Assessment of trace element concentrations in soil and plants from cropland irrigated with wastewater

Determining reclaimed water quality thresholds and farming practices to improve food crop yield: A meta-analysis combined with random forest model

Irrigated agricultural systems with reclaimed water (RW) play a crucial role in alleviating global water scarcity and increased food demand. However, appropriate reclaimed water quality thresholds and farming practices to improve food crop yield is virtually unclear. Therefore, for the first time, this study made a large compilation of previous studies using meta-analysis combined with a random forest (RF) model and analyzed the impact of RW versus freshwater (FW) on the yield of food crops (cereals, vegetables, and fruits). It was found that magnesium ion (Mg²⁺), calcium ion (Ca²⁺), electrical conductivity (EC), total nitrogen (TN), and potential of hydrogen (pH) were the most important factors for RW quality indicators. Based on the results, water managers should establish more conservative RW quality thresholds to promote food crop production, especially for salts and pollutants in RW. Compared to international water quality standards, it could be slightly relaxed the restrictions of TN in RW. The optimal farming practices obtained that irrigation amount of the mixed RW and FW (RW + FW) was from 1000 m³ ha^-1 to 5000 m³ ha^-1, and the cultivation period was no more than three years. Flood irrigation (FI) and drip irrigation (DI) for cereals were also recommended. Finally, a comparison of the determined results from this method with other scenarios published, finding a good agreement.

Status, Sources and Assessment of Potentially Toxic Element (PTE) Contamination in Roadside Orchard Soils of Gaziantep (Türkiye)

To identify the sources of contamination with potentially toxic elements (PTEs) in roadside orchard soils and to evaluate the potential ecological and environmental impacts in Gaziantep, soil samples from 20 mixed pistachio and olive orchards on roadsides with different traffic densities and at different distances to the roads were analyzed. Concentrations were 23,407.36 ± 4183.76 mg·kg^-1 for Fe, 421.78 ± 100.26 mg·kg^-1 for Mn, 100.20 ± 41.92 mg·kg^-1 for Ni, 73.30 ± 25.58 mg·kg^-1 for Cr, 65.03 ± 12.19 mg·kg^-1 for Zn, 60.38± 7.91 mg·kg^-1 for Pb, 17.74 ± 3.35 mg·kg^-1 for Cu, 14.93 ± 4.94 mg·kg^-1 for Co, and 0.30 ± 0.12 mg·kg^-1 for Cd. It was found that the Ni content in 51% and the Cr content in 18% of orchard soils were above the legal limits for agricultural soils (pH > 6) in Türkiye. Factor analysis (FA) showed that Co, Cr, Cu, Fe, Mn, Ni, and Pb loaded on the first factor (FC1), while Cd and Zn loaded mostly on the second factor (FC2). It was found that Cr, Ni, and Pb were primarily enriched through pedogenic processes, whereas Cd most likely originated from agricultural activities, while the impact of road traffic as source of PTE contamination was insignificant. It has been revealed that the soils are of low quality for agricultural production due to PTE contamination (PIave ≥ 1). The SOPI values from environmental and ecological individual indices showed that the soil pollution level was moderate for Cd, Ni, and Pb, and low for Cr. The soil pollution index (SOPI) proved to be suitable for evaluating and comparing PTE pollution in regions with different soil properties.

Artisanal gold mine spoil types within a common geological area and their variations in contaminant loads and human health risks

This study answered the question of whether mine spoils occurring in a common geological location had similarities in their contaminant load and associated health risks. Using inductively coupled plasma mass spectrometry, the total contents of Cd, Pb, As, Hg, Zn, Fe, and Al were determined for 110 digested soil samples obtained from underground rock ore (URS), oxide ore (OXS), and alluvial ore (AVS) mine spoils. Independent sample Kruskal-Wallis test and pairwise comparisons of sources were used to ascertain the variation in elemental load between the mine spoil investigated. The results showed that mine spoil contaminations and their ecological and health risk significantly varied (p < 0.01) from each other and fell in the order OXS > URS > AVS > forest soils because of their geochemistry. Determined enrichment and geo-accumulation indices revealed that OXS and URS sites were severely-extremely polluted with Cd, Hg, and As, while AVS mine spoils were only moderately contaminated by Cd and As contents. Children had the highest tendency for developing noncarcinogenic health defects largely due to toxic contents of As, Cd, and Hg in soil materials near them than adult men and women would after obtaining a hazard index of 73.5 and 67.7 (unitless) at both OXS and URS sites. Mine spoils especially where hard rocks and oxide ores were processed are not fit for agricultural use or human habitation. The restriction of human access and sustainable remediation approaches are required to avert health defects. Even so, area-specific potentially toxic elements must be targeted during soil cleaning due to the significant variations in contaminant load between mined sites.

Distribution and Interactive Effects of Heavy Metals in Soil-Maize (Zea Mays L.) System in the Mercury Mining Area, Southwestern China

The concentrations and interactive effects of beneficial elements (i.e., Se, Mo, and Zn) and heavy metals (As, Cd, Hg, and Pb) of maize (Zea mays L.) grown on lime soil and/or soil with mercury tailing were investigated in this study. The results show that the concentrations of heavy metals (i.e., As, Hg, and Pb) in soil with tailing were higher than those in lime soil. The concentrations of beneficial elements (i.e., Mo and Zn) in maize grown on soil with tailing were higher than those of maize grown on lime soil. The mean concentrations of Se, Mo, and Zn in maize grown on soil with tailing were 3.67 mg/kg, 0.530 mg/kg, and 27.4 mg/kg. The pH and an antagonistic effect played an important role in the concentrations of Mo and Zn in maize. The Se concentration in maize was controlled by the planting media.

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.

Heavy Metals in Unprocessed or Minimally Processed Foods Consumed by Humans Worldwide: A Scoping Review

Heavy metals (HM) can be accumulated along the food chain; their presence in food is a global concern for human health because some of them are toxic even at low concentrations. Unprocessed or minimally processed foods are good sources of different nutrients, so their safety and quality composition should be guaranteed in the most natural form that is obtained for human consumption. The objective of this scoping review (ScR) is to summarize the existing evidence about the presence of HM content (arsenic (As), lead (Pb), cadmium (Cd), mercury (Hg), methylmercury (MeHg), and aluminum (Al)) in unprocessed or minimally processed foods for human consumption worldwide during the period of 2011–2020. As a second objective, we identified reported HM values in food with respect to Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) International Food Standards for Maximum Limits (MLs) for contaminants in food. This ScR was conducted in accordance with the Joanna Briggs Institute (JBI) methodology and PRISMA Extension for Scoping Reviews (PRISMA-ScR); advance searches were performed in PubMed, ScienceDirect and FAO AGRIS (Agricultural Science and Technology Information) databases by two reviewers who independently performed literature searches with specific eligibility criteria. We classified individual foods in food groups and subgroups according to the Global Individual Information Food Consumption Data Tool (FAO/WHO GIFT). We homologated all the reported HM units to parts per million (ppm) to determine the weighted mean HM concentration per country and food group/subgroup of the articles included. Then, we compared HM concentration findings with FAO/WHO MLs. Finally, we used a Geographic Information System (GIS) to present our findings. Using our search strategy, we included 152 articles. Asia was the continent with the highest number of publications (n = 79, 51.3%), with China being the country with the largest number of studies (n = 34). Fish and shellfish (n = 58), followed by vegetables (n = 39) and cereals (n = 38), were the food groups studied the most. Fish (n = 42), rice (n = 33), and leafy (n = 28) and fruiting vegetables (n = 29) were the most studied food subgroups. With respect to the HM of interest, Cd was the most analyzed, followed by Pb, As, Hg and Al. Finally, we found that many of the HM concentrations reported exceeded the FAO/OMS MLs established for Cd, Pb and As globally in all food groups, mainly in vegetables, followed by the roots and tubers, and cereals food groups. Our study highlights the presence of HM in the most natural forms of food around the world, in concentrations that, in fact, exceed the MLs, which affects food safety and could represent a human health risk. In countries with regulations on these topics, a monitoring system is recommended to evaluate and monitor compliance with national standards. For countries without a regulation system, it is recommended to adopt international guidelines, such as those of FAO, and implement a monitoring system that supervises national compliance. In both cases, the information must be disseminated to the population to create social awareness. This is especially important to protect the population from the consumption of internal production and for the international markets of the globalized world.

Concentration of potentially harmful elements (PHEs) in eggplant vegetable (Solanum melongena) irrigated with wastewater: a systematic review and meta-analysis and probabilistic health risk assessment

The main objectives of this study were PHEs concentration meta-analysis (Fe, Zn, Cr, Ni, Cu, Pb, and Cd) in eggplant irrigated by wastewater and the following estimation of non-carcinogenic (n-CR) risk for the consumers based on countries. According to the results, the rank order of PHEs concentration in eggplant was Fe (88.3 mg/kg -dry weight) > Zn (10.1 mg/kg -dry weight) > Pb (3.0 mg/kg -dry weight) > Ni (2.7 mg/kg -dry weight) > Cu (1.1 mg/kg -dry weight) > Cd (0.9 mg/kg -dry weight) > Cr (0.05 mg/kg -dry weight). Moreover, n-CR risk showed that all investigated countries (China, India, Pakistan, Turkey, and Jordan) except for United Arab Emirates (UAE) had a considerable n-CR in both age groups (adults and children).

Bioavailability, distribution and health risk assessment of arsenic and heavy metals (HMs) in agricultural soils of Kermanshah Province, west of Iran

Kermanshah Province as an agricultural hub exports food crops to neighboring countries. In this study, contamination status, bioavailability, spatial distribution, and ecological and human health risk of arsenic and heavy metals (HMs) in soil were investigate. For this purpose, 121 agricultural soil samples were collected and analyzed using ICP-MS. The data were studied by calculating some geochemical indices, and using geographical information system and statistical analysis. Results showed that Cd has the highest bioavailability, following by Cu and As. Also, Cu was severely associated with organic matter. Enrichment factor (EF) followed the order of As > Cu > Pb > Se > Cd > Zn > Ni > Cr, and the soil pollution index (SPI) ranged from 0.82 to 2.65. Low potential ecological risk was measured for most of the samples. However, Kermanshah County and Eastern parts of the Province showed the highest HMs enrichment and ecological risk. Moreover, high carcinogenic risk of Cr and Ni threatens the children. Cr showed also high non-carcinogenic hazard index (HI) for children. Principal component analysis (PCA) indicated the anthropogenic origins for As, Cd, Cu, Pb, Se and Zn, while Cr and Ni originated mainly from a geogenic source. Furthermore, Kruskal-Wallis H test revealed that As, Cd, Cr, Cu, Ni, Pb, Se and Zn concentrations were significantly different (p < 0.05) between 16 Counties of the Kermanshah Province. Overall, the management of urban and industrial contamination sources is required to minimize the concentration of bioavailable portion of HMs and preventing residents of the area from being exposed to contaminants.

Influence of Treated Wastewater Irrigation on Soil Nutritional-Chemical Attributes Using Soil Quality Index

Dwindling water resources have drawn global attention to the reuse of treated wastewater (TWW) for irrigation. However, the impact of continuous TWW applications on soil quality and the proper quantification and monitoring frameworks have not been well-understood. This study aims to provides an insight into the impact of flood irrigation of urban TWW on soil nutritional-chemical attributes and the potential application of multiple soil quality indices for a corn cropping system. To achieve that goal, we pursued the Total Data Set (TDS) and Minimum Data Set (MDS) approaches, as well as the Integrated Quality Index (IQI) and Nemoro Quality Index (NQI) models. A total of 17 soil nutritional-chemical indicators (0–50 cm depths) were determined for the soils irrigated with TWW (five sites) and well water (one site as control) in West Azerbaijan province in northwestern Iran. Results revealed a significant difference in the majority of soil nutritional-chemical attributes, IQI-TDS, NQI-TDS, IQI-MDS, NQI-MDS, and corn yield between the TWW-irrigated and well-irrigated soils. Irrigation with TWW resulted in a significant increase in the amount of organic matter and cation exchange capacity by 9–17% and 17–26%, respectively, macronutrients (N, P, K, Ca, and Mg) by 22–164%, and the majority of trace metals (Fe, Mn, Zn, and Cu) by 17–175%, suggesting an improvement in soil nutrients and an increase in productivity. Comparing to the soil in control sites, the TWW irrigation caused a notable increase in the values of IQI-TDS, NQI-TDS, IQI-MDS, and NQI-MDS models ranging 14.6–29.5%, 19.1–25.5%, 21.7–33.3%, and 18.4–23.7%, respectively. This implies that soil quality was ameliorated to a significant extent with TWW irrigation. These improvements resulted in a remarkable increase in corn yield ranging from 12.5% to 28.1%. The regression equations revealed that up to 78%, 47%, 72%, and 36% of the variance in the IQI-TDS, NQI-TDS, IQI-MDS, and NQI-MDS models, respectively, could be captured by corn yield. The results of the regression and correlation analyses showed that the IQI-MDS model was more accurate than the other models in assessing soil quality and predicting crop yield. These findings may be an effective and practical tool for policy making, implementation, and management of soil irrigated with TWW.

The systematic exploration of cadmium-accumulation characteristics of maize kernel in acidic soil with different pollution levels in China

Cadmium is a toxic element with a half-life of more than a few decades that can be absorbed by crops and threaten human health. The problem of food security caused by cadmium through soil-crop systems has received great attention in China. Maize is a staple food widely cultivated throughout the world. However, the lack of systematic study makes it difficult to draw an accurate conclusion on its exact characteristics of cadmium accumulation and the corresponding health risk assessment. The availability of cadmium increased with the decrease of soil pH in acidic soil, enhancing the uptake of cadmium by crops and thus posing a major threat to food safety. In this study, the performance of kernel cadmium accumulation in abundant maize inbred and important hybrid lines were analyzed on acidic fields with different pollution levels in China. It was found that the kernel cadmium concentration both in inbred and hybrid lines showed left skewed distribution and concentrated significantly in a low interval under different soil cadmium gradients with good correlation. The classification of cadmium risk level in maize germplasm and cultivars and the analysis of soil cadmium threshold for maize safe planting can provide references to utilize the crop more feasibly and effectively. Maize may be an important staple crop to reduce human exposure to cadmium in agricultural soil.

Human health risk from consumption of two common crops grown in polluted soils

Contamination of agricultural soils by trace elements is a recurrent hazard for human health because of the possibility of pollutants entering the food chain. Aim of this study was to assess the human health risk from consumption of the common leafy (Lactuca sativa L.) and fruit (Cucurbita pepo L.) crops, in an agricultural area of Southern Italy. Along with agricultural practices, a major pollutant source is recurrent flooding from the highly polluted Solofrana river. Soil samples and edible parts of crops from 14 sites (10 flooded and 4 not flooded) were analyzed for total amounts of As, Cd, Co, Cr, Cu, Ni, Pb, V, Zn. The bio-accumulation factor (BAF) and Health Risk Index (HRI) were calculated for each element, crop and site and as average values of all sites (BAF_mean and HRI_mean). Moreover, the Hazard Index (HI) was determined for each site, as the sum of HRI for all elements. Cr and Cu, mostly derived from river flooding and agricultural practices, respectively, were the only elements whose levels exceeded law thresholds and/or the natural background of the study area. Of the two considered crops, L. sativa accumulated more Cd, Cr and Ni, whereas C. pepo was a more effective bioaccumulator of Zn. Both HRI_mean (for As, Cd, Cr and Ni) and HI were higher for L. sativa than for C. pepo. A low health risk was associated to major soil pollutants (Cr and Cu) found in the study area; in contrast, combined data on soil pollution and plant bio-accumulation points to accumulation of Cd and As, mainly in lettuce, as a potential risk for human health. The results suggest that soil pollution data alone is not sufficient to assess health risk.

Accumulation of trace elements by corn (Zea mays) under irrigation with treated wastewater using different irrigation methods

Treated wastewater reuse for irrigation has gained a greater significance as an alternative resource to meet the growing water demands for agriculture and reduce the pressure on limited existing fresh water. However, this reuse needs adapted management in order to avoid environmental and health risks. An experiment was conducted in a greenhouse to evaluate the effect of different irrigation methods on the Metallic Trace elements and metals concentrations of a Tunisian soil (pH = 8.6) and corn when using treated wastewater. Four irrigation methods: surface irrigation, sprinkler irrigation, drip irrigation and subsurface drip irrigation, and two water qualities were used: treated wastewater and fresh water. Samples of soil and corn were analyzed for several Metallic Trace elements. Results for soil showed that treated wastewater increased electrical conductivity, nutrients and metallic trace elements. The highest levels of salinity and Metallic Trace elements were recorded with using surface irrigation and the lowest were noticed by using subsurface drip irrigation. Whereas the highest levels of nutrients elements were recorded by using subsurface drip irrigation. Results for corn showed that irrigation with treated wastewater improved corn biomass, increased nutrient elements, nitrate reductase activity and chlorophyll content. The concentrations of Metallic Trace elements in different parts of corn were significantly higher under treated wastewater irrigation than fresh water irrigation and were reduced in case of subsurface drip irrigation. Among studied metals, Nickel concentration exceeded the permissible limits of 10 mg kg^-1. Bio-concentration factor values were, in order, Iron > Zinc > Nickel > Copper > lead > Cadmium, whereas, translocation factor values were, in order, Copper > Zinc > Cadmium > iron > lead > Nickel. Because of translocation factor < 1 and bio-concentration factor ≥ 0.2, maize could be considered as both an excluder and an accumulator plant. Results of this study indicate that the use of subsurface drip irrigation decreased the amount of soil and corn contamination by Metallic Trace elements.

Effects of grafting on root-to-shoot cadmium translocation in plants of eggplant (Solanum melongena) and tomato (Solanum lycopersicum)

Heavy metal cadmium (Cd) pollution in farmland has become a serious threat to food security globally. In this work, a grafting technique was applied to eggplant (Solanum melongena) and tomato (Solanum lycopersicum) plants using Solanum torvum as rootstock to investigate effects of grafting on Cd accumulation in shoots. The un-grafted, self-grafted, and grafted plants were grown in soils containing 2 mg kg^-1 Cd. Results showed that grafting on S. torvum could efficiently reduce Cd accumulation in leaves of eggplant and tomato, and the decrease was 89% and 72%, respectively. With S. torvum as rootstock, Cd concentrations were 1.11 mg kg^-1 and 6.58 mg kg^-1 in leaves of grafted eggplant and tomato, which were significantly decreased as compared with un-grafted plants (10.12 mg kg^-1 and 23.19 mg kg^-1, respectively, p < 0.05). In addition, Cd concentrations were 12.11 mg kg^-1 and 29.47 mg kg^-1 in leaves of self-grafted eggplant and tomato, respectively, which was similar to those in un-grafted eggplant, but more than those in un-grafted tomato (p < 0.05). This suggests that the S. torvum rootstock, and not the grafting operation, was responsible for efficient reduction of Cd accumulation in shoots of eggplant and tomato plants. Furthermore, total sulfur and sulfate (SO₄^2-) concentrations analysis revealed that there was a similar trend between Cd accumulation and total sulfur or SO₄^2- concentrations in leaves of plants tested. Additionally, a strong positive correlation between Cd accumulation and total sulfur or SO₄^2- concentrations occurred in leaves of eggplant and tomato plants. Thus, sulfur, mainly SO₄^2-, in leaves may play an important regulatory role in Cd accumulation of eggplant and tomato plants. This study provides the theoretical and technical support for applying grafting technique for the safe practice of farming in Cd-contaminated agricultural soil.

Distribution, pollution, bioaccumulation, and ecological risks of trace elements in soils of the northeastern Qinghai-Tibet Plateau

Environmental quality of the northeastern Qinghai-Tibet Plateau has attracted more attention due to increasing anthropogenic disturbance. Therefore, this study investigated the distribution, pollution, ecological risks, and bioaccumulation of 12 target heavy metals and 16 rare earth elements (REEs) in soils of this area. The average concentrations of target trace elements in soils ranged from 0.16 (Hg) to 500.46 (Cr) mg/kg. Pb caused more serious pollution than the other elements based on geo-accumulation index evaluation. Hg exhibited the strongest enrichment feature with the average enrichment factor of 8.41. Compare with modified contamination degree and pollution load index, Nemerow pollution index method obtained the most serious evaluation results that 45.67% and 16.54% of sampling sites possessed high and moderate pollution. Evaluation results of potential ecological risk index showed that trace elements in soils posed very high and considerable ecological risks in 34.65% and 7.09% of sampling sites, respectively. Mining area was the region with the most serious pollution and ecological risks. Average bioaccumulation factor (BCF) values of target trace elements ranged from 0.05 (REEs) to 2.67 (Cr). Cr was the element that was easier to bio-accumulate in plants of the study area than the other target elements. It is in urgent need to take effective measures for controlling current pollution and potential ecological risks of trace elements in soils of the northeastern Qinghai-Tibet Plateau.

Impact of the uncontrolled leakage of leachate from a municipal solid waste landfill on soil in a cultivated-calcareous environment

The heavy metal pollution generated by landfill leachate becomes increasingly concerning due to its potential to impact human health through the food chain. In the present study, the accumulation and potential health risk of heavy metals (Zn, Cu, Cd, Pb, and Ni) were investigated in a calcareous soil -wheat system affected by an uncontrolled landfill leachate. The results showed soils were significantly enriched by both the available and total fractions of the metals in the sequences of Zn > Pb > Ni > Cd > Cu and Cd > Zn > Ni > Pb > Cu, respectively. Nevertheless, only the Cd content exceeded the standard levels. For the various population groups, the mean hazard quotient (HQ) was lower than the unity, implying a lack of non-carcinogenic health risk for the local residents, while the average hazard index (HI) was 2.3 and 1.1 for people aged 0-5 and 6-18 years, respectively, illustrating a moderate non-carcinogenic health risk for the two groups. Cd and Pb contributed the most to HI, followed by Cu, Zn, and Ni. In addition, the carcinogenic health risk of Cd, ranging from 1 × 10^-5 to 1 × 10^-6, showed a low potential risk in the different population groups exposed to wheat grains and decreased in the sequence of adult > population 6-18 years > population 0-5 years. The findings of the study, which can be used in regions under similar environmental conditions, provide a valuable benchmark for the design of appropriate strategies to manage these agroecosystems by both local and national managers of such macrosystems.

Distribution of Chemical Species in the Water-Soil-Plant (Carya illinoiensis) System near a Mineralization Area in Chihuahua, Mexico-Health Risk Implications

The aim of this study was to quantify major and trace elements in the water, soil, and plants (Carya illionensis) in an agricultural area; and to determine the health risks associated with the walnuts ingestion by calculating the risk quotient. Samples of water, soil, tree leaves, and walnuts were collected; in total, 135 samples were analyzed. Physicochemical parameters were obtained in irrigation water and soil samples. Elemental measurements were performed in an ICP, -OES and -MS. In addition, the distribution coefficient (soil–water), transfer factor (soil–plant), and hazard quotient were evaluated. In the irrigation water, As, Cr, and Pb, showed concentrations above the maximum allowable limits. Likewise, high concentrations of As, Cr, Pb, and Sb were found in tree leave samples, indicating a possible tendency of hyperaccumulation of those elements. Furthermore, Cr concentrations in walnuts were high by far than the reference value (FAO/WHO). A possible competition between chemical congeners were detected from transfer factors. Although, Sb concentrations in walnuts were also high, and no legislation for it in fruits exists. The hazard risk quotient for Sb did indicate a potential health risk. Finally, it is important to consider that the health risk increases when exposure through consumption takes place over a prolonged period of time, even in low concentrations.

Soil contamination with cadmium, consequences and remediation using organic amendments

Cadmium (Cd) contamination of soil and food crops is a ubiquitous environmental problem that has resulted from uncontrolled industrialization, unsustainable urbanization and intensive agricultural practices. Being a toxic element, Cd poses high threats to soil quality, food safety, and human health. Land is the ultimate source of waste disposal and utilization therefore, Cd released from different sources (natural and anthropogenic), eventually reaches soil, and then subsequently bio-accumulates in food crops. The stabilization of Cd in contaminated soil using organic amendments is an environmentally friendly and cost effective technique used for remediation of moderate to high contaminated soil. Globally, substantial amounts of organic waste are generated every day that can be used as a source of nutrients, and also as conditioners to improve soil quality. This review paper focuses on the sources, generation, and use of different organic amendments to remediate Cd contaminated soil, discusses their effects on soil physical and chemical properties, Cd bioavailability, plant uptake, and human health risk. Moreover, it also provides an update of the most relevant findings about the application of organic amendments to remediate Cd contaminated soil and associated mechanisms. Finally, future research needs and directions for the remediation of Cd contaminated soil using organic amendments are discussed.

Health risk assessment of potentially harmful elements and dietary minerals from vegetables irrigated with untreated wastewater, Pakistan

In the developing world, vegetables are commonly grown in suburban areas irrigated with untreated wastewater containing potentially harmful elements (PHEs). In Pakistan, there is no published work on the bioaccessibility aspect of PHEs and dietary minerals (DMs) in sewage-irrigated soil or the vegetables grown on such soils in Pakistan. Several industrial districts of Pakistan were selected for assessment of the risk associated with the ingestion of vegetables grown over sewage-irrigated soils. Both the total and bioaccessible fraction of PHEs (Cd, Co, Cr, Ni, and Pb) and DMs (Fe, Cu, Mn, Zn, Ca, Mg, and I) in soils and vegetable samples were measured. The concentrations of these PHEs and DMs in sewage-irrigated and control soils were below published upper threshold limits. However, compared to control soils, sewage irrigation over the years decreased soil pH (7.7 vs 8.1) and enhanced dissolved organic carbon (1.8 vs 0.8 %), which could enhance the phyto-availability of PHEs and DMs to crops. Of the PHEs and DMs, the highest transfer factor (soil to plant) was noted for Cd and Ca, respectively. Concentrations of PHEs in most of the sewage-irrigated vegetables were below the published upper threshold limits, except for Cd in the fruiting portion of eggplant and bell pepper (0.06-0.08 mg/kg Cd, dry weight) at three locations in Gujarat and Kasur districts. The bioaccessible fraction of PHEs can reduce the context of dietary intake measurements compared to total concentrations, but differences between both measurements were not significant for Cd. Since the soils of the sampled districts are not overly contaminated compared to control sites, vegetables grown over sewage-irrigated soils would provide an opportunity to harvest mineral-rich vegetables potentially providing consumers 62, 60, 12, 104, and 63 % higher dietary intake of Cu, Mn, Zn, Ca, and Mg, respectively. Based on Fe and vanadium correlations in vegetables, it is inferred that a significant proportion of total dietary Fe intake could be contributed by soil particles adhered to the consumable portion of vegetables. Faecal sterol ratios were used to identify and distinguish the source of faecal contamination in soils from Gujranwala, Gujarat, and Lahore districts, confirming the presence of human-derived sewage biomarkers at different stages of environmental alteration. A strong correlation of some metals with soil organic matter concentration was observed, but none with sewage biomarkers.

A field study on the dynamic uptake and transfer of heavy metals in Chinese cabbage and radish in weak alkaline soils

Vegetables and crops can take up heavy metals when grown on polluted lands. The concentrations and dynamic uptake of heavy metals vary at different growth points for different vegetables. In order to assess the safe consumption of vegetables in weak alkaline farmlands, Chinese cabbage and radish were planted on the farmlands of Baiyin (polluted site) and Liujiaxia (relatively unpolluted site). Firstly, the growth processes of two vegetables were recorded. The growth curves of the two vegetables observed a slow growth at the beginning, an exponential growth period, and a plateau towards the end. Maximum concentrations of copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd) were presented at the slow growth period and showed a downtrend except the radish shoot. The concentrations of heavy metals (Cu, Zn, and Cd) in vegetables of Baiyin were higher than those of Liujiaxia. In the meanwhile, the uptake contents continued to increase during the growth or halted at maximum at a certain stage. The maximum uptake rates were found on the maturity except for the shoot of radish which took place at the exponential growth stages of root. The sigmoid model could simulate the dynamic processes of growth and heavy metals uptake of Chinese cabbage and radish. Conclusively, heavy metals have higher bioaccumulation tendency for roots in Chinese cabbage and for shoots in radish.

Concentration of heavy metals and trace elements in soils, waters and vegetables and assessment of health risk in the vicinity of a lignite-fired power plant

The pollution of agricultural soils, waters and products in the regions of lignite mines and fired power plants is of great importance. The concentration of As, Βa, Co, Cr, Sr, Sc, Th, U, Zn in soils and waters in the vicinity of a lignite-fired power plant in Northern Greece was determined using Instrumental Neutron Activation Analysis. The determination frequency was every three months during a period of one year in order to evaluate the seasonal impact of the pollution to the environment. Measurements were performed in three locations around the lignite mine as well as in one reference location at a certain distance from the mine. The results, which exhibited a slight seasonal variation, were compared, where possible, with literature values from other countries. The obtained data in most of the cases did not exceed the normal levels and indicated that the investigated area was only slightly contaminated. The concentration of heavy and trace metals was also measured in three common garden crops (tomato, cucumber and parsley) grown in this area. The calculated transfer factors (TF) from soil to vegetables and health risk quotients (HQ) do not denote a health risk.

Effects of long-term irrigation with untreated municipal wastewater on soil properties and crop quality

Irrigating crops with untreated wastewater leads to elevated concentrations of heavy metals both in soil and cultivated crops. The current study was designed to determine heavy metal (i.e., Pb, Cd, Cr, Cu, Ni, Zn, Hg) accumulation in Konya soils in selected nine sites irrigated with wastewater for over 40 years. Non-irrigated soil samples and soil samples irrigated with well water were taken as control samples. Transport of these pollutants to the wheat samples cultivated in the investigated site was also examined. The obtained results reveal that high alkaline properties and clay structure of Konya soil reduce the mobility of contaminants and cause accumulation in the top layer of soil. Intense effect of wastewater irrigation on soil EC was determined. The highest concentrations of Pb, Cr, Cu, Cd, Zn, Ni, and Hg in wastewater irrigated soil were 5.32, 37.1, 31.5, 11.4, 91.5, 134, and 0.34 mg kg(-1), respectively. Wastewater irrigated soils were strongly polluted by means of Cd (8.23-11.6 mg kg(-1)) and moderately to strongly polluted by means of Ni (47.7-134 mg kg(-1)), exceeding Maximum Admissible Concentrations for Trace Elements in Agricultural Soils and Sewage Sludge Regulation limit values of Turkey. Maximum concentrations found for Pb, Cr, Cu, Cd, Zn, and Ni in wastewater irrigated wheat grain were 8.44, 1.30, 9.10, n.d, 29.31, and 0.94 mg kg(-1), respectively. Besides, Hg was not detected in any samples of wheat grain. Based on the regulation of Turkish Food Codex, Pb contamination in wheat samples grown in the sampling site was evidenced.

Metal uptake via phosphate fertilizer and city sewage in cereal and legume crops in Pakistan

Crop irrigation with heavy metal-contaminated effluents is increasingly common worldwide and necessitates management strategies for safe crop production on contaminated soils. This field study examined the phytoavailability of three metals (Cd, Cu, and Zn) in two cereal (wheat, maize) and legume (chickpea, mungbean) crops in response to the application of either phosphatic fertilizer or sewage-derived water irrigation over two successive years. Five fertilizer treatments, i.e. control, recommended nitrogen (N) applied alone and in combination of three levels of phosphorus (P), half, full and 1.5 times of recommended P designated as N0P0, N1P0, N1P0.5, N1P1.0, and N1P1.5, respectively. Tissue concentrations of Cd, Cu, Zn, and P were determined in various plant parts, i.e., root, straw, and grains. On the calcareous soils studied while maximum biomass production was obtained with application of P at half the recommended dose, the concentrations of metals in the crops generally decreased with increasing P levels. Tissue metal concentrations increased with the application of N alone. Translocation and accumulation of Zn and Cu were consistently higher than Cd. And the pattern of Cd accumulation differed among plant species; more Cd being accumulated by dicots than monocots, especially in their grains. The order of Cd accumulation in grains was maize > chickpea > mungbean > wheat. Mungbean and chickpea straws also had higher tissue Cd concentration above permissible limits. The two legume species behaved similarly, while cereal species differed from each other in their Cd accumulation. Metal ion concentrations were markedly higher in roots followed by straw and grains. Increasing soil-applied P also increased the extractable metal and P concentrations in the post-harvest soil. Despite a considerable addition of metals by P fertilizer, all levels of applied P effectively decreased metal phytoavailability in sewage-irrigated soils, and applying half of the recommended dose of P fertilizer was the most feasible solution for curtailing plant metal uptake from soils. These findings may have wide applications for safer crop production of monocot species when irrigating crops with sewage effluent-derived waters.

Heavy Metal Residues in Soil and Accumulation in Maize at Long-Term Wastewater Irrigation Area in Tongliao, China

Soil and plant samples were collected from Tongliao, China, during the maize growth cycle between May and October 2010. Heavy metals, such as Cr, Pb, Ni, and Zn, were analyzed. The concentrations of Cr, Pb, Ni, and Zn in the wastewater-irrigated area were higher than those in the topsoil from the groundwater-irrigated area. The concentrations of metals in the maize increased as follows: Pb < Ni < Zn < Cr. In addition, Cr, Pb, and Ni mainly accumulated in the maize roots, and Zn mainly accumulated in the maize fruit. The results of translocation factors (TF) and bioconcentration factors (BCF) of maize for heavy metals revealed that maize is an excluder plant and a potential accumulator plant and can serve as an ideal slope remediation plant. In addition, the increasing heavy metal contents in soils that have been polluted by wastewater irrigation must result in the accumulation of Cr, Pb, Ni, and Zn in maize. Thus, the pollution level can be decreased by harvesting and disposing of and recovering the plant material.

Heavy metal pollution in vegetables grown in the vicinity of a multi-metal mining area in Gejiu, China: total concentrations, speciation analysis, and health risk

A field survey was conducted to investigate the present situation and health risk of arsenic (As), lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) in soils and vegetables in a multi-metal mining area, Gejiu, China. Furthermore, three vegetables (water spinach, potato, and summer squash) containing high metal concentrations were selected to further analyze metal speciation. The results showed that the average concentrations of five metals in soil exceeded the limiting values, and their bioavailable concentrations were significantly positively correlated to the total ones. Heavy metals in the edible parts of vegetables also exceeded the corresponding standards. The leaves of pakchoi, peppermint, and coriander had a strong metal-accumulative ability and they were not suitable for planting. Except the residue forms, the main forms of metals in the edible parts of three selected vegetables were ethanol-, NaCl-, and HAc-extractable fractions for As, Pb, and Cd, respectively; however, Cu was mainly presented as NaCl-extractable and Zn as HAc-extractable fractions. A high proportion of ethanol-extractable As showed that As bioactivity and toxic effects were the highest. Although the total and bioavailable Cd were high in soil, its speciation in vegetables was mainly presented as HAc-extractable fraction, which has a relatively low bioactivity. Lead and arsenic were imposing a serious threat on the local residents via vegetable consumption.