N losses in feed production. The total N entering the crop-livestock system is estimated to be 53.9 Tg with total N losses of 41.3 Tg in 2050 under a business-as-usual scenario. However, this amount could be significantly decreased through combined measures that indicate a considerable potential for future improvements. Overall, our results provide new insights into N use and the management of livestock production.

Endocrine-disrupting chemicals (EDCs) in water are receiving particular attention as they pose adverse effects on aquatic systems, even at trace concentrations. A comprehensive study was conducted on 14 EDCs (five estrogens and nine household and personal care products (HPCPs)) in the water of the urbanized Jiaozhou Bay in the Yellow Sea during summer and winter. Results showed that the total concentration of 14 EDCs ranged from 100 to 658 ng L⁻¹ and 56.7–212 ng L⁻¹ in the estuarine and bay water, respectively. The average total concentration of five estrogens in summer was significantly (p < 0.05) lower than that in winter due to the higher precipitation dilution and degradations during summer, whereas the average total concentration of nine HPCPs was significantly (p < 0.05) higher during the summer than that during the winter because of the higher usage and emissions during the summer. Estrogens and HPCPs were dominated by 17α-ethinylestradiol and p-hydroxybenzoic acid (PHBA), respectively. High PHBA concentrations may be related to the hydrolysis of parabens. The total concentrations of EDCs were higher in the eastern coastal seawater of the bay due to the strong influence of domestic and industrial wastewater discharge. Estrogens may interfere with the endocrine system of aquatic organisms in the bay because the total estradiol equivalent concentration exceeded 1 ng L⁻¹. 17α-ethinylestradiol was the main contributor to the estrogenic activity. The EDC mixtures posed high risks (RQ > 1) to mollusks, crustaceans, and fish, and low to moderate risks (RQ < 1) to algae. Fish was the most sensitive aquatic taxon to the EDC mixtures. Given the concentration and frequency of EDCs, the optimized risk quotient method revealed that 17α-ethinylestradiol, estrone, triclocarban, triclosan, and 17β-estradiol should be prioritized in ecological management because of their high risks (prioritization index of >1).

Pregnant women are widely exposed to organophosphate (OP) pesticides, which are potentially neurotoxicant for the developing fetus. We aimed to identify principal demographic and dietary predictors of OP pesticide exposure among 450 pregnant women participating in the New York University Children’s Health and Environment Study (enrolled 2016–19). Urinary concentrations of six dialkyl phosphate (DAP) metabolites (3 dimethyl (DM) metabolites and 3 diethyl (DE) metabolites) of OP pesticides were determined at three time points across pregnancy. At mid-gestation, the Diet History Questionnaire II was used to assess women’s dietary intake over the past year. Demographic characteristics were obtained using questionnaires and/or electronic health records. We used linear mixed models to evaluate the associations of demographic and food groups with DAP metabolite levels, and partial-linear single-index (PLSI) models to analyze the contribution proportions of food groups to DAP metabolite concentrations and the dose-response relationships between them. We observed that pregnant women in NYC had lower levels of OP pesticide metabolites than pregnant populations in Europe, Asia, and other regions in the U.S. Having lower pre-pregnancy body mass index and being Asian, employed, and single were associated with higher DAP metabolite concentrations. Fruit and grain intakes were associated with higher ∑DM, ∑DE, and ∑DAP levels. ∑DE concentrations increased 9.0% (95% confidence interval (CI) = 1.2%, 17.4%) per two-fold increase in dairy consumption, whereas ∑DE concentrations decreased 1.8% (95%CI = −3.1%, −0.4%) per two-fold increase in seafood consumption. The PLSI model indicated that among the food mixture, fruit and grains were the main food groups contributed to higher levels of ∑DAP, while meat contributed to lower levels of ∑DAP. The contribution proportions of fruit, grains, and meat were 18.7%, 17.9%, and 39.3%, respectively. Our results suggest that fruit, grains, and meat are major dietary components associated with OP pesticide exposure in urban pregnant women.

Elevated CO₂ concentrations can change the multi-level nutritional relationship of the ecosystem through the cascading effect of the food chain. To date, few studies have investigated the effects of elevated CO₂ concentration on the Araneae species through the tritrophic system. Hylyphantes graminicola (Araneae: Linyphiidae) is distributed widely in Asia and is a dominant predator in cotton fields. This study investigated chemical components in the food chain of cotton (Gossypium hirsutum)—cotton aphid (Aphis gossypii)—predator (H. graminicola) and compared the development, reproduction, and predation of H. graminicola under ambient (400 ppm) and elevated concentration of CO₂ (800 ppm). The results showed that the elevated CO₂ concentration increased the chemicals of cotton and cotton aphid, but it did not affect the nutrients, development, reproduction, and predation of the spider. However, the survival rate of the spider was significantly decreased in elevated CO₂. The results will further our understanding of the role of natural enemies in an environment with elevated CO₂ concentration.

Black carbon transport from the Santiago Metropolitan Area, Chile, up to the adjacent Andes Cordillera and its glaciers is of major concern. Its deposition accelerates the melting of the snowpack, which could lead to stress on water supply in addition to climate feedback. A proposed pathway for this transport is the channelling through the network of canyons that connect the urban basin to the elevated summits, as suggested by modelling studies, although no observations have validated this hypothesis so far. In this work, atmospheric measurements from a dedicated field campaign conducted in winter 2015, under severe urban pollution conditions, in Santiago and the Maipo canyon, southeast of Santiago, are analysed. Wind (speed and direction) and particulate matter concentrations measured at the surface and along vertical profiles, demonstrate intrusions of thick layers (up to 600 m above ground) of urban black carbon deep into the canyon on several occasions. Transport of PM down-valley occurs mostly through shallow layers at the surface except in connection with deep valley intrusions, when a secondary layer in altitude with return flow (down-valley) at night is observed. The transported particulate matter is mostly from the vicinity of the entrance to the canyon and uncorrelated to concentrations observed in downtown Santiago. Reanalyses data show that for 10% of the wintertime days, deep intrusions into the Maipo canyon are prevented by easterly winds advecting air pollutants away from the Andes. Also, in 23% of the cases, intrusions proceed towards a secondary north-eastward branch of the Maipo canyon, leaving 67% of the cases with favourable conditions for deep penetrations into the main Maipo canyon. Reanalyses show that the wind directions associated to the 33% anomalous cases are related to thick cloud cover and/or the development of coastal lows.

Sanitary landfill is the most popular way to dispose solid wastes with one major drawback: the generation of landfill leachate resulting from percolation of rainfall through exposed landfill areas or infiltration of groundwater into the landfill. The landfill leachate impacts on the environment has forced authorities to stipulate more stringent requirements for pollution control, generating the need for innovative technologies to eliminate waste degradation by-products incorporated in the leachate. Natural attenuation has no effect while conventional treatment processes are not capable of removing some the pollutants contained in the leachate which are reported to reach the natural environment, the aquatic food web, and the anthroposphere. This review critically evaluates the state-of-the-art engineered materials and technologies for the treatment of landfill leachate with the potential for real-scale application. The study outcomes confirmed that only a limited number of studies are available for providing new information about novel materials or technologies suitable for application in the removal of pollutants from landfill leachate. This paper focuses on the type of pollutants being removed, the process conditions and the outcomes reported in the literature. The emerging trends are also highlighted as well as the identification of current knowledge gaps and future research directions along with recommendations related to the application of available technologies for landfill leachate treatment.

Effective remediation of Cd polluted sediment is imperative for its potential damages to aquatic ecosystem. Biochar (BC) and nano-Fe₂O₃ modified BC (nFe₂O₃@BC) were conducted to remedy Cd highly contaminated sediments, and their performances, applicable conditions, and mechanisms were investigated. After 60 d capping, both BC and nFe₂O₃@BC capping inhibited Cd release from sediment to overlying water and porewater (reduction rates >99%). The released Cd concentrations in overlying water with nFe₂O₃@BC capping decreased by 1.6–11.0 times compared to those of BC capping, indicating nFe₂O₃@BC presented a higher capping efficiency. Notably, the increases of acidity and disturbance intensity of overlying water weakened the capping efficiencies of nFe₂O₃@BC and BC. BC capping was inappropriate in acidic and neutral waters (pH 3, 5, and 7) because Cd maintained a continuous release after 15 d, while nFe₂O₃@BC capping was valid in all pH treatments. Under 150 rpm stirring treatment, Cd release rates with BC and nFe₂O₃@BC capping decreased after 15 d and 30 d, respectively. At 0 and 100 rpm treatments, Cd releases treated by nFe₂O₃@BC capping finally kept a balance, indicating nFe₂O₃@BC was valid at low disturbance intensity. BC and nFe₂O₃@BC capping inhibited Cd release via weakening the influences of pH and disturbance on sediment. However, capping layers should be further processed because most adsorbed Cd in capping layers (>98%) would be re-released into overlying water. Meanwhile, excessive application of nFe₂O₃@BC could increase the risk of Fe release. The results provide novel insights into the potential applications of nFe₂O₃@BC and BC in situ capping of Cd polluted sediments in field remediation.

Novel stressors introduced by human activities increasingly threaten freshwater ecosystems. The annual application of more than 2.3 billion kg of pesticide active ingredient and 22 billion kg of road salt has led to the contamination of temperate waterways. While pesticides and road salt are known to cause direct and indirect effects in aquatic communities, their possible interactive effects remain widely unknown. Using outdoor mesocosms, we created wetland communities consisting of zooplankton, phytoplankton, periphyton, and leopard frog (Rana pipiens) tadpoles. We evaluated the toxic effects of six broad-spectrum insecticides from three families (neonicotinoids: thiamethoxam, imidacloprid; organophosphates: chlorpyrifos, malathion; pyrethroids: cypermethrin, permethrin), as well as the potentially interactive effects of four of these insecticides with three concentrations of road salt (NaCl; 44, 160, 1600 Cl⁻ mg/L). Organophosphate exposure decreased zooplankton abundance, elevated phytoplankton biomass, and reduced tadpole mass whereas exposure to neonicotinoids and pyrethroids decreased zooplankton abundance but had no significant effect on phytoplankton abundance or tadpole mass. While organophosphates decreased zooplankton abundance at all salt concentrations, effects on phytoplankton abundance and tadpole mass were dependent upon salt concentration. In contrast, while pyrethroids had no effects in the absence of salt, they decreased zooplankton and phytoplankton density under increased salt concentrations. Our results highlight the importance of multiple-stressor research under natural conditions. As human activities continue to imperil freshwater systems, it is vital to move beyond single-stressor experiments that exclude potentially interactive effects of chemical contaminants.