Effect of biochar on heavy metal accumulation in potatoes from wastewater irrigation

Effect of fertilization on the accumulation and health risk for heavy metals in native Andean potatoes in the highlands of Perú

Soil infertility is a global problem, amendments such as organic fertilizers and mineral fertilizers are used to improve crop yields. However, these fertilizers contain heavy metals as well as essential mineral elements. The objective of the study was to determine the effect of organic and inorganic fertilizer on the accumulation and health risk of heavy metals in tubers. The plants were cultivated at an altitude of 3970 m using four treatments (poultry manure, alpaca manure, island guano and inorganic fertilizer) and a control group. Soil contamination levels and the degree of metal accumulation in the tubers were also determined. As a result, it was found that the use of inorganic fertilizer and poultry manure increased the values of Cu and Zn in soils, exceeding the recommended standards. The accumulation of heavy metals in potato tubers did not exceed the maximum recommended limits with the exception of Pb, which exceeded the limit allowed by the FAO/WHO (0.1 mg kg-1). Poultry manure contributed to the highest accumulation of Zn, Cu and Pb in tubers with 11.62±1.30, 3.48±0.20 and 0.12 ±0.02 mg kg-1 respectively. The transfer of metals from the soil to the tubers was less than 1. Individual and total non-carcinogenic risk values were less than 1, indicating a safe level of consumption for children and adults. The cancer risk was found to be within an acceptable range. However, poultry manure and inorganic fertilizer treatments had the highest total cancer risk values in both age groups, suggesting a long-term carcinogenic risk.

Distribution of nitrate/nitrite and toxic metals in the soil-potato system and its health risk assessment in Iran

Potato is one of the essential food products whose health quality is greatly influenced by soil contamination and properties. In the current study, we have investigated the physicochemical characteristics of agricultural areas and the accumulation of nitrite/nitrate and metals in potato products in Hamedan, Iran. After determining the physicochemical characteristics of soil samples from four agricultural regions of Hamedan, 48 potato samples were collected from these regions. The heavy metals and nitrate/nitrite content were determined by ICP-OES and calorimetric methods, respectively. A negative correlation was observed between soil pH changes with nitrite/nitrate content and the accumulation of some heavy elements in potatoes. Furthermore, a positive correlation was found between soil phosphorus content and lead accumulation in potato. In present study, the amounts of lead, nitrate, and nitrite in 83.3%, 56%, and 12% of the collected samples were higher than the permissible limit reported by the World Health Organization (WHO), respectively. The EDI range for nitrate and nitrite was determined to be 130-260 and 1.4-2.7 µg/kg/day, respectively, which is much lower than the RfD set by the US Environmental Protection Agency (USEPA) for nitrite and nitrate. Among metal pollutants, the toxic risk caused by lead in potato consumers was higher than the threshold limit. In conclusion, our findings showed that the physicochemical characteristics of the soil could effectively increase the availability of metal pollutants and nitrite/nitrate to the potato product and significantly reduce its health quality. Therefore, monitoring these pollutants in the soil-potato system, preventing the entry of industrial wastewater, and managing the use of agricultural fertilizers can effectively improve the health of this product for consumers.

Eco-friendly approach to decrease the harmful effects of untreated wastewater on growth, yield, biochemical constituents, and heavy metal contents of carrot (Daucus carota L.)

Here, the impact of irrigation using untreated wastewater (WW) on carrots (Daucus carota L.) was examined. We hypothesized that the addition of ethylenediaminetetraacetic acid (EDTA), dry algal powder (Spirulina platensis or Chlorella vulgaris), and Salix alba leaves powder would function as chelators for harmful contaminants in wastewater. The findings showed that irrigation of carrot plants with the sampled untreated wastewater led to significant decreases in the shoot lengths, fresh, dry weights of shoots and roots at stage I, the diameter of roots, pigment content, carotenoids, total soluble carbohydrate content, and soluble protein content. Furthermore, a significantly increased level of proline, total phenols, and the activities of polyphenol oxidase (PPO), peroxidase (POX), superoxide dismutase (SOD), and catalase (CAT) was identified in stage I samples. In contrast to the stage I, the length of the roots, the number of leaves on each plant, wet and dry weights of the stage II roots were all greatly enhanced. In spite of the increased yield due to the wastewater irrigation, carrot roots irrigated with wastewater had significantly more cadmium (Cd), nickel (Ni), cobalt (Co), and lead (Pb) than is considered safe. Our data clearly show that the application of Spirulina platensis, Chlorella vulgaris, EDTA, and leaves powder of salix was able to alleviate the toxicity of wastewater on carrot plants. For example, we recorded a significant decrease in the accumulation of carrot's Cd, Ni, Co, and Pb contents. We conclude that the treatments with Spirulina platensis and Chlorella vulgaris can be utilized as eco-friendly tools to lessen the damaging effects of wastewater irrigation on carrot plants.

Impacts of long-term irrigation with coalmine effluent contaminated water on trace metal contamination of topsoil and potato tubers in Dinajpur area, Bangladesh

Rapid depletion of groundwater and climate change mediated shifting precipitation pattern is forcing farmers to look for alternative irrigation options like wastewater. However, routine irrigation with trace metal contaminated wastewaters could potentially pollute soil as well as cause health risks through the consumption of food products grown in contaminated soil. Thus, the present study aimed to investigate the trace metals build-up status in topsoil and potato (Solanum tuberosum L.) tubers upon continuous irrigation with coalmine effluent contaminated wastewater compared to irrigation with groundwater and surface water over three consecutive years. Soil pollution status and human health risk associated with consumption of potato tubers grown on wastewater-irrigated soil was also assessed in this study. Three separate experimental sites differing in irrigation source (groundwater, surface water, and coalmine wastewater) were selected near Barapukuria Coal Mining Company Limited located at Parbatipur upazilla of Dinajpur district, Bangladesh. Nine trace metals namely arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) were estimated. Results showed significantly higher trace metal content in both soil and potato tubers due to wastewater irrigation. Wastewater suitability for irrigation regarding Cd, Cr, Cu, Fe, Ni and Pb were off the permissible level although the soil contamination with trace metals and their levels in potato tubers remained within the safety limit. Health risk assessment revealed that, consumption of potato tubers grown in wastewater-irrigated soil remained safe although health risk associated with Cr was almost at the border. The study exclusively highlighted the core massage that, trace metal contamination of both soil and potatoes cultivated in them was increasing alarmingly due to three years of wastewater-irrigation. Although the extent of contamination was below critical limit, it can potentially become hazardous in years to come unless wastewater-irrigation is checked. This study was successful to provide valuable insights regarding the potential environmental and human health threats that might arise due to unmindful irrigation of contaminated coalmine wastewater. Besides, this study should prove useful in strategizing safety measures for cropping under trace metal contaminated soils and for planning industrial effluent disposal to avoid agricultural soil contamination.

Macroporous honeycomb-like magnesium oxide fabricated as long-life and outstanding Pb(II) adsorbents combined with mechanism insight

The macroporous honeycomb-like MgO (MHM) had been successfully prepared by hard template method using polystyrene (PS) spheres with different particle sizes of about 400, 600, and 800 nm, respectively. The adsorption performance (3700, 3470, and 3087 mg/g) and specific surface areas (64.0, 51.4, and 34.4 m2/g) of MHM materials were inversely proportional to their pore diameters. Among the prepared MHM materials, MHM-400 exhibited the most excellent adsorption performance of 3700 mg/g towards Pb(II) at 25 °C. In this study, the macropore size in MHM played a major role in the adsorption process; Dubinin-Radushkevich (D-R) model further indicated that Pb(II) removal by MHM-400 was dominated by chemical adsorption. The thermodynamic analysis (ΔG0 < 0, ΔH0 > 0, and ΔS0 > 0) revealed that the Pb(II) adsorption was spontaneous and endothermic. After storing for 360 days, the Pb(II) removal efficiency of MHM-400 was still higher than 98.2%, exhibiting ultra-long life for Pb(II) capture. MHM-400 also exhibited high anti-interference ability towards typically coexisting ions (Na+ and K+). According to the density functional theory (DFT) calculation, the Pb could be adsorbed on the top site of the oxygen atom at the surface of the cubic MgO (200) plane; the adsorption energy (Ead) was 0.159 eV. The XRD and FTIR analyses revealed the further formation of Pb3(CO3)2(OH)2 and PbO after Pb(II) adsorption. Furthermore, MHM-400 could effectively remove both Cd(II) and Pb(II) ions from wastewater within 20 min, and the adsorption efficiency achieved > 99%, suggesting that MHM-400 was a potential material for effective Pb(II) removal.

Biochar-plant interaction and detoxification strategies under abiotic stresses for achieving agricultural resilience: A critical review

The unpredictable climatic perturbations, the expanding industrial and mining sectors, excessive agrochemicals, greater reliance on wastewater usage in cultivation, and landfill leachates, are collectively causing land degradation and affecting cultivation, thereby reducing food production globally. Biochar can generally mitigate the unfavourable effects brought about by climatic perturbations (drought, waterlogging) and degraded soils to sustain crop production. It can also reduce the bioavailability and phytotoxicity of pollutants in contaminated soils via the immobilization of inorganic and/or organic contaminants, commonly through surface complexation, electrostatic attraction, ion exchange, adsorption, and co-precipitation. When biochar is applied to soil, it typically neutralizes soil acidity, enhances cation exchange capacity, water holding capacity, soil aeration, and microbial activity. Thus, biochar has been was widely used as an amendment to ameliorate crop abiotic/biotic stress. This review discusses the effects of biochar addition under certain unfavourable conditions (salinity, drought, flooding and heavy metal stress) to improve plant resilience undergoing these perturbations. Biochar applied with other stimulants like compost, humic acid, phytohormones, microbes and nanoparticles could be synergistic in some situation to enhance plant resilience and survivorship in especially saline, waterlogged and arid conditions. Overall, biochar can provide an effective and low-cost solution, especially in nutrient-poor and highly degraded soils to sustain plant cultivation.

Cotton straw biochar and compound Bacillus biofertilizer reduce Cd stress on cotton root growth by regulating root exudates and antioxidant enzymes system

INTRODUCTION

Cotton straw biochar (biochar) and compound Bacillus biofertilizer (biofertilizer) have attracted wide attentions in the remediation of heavy metal-contaminated soils in recent years. However, few studies have explored the metabolomics of lateral roots of Cd-stressed cotton to determine the mechanism of biochar and biofertilizer alleviating Cd stress.

METHODS

In this pot experiment, biochar and biofertilizer were applied to the soils with different Cd contamination levels (1, 2, and 4 mg kg^-1). Then, the responses of cotton root morphology, vitality, Cd content, and antioxidant enzyme activities were analyzed, and the mechanism of biochar and biofertilizer alleviating Cd stress was determined by metabolomic analysis.

RESULTS

The results showed that exogenous Cd addition decreased the SOD and POD activities in cotton taproot and lateral root. Besides, with the increase of soil Cd content, the maximum Cd content in taproot (0.0250 mg kg^-1) and lateral root (0.0288 mg kg^-1) increased by 89.11% and 33.95%, respectively compared with those in the control (p< 0.05). After the application of biochar and biofertilizer, the SOD and POD activities in cotton taproot and lateral root increased. The Cd content of cotton taproot in biochar and biofertilizer treatments decreased by 16.36% and 19.73%, respectively, and that of lateral root decreased by 13.99% and 16.68%, respectively. The metabolomic analysis results showed that the application of biochar and biofertilizer could improve the resistance of cotton root to Cd stress through regulating the pathways of ABC transporters and phenylalanine metabolism.

DISCUSSION

Therefore, the application of biochar and biofertilizer could improve cotton resistance to Cd stress by increasing antioxidant enzyme activities, regulating root metabolites (phenols and amino acids), and reducing Cd content, thus promoting cotton root growth.

Nano-hydroxyapatite modified biochar: Insights into the dynamic adsorption and performance of lead (II) removal from aqueous solution

Adsorption of lead as Pb(II) using biochar is an environmentally sustainable approach to remediate this kind of pollution affecting wastewater. In this study, rice straw biochar (BC) was modified by combination with nano-hydroxy-apatite (HAP), resulting in a material designated as BC@nHAP, with enhanced adsorption performance. Based on Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses, it was evidenced that, after modification, HAP greatly enhanced surface functional groups (i.e., -COOH and/or -OH) of raw biochar's surface. Batch tests showed that the maximum sorption capacity of BC (63.03 mg g^-1) was improved due to the modification, reaching 335.88 mg g^-1 in BC@nHAP. Pseudo-second order (PSO) kinetics fitted well the adsorption data (R² = 0.99), as well as the Langmuir isotherm model (showing an adsorption value of 335.88 mg g^-1 for q_e). The results of thermodynamic calculations showed that the adsorption was primarily governed by chemisorption process. FTIR spectroscopy and XPS spectrum after adsorption further confirmed that the adsorption mechanisms were ion exchange with Pb²⁺ and surface complexation by -OH and -COOH. In addition, BC@nHAP revealed a brilliant regeneration capability. The maximum adsorption capacity by BC@nHAP was higher than that of raw biochar or other previously reported adsorbents. Therefore, BC@nHAP could be seen as a new sorbent material with high potential for real-scale heavy metal removal from wastewater, and specifically as a capable candidate new sorbent for Pb(II) removal from wastewater, which has clear implications as regard preservation of environmental quality and public health.

Biochar Is Not Durable for Remediation of Heavy Metal-Contaminated Soils Affected by Acid-Mine Drainage

Biochar is a soil conditioner for enhancing plant growth and reducing plants' uptake of heavy metals. However, the protonation of biochar surfaces in acid soils can weaken the capacity of biochar to reduce the phytoavailability of soil-borne heavy metals over time. The aim of this study was to test this hypothesis by performing a plant-growth experiment with five harvest cycles to examine the durability of rice-straw biochar for the remediation of an acidic-mine-water-contaminated soil. The application of the biochar significantly reduced the phytoavailability of the heavy metals and inhibited the plant uptake of cationic heavy metals but not anionic Cr. The beneficial effects of the biochar were weakened with the increasing number of harvest cycles caused by the gradual protonation of the biochar surfaces, which resulted in the desorption of the adsorbed heavy metals. The weakening capacity of the biochar to reduce the heavy-metal uptake by the vegetable plants was more evident for Cu, Zn, and Pb compared to Ni and Cd. The experimental results generally confirmed the hypothesis. It was also observed that the bioaccessible amount of various metals in the edible portion of the vegetable was also reduced as a result of the biochar application.

Heavy-Metal Speciation Distribution and Adsorption Characteristics of Cr (VI) in the Soil within Sewage Irrigation Areas

While sewage irrigation relieves water shortages in Northern China, its excessive application triggers a series of environmental problems, such as heavy-metal pollution. Soil profile and river sediment profile samples from the sewage irrigation area (SIA) were collected by selecting the farmlands in which sewage irrigation activity has been reported since the 1960s, around Huiji River (HJR) and Huafei River (HFR) in Kaifeng, Henan Province, China, as research areas. In this study, the total amount of heavy metals (Cr, Cd, Pb, Mn, Zn, and Ni) and the heavy-metal speciation analysis using the modified BCR sequential extraction method were used to evaluate the impacts of wastewater on agricultural soils and the potential risk. Furthermore, the least contaminated Cr (VI) was selected for the study of adsorption characteristics to determine the environmental capacity of soils for heavy metals when the composition of wastewater changes under long-term effluent irrigation conditions. The results show that: (1) the concentrations of heavy metals in soil continuously decreased with depth, while the opposite was observed in sediment, reflecting the continuous improvement in water quality over the historical period; (2) In the topsoil, the mean concentrations (mg·kg−1) in rank order are as follows: Mn (588.68) > Zn (284.21) > Pb (99.76) > Cr (76.84) > Ni (34.71) > Cd (3.25), where Cd exceeded the control value by 3.15 times around HFR, and sediment samples also showed higher heavy metal concentrations in HFR than in HJR; (3) Speciation distribution and risk assessment code (RAC) indicate that Mn and Cd were at medium risk and that Cd warrants attention due to its being a non-essential toxic element in humans; (4) The adsorption rates of soil in various layers in different profiles within SIAs for Cr (VI) gradually increased with the increasing initial content of Cr (VI). Among the three isothermal adsorption models, the fit result obtained by the Langmuir equation was superior to those obtained by the Freundlich equation and the linear equation.

Barley Straw Biochar and Compost Affect Heavy Metal Transport in Soil and Uptake by Potatoes Grown under Wastewater Irrigation

Wastewater can supplement freshwater in agriculture; however, it contains toxic heavy metals such as cadmium, chromium, and lead that are hazardous to humans and the environment. We investigated the effects of barley straw biochar, green and table waste compost, and their mix on heavy metal transport in soil and uptake by potatoes (Solanum tuberosum L.) irrigated with synthetic wastewater for two years. In both years, amending soil with compost significantly reduced (p ≤ 0.05) cadmium uptake in potato flesh, skin, roots, and stems; zinc uptake in potato skin and roots; and copper uptake in potato flesh due to increased soil cation-exchange capacity, dissolved organic carbon, and soil pH. Co-amending the soil with compost and 3% biochar significantly reduced (p ≤ 0.05) the bioavailability of cadmium, copper, and zinc in the contaminated soil. Relative to the non-amended soils, soil amendment with biochar, compost, and their mix affected neither the transport of chromium, iron, and lead in the soils nor their uptake by potatoes. It was concluded that amending soil with barley straw biochar and/or compost produced from city green table waste could be used to improve the safety of wastewater irrigated potatoes, depending on the biochar application rate and heavy metal type.

Crop selection reduces potential heavy metal(loid)s health risk in wastewater contaminated agricultural soils

Vegetable crops have varied heavy metal(loid)s accumulation rates from soils to their edible tissues. However, crop selection has been seldom evaluated as a strategy for reducing the health risks of ingesting vegetables grown in soils contaminated by treated wastewater (TWW) irrigation. We cultivated twenty commonly grown vegetables using soils with an approximately 50-year history of TWW irrigation, and their ingestion risks were evaluated by the health risk index (HRI). Results showed that twenty vegetable species had varied abilities in accumulating heavy metal(loid)s from soils to their edible parts (e.g., >100 times of difference for Cd). We found higher potential health risks (HRI > 1) due to As, Cd, and Pb for adults ingesting few vegetable species and all the studied vegetables had negligible health risks (HRI < 1) for Cr, Cu, and Zn. These results suggest that remediation strategies should be targeted towards As, Cd, and Pb removal in agricultural soils in this region. Total HRI > 5 was obtained for ingesting spinach, Chinese lettuce, and Chinese chives, suggesting a high potential of severe health risks. Negligible risks (total HRI < 1) were found for tomato, kidney bean, potato, and cabbage. Our study highlights crop selection as a feasible strategy for ensuring food safety in TWW contaminated farmlands.

Can Potato Crop on Sandy Soil Be Safely Irrigated with Heavy Metal Polluted Water?

Heavy metal (HM) accumulation in soil and plants can occur when water contaminated with HMs is used as a source of irrigation (El-Salam Canal, Egypt). In this study, the effect of watering potato crop in sandy soil from a polluted water source under flood irrigation (FI), sprinkler irrigation (SI), and surface drip irrigation (DI) on the transport of the HMs copper (Cu), manganese (Mn), lead (Pb), and zinc (Zn) in the root zone was experimentally investigated. HM concentrations in potato plant parts was also determined. The field experiments were conducted in a completely randomized block with three replicates for each irrigation method by using nine field lysimeters. Soil and plant samples were collected at the end of the growing season to determine their HM content. The results showed that regardless of irrigation method, irrigation with HM contaminated water raised HM concentrations in both soil and potato plants. DI produced the highest concentrations of most HMs (Cu, Mn, and Pb) in the upper soil layer (0–40 cm) and highest Cu, Pb, and Zn concentrations in plant tubers as well. Maximum Zn concentration in the upper soil layer and maximum Mn concentration in plant tubers occurred under SI. The maximum concentrations of Cu, Mn, Pb, and Zn in both the upper soil layer and plant tubers were 12.0, 140.0, 11.6 and 67.9 mg/kg and 6.3, 9.4, 2.3 and 23.9 mg/kg, respectively. However, FI produced the highest concentrations in the deep soil layer (40–60 cm) and the least concentration of HMs in plant tubers. These concentrations were 18.8, 203.8, 13.3 and 70 mg/kg and 4.0, 6.0, 0.6 and 17.1 mg/kg in soil and plant tubers for Cu, Mn, Pb, and Zn, respectively. The maximum concentrations of HMs in soil and potato plants were lower than the maximum permissible limits. Therefore, El-Salam Canal water appears not to be harmful in the short term. However, as shown in the results, HM accumulation depends on irrigation technique; thus, more studies are needed to determine harmful effects in the long term.

Effects of Cu and Zn contamination on chicken manure-based bioponics: Nitrogen recovery, bioaccumulation, microbial community, and health risk assessment

In bioponics, although chicken manure is an efficient substrate for vegetable production and nitrogen recovery, it is often contaminated with high Cu and Zn levels, which could potentially cause bioaccumulation in plants and pose health risks. The objectives of this study were to assess nitrogen recovery in lettuce- and pak choi-based bioponics with Cu (50-150 mg/kg) and Zn (200-600 mg/kg) supplementation, as well as their bioaccumulation in plants, root microbial community, and health risk assessment. The supplementation of Cu and Zn did not affect nitrogen concentrations and plant growth (p > 0.05) but reduced nitrogen use efficiency. Pak choi showed higher Cu and Zn bioconcentration factors than lettuce. Bacterial genera Ruminiclostridium and WD2101_soil_group in lettuce roots and Mesorhizobium in pak choi roots from Cu and Zn supplemented conditions were significantly higher (p < 0.05) than controls, suggesting microbial biomarkers in plant roots from Cu and Zn exposure bioponics depended on plant type. Health risk assessment herein revealed that consumption of bioponic vegetables with Cu and Zn contamination does not pose long-term health risks (hazard index <1) to children or adults, according to the US EPA. This study suggested that vegetable produced from chicken manure-based bioponics has low health risk in terms of Cu and Zn bioaccumulation and could be applied in commercial-scale system for nutrient recovery from organic waste to vegetable production; however, health risk from other heavy metals and xenobiotic compounds must be addressed.

Physiological of biochar and α-Fe2O3 nanoparticles as amendments of Cd accumulation and toxicity toward muskmelon grown in pots

BACKGROUND

Due to the severe cadmium (Cd) pollution of farmland soil, effective measures need to be taken to reduce the Cd content in agricultural products. In this study, we added α-Fe2O3 nanoparticles (NPs) and biochar into Cd-contaminated soil to investigate physiological responses of muskmelon in the whole life cycle.

RESULTS

The results showed that Cd caused adverse impacts on muskmelon (Cucumis melo) plants. For instance, the chlorophyll of muskmelon leaves in the Cd alone treatment was reduced by 8.07-32.34% in the four periods, relative to the control. The treatments with single amendment, α-Fe2O3 NPs or 1% biochar or 5% biochar, significantly reduced the soil available Cd content, but the co-exposure treatments (α-Fe2O3 NPs and biochar) had no impact on the soil available Cd content. All treatments could reduce the Cd content by 47.64-74.60% and increase the Fe content by 15.15-95.27% in fruits as compared to the Cd alone treatment. The KEGG enrichment results of different genes in different treatments indicated that single treatments could regulate genes related to anthocyanin biosynthesis, glutathione metabolism and MAPK signal transduction pathways to reduce the Cd toxicity.

CONCLUSIONS

Overall the combination of biochar and α-Fe2O3 NPs can alleviate Cd toxicity in muskmelon. The present study could provide new insights into Cd remediation in soil using α-Fe2O3 NPs and biochar as amendments.

Pathogen and heavy metal contamination in urban agroecosystems of northern Ghana: Influence of biochar application and wastewater irrigation

The benefit of biochar as a soil fertility enhancer is well known and has been broadly investigated. Equally, many tropical and subtropical countries use wastewater for irrigation in urban agriculture. To assess the related health risks, we determined pathogen and heavy metal fate associated with biochar application and wastewater irrigation in the urban agriculture of northern Ghana. Rice (Oryza L.) husk biochar (20 t ha^-1 ), N-P-K 15-15-15 fertilizer (212.5 kg ha^-1 ), and their combinations were evaluated in a field-based experiment. Untreated wastewater and tap water served as irrigation water. Red amaranth (Amaranthus cruentus L.) was used as a test crop and was grown in wet (WS) and dry (DS) cropping seasons. Irrigation water, soil, and vegetables were analyzed for heavy metals, Escherichia coli, fecal coliform, helminth eggs, and Salmonella spp. Unlike the pathogens, analyzed heavy metals from irrigation water and soil were below the FAO/WHO permissible standard for agricultural activities. Wastewater irrigation caused E. coli concentrations ranging from 0.5 to 0.6 (WS) and from 0.7 to 0.8 (DS) log₁₀ colony forming units per gram fresh weight (CFU g_FW ^-1 ) on vegetables and from 1.7 to 2.1 (WS) and from 0.6 to 1.0 (DS) log₁₀ CFU per gram dry weight (g_DW ^-1 ) in soil. Average log₁₀ CFU g_FW ^-1 rates of 6.19 and 3.44 fecal coliform were found on vegetables, whereas in soil, 4.26 and 4.58 log₁₀ CFU g_DW ^-1 were observed in WS and DS, respectively. Helminth egg populations were high in wastewater and were transferred to the crops and soil. Biochar did not affect bacteria contamination. Pathogen contamination on vegetables and in soil were directly linked to the irrigation water, with minimal or no difference observed from biochar application.

The role of soils in regulation of freshwater and coastal water quality

Water quality regulation is an important ecosystem service function of soil. In this study, the mechanism by which soil regulates water quality was reviewed, and the effects of soil management on water quality were explored. A scientometrics analysis was also conducted to explore the research fields and hotspots of water quality regulation of soil in the past 5 years. This review found that the pollutants entering the soil can be mitigated by precipitation, adsorption and desorption, ion exchange, redox and metabolic decomposition. As an optimal substrate, soil in constructed wetlands has perfect performance in the adsorption and passivation of pollutants such as nitrogen, phosphorus and heavy metals in water, and degradation of pesticides and emerging contaminants. Mangrove wetlands play an important role in coastal zone protection and coastal water quality restoration. However, the excessive application of agricultural chemicals causes soil overload, which leads to the occurrence of agricultural non-point source pollution. Under the dual pressures of climate change and food insecurity in the future, developing environmentally friendly and economically feasible sustainable soil management measures is crucial for maintaining the water purification function of soil by relying on the accurate quantification of soil function based on big data and modelling. This article is part of the theme issue 'The role of soils in delivering Nature's Contributions to People'.

Lead(II) adsorption on microwave-pyrolyzed biochars and hydrochars depends on feedstock type and production temperature

Adsorption of lead(II) using carbon-rich chars is an environmentally sustainable approach to remediate lead(II) pollution in industrial wastewater. We studied mechanisms for lead(II) adsorption from synthetic wastewater by biochars produced by microwave-assisted pyrolysis and hydrochars by hydrothermal carbonization at three temperatures using four feedstocks. Lead(II) adsorption was highest (165 mg g^-1) for canola straw biochar produced at 500 °C. Except for chars derived from sawdust, biochars outperformed hydrochars for lead(II) adsorption due to changes in solution pH driven by char pH. As char production temperature increased, lead(II) adsorption decreased in hydrochar mainly due to interaction with aromatic carbon but increased in biochar due to precipitation as hydrocerussite and lead oxide phosphate. Lead(II) adsorption also occurred via surface complexation and cation-ᴨ interaction, as the data fitted well to Freundlich, Langmuir and Temkin models, and the pseudo-first and pseudo-second order kinetic models, depending on feedstock type and production temperature. More than 80% of lead(II) adsorption occurred in the first 3 h for both types of chars; with a few exceptions, adsorption continued for almost 24 h. We conclude that production method, production temperature and feedstock type are crucial factors to consider in designing chars as adsorbents for removing lead(II) from wastewater.

Investigation of Direct Applicability of Modified Agricultural Waste for Contaminant Removal from Real Textile Wastewater

The textile industry produces enormous volumes of wastewater which must be treated effectively. In this study, biosorbent from the agricultural waste of potato peels (PP), which is environmentally friendly and easy to find everywhere, was used for the treatment of real textile wastewater. Physical modification, chemical activation, bio-hybrid and high-pressure modification processes were applied to PP to investigate the organic pollutant removal (chemical oxygen demand (COD)) and inorganic (Fe2+, Ni2+, Cu2+ and Cd2+) from original textile wastewater. Additionally, the effects of contact time (5, 15, 30, 60, 120, and 1440 min) and particle sizes (1.5–1.0 mm, 1.0–0.5 mm, and smaller than 0.5 mm in diameter) were investigated in a batch treatment system. Application of the physical modification process to PP presented an attractive solution for COD removal efficiency (69.50%) and removal efficiencies for four divalent metal ions; 78.6% for Cu2+, 63.6% for Ni2+, 40% for Fe2+, and 34.6% for Cd2+. FT-IR, SEM, and EDX analysis were performed to reveal the adsorption mechanism of the modified adsorbents. The FT-IR results indicate that the adsorption process fits the chemical and physical removal mechanisms, which were also supported by SEM images and EDX results.

Quality and yield of Pseudostellaria heterophylla treated with GGBS as pH adjuster against the toxicity of Cd and Cu

The contamination of Cd and Cu in soil is a great threat to medicinal plant. Ground granulated blast furnace slag (GGBS) is a potential soil pH adjuster to reduce metal toxicity. However, how GGBS affects the quality and yield of herbal plants under the stress of Cd and Cu is not clear. This study aims to investigate the quality and yield of a medicinal plant (Pseudostellaria heterophylla) responding to GGBS treatment in Cd and Cu contaminated soil. GGBS with three mass percentages (0%, 3%, 5%) was added into contaminated lateritic soils for planting. Each condition had 21 replicated seedlings. The concentrations of Cd and Cu in plant, amounts of active ingredients (polysaccarides and saponins) in medicinal organ, and tuber properties were measured after harvest. The results showed that under 3% and 5% GGBS treatments, Cd and Cu accumulations in all plant organs (leaf, stem, root and tuber) were reduced by 69.4-86.0% and 10.3-30.1%, respectively. They were below the permissible limits (World Health Organization, WHO). Even though the concentrations of active ingredients in P. heterophylla tuber decreased by up to 35.8%, they still met Hong Kong Chinese Materia Medica standard. Besides, the biomass of root tuber increased by 9.8% and 46%, due to 3% and 5% GGBS treatments, respectively. The recommended 5% GGBS treatment in practice can balance the reduction of active ingredients and the increase of plant yield when minimizing Cd and Cu accumulation in tuber.

Improving Pesticide Uptake Modeling into Potatoes: Considering Tuber Growth Dynamics

To explore pesticide uptake from soil into a growing potato, a moving-boundary dynamic model is proposed on the basis of the radical diffusion process of a chemical to a sphere. This model, which considers the logistic growth of the potato tuber, describes two hypothetical processes of chemical diffusion within a growing tuber. The model was tested in an illustrative case study for an application of chlorpyrifos. Results indicate that the distribution of chlorpyrifos concentrations along the potato radius is significantly affected by the tuber development. In comparison of our results to results from a classic model using a fixed boundary, the proposed dynamic model yields a quick and big jump for both the average concentration and bioconcentration factor (BCF) of chlorpyrifos in the potato as a result of the sigmoid expansion boundary. Overall, the dynamic model predicts that chlorpyrifos BCFs in the potato at harvest are higher than those using the classical model. In comparison of model results to measured uptake of chlorpyrifos into potato at harvest, the dynamic model shows better performance than the classical model. Our results provide a new perspective on pesticide uptake into potatoes and inform human health risk assessment for pesticides applied at different tuber growth stages.

Integrated Assessment of Nickel Electroplating Industrial Wastewater Effluent as a Renewable Resource of Irrigation Water Using a Hydroponic Cultivation System

Nickel, a micronutrient essential for plant growth and development, has been recognized as a metallic pollutant in wastewater. The concentration of nickel ions in the water course, exceeding the maximum tolerable limit, has called for an alarming attention, due to the bioaccumulative entry in the water-plant-human food chain, leaving a burden of deteriorative effects on visible characteristics, physiological processes, and oxidative stress response in plants. In this work, the renewable utilization of nickel electroplating industrial wastewater effluent (0, 5, 10, 25, 50, and 100%) as a viable source of irrigation water was evaluated using a hydroponic cultivation system, by adopting Lablab purpureus and Brassica chinensis as the plant models, in relation to the physical growth, physiological and morphological characteristics, photosynthetic pigments, proline, and oxidative responses. The elongation of roots and shoots in L. purpureus and B. chinensis was significantly inhibited beyond 25 and 5% of industrial wastewater. The chlorophyll-a, chlorophyll-b, total chlorophyll, and carotenoid contents, accompanied by alterations in the morphologies of xylem, phloem, and distortion of stomata, were recorded in the industrial wastewater-irrigated groups, with pronounced toxicity effects detected in B. chinensis. Excessive proline accumulation was recorded in the treated plant models. Ascorbate peroxidase (APX), guaiacol peroxidase (POD), and catalase (CAT) scavenging activities were drastically altered, with a profound upregulation effect in the POD activity in L. purpureus and both POD and APX in B. chinensis, predicting the nickel-induced oxidative stress. Conclusively, the diluted industrial wastewater effluent up to the optimum concentrations of 5 and 25%, respectively, could be feasibly reused as a renewable resource for B. chinensis and L. purpureus irrigation, verified by the minimal or negligible phytotoxic implications in the plant models. The current findings have shed light on the interruption of nickel-contaminated industrial wastewater effluent irrigation practice on the physical and biochemical features of food crops and highlighted the possibility of nutrient recycling via wastewater reuse in a sustainable soilless cultivation.

Differences in absorption of cadmium and lead among fourteen sweet potato cultivars and health risk assessment

Planting sweet potato (Ipomoea batatas (L.) Lam.) instead of rice in the area contaminated with heavy metals is one of the measures to ensure people's health and agricultural economy. Therefore, it is important to screen the low accumulation cultivars of sweet potato and to find out the concentration rule of cadmium (Cd) and lead (Pb) in edible parts along with the associated health risks to humans. A field experiment was performed with fourteen of three main types (starch, purple, and edible-type) of sweet potato cultivars grown on farmland polluted with Cd and Pb in eastern Hunan Province, China. The Cd and Pb concentrations in the sweet potato tissues as well as the yield were measured. The yield of the shoot and tuberous root of the fourteen sweet potato cultivars ranged from 14.59 to 68.57 and 26.35-50.76 t ha^-1 with mean values of 33.09 and 33.46 t ha^-1, respectively. Compared with purple and edible-type cultivars, the starch-type cultivar had lower Cd and Pb concentrations in the flesh, but higher in the shoot. The Cd and Pb concentrations in the flesh of cultivars Shangshu 19, Sushu 24, Yushu 98, and Xiangshu 98 were lower than MCL provided in Chinese National Food Safety Standards GB2762-2017. Based on the hazard index (HI), the consumption of sweet potato flesh is lower health risk, while shoots pose a greater health risk to local people and Cd is the main cause of the risk. As a result, sweet potato cultivars Shangshu 19, Sushu 24, Yushu 98 and Xiangshu 98 can be plant in serve Cd and Pb contaminated soils with the advantages of easy cultivation, high yield and economic benefits without stopping agricultural production.

Combined use of municipal solid waste biochar and bacterial biosorbent synergistically decreases Cd(II) and Pb(II) concentration in edible tissue of forage maize irrigated with heavy metal-spiked water

A pot experiment was carried out to evaluate the effect of a municipal solid waste (MSW) biochar and a bacterial strain on the forage maize growth and the concentration of lead (Pb) and cadmium (Cd) in the edible tissue of maize irrigated with water contaminated with Cd (5 mg L⁻¹) and Pb (100 mg L⁻¹). Experimental treatments included (i) bacterial strain at two levels: no bacterial strain and Enterobacter cloacae R7; (ii) MSW biochar at three levels: 0, 1, and 3% (w/w); and (iii) irrigation water quality at five levels: plants irrigated with 100% freshwater (FW), plants irrigated with 75%FW + 25% contaminated water (CW), plants irrigated with 50%FW + 50% CW, plants irrigated with 25%FW + 75% CW, and plants irrigated with 100% CW. The effect of various treatments on maize growth indices and concentration of Pb(II) and Cd(II) in the plant was significant at 5% level. The concentration of these metals in the shoot of plants irrigated with 75 and 100% CW was higher than the permissible limits for Cd(II) and Pb(II) in livestock feed. However, the concentration of these metals in the shoot of the plants irrigated with 25 and 50% CW was lower than the permissible limit for this use. In this study, the combined application of 3%biochar and E. cloacae R7 had a significant effect on increased root dry weight (ranging from 29 to 33%), shoot dry weight (ranging from 32 to 43%) and bacterial root colonization (ranging from 33 to 53%) and on reduced concentration of Pb (ranging from 78 to 80%) and Cd (ranging from 72 to 76%) of the shoot of maize plant (edible tissues used by livestock), which was below the permissible limits for livestock feed, compared to corresponding controls. According to the results of this study, to reduce the concentration of the heavy metals in forage maize shoot (below the permissible limits for livestock feed), it is suggested using heavy metal–contaminated water either in combination with freshwater (50 or 75% FW) or in combination with biochar and bacterial biosorbent, averting human/animal health risk.

Biochar—A Panacea for Agriculture or Just Carbon?

The sustainable production of food faces formidable challenges. Foremost is the availability of arable soils, which have been ravaged by the overuse of fertilizers and detrimental soil management techniques. The maintenance of soil quality and reclamation of marginal soils are urgent priorities. The use of biochar, a carbon-rich, porous material thought to improve various soil properties, is gaining interest. Biochar (BC) is produced through the thermochemical decomposition of organic matter in a process known as pyrolysis. Importantly, the source of organic material, or ‘feedstock’, used in this process and different parameters of pyrolysis determine the chemical and physical properties of biochar. The incorporation of BC impacts soil–water relations and soil health, and it has been shown to have an overall positive impact on crop yield; however, pre-existing physical, chemical, and biological soil properties influence the outcome. The effects of long-term field application of BC and how it influences the soil microcosm also need to be understood. This literature review, including a focused meta-analysis, summarizes the key outcomes of BC studies and identifies critical research areas for future investigations. This knowledge will facilitate the predictable enhancement of crop productivity and meaningful carbon sequestration.

Biochar applied to soil under wastewater irrigation remained environmentally viable for the second season of potato cultivation

The environmental effectiveness of plantain peel biochar in the second season of its application to soil was studied using outdoor lysimeters (0.45 m diameter x 1.0 m height) packed with sandy soil, cultivated with potatoes (Solanum tuberosum) and irrigated with wastewater. Biochar (1% w/w) was amended in the soil one-time in the first season. For two seasons, the biochar improved the soil properties, immobilized the heavy metals in the soil, and reduced their uptake by the crop. The CEC of the biochar-amended soil (WW + B) for example, as compared to the unamended treatment (WW-B), was significantly higher (p<0.05; >65%) for both seasons due to higher pH which controls the availability of cations in soils, influencing their CECs. The soil sampled in the second season showed accumulation of all the heavy metals in the topsoil, while only Zn, Pb and Fe moved to the 0.1 m depth. The Fourier transform infra-red spectra of the soil and soil-biochar mix were similar and suggested that oxygen-containing functional groups were partly responsible for binding the heavy metals. The heavy metals translocated to all the potato parts (flesh, peel, root, stem and leaves). The concentrations of the heavy metals in potato parts under freshwater were lower than those under wastewater irrigated condition. After the second season of being in the soil, biochar significantly reduced (p < 0.05) the concentrations of Cd, Cu, Cr, Pb and Zn in the edible flesh suggesting that biochar immobilized wastewater-laden heavy metals in soil and reduced their uptake in potatoes for at least two seasons.

Effect of Nano Fe-oxide and Endophytic Fungus (P. indica) on Petroleum Hydrocarbons Degradation in an Arsenic Contaminated Soil under Barley Cultivation

BACKGROUND

Heavy metals and petroleum hydrocarbon pollution are important environmental problems. This research was conducted to evaluate the effect of nano Fe-oxide and endophytic fungus (P. indica) on petroleum hydrocarbons degradation in an arsenic and petroleum hydrocarbons contaminated soil using barley plant.

METHODS

Treatments consisted of the presence (E⁺) and the absence (E^-) of P.indica fungi, soil contaminated with As in the rates of 0 (AS₀), 12 (AS₁₂) and 24 (As₂₄) mg As /kg of soil, and application of 0 (Fe₀) and 1% (Fe₁) (W/W) nano Fe-oxide. The plant used in this study was the barley plant. After 7 weeks, the root and shoot As concentration was measured using atomic absorption spectroscopy. The concentration of total soil petroleum hydrocarbon (TPHS) was measured using GC-mass.

RESULTS

Application of nano Fe-oxide in soil treated with 12 and 24 mg As/kg soil decreased root As concentration by 30 and 20.6%, respectively. The presence of P.indica caused a significant reduction in the shoot As concentration. With increasing shoot Fe concentration the shoot As concentration was decreased. The highest TPHS degradation was observed in non As-polluted soil that containing 1% (W/W) nano Fe-oxide in the presence of P.indica, while the lowest that was in As polluted soil (24 mg As/kg soil) without applying nano Fe-oxide and in the absence of P.indica.

CONCLUSION

Increasing soil sorption properties due to nano Fe-oxide application had significant effect on TPHS degradation in the presence of P.indica. However the role of soil condition on the amount of TPHS degradation cannot be ignored.

Effects of crop straw and its derived biochar on the mobility and bioavailability in Cd and Zn in two smelter-contaminated alkaline soils

In this study, comparative investigations on the effects of crop straw and its derived biochars on soil Cd and Zn mobility and availability were conducted. Crop straws (i.e. maize straw, rapeseed straw, and wheat straw) and their derived biochars were incubated with two contaminated alkaline soils (FX and TG soils) at 2.5% (w/w). The changes of soil properties like pH, EC, organic matter content, and dissolved organic matter content were investigated along with metal mobility, speciation distribution, and accumulation in ryegrass (Lolium multiflorum Lam.). Results indicated biochar, especially those were high in pH, enhanced soil pH (>0.2 units, p < 0.05), whereas a continuous reduction of soil pH was observed among treatments with crop straws. Both soil EC and the organic matter content increased with the application of both crop straws and biochars. In term of metals, Cd and Zn mobility were reduced with 6-14%/1-5% and 6-27%/7-15% reduction in the DTPA extractable Cd and Zn contents in TG and FX soil treatments, respectively. Moreover, distinct changes of metals in different fractions were also observed (acid soluble and reducible fraction → oxidizable fraction in straw treatments; acid soluble fraction → reducible soluble fraction in biochar amendments). Furthermore, the biological analysis revealed that the growth of ryegrass was promoted, but the accumulation of metals in ryegrass shoots was reduced, especially in MS₇₀₀ treatment. Apart from the amendments, metal immobilization efficiencies were negatively correlated with the contamination status. Despite that, a higher rate of biochar application (>10%) could dramatically reduce the amount of available metal in soil extracts, except for Zn in FX soil treatments. This present work demonstrated that biochars, especially those produced at a higher temperature, are superior to crop straws to immobilize metals in soils. However, the remediation efficiencies were strongly restricted by soil pH and contamination status.

Temporal effect of MgO reactivity on the stabilization of lead contaminated soil

Elevated soil lead (Pb) concentrations are a global concern owing to the toxic effects of this heavy metal. Solidification/stabilization (S/S) of soils using reagents like Portland cement (PC) is a common approach for the remediation of Pb contaminated sites. However, it has been reported that under long-term field conditions, the performance of PC treatments can diminish significantly. Therefore, novel reagents that provide longer-term stabilization performance are needed. In this study, four magnesium oxide (MgO) products of different reactivity values were applied (5 wt%) to a Pb contaminated clayey soil. The short-term (1-49 days) and long-term (25-100 years) temporal stabilization effects were investigated by laboratory incubation and accelerated ageing methods, respectively. The concentration of Pb in Toxicity Characterization Leaching Procure (TCLP) leachate was ~14 mg/L for the untreated soil; ~1.8 times higher than the TCLP regulatory level (5 mg/L). Only one day after treatment with MgO, the leachate concentration was reduced to below the regulatory level (a reduction of 69.4%-83.2%), regardless of the MgO type applied. However, in the long-term accelerated ageing experiments, only treatments using the most reactive MgO type could provide leachate concentrations that were consistently below the TCLP threshold throughout the 100 years of simulated ageing. The soil treated with the MgO of lowest reactivity was the first to exceed the regulatory level, at simulated year 75. It is thus demonstrated that MgO reactivity has a significant effect on its long-term effectiveness for contaminated soil stabilization. This is attributed to differences in their specific surface area and readiness to carbonate, which may facilitate the immobilization of Pb in the long term. It is also noteworthy that compared to PC, reactive MgO is more environmentally friendly owing to lower energy consumption and reduced CO₂ emissions during its manufacture.

Soil amendments enhanced the growth of Nicotiana alata L. and Petunia hydrida L. by stabilizing heavy metals from wastewater

Due to the non-degradable nature of heavy metals (HMs), the industrial effluent, whether treated or untreated, carrying HMs, eventually end up into the water bodies, soil, and sediments. Numerous countermeasures were applied, but the use of ornamental plants for the stress mitigation associated with HMs on the environment is a neglected research domain. The composition of wastewater influences bioremediation strategies. As the wastewater is contaminated with multiple HMs, many lab studies, with the plants, failed in the industrial field. This work focuses on the potential of Nicotiana alata L. and Petunia hydrida L. against multiple HMs contaminated synthetic wastewater. To improve plant tolerance, soil amendments (biochar, compost, and moss, each at 5% v/v in soil) were used, individually and in combination. After 6 weeks of the exposure, plant physiological, biochemical and enzymatic parameters, as well as the distribution of HMs, (Cd, Cr, Cu, Pb, Mn, Ni, and Zn) in the plant (flower, leaves, root, and shoot) and soil, were measured. The HMs uptake positivity influenced the malondialdehyde content, hydrogen peroxide content and electrolyte leakage, while negatively to photosynthetic pigments, and resulted in increased catalase, guaiacol peroxidase, glutathione s-transferase, ascorbate peroxidase, while reduced superoxide dismutase activity. It was found that all amendments improved the plant growth by metal stabilization, and best results were obtained with the combined application of biochar + compost + moss. So, HMs stabilization can be achieved by growing ornamental plants, like Nicotiana alata L. and Petunia hydrida L. along with soil amendments.