Uptake and translocation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals by maize from soil irrigated with wastewater

Ryegrass uptake behavior and forage risk assessment after exposing to soil with combined polycyclic aromatic hydrocarbons and cadmium

Internalization of chemicals and the forage risks of ryegrass under the combined exposure to PAHs and Cd at environmental concentrations were studied here. The effect of soil pH was also concerned due to the widely occurred soil acidification and general alkali remediation for acidification soil. Unexpectedly, as same as the acid-treated group (pH 6.77), the alkali-treatment (pH 8.83) increased Cd uptake compared with original soil pH group (pH 7.92) for the reason of CdOH+ and CdHCO3+ formed in alkali-treated group. Co-exposure to PAHs induced more oxidative stress than Cd exposure alone due to PAHs aggregated in young root regions, such as root tips, and consequently, affecting the expression of Cd-transporters, destroying the basic structure of plant cells, inhibiting the energy supply for the transporters, even triggering programmed cell death, and finally resulting in decreased Cd uptake. Even under environmental concentrations, combined exposure caused potential risks derived from both PAHs and Cd. Especially, ryegrass grown in alkali-treated soil experienced an increased forage risks despite the soil meeting the national standards for Cd at safe levels. These comprehensive results reveal the mechanism of PAHs inhibiting Cd uptake, improve the understanding of bioavailability of Cd based on different forms, provide a theoretical basis to formulate the safety criteria, and guide the application of actual soil management.

Polycyclic aromatic hydrocarbons in sewage-irrigated vegetables from industrial cities in Haryana, India

The majority of Indians consume a lot of vegetables because of their health advantages. High concentrations of polycyclic aromatic hydrocarbons (PAHs) in vegetables may be seriously harmful to consumers' health. The method for identifying and measuring 16 USEPA polycyclic aromatic hydrocarbons (PAHs) in samples of sewage-irrigated vegetables from three industrial cities in Haryana, India, is described in this research. Ultrasonication, liquid-liquid extraction using n-hexane as a solvent, clean-up using a Florisil column, and reversed-phase high-performance liquid chromatography with a UV detector were all included in the process. The PAHs were successfully linearized (R2 > 0.99) at various doses. Results for PAH recovery ranged from 90 to about 100%. The limit of quantification was 0.002-0.580, and the limit of detection was 0.0006-0.174 µgkg-1. Data indicated that the highest mean concentrations of ∑16 PAHs were detected in Spinach (123.36 µgkg-1), in carrot (105.09 µgkg-1), and in cucumber (63.40 µgkg-1) among leafy, underground, and fruity vegetables, respectively.

Seasonal variations in the distribution of aliphatic hydrocarbons in surface sediments from the Selangor River, Peninsular Malaysia's West Coast

The seasonal variation of petroleum pollution including n-alkanes in surface sediments of the Selangor River in Malaysia during all four climatic seasons was investigated using GC-MS. The concentrations of n-alkanes in the sediment samples did not significantly correlate with TOC (r = 0.34, p > 0.05). The concentrations of the 29 n-alkanes in the Selangor River ranged from 967 to 3711 µg g-1 dw, with higher concentrations detected during the dry season. The overall mean per cent of grain-sized particles in the Selangor River was 85.9 ± 2.85% sand, 13.5 ± 2.8% clay, and 0.59 ± 0.34% gravel, respectively. n-alkanes are derived from a variety of sources, including fresh oil, terrestrial plants, and heavy/degraded oil in estuaries. The results of this study highlight concerns and serve as a warning that hydrocarbon contamination is affecting human health. As a result, constant monitoring and assessment of aliphatic hydrocarbons in coastal and riverine environments are needed.

Assessing emerging and priority micropollutants in sewage sludge: environmental insights and analytical approaches

The application of sewage sludge (SS) in agriculture, as an alternative to manufactured fertilizers, is current practice worldwide. However, as wastewater is collected from households, industries, and hospitals, the resulting sludge could contaminate land with creeping levels of pharmaceuticals, pesticides, heavy metals, polycyclic aromatic hydrocarbons, and microplastics, among others. Thus, the sustainable management of SS requires the development of selective methods for the identification and quantification of pollutants, preventing ecological and/or health risks. This study presents a thorough evaluation of emerging and priority micropollutants in SS, through the lens of environmental insights, by developing and implementing an integrated analytical approach. A quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction method, coupled with gas chromatography and liquid chromatography, was optimized for the determination of 42 organic compounds. These include organophosphorus pesticides, organochlorine pesticides, pyrethroid pesticides, organophosphate ester flame retardants, polybrominated diphenyl ethers, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. The optimization of the dispersive-solid phase for clean-up, combined with the optimization of chromatographic parameters, ensured improved sensitivity. Method validation included assessments for recovery, reproducibility, limit of detection (LOD), and limit of quantification (LOQ). Recoveries ranged from 59.5 to 117%, while LODs ranged from 0.00700 to 0.271 µg g-1. Application of the method to seven SS samples from Portuguese wastewater treatment plants revealed the presence of sixteen compounds, including persistent organic pollutants. The quantification of α-endosulfan, an organochlorine pesticide, was consistently observed in all samples, with concentrations ranging from 0.110 to 0.571 µg g-1. Furthermore, the study encompasses the analysis of agronomic parameters, as well as the mineral and metal content in SS samples. The study demonstrates that the levels of heavy metals comply with legal limits. By conducting a comprehensive investigation into the presence of micropollutants in SS, this study contributes to a deeper understanding of the environmental and sustainable implications associated with SS management.

Synergistic/antagonistic toxicity characterization and source-apportionment of heavy metals and organophosphorus pesticides by the biospectroscopy-bioreporter-coupling approach

Many anthropogenic chemicals are manufactured and eventually enter the surrounding environment, threatening food security and human health. Considering the additive or synergistic effects of pollutant mixtures, there is an expanding need for rapid, cost-effective and field-portable screening methods in environmental monitoring. This study used a recently developed biospectroscopy-bioreporter-coupling (BBC) approach to investigate the binary toxicity of Ag(I), Cr(VI) and four organophosphorus pesticides (dichlorvos, parathion, omethoate and monocrotophos). Ag(I) and Cr(VI) altered the toxicity mechanisms of pesticides, explained by the synergistic or antagonistic effect of Ag/Cr-induced cytotoxicity and pesticide-induced genotoxicity. The discriminating Raman spectral peaks associated with organophosphorus pesticides were 1585 and 1682 cm-1, but 750, 1004, 1306 and 1131 cm-1 were found in heavy metal and pesticide mixtures. More spectral alterations were related to pesticides rather than Ag(I) or Cr(VI), hinting at the dominant toxicity mechanisms of pesticides in mixtures. Ag(I) supplement significantly increased the levels of reactive oxygen species induced by organophosphorus pesticides, attributing to the increased permeability of cell membrane and entrance of toxic substances into the cells by the oligodynamic actions. This study lends deeper insights into the interactions between microbes and pollutant mixtures, offering clues to assess the cocktail effects of multiple pollutants comprehensively.

Integrative effects of microbial inoculation and amendments on improved crop safety in industrial soils co-contaminated with organic and inorganic pollutants

Soils co-contaminated by organic and inorganic pollutants usually pose major ecological risks to soil ecosystems including plants. Thus, effective strategies are needed to alleviate the phytotoxicity caused by such co-contamination. In this study, microbial agents (a mixture of Bacillus subtilis, Sphingobacterium multivorum, and a commercial microbial product named OBT) and soil amendments (β-cyclodextrin, rice husk, biochar, calcium magnesium phosphate fertilizer, and organic fertilizer) were evaluated to determine their applicability in alleviating toxicity to crops (maize and soybean) posed by polycyclic aromatic hydrocarbon (PAHs) and potentially toxic metals co-contaminated soils. The results showed that peroxidase, catalase, and superoxide dismutase activity levels in maize or soybean grown in severely or mildly contaminated soils were significantly enhanced by the integrative effects of amendments and microbial agents, compared with those in single plant treatments. The removal rates of Zn, Pb, and Cd in severely contaminated soils were 49 %, 47 %, and 51 % and 46 %, 45 %, and 48 %, for soybean and maize, respectively. The total contents of Cd, Pb, Zn, and PAHs in soil decreased by day 90. Soil organic matter content, levels of nutrient elements, and enzyme activity (catalase, urease, and dehydrogenase) increased after the amendments and application of microbial agents. Moreover, the amendments and microbial agents also increased the diversity and distribution of bacterial species in the soil. These results suggest that the amendments and microbial agents were beneficial for pollutant purification, improving the soil environment and enhancing both plant resistance to pollutants and immune systems of plants.

Uptake, translocation and subcellular distribution of organophosphate esters in rice by co-exposure to organophosphate esters and copper oxide nanoparticle

This study investigated the influence of copper oxide nanoparticles (CuONPs) and Cu²⁺ on the uptake, translocation and subcellular distribution of organophosphate esters (OPEs) in rice seedlings using hydroponic experiments. The OPE concentrations in roots and shoots under the OPEs+CuONPs treatment were significantly lower than those with the OPEs+Cu²⁺ (low level) or OPEs-only treatments, indicating that CuONPs can hinder the uptake of OPEs by root via competitive adsorption under short-term exposure. The plasma membrane permeability and antioxidant enzyme activity implied that CuONPs had a negligible impact on rice seedlings and could even reduce the toxicity of OPEs to rice root. A significant negative correlation between translocation factor and octanol-water partition coefficient was observed for the three treatments, implying an important role of hydrophobicity on the acropetal translocation of OPEs. Relatively hydrophobic OPEs were mainly adsorbed on cell wall, while hydrophilic OPEs were concentrated in cell sap. The subcellular distributions of OPEs in the OPEs+Cu²⁺ (high level) or OPEs+CuONPs treatments slightly differed from the OPEs-only treatment, indicating that the coexistence of Cu²⁺ or CuONPs with OPEs can influence the subcellular distribution of OPEs by affecting their adsorption or partitioning processes. Inhibition experiment suggested that root uptake of OPEs is a non-energy-consuming facilitated diffusion mediated by aquaporin channel, which can be slightly changed by the co-exposure of CuONPs. This study improved the understanding of uptake and translocation of OPEs by rice under the co-exposure to CuONPs.

Research on Risk Assessment and Contamination Monitoring of Potential Toxic Elements in Mining Soils

Potentially toxic element (PTE) contamination in soils has serious impacts on ecosystems. However, there is no consensus in the field of assessment and monitoring of contaminated sites in China. In this paper, a risk assessment and pollution monitoring method for PTEs was proposed and applied to a mining site containing As, Cd, Sb, Pb, Hg, Ni, Cr, V, Zn, Tl, and Cu. The comprehensive scoring method and analytical hierarchical process were used to screen the priority PTEs for monitoring. The potential ecological risk index method was used to calculate the risk index of monitoring point. The spatial distribution characteristics were determined using semi-variance analysis. The spatial distribution of PTEs was predicted using ordinary kriging (OK) and radial basis function (RBF). The results showed that the spatial distribution of As, Pd, and Cd are mainly influenced by natural factors, while Sb and RI are influenced by both natural and human factors. OK has higher spatial prediction accuracy for Sb and Pb, and RBF has higher prediction accuracy for As, Cd, and RI. The areas with high ecological risk and above are mainly distributed on both sides of the creek and road. The optimized long-term monitoring sites can achieve the monitoring of multiple PTEs.

Occurrence, source delineation, and health hazard of polycyclic aromatic hydrocarbons in tissues of Sarotherodon melanotheron and Chrysichthys nigrodigitatus from Okulu River, Nigeria

Polycyclic aromatic hydrocarbons (PAHs) are mistakenly consumed by people through their diet, including food and water. The occurrence, source, and health hazards of 16 PAHs in 36 tilapia (Sarotherodon melanotheron) and silver catfish (Chrysichthys nigrodigitatus) samples from Okulu River, Nigeria were investigated in this study. The total PAH concentration ranged from 11.70-24.20 to 13.40-19.60 µg/kg, being statistically different between the two species. The values were higher than the European Commission limits of 12 µg/kg and within the World Health Organization limit of 20 µg/kg. The 16 PAHs were detected in both fish species. The diagnostic ratio revealed that petroleum, fossil fuel, and incomplete combustion of biomass wastes were the sources of PAHs in the fishes. Pearson's correlation showed that the PAHs can come from diverse sources. The non-carcinogenic risk quotients (HQs) and hazard index (HI) in both fish species were 1, an indication of no adverse health effects. Among the 9 PAHs that were used to calculate the HI, BaP and BgP accounted for 31% and 62%, respectively, for Chrysichthys nigrodigitatus, and 25% and 69%, respectively, for Sarotherodon melanotheron. The carcinogenic hazard of the 7 PAHs assessed was within the acceptable range of 10^-6-10^-4. But the sum of the carcinogenic hazard was on the order of 10^-3 in both species of fish, an indication of carcinogenic health effects. 79% and 75% of the total carcinogenic risk for Chrysichthys nigrodigitatus and Sarotherodon melanotheron, respectively, are from DaA and InP. The consumption of PAHs by residents of the study area and other population groups through fish foods from the studied river underlines the importance of checking PAHs in aquatic foods for health concerns on a frequent basis.

Combined pollution of heavy metals and polycyclic aromatic hydrocarbons in the soil in Shenfu Region, China: a case of three different cities

It is a challenging issue to investigate the combined pollution of heavy metals and polycyclic aromatic hydrocarbons (PAHs) in urban soils. The purpose of this study was to determine the concentrations of these two pollutants in soils in Shenyang, Fushun, and Fushun New District, to analyze their distribution, their interaction, and co-contamination levels. The concentrations of heavy metals were measured by inductively coupled plasma mass spectrometry (ICP-MS), while the concentrations of 21 kinds of PAH were analyzed by gas chromatography-mass spectrometry (GC-MS). Based on the analysis of pollution concentrations and distribution patterns, the intrinsic links between heavy metals and PAHs in three different cities were assessed using a variety of multivariate analysis methods. Compared to Shenfu New District, the concentration of pollutants in Shenyang and Fushun shows a higher level. Moreover, the results of redundancy analysis (RDA) of samples may quantify the possibility of combined pollution of different heavy metal elements and PAHs. This study also affirms the important role of multivariate analysis in being used to reveal the complex interactions and spatial distribution of different pollutants.

Contributions of Beneficial Microorganisms in Soil Remediation and Quality Improvement of Medicinal Plants

Medicinal plants (MPs) are important resources widely used in the treatment and prevention of diseases and have attracted much attention owing to their significant antiviral, anti-inflammatory, antioxidant and other activities. However, soil degradation, caused by continuous cropping, excessive chemical fertilizers and pesticide residues and heavy metal contamination, seriously restricts the growth and quality formation of MPs. Microorganisms, as the major biota in soil, play a critical role in the restoration of the land ecosystem. Rhizosphere microecology directly or indirectly affects the growth and development, metabolic regulation and active ingredient accumulation of MPs. Microbial resources, with the advantages of economic efficiency, harmless to environment and non-toxic to organisms, have been recommended as a promising alternative to conventional fertilizers and pesticides. The introduction of beneficial microbes promotes the adaptability of MPs to adversity stress by enhancing soil fertility, inhibiting pathogens and inducing systemic resistance. On the other hand, it can improve the medicinal quality by removing soil pollutants, reducing the absorption and accumulation of harmful substances and regulating the synthesis of secondary metabolites. The ecological and economic benefits of the soil microbiome in agricultural practices are increasingly recognized, but the current understanding of the interaction between soil conditions, root exudates and microbial communities and the mechanism of rhizosphere microecology affecting the secondary metabolism of MPs is still quite limited. More research is needed to investigate the effects of the microbiome on the growth and quality of different medicinal species. Therefore, the present review summarizes the main soil issues in medicinal plant cultivation, the functions of microbes in soil remediation and plant growth promotion and the potential mechanism to further guide the use of microbial resources to promote the ecological cultivation and sustainable development of MPs.

Biochar Effect on the Benzo[a]pyrene Degradation Rate in the Cu Co-Contaminated Haplic Chernozem under Model Vegetation Experiment Conditions

The research of the fundamentals of the behavior of behavior in the soil–plant system during their co-contamination is of high interest because of the absence of technologies for the creation of effective, environmentally friendly and cost-effective remediation methods, as well as integrated systems for predicting the quality of soils co-contaminated with HMs and PAHs. The unique model vegetation experiment was studied with Haplic Chernozem contaminated by one of the priority organic toxicants, benzo[a]pyrene (BaP), applied alone and co-contaminated with Cu with the subsequent vegetation of tomato (Solanum lycopersicum) and spring barley plants (Hordeum sativum Distichum). Biochar obtained from sunflower husks was used as a sorbent for the remediation of the contaminated soil. It was established that by increasing the BaP amount applied to the soil, the rate of BaP degradation improved. The effect was enhanced in the presence of biochar and decreased in the case of joint co-contamination with Cu, which is especially expressed for the soil of tomato plants. The half-degradation time of the BaP molecule varied from 8 up to 0.2 years for tomatoes and barley.

Bioremediation of PAHs and heavy metals co-contaminated soils: Challenges and enhancement strategies

Systemic studies on the bioremediation of co-contaminated PAHs and heavy metals are lacking, and this paper provides an in-depth review on the topic. The released sources and transport of co-contaminated PAHs and heavy metals, including their co-occurrence through formation of cation-π interactions and their adsorption in soil are examined. Moreover, it is investigated that co-contamination of PAHs and heavy metals can drive a synergistic positive influence on bioremediation through enhanced secretion of extracellular polymeric substances (EPSs), production of biosynthetic genes, organic acid and enzymatic proliferation. However, PAHs molecular structure, PAHs-heavy metals bioavailability and their interactive cytotoxic effects on microorganisms can exert a challenging influence on the bioremediation under co-contaminated conditions. The fluctuations in bioavailability for microorganisms are associated with soil properties, chemical coordinative interactions, and biological activities under the co-contaminated PAHs-heavy metals conditions. The interactive cytotoxicity caused by the emergence of co-contaminants includes microbial cell disruption, denaturation of DNA and protein structure, and deregulation of antioxidant biological molecules. Finally, this paper presents the emerging strategies to overcome the bioavailability problems and recommends the use of biostimulation and bioaugmentation along with the microbial immobilization for enhanced bioremediation of PAHs-heavy metals co-contaminated sites. Better knowledge of the bioremediation potential is imperative to improve the use of these approaches for the sustainable and cost-effective remediation of PAHs and heavy metals co-contamination in the near future.

Micro-distribution of arsenic and polycyclic aromatic hydrocarbons and their interaction in Pteris vittata L

Interactive effects of inorganic arsenic (As) species and polycyclic aromatic hydrocarbons (PAHs) on their uptake, accumulation and translocation in the hyperaccumulator Pteris vittata L. (P. vittata) were studied hydroponically. The presence of PAHs hindered As uptake and acropetal translocation by P. vittata, decreasing As concentrations by 29.8%-54.5% in pinnae, regardless of the initial As speciation. The inhibitive effect of PAHs was 1.6-8.7 times greater for arsenite [As(III)] than for arsenate [As(V)]. Similarly, inorganic As inhibited the uptake of fluorene (FLU) and benzo[a]pyrene (BaP) by P. vittata roots by 0.4%-21.7% and by 33.1%-69.7%, respectively. Interestingly, coexposure to As and PAHs slightly enhanced the translocation of PAHs by P. vittata with their concentrations increased 0.3 to 0.8 times in shoots, except for the As(III)+BaP treatment. The antagonistic interaction between As and PAHs uptake is likely caused by competitive inhibition or oxidative stress injury. By using synchrotron radiation micro X-ray fluorescence imaging, high concentrations of As were found distributed throughout the microstructures far from main vein of the pinnae when coexposed with PAHs, the opposite of what was observed with exposure to As only. PAHs could also significantly inhibit the accumulation and distribution of As in vascular bundles in rachis treated with As(III). The results of two-photon laser scanning confocal microscopy revealed that PAHs were mainly distributed in the vascular cylinder, epidermal cells, vascular bundles, epidermis and vein tissues, and this was independent of As speciation and treatment. This work offers new positive evidence for the interaction between As and PAHs in P. vittata, presents new information on the underlying mechanisms for interactions of As and PAHs affecting their uptake and translocation within P. vittata L., and provides direction for future research on the mechanisms of PAHs uptake by plants.

Analysis of Polycyclic Aromatic Hydrocarbons and Phthalate Esters in Soil and Food Grains from the Balkan Peninsula: Implication on DNA Adduct Formation by Aristolochic Acid I and Balkan Endemic Nephropathy

Balkan endemic nephropathy (BEN) is a chronic tubulointerstitial nephropathy affecting residents of rural farming areas in many Balkan countries. Although it is generally believed that BEN is an environmental disease caused by multiple geochemical factors with much attention on aristolochic acids (AAs), its etiology remains controversial. In this study, we tested the hypothesis that environmental contamination and subsequent food contamination by polycyclic aromatic hydrocarbons (PAHs) and phthalate esters are AA toxicity factors and important to BEN development. We identified significantly higher concentrations of phenanthrene, anthracene, diethyl phthalate (DEP), dibutyl phthalate (DBP), and benzyl butyl phthalate (BBP) in both maize and wheat grain samples collected from endemic villages than from nonendemic villages. Other PAHs and phthalate esters were also detected at higher concentrations in the soil samples from endemic villages. Subsequent genotoxicity testing of cultured human kidney cells showed an alarming phenomenon that phenanthrene, DEP, BBP, and DBP can interact synergistically with AAs to form elevated levels of AA-DNA adducts, which are associated with both the nephrotoxicity and carcinogenicity of AAs, further increasing their disease risks. This study provides direct evidence that prolonged coexposure to these environmental contaminants via dietary intake may lead to greater toxicity and accelerated development of BEN.

Adsorption-Degradation of Polycyclic Aromatic Hydrocarbons in Soil by Immobilized Mixed Bacteria and Its Effect on Microbial Communities

The combined action of biosorption and biodegradation can achieve a remarkable reduction of organic pollutants. In this study, Pseudomonas sp. SDR4 and Mortierella alpina JDR7 were selected as the representative microorganisms to investigate adsorption and degradation of polycyclic aromatic hydrocarbons (PAHs) in soil using immobilization technology and the subsequent change of the microbial community structure. The results showed that the adsorption capacity of immobilized carriers was much higher than that of dead microorganisms and that the addition of dead microorganisms did not affect the adsorption characteristics of immobilized carriers. The chemical reaction was the major factor controlling the adsorption rate of PAHs in sterilized soil (CK), nonsterilized soil (CK-1), and soil amended with dead body immobilized JDR7 and SDR4 mixed bacteria (MB-D). The growth and metabolism of Pseudomonas sp. SDR4 and M. alpina JDR7 are the main reason for enhanced PAH degradation in the soil amended with living body immobilized JDR7, SDR4 mixed bacteria (MB).

Influence of ligand's directional configuration, chrysenes as model compounds, on the binding activity with aryl hydrocarbon receptor

Understanding what and how physico-chemical factors of a ligand configure conditions for ligand-receptor binding is a key to accurate assessment of toxic potencies of environmental pollutants. We investigated influences of the dipole-driven orientation and resulting directional configuration of ligands on receptor binding activities. Using physico-chemical properties calculated by ab initio density functional theory, directional reactivity factors (DRF) were devised as main indicators of toxic potencies, linking molecular ligand-receptor binding to in vitro responses. The directional reactive model was applied to predict variation of aryl hydrocarbon receptor-mediated toxic potencies among homologues of chrysene with structural modifications such as the numbers of constituent benzene rings, methylation and hydroxylation. Results of predictive models were consistent with empirical potencies determined by use of the H4IIE-luc transactivation bioassay. The experiment-free approach based on first principles provides an analytical framework for estimating molecular bioactivity in silico and complements conventional empirical approaches to studying molecular initiating events in adverse outcome pathways.

Integrated assessment of west coast of South Korea by use of benthic bacterial community structure as determined by eDNA, concentrations of contaminants, and in vitro bioassays

During the past few decades, contamination of sediments by persistent toxic substances (PTSs) has been observed in estuarine and coastal areas on the west coast of South Korea. The contaminants are suspected to cause toxicities in aquatic biota, but little is known about their ecological effects, particularly on benthic microbial communities. In this study, an eDNA-based assessment was applied along with classic assessments of exposure, such as chemistry and in vitro bioassays, to evaluate condition of benthic bacterial communities subjected to PTSs. Two strategies were adopted for the study. One was to conduct a comprehensive assessment in space (by comparing seawater and freshwater sites at five coastal regions) and in time (by following change over a 5-y period). Although we found that bacterial composition varied among and within years, some phyla, such as Proteobacteria (28.7%), Actinobacteria (13.1%), Firmicutes (12.7%), and Chloroflexi (12.5%) were consistently dominated across the study regions. Certain bacterial groups, such as Firmicutes and Verrucomicrobia have been linked to contamination at some sites in the study area and at specific points in time. Bacterial communities were not significantly correlated with salinity or AhR- and ER-mediated potencies, whereas concentrations of PAHs, APs, and certain metals (Cd and Hg) exhibited significant associations to the structure of bacterial communities at the phylum level. In fact, the relative abundance of microbes in the phylum Planctomycetes was significantly and negatively correlated with concentrations of PAHs and metals. Thus, the relative abundance of Planctomycetes could be used as an indicator of sedimentary contamination by PAHs and/or metals. Based on our correlation analyses, Cd and ER-mediated potencies were associated more with bacterial abundances at the class taxonomic level than were other PTSs and metals. Overall, the eDNA-based assessment was useful by augmenting more traditional measures of exposure and responses in a sediment triad approach and has potential as a more rapid screening tool.

Biodegradation of hydrocarbons by microbial strains in the presence of Ni and Pb

Microbial strains capable of degrading petroleum hydrocarbons were isolated from the Yellow River Delta and screened for bio-surfactant production. The bio-surfactant-producing characteristics of the isolates were evaluated, and all the isolates which could produce bio-surfactant were identified by 16S rRNA gene sequencing. The results showed that the isolates belong to Bacillus sp. (72%), Ochrobactrum sp. (0.16%), Brevundimonas sp. (0.06%) and Brevibacterium sp. (0.06%). The biodegradability of crude oil, gasoline, diesel oil and other hydrocarbons by microbial strains were studied, among which the biodegrading ability of strain P1 and strain P19 is higher than other strains. Both strains P1 and P19 can degrade n-hexane and n-hexadecane effectively and have wide substrate extensiveness. In addition, Ni promoted the biodegradability of toluene by both strain P1 and strain P19, while Pb inhibited the growth of strain P19 and decreased its ability to biodegrade toluene. The studies revealed that microbes including strain P1 and strain P19 can be utilized in bioremediation of co-contaminated water with petroleum and heavy metals including Ni and Pb.

Study on removal of pyrene by Agropyron cristatum L. in pyrene-Ni co-contaminated soil

Heavy metals and polycyclic aromatic hydrocarbons (PAHs) co-contamination in the soil is widespread. Phytoremediation is often used to remediate co-contaminated soil, but few studies focused on the effects of nickel on the dissipation and uptake of pyrene in phytoremediation. The dissipation of pyrene, the uptake, and distribution of pyrene in Agropyron cristatum L. (A. cristatum) were investigated in this study in the presence of nickel. The pyrene removal rate in single pyrene-contaminated soil with A. cristatum cultivation (48.97%) was the highest, which was higher than that of the co-contamination (47.88%). This was due to the high soil microbial activity and high dissolved organic matter (DOM) contents. In single pyrene-contaminated soil, pyrene was mainly accumulated in the soluble fraction in shoots and on the cell wall in roots of A. cristatuma. Besides, nickel could promote the adsorption of pyrene on the cell wall. Pyrene in A. cristatum could be transported through the apoplast and symplast, and the pyrene contents in the symplast were 2-3 times that of the apoplast. The uptake of pyrene by A. cristatum included both active absorption and passive transportation. Active absorption involved H⁺ transport and energy conversion processes, and passive transport was associated with water protein channels.

Effect of soil pH and organic matter content on heavy metals availability in maize (Zea mays L.) rhizospheric soil of non-ferrous metals smelting area

Maize plant tissues and rhizosphere soil were collected from an agricultural area around the Huludao Zinc Plant in Liaoning Province, China, to investigate the effects of soil pH and organic matter content on heavy metal concentration and accumulation in different types of maize tissues. The mean pH of the soil samples was 7.02 (range 5.74-7.86), and the mean organic matter content was 31.03 g kg^-1 (range 18.80-52.20 g kg^-1). The average Cu, Zn, Pb, and Cd contents in soil were 2.92, 6.72, 7.95, and 16.28 times greater than the corresponding background values, respectively. The geo-accumulation index indicated that the soils were uncontaminated to moderately contaminated by Cu, moderately to strongly contaminated by Pb and Zn, and strongly contaminated by Cd. The average available Cu, Pb, Zn, and Cd contents in the soil samples were 16.34, 6.997, 69.77, and 0.190 mg kg^-1, respectively, while their bioavailability coefficients were 28.53%, 1.65%, 40.44%, and 10.83%, respectively. The respective mean Pb and Cd concentrations in grain samples were 0.341 and 0.342 mg kg^-1, which exceeded the maximum concentrations permitted by the Chinese National Standard. Thus, the maize grain is not safe for consumption and poses potential risks to human health. With the exception of Cu, the combined effect of pH and organic matter content had a stronger influence on the availability of heavy metals in soil compared with either factor alone. Cd uptake in maize plant tissues was affected by the combination of soil pH, organic matter content, and bioavailable Cd content in soil; however, the combination of these three factors had only slight effects on Cu, Zn, and Pb absorption in maize tissues.

Determination of influencing factors on historical concentration variations of PAHs in West Taihu Lake, China

The adsorption of polycyclic aromatic hydrocarbons (PAHs) by components such as elemental carbon (EC), total organic carbon (TOC), and particles is different, and EC and PAHs are good materials for reconstructing historical human activity patterns and pollution conditions. In this study, the effects of EC (soot and char), TOC and particles of different grain size on PAHs in surface sediments were quantitatively analysed, and their historical concentrations in a sediment core from western Taihu Lake were reconstructed. The contents of soot, TOC, clay, EC and char explained 57.2%, 27.6%, 26.0%, 24.0% and 16.4%, respectively, of the PAH concentrations in surface sediments. The correlation between the soot and PAH levels was significantly higher than that between the char, TOC, and clay contents and PAH levels, and PAHs were mainly affected by the local economic development and human activity, as indicated by metrics of population, highway mileage, coal burning, and industrial output. With the development of the economy of the Taihu Lake Basin, the composition of PAHs in the sediments has changed: the proportion of low-molecular-weight PAHs decreased from 42.4% to 17.5%, and that of high-molecular-weight PAHs increased from 58.7% to 82.5%. The concentration of PAHs in pore water from Taihu Lake over the past 100 years was reconstructed and ranged from 43.1 to 961.2 μg L^-1, with an average of 180.7 μg L^-1. After China's reform and opening up, the concentrations of various PAHs in Taihu Lake changed from safe to chronic pollution levels. The ratios of lead (Pb) isotopes and the diagnostic ratios of PAHs showed that the main sources of PAHs in western Taihu Lake sediments were human activities such as coal and petroleum combustion.

Impacts of heavy metals and soil properties at a Nigerian e-waste site on soil microbial community

Heavy metal contamination is a serious problem worldwide threatening soil environment and human health. In the present study, concentrations of 6 heavy metals at an electronic waste (e-waste) site in Nigeria were correlated to their mobility, showing distinct distribution pattern between surface soils and subsoils. Proteobacteria, Firmicutes, Acidobacteria and Planctomycetes dominated the indigenous soil microbial communities, and there was significant discrimination of bacterial taxonomic composition between the heavy metal contaminated and uncontaminated areas. The abundance of most bacterial taxa changed with heavy metal contamination level to different extent. The multivariate regression tree (MRT) analyses illustrated that main environmental variables influencing bacterial taxonomic composition included soil texture (31%) and organic carbon (14%), whereas microbial diversity was affected by soil pH (32%) and soil texture (14%). Our results surprisingly indicated that soil properties were more influential in determining soil bacterial composition and diversity than heavy metals even at the e-waste site which was seriously contaminated by heavy metals. The present study contributes to a deeper insight into the key environmental variables shaping the diversity and composition of soil microbes at heavy metal contaminated e-waste sites.

Heavy Metal Exposure Alters the Uptake Behavior of 16 Priority Polycyclic Aromatic Hydrocarbons (PAHs) by Pak Choi ( Brassica chinensis L.)

Polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) are predominant pollutants normally coexisting at electronic waste dumping sites or in agricultural soils irrigated with wastewater. The accumulation of PAHs and HMs in food crops has become a major concern for food security. This study explored the hydroponic uptake of 16 priority PAHs and 5 HMs (Cd, Cr, Cu, Pb, and Zn) by pak choi ( Brassica chinensis L.). PAHs exhibited stronger inhibition on pak choi growth and physiological features than HMs. Five HMs were categorized into high-impact HMs (Cr, Cu, and Pb) and low-impact HMs (Cd and Zn) with distinct behavior under the coexposure with PAHs, and low-impact HMs showed synergistic toxicity effects with PAHs. Coexposure to PAHs and HMs slightly decreased the uptake and translocation of PAHs by pak choi, possibly attributing to the commutative hindering effects on root adsorption or cation-π interactions. The bioconcentration factors in PAHs + HMs treatments were independent of the octanol-water partition coefficient ( K_ow), owing to the cation-π interaction associated change of K_ow and induced defective root system. This study provides new insights into the mechanisms and influential factors of PAHs uptake in Brassica chinensis L. and gives clues for reassessing the environmental risks of PAHs in food crops.

Effective phytoremediation of low-level heavy metals by native macrophytes in a vanadium mining area, China

Heavy metal contamination, particularly vanadium contamination in mining and smelting areas, is a worldwide serious problem threatening the ecological system and human health. The contamination level of vanadium, arsenic, cadmium, chromium, mercury, and lead in sediments and waters in a vanadium mining area in China was investigated in the present study. The behavior of heavy metal uptake by 12 native aquatic macrophytes was evaluated, including 5 species of emergent aquatic plants (Acorus calamus, Scirpus tabernaemontani, Typha orientalis, Phragmites australis, and Bermuda grass), 3 species of floating plants (Marsilea quadrifolia, Nymphaea tetragona, and Eleocharis plantagineiformis), and 4 species of submerged plants (Hydrilla verticillata, Ceratophyllum demersum, Myriophyllum verticillatum, and Potamogetom crispus). Different heavy metal accumulation abilities were found across these macrophytes. Generally, they tended to accumulate higher contents of chromium, and C. demersum showed a particularly higher accumulation capacity for vanadium. The heavy metals were preferentially distributed in roots, instead of translocation into leaves and stems, indicating an internal detoxification mechanism for heavy metal tolerance in macrophytes. In 24-day laboratory hydroponic experiments, the macrophytes had a satisfied phytoremediation performance for heavy metals, when their concentrations were at the microgram per liter level. Particularly, vanadium was effectively removed by P. australis and C. demersum, the removal efficiencies of which were approximately 50%. In addition, a combination of terrestrial plant (Bermuda grass) and aquatic macrophytes (P. australis, M. quadrifolia, and C. demersum) exhibited high uptake capacity of all the six heavy metals and their residual concentrations were 95 (vanadium), 39.5 (arsenic), 4.54 (cadmium), 17.2 (chromium), 0.028 (mercury), and 7.9 (lead) μg/L, respectively. This work is of significant importance for introducing native macrophytes to remove low-level heavy metal contamination, particularly vanadium, and suggests phytoremediation as a promising and cost-effective method for in situ remediation at mining sites.

Roles of saprotrophic fungi in biodegradation or transformation of organic and inorganic pollutants in co-contaminated sites

For decades, human activities, industrialization, and agriculture have contaminated soils and water with several compounds, including potentially toxic metals and organic persistent xenobiotics. The co-occurrence of those toxicants poses challenging environmental problems, as complicated chemical interactions and synergies can arise and lead to severe and toxic effects on organisms. The use of fungi, alone or with bacteria, for bioremediation purposes is a growing biotechnology with high potential in terms of cost-effectiveness, an environmental-friendly perspective and feasibility, and often representing a sustainable nature-based solution. This paper reviews different ecological, metabolic, and physiological aspects involved in fungal bioremediation of co-contaminated soils and water systems, not only addressing best methods and approaches to assess the simultaneous presence of metals and organic toxic compounds and their consequences on provided ecosystem services but also the interactions between fungi and bacteria, in order to suggest further study directions in this field.

Synergetic effects of plastic mulching and nitrogen application rates on grain yield, nitrogen uptake and translocation of maize planted in the Loess Plateau of China

Nitrogen (N) fertilization potentially affects the amount of N uptake and N translocation (NT) within plants, but the synergetic effects of plastic mulching and N application rates on the grain yield (GY), N uptake and NT of maize have not been studied. A fertilization experiment with six N application rates (0, 80, 160, 240, 350 and 450 kg ha-1) with or without mulch was conducted in 2015 and 2016 in the Loess Plateau of China. There were significant interactions between mulch and the N fertilizer rate on the GY. Under mulch treatments, the highest GY was observed at 450 kg ha-1, which was 53.9%, 36.4%, 20.2%, 1.6% and 0.3% higher than those obtained with N application rates of 0, 80, 160, 240 and 350 kg ha-1, respectively, in 2015. The ranking of NT to grain N accumulation was leaves > sheaths and stems > ear axis > bracts. The NT efficiency (NTE) levels averaged over the different N fertilization rates under the no-mulch treatment were 5.6% and 12.9% higher than those under the plastic mulch treatment in 2015 and 2016, respectively. We conclude that an N fertilizer application rate of 240 kg ha-1 with mulch can achieve a relatively higher NTE, GY, WUE and NUE.

Polycyclic aromatic hydrocarbons degradation by marine-derived basidiomycetes: optimization of the degradation process

Pyrene and benzo[a]pyrene (BaP) are high molecular weight polycyclic aromatic hydrocarbons (PAHs) recalcitrant to microbial attack. Although studies related to the microbial degradation of PAHs have been carried out in the last decades, little is known about degradation of these environmental pollutants by fungi from marine origin. Therefore, this study aimed to select one PAHs degrader among three marine-derived basidiomycete fungi and to study its pyrene detoxification/degradation. Marasmiellus sp. CBMAI 1062 showed higher levels of pyrene and BaP degradation and was subjected to studies related to pyrene degradation optimization using experimental design, acute toxicity, organic carbon removal (TOC), and metabolite evaluation. The experimental design resulted in an efficient pyrene degradation, reducing the experiment time while the PAH concentration applied in the assays was increased. The selected fungus was able to degrade almost 100% of pyrene (0.08mgmL^-1) after 48h of incubation under saline condition, without generating toxic compounds and with a TOC reduction of 17%. Intermediate metabolites of pyrene degradation were identified, suggesting that the fungus degraded the compound via the cytochrome P450 system and epoxide hydrolases. These results highlight the relevance of marine-derived fungi in the field of PAH bioremediation, adding value to the blue biotechnology.

Rhizospheric effects on atrazine speciation and degradation in laterite soils of Pennisetum alopecuroides (L.) Spreng

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) is a worldwide-used herbicide and often detected in agricultural soils and groundwater at concentrations above the permitted limit, because of its high mobility, persistence, and massive application. This study applied pot experiments to investigate the atrazine contents and speciation during the phytoremediation process by Pennisetum alopecuroides (L.) Spreng. in laterite soils. From the change of the total atrazine and bioavailable atrazine measured by diffusive gradients in thin film (DGT), P. alopecuroides significantly improved atrazine degradation efficiency from 15.22 to 51.46%, attributing to the increasing bioavailable atrazine in rhizosphere. Only a small amount of atrazine was taken up by P. alopecuroides root and the acropetal translocation from roots to shoots was limited. The atrazine speciation was significantly different between rhizosphere and non-rhizosphere, attributing to the declining pH and organic matters in rhizosphere. The relationship between pH and soil-bound/humus-fixed atrazine illustrated the pH-dependant release of the atrazine from soils and the competition between humus adsorption and uptake by P. alopecuroides. The present study reveals the important roles of soil pH and organic matters in atrazine speciation and availability in laterite soils, and provides new insights in the rhizospheric effects on effective phytoremediation of atrazine.