Graphene Quantum Dots Nonmonotonically Influence the Horizontal Transfer of Extracellular Antibiotic Resistance Genes via Bacterial Transformation.

Graphene quantum dots (GQDs) coexist with antibiotic resistance genes (ARGs) in the environment. Whether GQDs influence ARG spread needs investigation, since the resulting development of multidrug-resistant pathogens would threaten human health. This study investigates the effect of GQDs on the horizontal transfer of extracellular ARGs (i.e., transformation, a pivotal way that ARGs spread) mediated by plasmids into competent Escherichia coli cells. GQDs enhance ARG transfer at lower concentrations, which are close to their environmental residual concentrations. However, with further increases in concentration (closer to working concentrations needed for wastewater remediation), the effects of enhancement weaken or even become inhibitory. At lower concentrations, GQDs promote the gene expression related to pore-forming outer membrane proteins and the generation of intracellular reactive oxygen species, thus inducing pore formation and enhancing membrane permeability. GQDs may also act as carriers to transport ARGs into cells. These factors result in enhanced ARG transfer. At higher concentrations, GQD aggregation occurs, and aggregates attach to the cell surface, reducing the effective contact area of recipients for external plasmids. GQDs also form large agglomerates with plasmids and thus hindering ARG entrance. This study could promote the understanding of the GQD-caused ecological risks and benefit their safe application.

Estrogens and xenoestrogen residues in manure-based fertilizers and their potential ecological risks.

Optimal manure treatment aimed at usage as agricultural soil fertilizers is a prerequisite ecological pollution control strategy. In this work, livestock manure-based fertilizers were collected from 71 animal farms across 14 provinces in China. The contamination levels and potential ecotoxicological risks of residual steroid estrogens (SEs): estrone (E1), estriol (E3), 17α-estradiol (17α-E2), 17ß-estradiol (17ß-E2) and xenoestrogen (XE) bisphenol A (BPA), were investigated. The results showed that the occurrence frequencies for SEs and XE ranged from 66.67% to 100%, and the mean concentration varied considerably across the study locations. The total content of SEs and XE in Hebei province was the highest, and swine manure-based fertilizers concentrations were higher than the levels reported in other animal fertilizers. Compared with farm level manure, manure-based fertilizers are processed by composting, and the micropollutants quantities are significantly reduced (mean: 87.65 - 534.02 µg/kg). The total estradiol equivalent quantity (EEQ) that might migrate to the soil was estimated to be 1.23 µg/kg. Based on the estimated application rate of manure, 38% of the fertilizers risk quotients exceeded 0.1, indicating medium to high risks pressure on terrestrial organisms. Nonetheless, the estrogenic risk was lower in manure-based fertilizers than in manure. This study highlights the significance of proper treatment of livestock manure and designing an optimal manure fertilization strategy to mitigate the risks posed by SEs and XEs to the agroecosystems.

Ecological and human health risks of manure-borne steroid estrogens: A 20-year global synthesis study.

Estrone (E1), 17α-estradiol (17α-E2), 17ß-estradiol (17ß-E2), and estriol (E3) are persistent in livestock manure and present serious pollution concerns because they can trigger endocrine disruption at part-per-trillion levels. This study conducted a global analysis of estrogen occurrence in manure using all literature data over the past 20 years. Besides, predicted environmental concentration (PEC) in soil and water was estimated using fate models, and risk/harm quotient (RQ/HQ) methods were applied to screen risks on children as well as on sensitive aquatic and soil species. The estradiol equivalent values ranged from 6.6 to 4.78 × 104 ng/g and 12.4 to 9.46 × 104 ng/L in the solid and liquid fraction. The estrogenic potency ranking in both fractions were 17ß-E2> E1>17α-E2>E3. RQs of measured environmental concentration in the liquid fraction pose medium (E3) to high risk (E1, 17α-E2 & 17ß-E2) to fish but are lower than risks posed by xenoestrogens. However, the RQ of PECs on both soil organisms and aquatic species were insignificant (RQ < 0.01), and HQs of contaminated water and soil ingestion were within acceptable limits. Nevertheless, meticulous toxicity studies are still required to confirm (or deny) the findings because endocrine disruption potency from mixtures of these classes of compounds cannot be ignored.

Enhanced PAHs-contaminated site soils remediation by mixed persulfate and calcium peroxide.

Polycyclic aromatic hydrocarbons (PAHs) remain in the site soils after relocated coking plants and oil refineries pose huge constraints to the subsequent land utilization. However, single persulfate (PS) or calcium peroxide (CP) remediation strategies can only inefficiently oxidize some PAHs in soil. This work sought to optimize PS/CP oxidation remediation strategy and verify its practical application effect in soil samples spiked with PAHs. The results showed that the mixed PS/CP oxidation remediation was better than the single oxidants strategies; it had high remediation performance in different particles and pollution loads of PAHs-contaminated soils. Simultaneously, reactive radicals (SO4·- and ·OH) were detected, and one side-product (CaSO4) was characterized. This work optimized the mixed PS/CP system (0.3 mol/L PS, and 8 g/kg CP, together with 0.18 mol/L Fe2+ and 0.11 mol/L C2O42-), and the corresponding Total-PAHs removal rate was 85.41%. Compared to the cost based on benzopyrene (BaP) removal, the study provided a cost-effective mixed PS/CP oxidation remediation technique (1.22 $/ton), widely applicable in soils polluted with various organic contaminants represented such as PAHs.

A Fast and Easily Parallelizable Biosensor Method for Measuring Extractable Tetracyclines in Soils.

Quantification of extractable antibiotics in soils is important to assessing their bioavailability and mobility, and ultimately their ecotoxicological and health risks. This study aimed to establish a biosensor method for detecting extractable tetracyclines in soils (Alfisol, Mollisol, and Ultisol) using whole-cell biosensors containing a reporter plasmid (pMTGFP or pMTmCherry) carrying fluorescent protein genes tightly controlled by tetracyclines-responsive control region (tetRO). This whole-cell biosensor method can simultaneously measure 96 or more samples within 6 h and is easily parallelizable, whereas a typical high-performance liquid chromatography (HPLC) method may require 7 times more of analysis time and much greater cost to achieve similar analytical throughput. The biosensor method had a detection limit for each of six tetracyclines between 5.32-10.2 µg/kg soil, which is considered adequate for detecting tetracyclines in ethylenediaminetetraacetic acid (EDTA) extracts of soils. Relative standard deviation was between 19.8-51.2% for the biosensor Escherichia coli DH5α/pMTGFP and 2.98-25.8% for E. coli DH5α/pMTmCherry, respectively, suggesting that E. coli DH5α/pMTmCherry was superior to E. coli DH5α/pMTGFP for detecting extractable tetracyclines in soils. This new, fast, easily parallelizable, and cost-effective biosensor method has the potential for measuring extractable concentrations of tetracyclines for a large number of soil samples in large-scale monitoring studies.

Endophytic Bacteria in in planta Organopollutant Detoxification in Crops.

Microbe-assisted organopollutant removal, or in planta crop decontamination, is based on an interactive system between organopollutant-degrading endophytic bacteria (DEBOP) and crops in alleviating organic toxins in plants. This script focuses on the fast-growing body of literature that has recently bloomed in organopollutant control in agricultural plants. The various facets of DEBOP under study include their colonization, distribution, plant growth-promoting mechanisms, and modes of action in the detoxification process in plants. Also, an assessment of the biotechnological advances, advantages, and bottlenecks in accelerating the implementation of this decontamination strategy will be undertaken. The highlighted key research directions from this review will shape the future of agro-environmental sustainability and preservation of human health.

Pit latrine fill-up rates: variation determinants and public health implications in informal settlements, Nakuru-Kenya.

BACKGROUND: Pit latrine operational management and sludge accumulation rate, presents a challenging sanitation problem in low-income urban settlements. However, these challenges have been under-researched. This study was carried out between December 2014 and September 2015 in Nakuru, Kenya. Its objectives were to determine pit latrine management activities and content accumulation rates. METHODS: A longitudinal design was used to study 100 households and their respective pit latrines. Sludge accumulation in 73 pit latrines was monitored for 10 months using a digital laser range-finder. Data analysis included normality testing and descriptive statistics. Differences in fill up across and within the study areas were analysed using one-way analysis of variance and the Fisher's Exact Test used to determine areas with significant differences. RESULTS: Sixty-one percent of the pit latrines were used as solid waste disposal points while 45% of the respondents had no hygiene awareness. The annual fill-up rate and individual sludge contribution were 0.87 ± 0.20 m3 and 41.82 l respectively. The sludge accumulation rates across the study areas had statistically significant mean differences (p < 0.05). CONCLUSION: Operational management and design affect the fill-up rates and post fill-up management operations. This study argues for a need to link information and awareness to users, construction artisans, property owners and local authorities on appropriate vault volumes and management practices. Linking the variables would ensure efficient sanitation service delivery and public health protection.

Contributions of partition and adsorption to polycyclic aromatic hydrocarbons sorption by fractionated soil at different particle sizes.

Partition and adsorption of polycyclic aromatic hydrocarbons (PAHs) are critical mechanisms determining their fate at the solid-liquid interface. The complexity of soil composition makes it difficult to distinguish between partition and adsorption, and bates the accuracy of the research results. This study found that the composition and structure of the soil particles (SAs) of varying particle sizes were significantly different. Partition contributed significantly to phenanthrene (Phe) sorption in SAs over 0.002 mm. However, PAHs had the highest sorption coefficient (Kd) in SA less than 0.002 mm (SA-3), and the lower aqueous phase equilibrium concentration of Phe, the greater the adsorption effect. According to morphology and structural analysis, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS), interactions of micropores, soil organic matter (SOM) and minerals enhanced the sorption of PAHs. Additionally, thermogravimetry and mass spectrometry (TG-MS) results proved that SOM could inhibit the release of PAHs adsorbed in SAs during heating process. We observed that the Log Koc of PAHs was the most important factor in determining the Kd in SAs applying principal component analyses (PCA), and they have significant linear relationships (R2 = 0.79-0.93). These findings provide new understandings on interface reactivity of PAHs sorption to soils and the development of interface model.

Impact of hexachlorocyclohexane addition on the composition and potential functions of the bacterial community in red and purple paddy soil.

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.

Nitrogen addition enhanced the polycyclic aromatic hydrocarbons dissipation through increasing the abundance of related degrading genes in the soils.

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-1 nitrate and ammonium nitrogen resulted in higher PAHs removal efficiency, and the dissipation rate of PAHs was 59.61% and 62.09%, respectively. Nitrogen application could improve the abundance and the diversity of soil microbial community. Degrading genes involved in PAH detoxification were enhanced after nitrogen addition, particularly those encoding ring-hydroxylating and catechol dioxygenases such as nahAc and nidA, thus, accelerating PAH dissipation in the soil. The results will facilitate the development of beneficial microbiome-based remediation strategies and improve agricultural production safety in PAHs-contaminated soils.

Promoted oxidation of polycyclic aromatic hydrocarbons in soils by dual persulfate/calcium peroxide system.

In situ chemical oxidations (ISCO) have been demonstrated as effective ways for remediating soils contaminated with organic pollutants by complete mineralization. This work aims to develop a technology for the oxidation remediation of soils contaminated with Polycyclic Aromatic Hydrocarbons (PAHs) using a dual calcium peroxide (CP)/persulfate (PS) oxidant system activated by oxalic acid (OA)-chelating Fe2+. The dual peroxide system was set up, and the effects of 5 single factors (i.e., CP dosage, PS dosage, Fe2+ dosage, OA concentration, and soil/water ratio) on PAHs degradation were studied using the single-factor experiment. The response surface method was then introduced to obtain the optimized experimental conditions (CP dosage, PS dosage, OA concentration) of the dual peroxide system. The result shows that the dual peroxide system significantly increased the PAHs degradation and the maximum PAHs degradation efficiency (70.8%) was achieved by the dual peroxide system under optimal conditions (PS dosage, CP concentration, Fe2+/PS ratio, and Fe2+/OA ratio was 8.89 g/kg, 0.18 mol/L, 1/4 and 0.62) at neutral soil condition. This study is an illustration of the promising efficiency of the dual peroxide system for PAH oxidation in the neutral soil and has great potential for remediation of PAHs contaminated farmland soils.

Antibiotics in animal manure and manure-based fertilizers: Occurrence and ecological risk assessment.

The extensive use of antibiotics globally and their residues in the environment has become a serious concern. Intensive animal farming is considered to be a major contributor to the increased environmental burden of antibiotics. Although some antibiotic investigations have been advancing around the world, as an important agricultural country, the information on these pollutants in animal farms are very limited in China. Previous studies have explored few antibiotic residues in livestock farms, whereas information on some antibiotics has remained unknown. The current study analyzed residues of 32 common veterinary antibiotics in manure and manure-based fertilizers collected from Jiangsu Province, China. In most of the manure and fertilizer samples, sulfamethazine and tetracycline were present, with high concentration up to 5650 and 1920 µg·kg-1, respectively. These detected antibiotics have weak relationships with physicochemical properties. Ciprofloxacin, enrofloxacin, sulfamethazine, and sulfachlorpyridazine, hence pose a high potential risk to crops based on the toxicological data of organisms and plants in the soil environment. However, soil invertebrate, such as earthworms, Planococcus Citri. and Folsomia fimeraria., had low ecological risks. Our results showed the presence of antibiotics in livestock and poultry farms plus the potential risks to the soil ecosystem. Therefore, the findings can provide guidelines for monitoring antibiotic residues in agroecosystems, as well as insights into the associated ecological risks of using the two products.

Occurrence, formation, environmental fate and risks of environmentally persistent free radicals in biochars.

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.

Antibiotic-contaminated wastewater irrigated vegetables pose resistance selection risks to the gut microbiome.

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.

Enzymatic degradation of extracellular DNA exposed to chlorpyrifos and chlorpyrifos-methyl in an aqueous system.

The persistence of extracellular DNA (eDNA) is crucial for ensuring species diversity and ecological function in aquatic systems. However, scarce information exists about the impact of pesticides on eDNA, although they often co-exist in the aquatic environment. Using a variety of spectroscopic analyses, eDNA degradation and the associated alterations in DNA secondary structure was investigated by exposing DNase I to tested DNA in the presence of chlorpyrifos, a commonly used organophosphate pesticide. Molecular dynamics simulation was used to explore the weak interactions between the tested DNA and chlorpyrifos. The results indicated that chlorpyrifos significantly enhanced DNA degradation without affecting the enzyme activity of DNase I in an aqueous system. Spectroscopic experiments confirmed that chlorpyrifos and the analog chlorpyrifos-methyl could bind with DNA to cause the bases noncovalent stacking interaction. Molecular simulations further demonstrated that pesticide binding with DNA molecules caused widening of the DNA grooves and destruction of the hydrated layer, which enhanced DNA degradation. The findings presented herein provide novel insight into the genotoxicity and ecotoxicity of chlorpyrifos and chlorpyrifos-methyl, as well as their impacts on DNA persistence in aquatic environments.