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Over the past two decades, steroidal estrogens (SEs) such as 17α-ethylestradiol (EE2), 17β-estradiol (E2),17α-estradiol (17α-E2), estriol (E3) and estrone (E1) have elicited worldwide attention due to their potentially harmful effects on human health and aquatic organisms even at low concentration ng/L. Natural steroidal estrogens exhibit greater endocrine disruption potency due to their high binding effect on nuclear estrogen receptors (ER). However, less has been explored regarding their associated environmental risks and fate. A comprehensive bibliometric study of the current research status of SEs was conducted using the Web of Science to assess the development trends and current knowledge of SEs in the last two decades, from 2001 to 2021 October. The number of publications has tremendously increased from 2003 to 2021. We summarized the contamination status and the associated ecological risks of SEs in different environmental compartments. The results revealed that SEs are ubiquitous in surface waters and natural SEs are most studied. We further carried out an in-depth evaluation and synthesis of major research hotspots and the dominant SEs in the matrices were E1, 17β-E2, 17α-E2, E3 and EE2. Nonetheless, investigations of SEs in soils, groundwater, and sediments remain scarce. This study elucidates SEs distribution, toxicological risks, ecological fate and mitigation measures, which will be beneficial for future monitoring, management, and risk assessment. Further studies are recommended to assess the toxicological risks of different SEs in complex environmental matrices to pursue a more precise and holistic quantitative estimation of estrogenic risk.

Biochar application for soil and agro-environmental development has attracted great attention due to its numerous advantages: improving the soil, mitigating greenhouse gas emissions, increasing crop productivity, and augmenting soil carbon storage. However, during the pyrolytic conversion of waste biomass, polycyclic aromatic hydrocarbons (PAHs), a category of toxic organic pollutants, are inescapably generated and linger on the residual solid coproduct called biochar. Therefore, it is crucial to assess the environmental persistence, bioavailability, effects of biochar-borne PAHs on plant growth and soil microbial community dynamics, food safety, and human health after application into soils. This review highlights the basic need to unravel critical mechanisms driving PAH formation in biochar and the dynamics between the sorbent (biochar) and soil microbes, along with the possible mitigation strategies. Current research gaps, including the influence of biochar application on the short and long-term fate of PAHs, as well as the proper control measures for biochar quality and associated risks, will be discussed herein. The key research findings from this script will lead to proposals in technological and quality control measures during biochar production to ensure they are clean and safe.

Soil studies have reported the effect of Hexachlorocyclohexane (HCH) on soil microbial communities. However, how soil microbial communities and function shift after HCH addition into the red and purple soil remains unclear. Here, we analyzed the HCH residue fate, and the functional composition and structure of microbial communities to HCH in the two soils. Under the 100 g/ha and 1000 g/ha treatment, the dissipation rate of HCH was 0.0386 and 0.0273 in the purple soil, 0.0145 and 0.0195 in the red soil. The enrichment of HCH degrading genes leads to a higher HCH dissipation rate in the purple soil. PCoA results demonstrated that HCH addition has a different effect on the community diversity in the two soils, and Proteobacteria and Acidobacteria were the major phyla in the two soils. The soil microbiome average variation degree values of red soil were higher than purple soil, which indicated that the soil microbiome in the purple soil was more stable than in the red soil under HCH addition. PICRUSt2 results indicated that functional genes involved in the carbon, nitrogen biogeochemical cycles and HCH degradation were more tolerant to HCH addition in the purple soil. This study provides new insights into understanding of the effect of HCH addition on soil microbial communities and function in the red and purple paddy soil.

High concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) in the soils cause significant threats to human health. Since nitrogen plays a crucial role in controlling microbial composition and functions in terrestrial ecosystems, bio-stimulation based on nitrogen has been used in PAHs contaminated environments remediation. Recent studies show that microbial community composition and organic pollutants dissipation correlate with nitrogen addition. Here, we investigated the effect of nitrogen addition on the abundance of microbial community, degrading genes, and their relationship to PAHs dissipation. After a 32-day experiment, PAHs residues in nitrogen treatment soil were reduced by 23.23%-34.21%. The application of 80 mg·kg

Chlorpyrifos, a common organophosphorus pesticide, is widely used for agricultural pest control and can inhibit nitrogen-fixing bacteria biomass in paddy. In this study, the additions of chlorpyrifos (1 and 8 mg kg−1) to soil, with or without Pseudomonas stutzeri A1501, resulted in a significant decrease in nitrogen fixation, despite insignificant effects on the abundances of P. stutzeri A1501 and bacteria in soil. Toxic effect of chlorpyrifos on P. stutzeri A1501 nitrogenase activity in medium was also observed, accompanied by a significant reduction in the expression of nitrogen-fixing related genes (nifA and nifH). Furthermore, rhizosphere colonization and biofilm formation by P. stutzeri A1501 were repressed by chlorpyrifos, leading to decreased nitrogenase activity in the rhizosphere. Biofilm formation in medium was inhibited by bacterial hyperkinesis and reduction of extracellular polymeric substance, including exopolysaccharides and proteins. Together, these findings showed that chlorpyrifos-induced production of reactive oxygen species (ROS) which was directly responsible for reduced nitrogenase activity in the medium, soil, and rhizosphere by inhibiting the expressions of nitrogen-fixing related genes. Furthermore, the inhibition of biofilm formation by chlorpyrifos or ROS likely aggravated the reduction in rhizospherere nitrogenase activity. These findings provide potentially valuable insights into the toxicity of chlorpyrifos on nitrogen-fixing bacteria and its mechanisms. Furthermore, for sustainable rice production, it is necessary to evaluate whether other pesticides affect nitrogen fixation and select pesticides that do not inhibit nitrogen fixation.

Biochars are used globally in agricultural crop production and environmental remediation. However, environmentally persistent free radicals (EPFRs), which are stable emerging pollutants, are generated as a characteristic feature during biomass pyrolysis. EPFRs can induce the formation of reactive oxygen species, which poses huge agro-environmental and human health risks. Their half-lives and persistence in both biochar residues and in the atmosphere may lead to potentially adverse risks in the environment. This review highlights the comprehensive research into these bioreactive radicals, as well as the bottlenecks of biochar production leading up to the formation and persistence of EPFRs. Additionally, a way forward has been proposed, based on two main recommendations. A global joint initiative to create an all-encompassing regulations policy document that will improve both the technological and the quality control aspects of biochars to reduce EPFR generation at the production level. Furthermore, environmental impact and risk assessment studies should be conducted in the extensive applications of biochars in order to protect the environmental and human health. The highlighted key research directions proposed herein will shape the production, research, and adoption aspects of biochars, which will mitigate the considerable concerns raised on EPFRs. Keywords: Biochar, Environmentally persistent free radicals, Reactive oxygen species, Environmental fate, Risk

Soil amendment with biochars is currently being studied worldwide as a sustainable agricultural practice to improve soil and water quality, increase crop productivity, and augment soil carbon storage. However, the formation of polyaromatic hydrocarbons (PAHs) during biochar production is inevitable. Therefore, it is crucial to assess the risks in food safety and human health of crops grown in biochar-amended soils. This paper performed a synthesis study of PAH concentrations in biochars and estimated the risks of soils amended with biochars, based on refereed articles published between 2012 and 2018. The PAH concentrations in biochars ranged greatly, with the dominant proportion being 2–3 ringed PAHs (40%–71%). Biochar application increased the PAH levels in soils at drastically varying extents (0.02–3574 μg/kg), which led to a broad range of PAH concentrations in food crops grown in biochar-amended soils. A five-step method was then introduced to assess the toxicity of biochar-borne PAHs to human health. The total mean incremental lifetime cancer risk for adults was estimated to range between 2.0 × 10−6–1.9 × 10−5 via direct contact with and ingestion (inhalation) of contaminated soils or consumption of tainted crops. These results indicated that biochar amendment in soils might pose potential risks to food safety and human health, but the overall cancer risks through exposure to biochar-borne PAHs in soils and food crops were low. Higher application rates (e.g. ≥20 t/ha) of biochars with high PAH contents can be avoided to minimize human cancer risks. Although biochar application in arable farmlands has many environmental and agronomic benefits, holistic and systematic approaches are required to fully assess the benefits and risks before their large-scale adoption. PAHs in biochar may be reduced by improving the biochar production process and developing a cost-effective post-manufacturing treatment. Keywords: Biochar, Polyaromatic hydrocarbon, Soil, Crop, Human health, Contamination risk

The significance of the bacterial communities and PAH-degrading genes (PDGs) in PAH-contaminated soil has received extensive attention, however, little attention was focused on those in plants grown on contaminated farmland soil. This study aimed to dissect the interactive relationships among PAHs, PDGs, and bacterial communities in the rhizosphere soil and rice grain. Although the concentrations and compositions of PAHs varied greatly, PAHs was the most critical factor in shifting of community in the soil and rice grain. Diversity of the potential PAH-degrading bacteria (PDB) in the rhizosphere soil was higher than that in the rice grain; however, the relative and absolute abundances of PDB in the rhizosphere soil were lower than those in the rice grain. Abundances of four PDGs in the soil were higher than those in the rice grain, and many species of bacteria, including Pseudomonas, Sphingomonas, and so on, which may harbor PDGs were detected. Bacteria in the soil had stronger relationships and were more centrally clustered within the network compared to bacteria in the rice grain. The keystone species (Actiobacteria, Betaproteobacteria, and Chloroflexi) in the soil were different from those (Pseudomonas, Sphingomonas, and Comamonadaceae) in the rice grain. Pseudomonas and Sphingomonas in the rice grain seemed to be the most important bacteria associated with PAH degradation. Overall, these findings provided novel insights into bacterial communities and PDGs in both the soil and plant from the PAH-contaminated paddy soil.

Large amounts of glomalin-related soil protein (GRSP) are present in the soil; however, the impacts of GRSP on the chemical process of soil polycyclic aromatic hydrocarbons (PAHs) are far under investigation. This research sought to elucidate the sorption of phenanthrene as a representative PAH by soils, including Kandiudult, TypicPaleudalf, and Mollisols with co-existing GRSP (0–50 mg/L). The results indicated that soil sorption capacities for phenanthrene reduced significantly. Notably, GRSP changed the sorption process of phenanthrene by Kandiudult, well described as the Freundlich model. In contrast, the phenanthrene sorption isotherms were well described with the Linear model for TypicPaleudalf and Mollisols. The reduced percentage of phenanthrene sorption due to GRSP addition was 7.01%–49.21%, 23.92%–68.71%, and17.26%–66.80% for Kandiudult, TypicPaleudalf and Mollisols, respectively. It was noted that GRSP has a strong capacity for phenanthrene sorption in aqueous solutions and elevates the availability of phenanthrene for microorganisms or plants. During the sorption process, the introduction of GRSP resulted in the reduction of organic matter in soils and elevated the concentrations of dissolved organic matter in solutions, which was the primary mechanism of GRSP-reduced phenanthrene sorption by soils. The findings revealed that GRSP enrichment can increase the mobility of PAHs in contaminated soils.

Wastewater reuse in food crop irrigation has led to agroecosystem pollution concerns and human health risks. However, there is limited attention on the relationship of sub-lethal antibiotic levels in vegetables and resistance selection. Most risk assessment studies show non-significant toxicity, but overlook the link between antibiotics in crops and propagation of gut microbiome resistance selection. The review highlights the risk of antibiotics in treated water used for irrigation, uptake, and accumulation in edible vegetable parts. Moreover, it elucidates the risks to the adaptive resistance selection of the gut microbiome from sub-lethal antibiotic levels, as a result of dietary contaminated vegetables. Experiments have reported that bacterial resistance selection is possible at concentrations that are several hundred-folds lower than lethal effect levels on susceptible cells. Consequently, mutants selected at low antibiotic levels, such as those from vegetables, are fitter and more resistant compared to those selected at high concentrations. Necessary standardization, such as the development of minimum acceptable antibiotic limits allowable in food crop irrigation water, with a focus on minimum selection concentration, and not only toxicity, has been proposed. Wastewater irrigation offers environmental benefits and can contribute to food security, but it has non-addressed risks. Research gaps, future perspectives, and frameworks of mitigating the potential risks are discussed.

Biochars are added to soil to improve agronomic yield. This greenhouse- and field-scale study evaluated poly cyclic aromatic hydrocarbon (PAH) contamination in 35 commercial and laboratory-produced biochars, and assessed the effects of biochar amendment of soils on PAH accumulation in vegetables and the risk for cancer. The total and bioavailable PAH concentrations in biochars varied from 638 to 12,347 mu g/kg and from below the detection limit (BDL) to 2792 mu g/kg, respectively. PAH formation in biochars decreased with increasing production temperature (350-650 degrees C). Root exudates enhanced PAH release from biochars. The total PAH concentrations in eight edible vegetables growing in biochar-amended soil varied according to biochar and vegetables type from BDL to 565 mu g/kg. A health risk assessment framework was integrated with the benzo [a] pyrene toxic equivalency quotient and the incremental lifetime cancer risk (ILCR) to estimate the exposure risk for human beings via ingestion of PAH-contaminated vegetables. The total ILCR for adults was above 10(-6), which suggests a risk to human health from direct exposure to PAHs in vegetables grown in biochar-amended soil. These results demonstrate that biochar application may lead to contamination of plants with PAHs, which represents a risk to human health. The PAH levels in biochars produced using different conditions and/or feed-stocks need to be evaluated and biochars should be pretreated to remove PAHs before their large-scale agronomic application. Jiangsu Provincial Key Research and Development Plan, China [BE2017718, BE2015682]; Jiangsu Environmental Monitoring Research Fund, China [1706]; National Natural Science Foundation of China [41771523, 41877125, 31770549]; Special Fund for Agro-scientific Research in Public Interest, China [201503107] This work was supported by the Jiangsu Provincial Key Research and Development Plan, China (BE2017718, BE2015682), the Jiangsu Environmental Monitoring Research Fund, China (1706), the National Natural Science Foundation of China (41771523, 41877125, 31770549), and the Special Fund for Agro-scientific Research in Public Interest, China (201503107).