Heavy metal bioavailability and accumulation in winter wheat (Triticum aestivum L.) irrigated with treated wastewater in calcareous soils

The accumulation of cadmium and lead in wheat grains is primarily determined by the soil-reducible cadmium level during wheat tillering

The significant increase in cadmium (Cd) and lead (Pb) pollution in agricultural soil has greatly heightened environmental contamination issues and the risk of human diseases. However, the mechanisms underlying the transformation of Cd and Pb in soil as well as the influencing factors during their accumulation in crop grains remain unclear. Based on the analysis of the distribution trend of Cd and Pb in soil during the growth and development stages of wheat (tillering, filling, and maturity) in alkaline heavy metal-polluted farmland in northern China, this study investigated the response mechanism of soil heavy metal form transformation to soil physicochemical properties, and elucidated the main determining periods and influencing factors for Cd and Pb enrichment in wheat grains. The results showed that an increase in CEC and SOM levels, along with a decrease in pH level, contributed to enhancing the bioavailability of Cd in the soil. This effect was particularly evident during the tillering stage and grain filling stage of wheat. Nevertheless, the effects of soil physicochemical properties on bioavailable Pb was opposite to that on bioavailable Cd. The enrichment of Cd and Pb in grain was significantly influenced by soil pH (r = -0.786, p < 0.01), SOM (r = 0.807, p < 0.01), K (r = -0.730, p < 0.01), AK (r = 0.474, p = 0.019), and AP (r = -0.487, p = 0.016). The reducible form of Cd in soil during the wheat tillering stage was identified as the primary factor contributing to the accumulation of Cd and Pb in wheat grains, with a significant contribution rate of 84.5%. This study provides a greater scientific evidence for the management and risk control of heavy metal pollution in alkaline farmland.

Recalcification stabilizes cadmium but magnifies phosphorus limitation in wastewater-irrigated calcareous soil

Long-term wastewater irrigation leads to the loss of calcium carbonate (CaCO3) in the tillage layer of calcareous land, which irreversibly damages the soil's ability to retain cadmium (Cd). In this study, we selected calcareous agricultural soil irrigated with wastewater for over 50 years to examine the recalcification effects of sugar beet factory lime (SBFL) at doses of 0%, 2.5%, 5%, and 10%. We found that SBFL promoted Cd transformation in the soil from active exchangeable species to more stable carbonate-bonded and residual species, which the X-ray diffraction patterns also confirmed results that CdSO4 reduced while CdS and CaCdCO3 increased. Correspondingly, the soil bioavailable Cd concentration was significantly reduced by 65.6-84.7%. The Cd concentrations in maize roots and shoots were significantly reduced by 11.7-50.6% and 13.0-70.0%, respectively, thereby promoting maize growth. Nevertheless, SBFL also increased the proportion of plant-unavailable phosphorus (P) in Ca8-P and Ca10-P by 4.3-13.0% and 10.7-25.9%, respectively, reducing the plant-available P (Olsen P) content by 5.2-22.1%. Consequently, soil P-acquiring associated enzyme (alkaline phosphatase) activity and microbial (Proteobacteria, Bacteroidota, and Actinobacteria) community abundance significantly increased. Our findings showed that adding SBFL to wastewater-irrigated calcareous soil stabilized Cd, but exacerbated P limitation. Therefore, it is necessary to alleviate P limitations in the practice of recalcifying degraded calcareous land.

Pb contaminated soil from a lead-acid battery plant immobilized by municipal sludge and raw clay

Soil heavy metal pollution poses a serious threat to the eco-environment. Municipal sludge-based passivators and clay minerals have been widely applied to immobilize heavy metal contamination in soils. However, little is known about the immobilization effect and mechanisms of raw municipal sludge and clay in reducing the mobility and bioavailability of heavy metals in soils. Here, municipal sludge, raw clay and mixtures of thereof were used to remediate Pb-contaminated soil from a Pb-acid battery factory. The remediation performance was evaluated through acid leaching, sequential extraction, and plant assay. Results showed that the leachable Pb content in the soil decreased from 5.0 mg kg-1 to 4.8, 4.8 and 4.4 mg kg-1 after 30 d of remediation with MS and RC added at equal weights to give total dosage of 20, 40 wt% and 60 wt %, respectively. The leachable Pb further decreased to 1.7, 2.0 and 1.7 mg kg-1 after 180 d of remediation. Speciation analysis of the soil Pb indicated that the exchangeable and Fe-Mn oxide-bound Pb were transformed into residual Pb in the early stage of remediation, and the carbonate-bound Pb and organic matter-bound Pb were transformed into residual Pb in the later stage of remediation. As a result, Pb accumulation in mung beans decreased by 78.5%, 81.1% and 83.4% after 180 days of remediation. These results indicate that the leaching toxicity and phytotoxicity of Pb in remediated soils were significantly reduced, presenting a better and low-cost method for soil remediation.

Elevated Uptake and Translocation Patterns of Heavy Metals in Different Food Plants Parts and Their Impacts on Human Health

Irrigation with contaminated wastewater is a common practice in cultivation of crops and vegetables in many developing countries due to the scarcity of available fresh water. The present study has investigated the transfer and mobilization trends of heavy metals in different crops and vegetables plants grown in contaminated soil and waterbody. The translocation patterns of metals from polluted sources into different organs of plants bodies such as roots and edible parts and associated health risks have been evaluated simultaneously. Total of 180 different environmental samples including food plants, agricultural soil, and irrigation water were collected and analyzed. Heavy metal concentrations (Fe, Ni, Mn, Pb, Cu, Cd, As) in water, soil, and different parts of crops and vegetable plants were compared with the permissible levels reported by FAO/WHO, EU, and USEPA. Different metals contents within the food plants were found to be in the order of Fe > Mn > Ni > Cu > Pb > Cd > As. Pollution load index (PLI) data indicate that soil is highly polluted with Cd as well as moderately contaminated by As and Cu. Bioconcentration factor (BCF) analysis showed excessive accumulation of some heavy metals in crops and vegetables. Target hazard quotient (THQ) and target carcinogenic risk (TCR) analysis data showed higher carcinogenic and non-carcinogenic risks for both adult and children from the consumption of metal-contaminated food items. The results of metal pollution index (MPI), estimated daily intake (EDI), and hazard index (HI) analyses demonstrated the patterns of metals pollution in different food plants.

Effect of biological sewage sludge and its derived biochar on accumulation of potentially toxic elements by corn (Zea mays L.)

The land application of sewage sludge can cause different environmental problems due to the high content of potentially toxic elements (PTEs). The objective of this study was to compare the effect of urban biological sewage sludge (i.e. the waste of activated sludge process) and its derived biochar as the soil amendments on the bioavailability of PTEs and their bioaccumulation by corn (Zea mays L.) under two months of greenhouse conditions. The soil was treated by adding biochar samples at 0 (control), 1, 3, 5% w/w. The diethylenetriamine pentaacetic acid (DTPA)-extractable concentrations of PTEs including Zn, Pb, Cd, Cr, Ni, Fe, and Cu in soil and their accumulation by plant shoot and root were measured. Conversion of the biological sewage sludge into the biochar led to decrease the PTEs bioavailability and consequently decreased their contents in plant tissues. The DTPA extractable metal concentrations of produced biochar in comparison to the biological sewage sludge reduced 75% (Cd), 65% (Cr), 79% (Ni and Pb), 76% (Zn), 91% (Cu) and 88% (Fe). Therefore, the content of Ni, Fe, Zn and Cd in corn shoot was decreased 61, 32, 18 and 17% respectively in application of 5% biochar than of raw sewage sludge. Furthermore, the application of 5% biochar enhanced the physiological parameters of the plants including shoot dry weight (twice) and wet weight (2.25 times), stem diameter (1.70 times), chlorophyll content (1.03 times) in comparison to using 5% raw sewage sludge. The results of the study highlight that application of the biochar derived from urban biological sewage sludge in soil could decrease the risk of PTEs to the plant.

Screening of mustard cultivars for phytoremediation of heavy metals contamination in wastewater irrigated soil systems

The mustard (Brassica juncea L.) plant is a well-known and widely accepted hyper-accumulator of heavy metals. The genetic makeup of mustard's cultivars may significantly impact their phytoremediation capabilities. The present study aimed to investigate the growth performance, yield attributes, and heavy metal accumulation potential of B. juncea cv. Varuna, NRCHB 101, RH 749, Giriraj, and Kranti, cultivated in soil irrigated with wastewater (EPS) and bore-well water (MPS). EPS contributed more Cr, Cd, Cu, Zn, and Ni to tested mustard cultivars than the MPS. EPS reduced morphological, biochemical, physiological, and yield attributes of tested mustard cultivars significantly (p < 0.05) than the MPS. Among the tested cultivars of mustard plants, Varuna had the highest heavy metal load with the lowest harvest index (35.8 and 0.21, respectively). Whereas NRCHB 101 showed the lowest heavy metal load with the highest harvest index (26.9 and 0.43, respectively). The present study suggests that B. juncea cv. Varuna and NRCHB 101 could be used for the phytoextraction of heavy metals and reducing their contamination in food chain, respectively in wastewater irrigated areas of peri-urban India. The outcomes of the present study can also be utilized to develop a management strategy for sustainable agriculture in heavy metal polluted areas resulting from long-term wastewater irrigation.

Combined Remediation Effects of Sewage Sludge and Phosphate Fertilizer on Pb-Polluted Soil from a Pb-Acid Battery Plant

Pb soil pollution poses a serious health risk to both the environment and humans. Immobilization is the most common strategy for remediation of heavy metal polluted soil. In this study, municipal sewage sludge was used as an amendment for rehabilitation of Pb-contaminated soils, for agricultural use, near a lead-acid battery factory. The passivation effect was further improved by the addition of phosphate fertilizer. It was found that the leachable Pb content in soils was decreased from 49.6 mg kg-1 to 16.1-36.6 mg kg-1 after remediation of sludge for 45 d at applied dosage of municipal sewage sludge of 4-16 wt%, and further decreased to 14.3-34.3 mg kg-1 upon extension of the remediation period to 180 d. The addition of phosphate fertilizer greatly enhanced the Pb immobilization, with leachable Pb content decreased to 2.0-23.6  mg kg-1 with increasing dosage of phosphate fertilizer in range of 0.8-16 wt% after 180 d remediation. Plant assays showed that the bioavailability of Pb was significantly reduced by the soil remediation, with the content of absorbed Pb in mung bean roots decreased by as much as 87.0%. The decrease in mobility and biotoxicity of the soil Pb is mainly attributed to the speciation transformation of carbonate, Fe-Mn oxides and organic matter bound Pb to residue Pb under the synergism of reduction effect of sludge and acid dissolution and precipitation effect of phosphate fertilizer. This study suggests a new method for remediation of Pb-contaminated soil and utilization of municipal sewage sludge resources.

Inversion of heavy metal copper content in soil-wheat systems using hyperspectral techniques and enrichment characteristics

The growing problem of heavy metal contamination in soil will seriously threaten the China's grain safety. The development of hyperspectral remote sensing technology provides the possibility to achieve rapid and non-destructive monitoring of soil heavy metal content. In this study, we used hyperspectral techniques and enrichment characteristics to explore the potential of wheat leaf spectral inversion for heavy metal copper (Cu) content in the soil-wheat system. First, we conducted potting experiments to plant wheat on soil contaminated with varying concentrations of the heavy metal Cu. Then, we analyzed the migration characteristics, correlation characteristics and enrichment characteristics of Cu in the soil-wheat system under different soil heavy metal Cu concentration treatments. Next, we analyzed the spectral and correlation features of wheat leaves, and explored the potential of wheat leaf spectra for the inversion of Cu content in full-band and eigen-band modeling. Finally, using the estimated Cu content of wheat leaves from the best inversion model, we further conducted inversions to obtain the Cu content and precision of the grain, stem, root, total soil, and soil-available states based on the enrichment characteristics. The results showed that: (1) The accumulation pattern was root > grain > leaf > stem when the soil Cu concentration was <200 mg kg-1, and root > leaf > stem > grain when the soil Cu concentration was >200 mg kg-1. (2) The correlation coefficients between the different analyzed elements of the soil-wheat system were high, and all of them reached a highly significant level (P < 0.01). This supports the use of wheat leaves to estimate the Cu contents of soil and different parts of wheat. (3) The best inversion accuracies were obtained by modeling second derivative (SD) spectra that were pre-processed by screening the characteristic bands. The modeled R2cv, RMSEcv,R2ev and RMSEev were 0.94, 2.72 mg kg-1, 0.91 and 3.64 mg kg-1, respectively. This indicates an excellent ability to estimate Cu content in wheat leaves. (4) Using the hyperspectral estimation of Cu content in wheat leaves and the grouped inversion of enrichment characteristics, the inversion accuracy was lower only for grains, and the R2cv and R2ev for stems and roots exceeded 0.90, those for total soil exceeded 0.85, and those for the soil available state exceeded 0.70. Therefore, it is possible to use the spectra of wheat leaves in combination with the inversion of enrichment characteristics to estimate the soil-wheat Cu content. This study provides guarantee and support for the detection of grain safety.

Dual Regulatory Role of Penicillium oxalicum SL2 in Soil: Phosphorus Solubilization and Pb Stabilization

The mechanisms of the P. oxalicum SL2-mediated microbial community on phosphorus solubilization and Pb stabilization were investigated through a 90-day soil experiment. In the treatments inoculated with P. oxalicum SL2, the amount of P. oxalicum SL2-GFP remained at 77.8%-138.6% of the initial inoculation amount after 90 days, and the available phosphorus (AP) content increased 21.7%-40.8% while EDTA-Pb decreased 29.9%-43.2% compared with CK treatment. SEM-EDS results showed that P. oxalicum SL2 changed the agglomeration degree of microaggregates and promoted the combination of Pb with C and O elements. These phenomena were enhanced when applied with Ca3(PO4)2. Microbial community analysis showed that P. oxalicum SL2 improved soil microbial activity, in which the fungi absolute abundance increased about 15 times within 90 days. Correlation analyses and a partial least-squares path model showed that the activation of Penicillium, Ascobolus, Humicola, and Spizellomyces in a fungal community increased the content of oxalate and AP, which directly decreased EDTA-Pb content, while the change of Bacillus, Ramlibacter, Gemmatimonas, and Candidatus Solibacter in the bacterial community regulated Fe/Mn/S/N cycle-related functions, thus promoting the conversion of Pb to oxidizable state. Our findings highlight that P. oxalicum SL2 enhanced the microbial-induced phosphate precipitation process by activating soil microbial communities and regulating their ecological functions.

Investigating the effects of irrigation with indirectly recharged groundwater using recycled water on soil and crops in semi-arid areas

The utilization of direct wastewater for irrigation poses many environmental problems such as soil quality deterioration due to the accumulation of salts, heavy metals, micro-pollutants, and health risks due to undesirable microorganisms. This hampers its agricultural reuse in arid and semi-arid regions. To address these concerns, the present study introduces a recent approach that involves using indirectly recharged groundwater (GW) with secondary treated municipal wastewater (STW) for irrigation through a Soil Aquifer Treatment-based system (SAT). This method aims to mitigate freshwater scarcity in semi-arid regions. The study assessed GW levels, physicochemical properties, and microbial diversity of GW, and soil in both impacted (receiving recycled water) and non-impacted (not receiving recycled water) areas, before recycling (2015-2018) and after recycling (2019-2022) period of the project. The results indicated a significant increase of 68-70% in GW levels of the studied boreholes in the impacted areas. Additionally, the quality of indirectly recharged GW in the impacted areas improved notably in terms of electrical conductivity (EC), hardness, total dissolved solids (TDS), sodium adsorption ratio (SAR), along with certain cations and anions (hard water to soft water). No significant difference was observed in soil properties and microbial diversity of the impacted areas, except for EC and SAR, which were reduced by 50% and 39%, respectively, after the project commenced. The study also monitored specific microbial species, including total coliforms, Escherichia coli (as indicator organisms), Shigella, and Klebsiella in some of the harvested crops (beetroot, tomato, and spinach). However, none of the analysed crops exhibited the presence of the studied microorganisms. Overall, the study concludes that indirectly recharged GW using STW is a better sustainable and safe irrigation alternative compared to direct wastewater use or extracted hard GW from deep aquifers.

Foliar architecture differentially restrains metal sequestration capacity in wheat grains (Triticum aestivum L.) grown in hyper-chloride-contaminated soils

Anthropogenic activities, such as industrial wastewater and use of water softeners, cause hyper-accumulation of Cl- in water sources and soils. Currently, industries have no sustainable method to remove these Cl- ions from wastewater. This study was conducted to evaluate the integrative responses of wheat cultivated in five industrial effluent-affected areas (S2-S6) by investigating soil characters and bioaccumulation of metals in wheat plants and grains. The S4 site (near the second chloride outlet) exhibited a higher concentration of CO2, SO2, NO2, Cl-, Cd, Mn, Ni, Cr, and Zn. Soil from S6 (sewage wastewater downstream getting mixed with chloride-contaminated water) had a minimum level of nutrients (Na, K, and Ca), maximum metals (Cd, Fe, Pb, Mn), and reduction in plant biomass. In site S2 (sewage wastewater upstream of the chloride factory), a higher level of minerals and metals was noted in the roots. Maximum metals in grains occurred in S6 with higher organic osmolytes. The sequestration capacity of metals in leaves was also increased by alterations in anatomical traits. Results indicated that metals and hyper-Cl- concentration employed a negative influence on the plants because of poor soil quality, extremely damaged microstructures leading to reduced yield, poor grain quality, and excessive translocation from roots to wheat grains. These findings revealed that contaminated plants used as either green forage or hay are noxious to animals and if used as grain for feed or humans can lead to serious health hazards.

A critical analysis of wastewater use in agriculture and associated health risks in Pakistan

Freshwater shortage and its contamination with various types of pollutants are becoming the most alarming issues worldwide due to impacts on socioeconomic values. Considering an increasing freshwater scarcity, it is imperative for the growers, particularly in semiarid and arid areas, to use wastewater for crop production. Wastewaters generally contain numerous essential inorganic and organic nutrients which are considered necessary for plant metabolism. Besides, this practice provokes various hygienic, ecological and health concerns due to the occurrence of toxic substances such as heavy metals. Pakistan nowadays faces a severe freshwater scarcity. Consequently, untreated wastewater is used routinely in the agriculture sector. In this review, we have highlighted the negative and positive affectivity of wastewater on the chemical characteristics of the soil. This review critically delineates toxic metal accumulation in soil and their possible soil-plant-human transfer. We have also estimated and deliberated possible health hazards linked with the utilization of untreated city waste effluents for the cultivation of food/vegetable crops. Moreover, we carried out a multivariate analysis of data (144 studies of wastewater crop irrigation in Pakistan) to trace out common trends in published data. We have also compared the limit values of toxic metals in irrigation water, soil and plants. Furthermore, some viable solutions and future viewpoints are anticipated taking into account the on-ground situation in Pakistan-such as planning and sanitary matters, remedial/management technologies, awareness among local habitants (especially farmers) and the role of the government, NGOs and pertinent stakeholders. The data are supported by 13 tables and 7 figures.

Temporal distribution and accumulation pattern of cadmium and arsenic in the actual field calcareous soil-maize system, northwest China

The contrasting chemical behaviors of two toxic elements, arsenic (As) and cadmium (Cd) in co-contamination calcareous soil and its absorption by crops have not been thoroughly explored, especially in the implementation of the measure of prohibiting the use of wastewater to irrigate farmland. We propose that the present environmental characteristics of ecologically fragile areas and appropriate restoration measures are critical determinant of soil remediation. In this study, the typical field farmland irrigated by industrial and domestic wastewater in the Chinese Loess Plateau for >50 years was selected. The results showed that after the sewage irrigation was stopped, the mean contents of Cd (7.09 mg/kg) and As (13.47 mg/kg) in the soil were still rising, which might be a potential input source. The average values of soil risk indices such as the potential ecological risk (PERI = 2394), pollution load index (PLI > 4 for 60 % of studied samples), and degree of contamination (Dc = 86.6) showed severe soil pollution in the study area. The decrease of soil pH, the loss of soil texture and calcium carbonate were found to be the reasons for the high chemical activity of Cd. The bioconcentration factors (< 0.2) and translocation factor (> 1.0) of Cd indicate that corn is an excluder plant and an ideal phytoremediation method. Thus, 20 % of studied samples were higher than maximum permitted levels of Cd in grain, indicating potential related health hazards. On the contrary, As was mainly adsorbed in calcareous soil, and its bioavailability was lower compared with Cd. The difference between DTPA extraction and sequential extraction may be due to the transformation of chemical forms, resulting in unstable fractions increased the bioavailability of toxic elements. Overall, the findings provide new insights for solutions to manage and repair farmlands under the post-wastewater irrigation period.

Fermentation affects heavy metal bioaccessibility in Chinese mantou

Effect of different fermentation methods on heavy metal bioaccessibilities in wheat flour is undetermined. In this work, gastric and gastrointestinal heavy metal bioaccessibility in wheat flour products (control-wheat dough, T1-mantou made with normally fermented dough, T2-mantou made with over-fermented dough and T3-mantou made with over-fermented dough + Na₂CO₃) made from two wheat flour samples (NX and QD) was assessed via a modified physiologically-based extraction test. Cadmium, Zn and Mn bioaccessibility in the gastric phase (GP) was greater than in the gastrointestinal phase (GIP), yet the opposite was observed for Cu (p < 0.05). Lead bioaccessibility in the GIP of the QD sample was 1.37-4.08 times greater than that in the GP, while only the control had greater bioaccessibility in the GIP than that in the GP (p < 0.05) for the NX sample. Treatments T2 and T3 had greater Cd, Cu, Zn and Mn bioaccessibilities than the control and T1 in the GP (p < 0.05). In the GIP, however, only T3 had greater Mn bioaccessibility than the control for the NX sample. Enhanced degradation of the heavy metal-phytate following over-fermentation may have led to greater heavy metal bioaccessibility. Results should help food processors reduce human absorption of excessive heavy metals present in wheat flour foods.

Mobility of arsenic and vanadium in waterlogged calcareous soils due to addition of zeolite and manganese oxide amendments

Addition of manganese(IV) oxides (MnO₂ ) and zeolite can affect the mobility of As and V in soils due to geochemical changes that have not been studied well in calcareous, flooded soils. This study evaluated the mobility of As and V in flooded soils surface-amended with MnO₂ or zeolite. A simulated summer flooding study was conducted for 8 weeks using intact soil columns from four calcareous soils. Redox potential was measured in soils, whereas pH, major cations, and As and V concentrations were measured biweekly in pore water and floodwater. Aqueous As and V species were modeled at 0, 4, and 8 weeks after flooding (WAF) using Visual MINTEQ modeling software with input parameters of redox potential, temperature, pH, total alkalinity, and concentrations of major cations and anions. Aqueous As concentrations were below the critical thresholds (<100 μg L^-1 ), whereas aqueous V concentrations exceeded the threshold for sensitive aquatic species (2-80 μg L^-1 ). MnO₂ -amended soils were reduced to sub-oxic levels, whereas zeolite-amended and unamended soils were reduced to anoxic levels by 8 WAF. MnO₂ decreased As and V mobilities, whereas zeolite had no effect on As but increased V mobility, compared to unamended soils. Arsenic mobility increased under anoxic conditions, and V mobility increased under oxic and alkaline pH conditions. Conversion of As(V) to As(III) and V(V) to V(IV) was regulated by MnO₂ in flooded soils. MnO₂ can be used as an amendment in immobilizing As and V, whereas the use of zeolite in flooded calcareous soils should be done cautiously.

Enrichment and distribution characteristics of heavy metal(loid)s in native plants of abandoned farmlands in sewage irrigation area

Soil samples and native plants were collected from abandoned farmlands with a long history of sewage irrigation along Dongdagou stream, Baiyin City. We investigated the concentrations of heavy metal(loid)s (HMMs) in soil-plant system to evaluate the accumulation and transportation ability of HMMs in native plants. Results indicated that soils in study area were severely polluted by Cd, Pb, and As. With the exception of Cd, the correlation between total HMM concentrations in soil and plant tissues was poor. Among all investigated plants, no one was close to the criteria for the HMM concentrations of hyperaccumulators. The concentrations of HMMs in most plants were reached the phytotoxic level and the abandoned farmlands could not be used as forages, which showed that native plants may possess resistance capabilities or high tolerance for As, Cu, Cd, Pb, and Zn. The FTIR (Fourier transform infrared spectrometer) results suggested that the detoxification of HMMs in plants may depend on the functional groups (-OH, C-H, C-O, and N-H) of some compounds. Bioaccumulation factor (BAF), bioconcentration factor (BCF), and biological transfer factor (BTF) were used to identify the accumulation and translocation characteristics of HMMs by native plants. S. glauca had the highest mean values of BTF for Cd (8.07) and Zn (4.75). C. virgata showed the highest mean BAFs for Cd (2.76) and Zn (9.43). P. harmala, A. tataricus, and A. anethifolia also presented high accumulation and translocation abilities for Cd and Zn. High HMMs (As, Cu, Cd, Pb, and Zn) accumulation in the aerial parts of plants may lead to increased accumulation of HMMs in the food chain; additional research is desperately required. This study demonstrated the HM enrichment characteristics of weeds and provided a basis for the management of abandoned farmlands.

Citric Acid and Poly-glutamic Acid Promote the Phytoextraction of Cadmium and Lead in Solanum nigrum L. Grown in Compound Cd-Pb Contaminated Soils

Phytoextraction is an efficient strategy for remediating heavy metal-contaminated soil. Chelators can improve the bioavailability of heavy metals and increase phytoextraction efficiency. However, traditional chelators have gradually been replaced due to secondary pollution. In this study, a typical organic acid (citric acid, CA) and a novel biodegradable chelator (poly-glutamic acid, PGA), were investigated using pot experiments to compare the phytoextraction efficiency of Solanum nigrum L. (a Cd (hyper)accumulator) for cadmium (Cd) and lead (Pb) in contaminated soil. The results showed CA and PGA significantly improved plant growth, and total Cd and Pb amounts of S. nigrum, both CA and PGA significantly increased the shoot Cd and Pb concentrations. However, only PGA significantly increased the root Pb concentration. CA and PGA application promoted the bioavailability of Cd and Pb in rhizosphere soils and their translocations from roots to shoots in S. nigrum. Both CA and PGA increased the phytoextraction efficiency of Cd and Pb in S. nigrum plants, and the PGA for Cd and Pb phytoextraction was more effective than CA. Our findings demonstrate that the biodegradable chelator PGA has great potential for enhancing phytoextraction from compound Cd-Pb contaminated soils, suggesting that biodegradable chelator-assisted phytoextraction with (hyper)accumulator is strongly recommended in severely contaminated sites.

Modified bio-electrocoagulation system to treat the municipal wastewater for irrigation purposes

A modified biological-integrated electrocoagulation method was explored to treat municipal wastewater (MWW) for irrigation purposes. To use treated wastewater for irrigation purposes a wide range of contaminants removal was focused on in this study (turbidity, hardness, conductivity, TDS, TSS, chloride, Ammonia nitrogen, BOD, COD, and total coliform). Raw municipal wastewater (RMWW) was treated in a modified Bio-Electrocoagulation (BEC) cell. The cell was operated in a continuous flow mode and consisted of an electrocoagulation stage using aluminum (Al) electrodes followed by a bioremediation stage using a fixed bio-filter (BF), the design of the cell was further modified by the addition of a sand filter (SF). The effect of several parameters such as applied voltage (22, 26, and 30 V), inlet flow rate (1, 3, and 5 Lh^-1), and initial pH (pH 3, 5, 7, 7.4, and 9) was investigated to determine the optimum operating conditions for selected responses. The most effective operating conditions for the BEC were investigated for the different irrigation water quality (WQ) indicators. It was observed that pH 7.4 and 26 V provide maximum removal efficiency of contaminants at the flow rate of 1 Lh^-1. A fixed film BF plays a positive role to improve the degradation of contaminants after the EC unit up to 4% of NH₃-N, 9.3% of BOD, and 7.8% of COD. In addition, using the SF improved the turbidity removal to 42.6%. The WQ specifications of the treated MWW using the BEC cell were compared with the standard specifications for restricted and unrestricted agricultural irrigation water. The overall operating cost of MWW treatment for irrigation purposes by using a modified bio-integrated electrocoagulation method was 0.76 $m^-3.

Accumulation pattern and risk assessment of potentially toxic elements in selected wastewater-irrigated soils and plants in Vehari, Pakistan

There are scarce data about the accumulation pattern and risk assessment of potentially toxic elements (PTEs) in soil and associated potential ecological risks, especially in less-developed countries. This study aims to assess the pollution levels and potential ecological risks of PTEs (As, Cr, Cd, Cu, Ni, Mn, Pb and Zn) in wastewater-irrigated arable soils and different edible-grown plants in selected areas of Vehari, Pakistan. The results revealed that the values of PTEs in soil samples were higher than their respective limit values by 20% for As, 87% for Cd, 15% for Cu, 2% for Cr, 83% for Mn, 98% for Fe, and 7% for Zn. The values of soil risk indices such as the potential ecological risk (PERI >380 for all samples), pollution load index (PLI >4 for 94% of studied samples), and degree of contamination (Dc > 24 for all samples) showed severe soil contamination in the study area. Some vegetables exhibited a high metal accumulation index (e.g., 8.1 for onion), signifying potential associated health hazards. Thus, long-term wastewater irrigation has led to severe soil contamination, which can pose potential ecological risks via PTE accumulation in crops, particularly Cd. Therefore, to ensure food safety, frequent wastewater irrigation practices need to be minimized and managed in the study area.

Distribution, source apportionment, and risk analysis of heavy metals in river sediments of the Urmia Lake basin

The anthropogenic heavy metal dissemination in the natural environment through riverine sediments is a major ecological and public health concern around the world. This study gives insight into the source apportionment and potential ecological and health risks of heavy metals in river sediments of the Urmia Lake basin, a natural world heritage located in northwestern Iran. A comprehensive sediment sampling was conducted in seven major rivers feeding the basin during the summer and winter of 2021. Samples were analyzed for zinc (Zn), copper (Cu), cadmium (Cd), lead (Pb), and nickel (Ni) contents and a suite of chemical and physical properties. Subsequently, Pollution Index (PI), Pollution Load Index (PLI), Ecological Risk (ER), Hazard Quotients (HQ), Hazard Index (HI), and Carcinogenic Risk (CR) indices were determined. The mean concentration of heavy metals in all rivers' sediments exhibited the descending order of Ni > Zn > Pb > Cu > Cd during both summer and winter. Multivariate analysis suggested that Zn was primarily initiated from natural processes, Cd and Pb were affected by human activities, and Cu along Ni were derived from natural and anthropogenic factors. The PI unveiled that most sediment samples were unpolluted to slightly polluted by Zn, Cu, and Pb, and slightly to moderately polluted by Cd. PLI and ER indices demonstrated that the sediment poses non to moderate pollution and low to moderate ecological risk, respectively. Using a human health risk approach, we found that the HI values of all heavy metals and THI were less than one for children and adults implying non-carcinogenic risk in the analyzed sediments. Carcinogenic effects of Cd and Pb at all rivers sediments via ingestion, inhalation, and dermal contact were almost within tolerable risks (1 × 10^-6 to 1 × 10^-4) for children and adults. PI, PLI, ER, HQ, HI, and CR index values of sediment samples during the summer were higher than those during the winter. This is attributed to the greater heavy metal concentrations and the lower water flow during summer. Our results provide practical information for better management and control of heavy metal pollution in aquatic-sedimentary ecosystems.

Meta-analysis of public health risks of lead accumulation in wastewater, irrigated soil, and crops nexus

Lead (Pb) from different sources accumulate in the irrigation water, irrigated soil and in different parts of plants. Reports show contradictory findings and high variability of lead accumulation and associated public health risks. We hypothesized that lead accumulation in irrigation water, soil and edible plants is high enough to be a public health risk. By using the standard procedures for meta-analysis, 24 studies were qualified. The studies included in the meta-analysis are concentrated in few countries with strong authors' key words co-occurrence relationship. The mean concentration of Pb in the irrigation wastewater ranged from 0.0196 ± 0.01 mg/l to 52.4 ± 0.02 mg/l in wastewater and about 50% of the values are beyond the limits for irrigation water standard. The study also showed that the concentration of Pb in the irrigated soil vary significantly from a minimum of 0.04 ± 2.3 mg/l in Ethiopia to a maximum of 441 ± 19.8 mg/l in Iran (P < 0.01). Based on effect size analysis, the weight of the studies ranged from 0.1 to 5.4% indicating that the studies' contribution to the overall effect is barely different. The heterogeneity test statistics also indicates considerable variability between the studies (I² = 98%, P-value < 0.001). The subgroup analysis showed large between-studies heterogeneity in both groups (Tau² = 28.64; T² = 98%). A total of 44 crops were studied, of which 38 were leafy and non-leafy vegetables. Most popular crops including spinach, cabbage and lettuce are most frequently studied crops. In all crops, the Pb level in crops produced by using untreated wastewater are beyond the WHO limit for edibility. In all of the studies, the pollution load index (PLI) and soil accumulation factor (SAF) is much higher indicating that there is a buildup of Pb concentration in wastewater irrigated soil. The plant concentration factor (PCF) calculated shows the high Pb accumulation potential of the edible parts of the crops. The health risk index (HRI) calculated shows that in all of the studied crops from India, Iraq, Morocco and Egypt are much higher than one indicating the high health risk of consumption.

Comparison of Pb and Cd in wheat grains under air-soil-wheat system near lead-zinc smelters and total suspended particulate introduced modeling attempt

The excessive accumulation of wheat grain metals and metalloids caused by ambient air contamination has drawn an increasing concern. However, at present, the differences in the pathways of cadmium and lead accumulation in wheat grains in an air-soil-wheat system are not clear. In this study, wheat was grown around a lead‑zinc smelting area and exposed to different soil Pb and Cd levels and different ambient air Pb and Cd levels. Lead and Cd accumulation in wheat grains was examined in this study. Two models of wheat grain Pb and Cd concentrations were established based on the 3 variables including soil Pb and Cd concentration, ambient air Pb and Cd concentration, and soil pH. The results showed that total suspended particulate (TSP), soil, and wheat grains exhibited different degrees of Pb and Cd contamination in the study area, and the contamination of Cd is more serious than Pb contamination. The Pb in wheat grains was more likely to derive from ambient air than from soil, whereas the impact of ambient air on the accumulation of Cd in wheat grains might be very limited. This speculation was confirmed by the results of the predictor variable relative weight method based on the multiple regression analysis. Introduction of ambient air factor (TSP Pb and Cd) greatly improved the modeling effect of wheat grains Pb, while the modeling of grain Cd was more dependent on soil pH and total soil Cd. This research suggests that the reduction in wheat grain Pb is likely to be achieved by the control over ambient air Pb, whereas the reduction in the wheat grain Cd by the remediation of soil pollutants.

Assess long-term As, Pb and Cr contamination and uptake by Eriocaulon decangulare in the Apalachicola National Forest

Phytoremediation is an effective remediation process for heavy metal contamination. The primary zone of phytoremediation is the rhizosphere where the plants uptake the heavy metals from the soil matrix. The bioavailability of the contaminants in the rhizosphere is affected by the physical, chemical, and biological conditions of the rhizosphere. In the study area of the Apalachicola National Forest, the concentrations of As, Pb and Cr in the bulk soil (n = 20) were 515.81, 220.77, and 2.02 mg/kg soil, respectively. Using a sequential extraction method, the bioavailability of heavy metals in the bulk soil (S-NR) and rhizosphere soil (S-R) was characterized. The results showed that the bioavailability of the three heavy metals had the order of Cr > Pb > As for S-NR and Pb > As > Cr for S-R. The bioavailability of these metals was affected by the nature of the heavy metals and the soil physicochemical properties. Native plant Eriocaulon decangulare could uptake a large number of heavy metals from the natural soil, demonstrating great phytoremediation potential for metal contamination. Energy Dispersive Spectroscopy (EDS) mapping successfully located the dominant accumulation of heavy metals in aerial parts of E. decangulare. E. decangulare was also found to be highly selective and Pb and As were both extensively accumulated in the shoots and roots. Cr was significantly immobilized in the rhizosphere soil, and also accumulated in the root of E. decangulare. This study not only correlated the phytoremediation potential with heavy metal bioavailability and soil physicochemical properties, but also demonstrated the important role of the nature of heavy metals played during the phytoremediation.

Genotoxic hazard and oxidative stress induced by wastewater irrigated soil with special reference to pesticides and heavy metal pollution

Due to enhancement of industrial growth and urbanization, soil contamination is increasing prominently. Therefore, it is important to examine possible adverse effects of industrial waste. Soil samples were might to be polluted with several heavy-metals and pesticides. Gas chromatographic results showed occurrence of high-level of organochlorine and organophosphate pesticides in studied soil samples. Genotoxicity of soil extracts was assessed using environmental-risk assessment models. Soil samples were extracted in hexane and dichloromethane solvents and were evaluated for genotoxic potential by prokaryotic (Ames test, plasmid nicking assay and E. coli K-12 DNA repair defective mutants) and eukaryotic (Allium cepa root chromosomal aberration and Vigna radiata seed-germination test) bioassays. Strain TA98 was found the most susceptible among soil extracts. The mutagenicity of hexane soil extract from wastewater irrigation was found to be higher than that of DCM samples in terms of mutagenic index, mutagenic potential, and induction factor for Ames strains. The damage in DNA repair defective mutants of hexane extracts were found higher compared to DCM extracts at dose of 20 μl/ml of culture. Survival in polA, lexA and recA mutants were 39%, 47% and 55% while treated with hexane extract. Allium cepa test, mitotic index was decreased in dose-dependent way and various kinds of chromosomal aberrations were found. Vigna radiata seeds germination and other parameters were also affected when treated with wastewater irrigated (WWI) soil. Oxidative stress in V. radiata roots were also showed under CLS microscope. Genotoxicity of WWI soil extract was also confirmed by plasmid nicking test. Our study provides possible explanation for the assessment of potential health and environmental hazards of the industrial region.

Monitoring and evaluation of the efficiency of a mixed textile-domestic wastewater treatment plant for 3 years

In this study, the performance of the wastewater treatment plant, which treats approximately 80,000 m³/day of domestic and industrial wastewater in the Bursa, Turkey, for the 2018-2020 period, is evaluated based on the analysis of chemical oxygen demand (COD), biochemical oxygen demand (BOD), suspended solid (SS), total nitrogen (TN), total phosphorus (TP), color, and some heavy metals (Cr⁺⁶, CN^-, Cd, Fe, Cu, and Zn) parameters. Treatment plant removal efficiencies were 61-91% for COD; 78-97% for BOD; 54-94% for SS; and 57-84% for TN. It was detected in the range of 23-84% for TP and 40-68% for color. The operating costs per treated wastewater volume were calculated as 0.0675 USD/m³ and 2.94 USD/kg COD per organic load removed. The quality of treated water was compared with the discharge limits of the receiving medium, and no limit values were exceeded in any parameters during the monitoring years.

Heavy metal pollution and net greenhouse gas emissions in a rice-wheat rotation system as influenced by partial organic substitution

Substituting nitrogen fertilizer with organic manure is a common fertilization practice in farmland, but its potential effect on heavy metal pollution and greenhouse gas (GHG) emissions remains unclear. A three-year field experiment was conducted in the rice-wheat rotation system, with two different substitution ratios (25% and 50%) of sewage sludge compost (SS) and pig manure compost (PM). With the substitutions of SS and PM, the heavy metals, including Cu, Zn, Cd, and Pb were accumulated in the soil, but the pollution load index was <1 (0.39-0.66), indicating that soil was not polluted. Heavy metals Ni and Cu were mainly found in rice chaff, while Zn and Cd were accumulated in rice stalk, and the accumulation of Pb occurred in the leaf. For wheat, Ni, Cu, and Pb were accumulated in chaff, while grain and stalk had the highest concentrations of Zn and Cd, respectively. Moreover, the bioconcentration factor of heavy metals was 0-0.787, and their contents were below the standard limits for foods for rice and wheat in China, implying that the grains were unpolluted. Given the 5-8 fold increase in the sequestration rate of soil organic carbon with SS and PM substitutions, the annual net GHG emissions were reduced by 115-166%. Most importantly, 50% SS substitution exhibited the lowest net GHG emissions and highest rice and wheat yields. Overall, the results suggested that 50% SS substitution would be a feasible fertilization strategy that not only is unlikely to pose a high risk of soil and grain pollution but also significantly mitigates net GHG emissions and maintains high yields.

Urbanization influences the distribution, enrichment, and ecological health risk of heavy metals in croplands

The contamination of urban soils with heavy elements due to the rapid development of urbanization and urban services has become a major environmental and human health challenge. This study provides insight into the urbanization controls on combined pollution severity and health risk potential of heavy metals in corn-cultivated urban versus non-urban soils. A multifaceted assessment was conducted using enrichment factor (EF), ecological risk (ER), bioconcentration factor (BCF), transmission factor (TF), hazard index (HI), and carcinogenic risk (CR). The results indicate a significant increase in the concentration of all metals in urban farmlands. When compared to the non-urban soils, EF implies a significant increase of all metals in the urban soil, downgrading this index from minimal enrichment (EF < 2) in the control soils to moderate enrichment (2 ≤ EF < 5) in the urban soils. Likewise, the average ER value showed an increase in the urban soils than in the control soils in the order of Fluvisols (66.6%) > Regosols (66.1%) > Cambisols (59.8%) > Calcisols (47%). The BCF and TF values for different elements decreased in the order of Cd (0.41-0.92) > Cu (0.1-0.23) > Zn (0.1-0.18) > Ni (0.01-0.03) > Pb (0.005-0.011) and Zn (0.75-0.94) > Cu (0.72-0.85) > Pb (0.09-0.63) > Cd (0.17-0.22) > Ni (0.01-0.21), respectively, which indicates that certain metals were not mobilized to the extent that they had been accumulated in the plant roots. The total carcinogenic risk was ranged from 5.88E-05 to 1.17E-04 for children and from 1.17E-04 to 2.30E-04 for adults, which implies a greater associated health risk for children.

Heavy metals phytofiltration potential of Hydrocotyle umbellata from Nullah Lai wastewater and its environmental risk

This study aims to examine the heavy metal phytofiltration potential of Hydrocotyle umbellata from Nullah Lai wastewater and its environmental risk. Wastewater was initially analyzed for heavy metals and physicochemical parameters and compared with irrigation water standards. The phytofiltration potential of H. umbellata was determined by periodically monitoring heavy metal concentrations at time points T1 (day 05), T2 (day10), T3 (day 15), and T4 (day 20). This study shows that some water parameters reached the permissible limits after treatment with H. umbellata. Results of the risk analysis reveal a significant discharge (kg d^-y) of heavy metals to arable land. Phytofiltration efficiency of H. umbellata for water quality parameters was in order of Ni (98.75%), Cr (98.11%), Cd (95.84%), Pb (94.90%), Cu (94.10%), Zn (85.34%), BOD (53.67%), TDS (29.28%), EC (27.31%), Cl (6.65%), and SAR (6.34%). The growth of H. umbellata in wastewater resulted in heavy metal bioaccumulation in both roots and shoots of the plant. Less than 01 translocation factor (TF) values for cadmium, copper, lead, chromium, and zinc showed the metal tolerance ability of the tested plant. These results demonstrated that treated water could be used in water-deficient peri-urban areas as supplementary irrigation.

Migration of heavy metals in the soil-grape system and potential health risk assessment

The accumulation of heavy metals in soil may introduce them to the food chain and cause health risks for humans. In the present study, 43 pairs of soil and grape samples (leaf and fruit) were collected form vineyards in the suburbs of Kaifeng city (wastewater-irrigated area in Henan Province, China) to assess the heavy metal (Pb, Cd, Cu, Zn and Ni) pollution level in soil, heavy metal accumulation in different grape tissues and the potential health risk via consumption of grapes. The results showed that the average contents of Pb, Cd, Cu, Zn and Ni in vineyard soil were 42.27, 3.08, 62.33, 262.54 and 26.60 mg/kg, respectively. Some of these soil samples were severely contaminated with Cd and Zn, with an average pollution index (P_i) of 5.14 and 0.88, respectively. Most of these soil samples were severely polluted by heavy metals, with an average Nemerow integrated pollution index (P_N) of 3.77. The bioavailable heavy metals were negatively correlated with soil pH and positively correlated with soil organic matter (OM). In addition, heavy metals were more likely to accumulate in grape leaves, and their contents in grape pulp were all within the maximum permissible limit set by China (GB 2762-2017). The average bioaccumulation factors (BFs) of Pb, Cd, Cu, Zn and Ni in grape pulp were 0.007, 0.096, 0.160, 0.078 and 0.023, respectively. Health risk assessment indicated that there was no noncarcinogenic risk for grape consumers (adults and children). However, the carcinogenic risk (CR) ranged from 4.95 × 10^-7 to 2.17 × 10^-4, and the CR value of three grape samples was higher than 10^-4, indicating that a probability of carcinogenic disease existed for humans who regularly consumed the grapes from this region.

Impact of wastewater discharge on the plant diversity, community structure and heavy metal pollution of range plants in eastern Saudi Arabia

The main objectives of this study were to determine the floristic composition of the vegetation cover and to find the effects of wastewater pollution on the plant community structure in eastern Saudi Arabia. 28 stands which were distributed among polluted and unpolluted sites, were chosen for this study. A total of 42 plant species were recorded (14 in the polluted and 28 in the unpolluted sites). The recorded plants comprised of 13 perennial plant species and 29 annual plant species. Seven vegetation communities were determined using TWINSPAN and DCA classification and ordination techniques. Three in the polluted sites, two in the unpolluted sites and the remaining two were mixed communities. The (Sarcopoterium spinosum – Pistacia len‐tiscus) community in the polluted sites, had the highest values of soil moisture, salinity, sulphate, calcium and potassium. On the other hand, Juniperus phoenicea – Olea europaea community in the unpolluted site, had the lowest value of organic matter, salinity and magnesium. In respect of genetic diversity, the community of Foeniculum vulgare - Nicotiana glauca in the unpolluted site, was the most diverse, while Ricinus communis - Chrysanthemum coronarium in the polluted sites was the least one. Both soil and wastewater heavy metal analysis indicated that Pb, Cd, Cr, Cu and Ni concentrations in the polluted sites were significantly higher than those in the unpolluted ones. The impact of wastewater discharge led to the appearance of new invasive plant species that may significantly affect plant diversity and community structure in eastern Saudi Arabia. Finally wastewater discharge in open rangelands could adversely affect the growth of plant species in the rangelands and thus adversely affect plant community structure and diversity.

Arsenic exposure through drinking groundwater and consuming wastewater-irrigated vegetables in Multan, Pakistan

Arsenic (As) is one of the most toxic metalloids for humans. Above permissible levels of As cause severe health implications. Contaminated drinking water and food items may be the leading sources of As exposure to people all around the world. The current study assessed the levels of As in drinking water, vegetables, irrigation water, agricultural soils, and the human population (adult women and men) of rural and peri-urban areas of Multan (Pakistan). For a comparison between peri-urban (exposed site) and rural areas (control site), we sampled irrigation water, vegetables and vegetable-grown soils, drinking water, and human blood. In all sample types, As concentration was significantly higher at exposed site than at control site. Alarmingly, As concentration in drinking groundwater (34 µg As L^-1) of exposed site was 3.4-folds higher than the permissible limit (set by WHO). Among the studied vegetables, the cumulative daily dietary intake of As was recorded maximum by the consumption of okra (474 ng d^-1 on exposed site) and minimum by long melon (1 ng d^-1 on control site). However, As intake via drinking water was estimated to contribute ≥ 98% of total As intake at both sites. Hence, the health risks associated with drinking As-contaminated groundwater were recorded much higher than the health risks associated with the consumption of As-contaminated vegetables. Blood As levels in most of the subjects at exposed site exceeded the safe limit of 12 µg L^-1. Conclusively, the findings of the current study indicated that drinking contaminated groundwater may be the major cause of As-associated health risks in the region.

Heavy metals accumulation and risk assessment in a soil-maize (Zea mays L.) system around a zinc-smelting area in southwest China

Smelting of nonferrous metals causes significant concerns because of its emissions of heavy metals (HMs) into surface soil, and its potential threat to human health through the food chain. To investigate the HMs concentrations in a soil-maize system, a total of 41 paired soil-maize samples were collected from a typical indigenous zinc-smelting area of northwestern Guizhou Province, China. Results showed that the concentrations of the targeted HMs in the soil were significantly higher than their corresponding background values of Guizhou Province. Results obtained of the geo-accumulation index (I_geo) and the potential ecological risk factor of an individual metal (E _r ⁱ ) revealed that Cd and Pb were identified as the top-priority control HMs in the study area. The mean concentrations in maize grain decreased in the order of Zn > Pb > Cu > Cd. Bio-accumulation factor (BAF) indicated a strong ability for Cd to be accumulated in the maize root. Translocation factor (TF) and Fourier transform infrared (FTIR) spectroscopy revealed that the maize root played an important role in reducing the mobilization of HMs to stem, except for Zn. Kriging interpolation results illustrated that the spatial distribution patterns of HMs in the maize grain were generally similar to those in sampled soil, and the higher concentrations for the investigated HMs were partially overlapping between soil and maize grain. The average hazard quotient (HQ) of the investigated HMs for both children and adults were all lower than the threshold value (HQ = 1). The total hazard index (HI) was 5.51E-01 and 4.24E-01 for the two population groups, respectively, implying no potential non-carcinogenic risk for local maize-consumers. Sensitivity analysis demonstrated that the oral ingestion rate (IngR) of grain was the predominated contribution to the output of the risk assessment.

Heavy metal accumulation and genotoxic effect of long-term wastewater irrigated peri-urban agricultural soils in semiarid climate

Water scarcity is becoming an alarming issue in the Mediterranean countries. Therefore, using the treated wastewater in the irrigation is considered as a valuable option. However, uncontrolled and long-term irrigation by wastewater leads to human health and environmental damages, mainly related to some specific pollutants. The assessment of the availability and toxicity of the heavy metals after long term irrigation, under semi-arid climate, is not yet well documented. In this study, physicochemical properties, genotoxicity (Vicia faba micronucleus test), total and available (CaCl₂-extractable) concentrations of Cr, Pb, Cu, Zn, Co and Cd in eight soils of peri-urban farms irrigated with wastewater were examined to evaluate their accumulation. The results indicated that long-term irrigation with wastewater induced significant increase of electrical conductivity, organic matter, calcium carbonate equivalent and nutrient availability. Total and available concentration of heavy metals were significantly higher (P < 0.05) in irrigated soils by wastewater. The total concentrations of Zn, Pb, Cu, Cr, Cd and Co in irrigated soils by wastewater at 0-40 cm depth were 85.69, 43.94, 34.86, 14.62, 9.94 and 7.17 mg kg^-1, respectively. Furthermore, the increase of the available metal fraction in irrigated soils by wastewater at 0-40 cm depth followed the following order: Co (1270.1%) > Cd (914.5%) > Cu (881.5%) > Cr (471.2%) > Pb (230.8%) > Zn (223.8%). The micronucleus assay indicated significant increase of micronucleus frequencies (41.25‰, 35.48‰, 21.66‰, 16.23‰ and 13.62‰ respectively for P1, P2, P3, P4 and P7) which were higher than the negative control (0‰) and the irrigated soil by fresh water (3.29‰). The micronucleus induction was significantly correlated with the high available fraction of Cd, Co and Zn at P1, P2 and P7. The genotoxicity can be a powerful test to assess the ecological effects associated with the interactions of heavy metals with other pollutants.

The Salicornia europaea potential for phytoremediation of heavy metals in the soils under different times of wastewater irrigation in northwestern Iran

The use of wastewater for irrigation usually leads to the buildup of potentially toxic elements (PTEs) in soils. The objective of this study was to assess the capacity of Salicornia europaea L. to uptake heavy metal when irrigated with wastewater at the vegetative, flowering, and reproductive stages of S. europaea for 2 and 4 days (in each stage) in the coastal saline area of Lake Urmia. The concentrations of heavy metals were detected in irrigated water, soil, and plant samples, while transfer factor (TF), bioconcentration factor (BCF), and bioaccumulation factor (BAF) were calculated. The results revealed that metal concentrations in the wastewater were above the permissible limits. The wastewater irrigation caused higher shoot biomass despite the high uptake of PTEs. Levels of Fe and Cu in plants were higher when irrigated with wastewater at the reproductive stage as compared to flowering and vegetative stages. The TF of wastewater-irrigated plants was higher at the flowering stage. TF of different metals at the flowering stage were in order of Zn > Pb > Ni > Cd > Cu, while the BCF increased in the order Cd > Cu > Zn > Ni > Pb. The BAF of the investigated PTEs at the flowering stage increased in the order Cd > Pb > Ni > Zn > Cu. In conclusion, higher Pb and Zn in the shoot indicated that the plant exhibited the phytoextraction mechanism, while Salicornia used a phytostabilization mechanism for roots-Cu, Ni, and Cd.

Bioaccumulation and translocation of trace elements in soil-irrigation water-wheat in arid agricultural areas of Xin Jiang, China

Pollution resulting from toxic trace elements is an increasing concern around the world especially in developing countries such as China. Rapid industrialisation, urbanisation and agricultural development are the dominant sources of anthropogenic contamination contributed to an increased potential toxicity of trace elements in the irrigation water-soil-food chain. Xin Jiang in China is a reserved cultivated land development area that could provide the most extensive strategic support for food production and arable land security in China. Thus, it is crucial to investigate the bioaccumulation and translocation of trace elements in order to assess the ecological and human health risks in the traditional oasis system of the agricultural areas in Bay Cheng County, Xin Jiang. This study analysed the levels of trace elements in different layers of the soil, the irrigation water and the wheat plants, and the relationships among them. The results indicated that cadmium (Cd) and chromium (Cr) were the primary pollutants in soils and wheats respectively, and they fell into the serious pollution category. However, no trace elements over the pollution limits were detected in irrigation water. The maximum values of trace elements appeared in the soil layers at 5-10 cm and 10-15 cm. The pollution levels of trace elements in the soil layers were found at 0-5 cm and 0-20 cm, which were higher than those at 20-80 cm. In wheat, high amounts of absorption for Se, Cr, Zn and Cu, but low for Pb were detected in different parts of a plant. The roots of wheats were more eco-toxic to Cd, Co and Pb than other tissues, indicating that roots were more effective at absorbing Cd, Co and Pb, as these metals are usually toxic in the soil. Se, Cu and Zn showed a higher ability of being transferred from soils to the edible parts of crops. The bio-transfer factors of Zn, Mo, Cu, Mg and Mn were considerably higher than those of other elements. The average cancer risk of As, Cd, Co, Ni and TCR in wheat grains exceeded the safety reference limit (1 × 10^-4). For the exposed population, Cr in wheat was the major contributor to total cancer risk. The average values of HQ of Cr, Mn and As, and total non-cancer risk index exceeded the corresponding effective safe reference doses (HQ > 1).

Farmland heavy metals can migrate to deep soil at a regional scale: A case study on a wastewater-irrigated area in China

Heavy metal risks to human health in farmland of wastewater-irrigated areas have long been recognized. It remains to be shown whether farmland heavy metals from wastewater irrigation can migrate to deeper soil at a regional scale. In this study, nine soil cores deep to 30 m from three transects (A, B and C) of a linear wastewater reservoir and the adjacent farmland topsoils and wheat grains were sampled. Heavy metals including As, Cd, Cr, Cu, Pb and Zn in the soils and wheat grains were determined, and the grains' health risks were assessed using the Target Hazard Quotient (THQ). Considerably high contents of heavy metals in both total and soluble forms were detected in deep soils, especially for the transect B where total As of 73.0 mg kg^-1 at 29 m, Cd of 3.80 mg kg^-1 at 13 m and Pb of 214 mg kg^-1 at 30 m were detected. The silty clayey and silty layers of the transect B had higher contents of As, Cr, Cu, Pb and Zn compared with the sandy layers. Across the studied area, 19.5%-34.1% of the topsoil samples were contaminated by As, Cd, Cu, Pb and Zn, and 34.1% and 19.5% of the wheat grains were contaminated by Cd and Pb, respectively. Wheat grains from all the sampling sites had a combined target hazard quotient (TTHQ) value of >1, with As and Cd being the most important contributors. Our study revealed a wider and deeper risk of typical heavy metals originated from long-term wastewater irrigation in the sampling area, which may pose substantial health risks to the local residents via wheat grains and groundwater.

Availability of heavy metals to cabbage grown in sewage sludge amended calcareous soils under greenhouse conditions

Compared to noncalcareous soils, data on the soil-to-plant transfer of heavy metals and their response to sewage sludge (SS) in calcareous soils with diverse properties are limited. Cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) transfer from soil to cabbage (Brassica oleracea L. var. capitata) under greenhouse conditions in 30 diverse soils amended with two types of sewage sludge (non-spiked and spiked with heavy metals) were investigated. Three transfer factors were calculated for heavy metals in three treated soils including control soils (CS), soils treated with non-spiked SS (NSS), and soils treated with spiked SS (PSS). The bio-concentration factor of heavy metals from soil to root (BCF_Roots) in cabbage in three treatments was as follows: CS: Pb > Cu > Co > Zn > Ni; NSS: Pb > Co > Cu ≥ Zn > Ni; and PSS: Pb > Cd > Zn > Co > Cu > Ni. The same order was found for the bio-concentration factor of heavy metals from soil to shoots (BCF_Shoots) in PSS, and in CS and NSS treatments except that the position of Co, Cu, and Zn was changed. Based on the heavy metals translocation from plant roots to shoots, Cd, Cu, and Zn were the heavy metals that posed the highest risk due to the higher shoot content in all treatments, whereas Ni and Pb posed relatively lesser risk. Generally, the percentage of sand and silt in BCF_Roots and BCF_Shoots was quite effective for Co, Ni, and Zn and it seems that soil texture is an important variable in heavy metals bioavailability. In conclusion, our findings highlight the significance of using SS to increase cabbage growth in soils contaminated with heavy metals. Furthermore, cabbage may be a good choice for phytoremediation of heavy metal-contaminated calcareous soils in terms of soil remediation. Novelty statement In recent years, sewage sludge production has increased as well as related waste disposal strategies because of the increasing population and growing demand for agricultural products. Sewage sludge utilization as a low-cost fertilizer has spread in some parts of Iran and the world. On the other hand, unnecessary and unproductive use of sewage sludge results in the accumulation of heavy metals in soils, adding them to food and the potential risk to human health. Currently, work on the transfer of heavy metals from soil to plant after soil treated with sewage sludge has focused on the bioavailability of heavy metals using specific extractants. The assessment of the transfer of heavy metals from soil to different parts of plants using sewage sludge has been less studied. In this study, the transfer of heavy metals (Cd, Co, Cu, Ni, Pb, and Zn) from several soils (30 soils samples) having diverse physical and chemical properties to the tissues of the cabbage plant in control soils, and two types of sewage sludge (nonspiked and spiked with heavy metals) were investigated. The novelty of this study is that the measured bio-concentration factor of heavy metals from soil to root and from soil to shoot and translocation of heavy metals from plant roots to shoots and correlations between these parameters and soil properties are reported for the first time in diverse calcareous soils.

Treated wastewater reuse for irrigation: Pros and cons

The appropriateness of using treated wastewater for crop or agricultural irrigation remains a bone of contention among experts and policymakers. Here, we outline and analyze not only the benefits but also the drawbacks of such a practice in order to suggest a way forward. To ensure that our review reflects the state-of-the-art in terms of technological advances and best practices, only literature published in the last decade is considered except for literature on the history of reuse. The review begins by highlighting growing water scarcity, the history of wastewater reuse in agriculture, and the limitations of existing studies. A short overview of the approach used in the write-up is outlined after the introduction. It then proceeds with an in-depth look at three broad areas: environmental impacts, public health impacts, and economic impacts. In terms of environmental impacts, effects on soil quality, water resources, plant growth, and soil microbial communities are analyzed. For each sub-area, the positive effects are described before the negative ones. The same approach is then applied to public health impacts, the focus of which is on human exposure to heavy metals and pathogens, and economic impacts, which are assessed with particular reference to investment cost, financial benefit to wastewater treatment plants (WWTPs), farm expenditure and income. Having weighed the advantages and disadvantages in each area, innovative measures are proposed for optimizing the benefits and mitigating the drawbacks of using treated wastewater for crop irrigation. Special consideration was given to contaminants of emerging concern and the known or perceived environmental and health risks associated with these contaminants.

Lead smelting alters wheat flour heavy metal concentrations and health risks

Wheat (Triticum aestivum L.) flour consumption may be a major source of human metal intake, especially when wheat is cultivated in metal-contaminated soils. This work investigated Cd, Cu, Pb, and Zn distribution in whole wheat flour, wheat flour, and wheat bran when grown in an area polluted by Pb smelting. Wheat product heavy metal concentrations were analyzed, and the (non)carcinogenic risks were assessed. Mean Cd, Cu, Pb, and Zn concentrations in whole wheat flour were 0.38, 3.83, 0.48, and 29.3 mg kg^-1 , respectively; those in flour were only slightly reduced. The ratios between noncarcinogenic average daily dose of whole wheat flour and wheat flour consumption ranged from 1.06 to 3.76, with Pb having the greatest values compared with other metals. For children, the average hazard quotients (HQs) of whole wheat flour consumption of Cd, Cu, Pb, and Zn were 4.19, 1.06, 1.53, and 1.07; those for wheat flour consumption were 3.81, 0.68, 0.70, and 0.98, respectively. The HQs of adults were less than those of children. Overall results indicated that consumption of wheat products may lead to health concerns in the heavy metal contaminated area, yet when wheat flour rather than whole wheat flour is consumed, only the human health risk from Pb ingestion is reduced. Altering or removing human edible crops in the most contaminated areas should be considered.

Low Molecular Weight Organic Acids Increase Cd Accumulation in Sunflowers through Increasing Cd Bioavailability and Reducing Cd Toxicity to Plants

The use of low molecular weight organic acids (LMWOAs) for the phytoremediation of heavy metals has become a promising technique. We chose five kinds of organic acids (oxalic acid (OA), acetic acid (AA), tartaric acid (TA), malic acid (MA), and citric acid (CA)) with six application rates (1, 2, 3, 4, 5, and 6 mmol/kg) and planted sunflowers (Helianthus annuus L.) in Cd-polluted soil to study the efficiency of the phytoremediation of Cd and the degree of Cd toxicity to plants. Treatment with no acid application served as the control (CK). We analyzed the plant height dry matter and the Cd and nonprotein sulfhydryl (NPT) contents in the soil and plant tissues. OA, AA, TA, MA, and CA increased plant heights by 17.6–47.40%, 21.25–39.17%, 12.5–35.52, 5.10–30.50%, and 16.15–49.17%, respectively; shoot biomass of the sunflowers was increased except with MA. NPT decreased under LMWOA application, which, in the roots, increased with the increase in root Cd under LMWOA treatment; however, there was no obvious relationship in the stems and leaves. The composition of Cd in the soil changed significantly under the LMWOA treatments compared to the CK, and the changes in carbonate Cd and Fe-Mn oxide Cd were the most prominent. The plant Cd accumulation of OA, AA, TA, MA, and CA increased by 43.31%, 55.25%, 48.69%, 0.52%, and 32.94%, respectively, and the increase in root Cd content and shoot dry matter quality promoted the increase in Cd accumulation. The LMWOAs were more likely to affect the phytoremediation of Cd by changing total P (TP) rather than total N (TN).

Insights into the effects of heavy metal pressure driven by long-term treated wastewater irrigation on bacterial communities and nitrogen-transforming genes along vertical soil profiles

Irrigation with treated wastewater (TWW) influences soil ecological function due to the accumulation of heavy metals (HMs) and nutrients in soils. However, the interaction between HMs and microbial processes in TWW-irrigated soil has not been fully explored. We investigated the effect of HMs on bacterial communities and nitrogen-transforming (N-transforming) genes along vertical soil profiles irrigated with domestic TWW (DTWW) and industrial TWW (ITWW) for more than 30 years. Results indicate that long-term TWW irrigation reshaped bacterial community structure and composition. Irrigation with ITWW led to increased accumulation of Cd, Cr, Cu, Pb, Zn, and Ni in soils than DTWW. Accumulation of inorganic N, soil organic carbon, and HMs in topsoil irrigated with ITWW contributed to the activities of Micrococcaceae. The effect of the activation of nutrient factors on Bacillus, which was the dominant species in DTWW-irrigated soils, was greater than that of HMs. HM pressure driven by ITWW irrigation changed the vertical distribution of N-transforming functional genes, increasing the abundance of amoA gene and decreasing that of nifH through soil depth. ITWW irrigation enhanced the denitrification capacity in topsoil; ammonia-oxidizing capacity in deeper soil was increased after long-term irrigation with DTWW and ITWW, suggesting a potential risk of nitrogen loss.

Temporal changes of calcareous soil properties and their effects on cadmium uptake by wheat under wastewater irrigation for over 50 years

Calcareous soil has a strong buffering capacity for neutralizing acid and stabilizing cadmium (Cd) because of the high calcium carbonate (CaCO₃) content. However, it is not clear whether the buffering capacity of calcareous soil can be maintained after long-term wastewater irrigation. We selected a typical area in western China that has been irrigated with wastewater for over 50 years to study the temporal changes of soil properties and their effects on Cd uptake by wheat. The results showed that compared with the background level before the 1960s, the soil pH and CaCO₃ content in 2018 were lower by 0.80 units and 35%, respectively, while the soil organic matter (SOM) content, Olsen phosphorus (P) content, and soil total Cd content in 2018 increased by 1.54, 13.05, and 164 times, respectively. Due to the significant decrease in the soil pH and CaCO₃, the high load of soil total Cd and electrical conductivity, the low soil clay content, and the coupling of SOM with soil nitrogen and P, the input Cd was activated. Furthermore, the activated Cd was effectively taken up by wheat roots and transported to grains with the assistance of dissolved organic carbon. Our results highlight that long-term wastewater irrigation caused irreversible damage to soil buffering capacity, resulting in the Cd activation and the enhancement of Cd uptake by wheat.

Promotion of growth and phytoextraction of cadmium and lead in Solanum nigrum L. mediated by plant-growth-promoting rhizobacteria

Plant growth-promoting rhizobacteria (PGPR) are a specific category of microbes that improve plant growth and promote greater tolerance to metal stress through their interactions with plant roots. We evaluated the effects of phytoremediation combining the cadmium accumulator Solanum nigrum L. and two Cd- and Pb-resistant bacteria isolates. To understand the interaction between PGPR and their host plant, we conducted greenhouse experiments with inoculation treatments at Nanjing Agricultural University (Jiangsu Province, China), in June 2018. Two Cd- and Pb-resistant PGPR with various growth-promoting properties were isolated from heavy metal-contaminated soil. 16S rRNA analyses indicated that the two isolates were Bacillus genus, and they were named QX8 and QX13. Pot experiments demonstrated that inoculation may improve the rhizosphere soil environment and promote absorption of Fe and P by plants. Inoculation with QX8 and QX13 also enhanced the dry weight of shoots (1.36- and 1.7-fold, respectively) and roots (1.42- and 1.96-fold) of plants growing in Cd- and Pb-contaminated soil, and significantly increased total Cd (1.28-1.81 fold) and Pb (1.08-1.55 fold) content in aerial organs, compared to non-inoculated controls. We also detected increases of 23% and 22% in the acid phosphatase activity of rhizosphere soils inoculated with QX8 and QX13, respectively. However, we did not detect significant differences between inoculated and non-inoculated treatments in Cd and Pb concentrations in plants and available Cd and Pb content in rhizosphere soils. We demonstrated that PGPR-assisted phytoremediation is a promising technique for remediating heavy metal-contaminated soils, with the potential to enhance phytoremediation efficiency and improve soil quality.

Differential effects of three amendments on the immobilisation of cadmium and lead for Triticum aestivum grown on polluted soil

Conventional chemical soil amendments and novel material biochars have been widely reported for the immobilisation of cadmium (Cd) and lead (Pb) in polluted soil. However, information regarding their comparative effectiveness is poor. In the present study, rice husk biochar (RHB) was compared with two chemical soil amendments including hydroxyapatite (HAP) and hydrated lime (HDL) for their effectiveness to enhance plant growth and the reduction of Cd uptake and translocation by Triticum aestivum L. grown in heavy-metal-polluted soil. Compared with control and two chemical soil amendments, RHB rapidly improved wheat growth. The HAP, HDL, and RHB treated plants retained Cd and Pb in roots and restricted their translocation. The RHB treatment had the best effect on growth, yield promotion and the reduction of Cd and Pb in wheat grain. Furthermore, the soils treated with RHB and HAP showed lower DTPA-extracted Cd concentrations, and the maximum reduction was observed in HAP-amended soil. However, the DTPA-extracted Pb concentration was not significantly decreased after the application of two chemical soil amendments for 40 days; the maximum reduction was found in soil treated with RHB for 80 days. In all treatments, Cd in post-harvest soil was mainly present in exchangeable, carbonate bound, and Fe-Mn oxide Cd, while the dominant chemical form of Pb was Fe-Mn oxide Pb. Three soil amendments application decreased exchangeable and organic bound- Cd and Pb levels. HAP and RHB displayed significantly immobilisation for soil Cd and reduced translocation of heavy metal as well as its availability in soil, but the HAP had significant inhibition on growth of wheat in contaminated soil. Therefore, RHB shows a promising potential for the reduction of Cd and Pb bioaccumulation in grains from wheat grown on heavy-metal-polluted soils.

Fate and transfer of heavy metals following repeated biogas slurry application in a rice-wheat crop rotation

The application of biogas slurry, from anaerobic digestion of livestock excreta, to cropland has proven to be an effective mechanism for recycling nutrients within farms. However, the potential pollution of heavy metals from repeated biogas slurry fertilization has not received much attention. Here we present the results of a field experiment under rice-wheat rotation demonstrating the accumulation, speciation distribution and plant uptake of heavy metals (Cu, Zn, Pb and Cd) in soil following biogas slurry application. The treatments were: zero biogas slurry application (BS0), and biogas slurry application for three (BS3) and five (BS5) years, at a rate of 450 m³ ha^-1 y^-1. Our findings show that biogas slurry fertilization resulted in accumulation of Cu and Zn in the soil. The concentrations of soil Cu and Zn under BS5 were, respectively, 38 and 29% greater in the wheat season and 35 and 35% greater in the rice season relative to BS0 (p < 0.05). The bioavailability of soil Cu and Zn increased following biogas slurry application. Plant uptake of Cu and Zn to all parts of wheat and rice plants (excluding Cu in wheat straw) increased with the years of biogas slurry application (p < 0.05), and the concentration of Cd in wheat grain was significantly greater in BS5 relative to BS0 (p < 0.05). After five years of biogas slurry fertilization, concentrations of Cu, Zn, Pb and Cd in wheat grains were 3.28, 25.19, 0.11 and 0.053 mg kg^-1 and 4.24, 33.78, 0.12 and 0.035 mg kg^-1 for rice grains, respectively, all within the safety limits. Our results demonstrate that repeated biogas slurry fertilization for five years has a relatively low pollution risk of heavy metals. However, long-term field monitoring and co-application with metal-immobilizing materials are required to ensure the safety of its application to cropland.

Effect of industrial wastewater on wheat germination, growth, yield, nutrients and bioaccumulation of lead

Due to fresh water scarcity, farmers are using polluted water for irrigation. This research was conducted to study the bioaccumulation of Pb in wheat (Cv. Shafaq-2006). The experiment was comprised of seven treatments of lead i.e. 0–1,000 mg Pb/kg. The results revealed that lead severely reduces germination (− 30%), seedling fresh weight (− 74%), seedling dry weight (− 77%), vigor index (− 89%), tolerance index (− 84%), plant height (− 33%), number of leaves (− 41%), root fresh weight (− 50%), shoot fresh weight (− 62%), root dry weight (− 63%), shoot dry weight (− 71%), and root length (− 45%). The physiological parameters also respond negatively like stomatal conductance (− 82%), transpiration rate (− 72%) and photosynthetic rate (− 74%). Similarly, biochemical parameters also showed negative impacts, like carotenoids (− 41), total chlorophyll (− 43), chlorophyll a (− 42) and chlorophyll b (− 53). Yield parameters like the number of seed/plant, seed weight/plant, 1,000 seed weight and harvest index were reduced by 90%, 88%, 44% and 61%, respectively in T₆. In addition, protein contents (− 81%), phosphorous (− 60%) and potassium (− 55%) were highly effected in the highest lead concentration (T₆). Lead accumulation was extremely higher in seeds (119%) as compared to control plants. Lead bio-accumulation above threshold concentrations in crop parts is a serious human health concern.

Towards a new biological control approach for Photorhabdus temperata bioinsecticide production through the bioconversion of Tunisian industrial wastewater

A novel bioconversion approach of Tunisian wastewater to low-cost Photorhabdus temperata bioinsecticide is presented in this study. Our results showed that when cultured on the food industry wastewater (WS4), P. temperata cells exhibited oral toxicity of about 42%, which is the same as those cultured in complex medium (CM), used as control. Moreover, variants small colony polymorphism (Vsm) of the strain K122 was completely avoided after a prolonged incubation. However, viable but non-culturable (VBNC) state was enhanced with the maximum colony-forming units (CFU) count of 9 × 106 cells/mL obtained after 48 h of incubation in the WS4. According to flow cytometry analysis, almost 100% of P. temperata cells were viable until 48 h of incubation. The appearance of propidium iodide (PI) positively stained cells was observed after a prolonged incubation with a maximum of 17% of damaged cells in WS1. In order to follow the progress of P. temperata fermentation process carried out in industrial wastewater, we established for the first time, the mathematical relationship between total cell counts, CFU counts and oral toxicity of P. temperata strain K122. Indeed, irrespective of the medium used, the relationship between CFU count and total cell count followed a power law. Additionally, when plotting CFU count, or total cell count against toxicity, a semi-log linear relationship was obtained. Our results proved the efficiency of this bioconversion approach to produce bioinsecticide based on the entomopathogenic bacterium P. temperata, with practical benefits in terms of cost production and wastewater management.