Accumulation status, sources and phytoavailability of metals in greenhouse vegetable production systems in Beijing, China

Thallium content in vegetables and derivation of threshold for safe food production in soil: A meta-analysis

Soil thallium (Tl) pollution is a serious environmental problem, and vegetables are the primary pathway for human exposure to Tl. Therefore, it is important to investigate the characteristics of soil Tl uptake by vegetables. In this study, the meta-analysis approach was first applied to explore the relationship between Tl content in vegetables and soil environment, as well as key factors influencing soil physical-chemical properties, and to derive soil thresholds for Tl. The results indicated that various types of vegetables have different capabilities for Tl accumulation. Vegetables from contaminated areas showed high Tl accumulation, and the geomean Tl content in different types of vegetables was in the following order: leafy > root-stalk > solanaceous vegetables. Taro and kale had significantly higher capability to accumulate soil Tl among the 35 species studied, with Tl bioconcentration factor values of 0.060 and 0.133, respectively. Pearson correlation analysis and meta-analysis revealed that the Tl content in vegetables was significantly correlated with soil pH and Tl content in soil. The linear predictive model for Tl accumulation in vegetables based on soil Tl content described the data well, and the fitting coefficient R2 increased with soil pH value. According to potential dietary toxicity, the derived soil Tl thresholds for all, leafy and root-stalk vegetables increased with an increase in soil pH, and were in the range of 1.46-6.72, 1.74-5.26 and 0.92-6.06 mg/kg, respectively. The soil Tl thresholds for kale, lettuce and carrot were in the range of 0.24-4.89, 2.94-3.32 and 3.77-14.43 mg/kg, respectively. Ingestion of kale, beet, sweet potato, potato, taro, pepper, turnip, Chinese cabbage, eggplant and carrot poses potential health risks. The study provides scientific guidance for vegetable production in Tl-contaminated areas and can help with the selection of vegetable species suitable for avoiding the absorption of Tl from contaminated soil.

Cadmium and lead accumulation in important food crops due to wastewater irrigation: Pollution index and health risks assessment

The contamination of farm soils with heavy metals (HMs) has raised significant concerns due to the increased bioavailability and accumulation of HMs in agricultural food crops. To address this issue, a survey experiment was conducted in the suburbs of Multan and Faisalabad to investigate the spatial distribution, bioaccumulation, translocation, and health risks of cadmium (Cd) and lead (Pb) in agricultural crops. The results show a considerable concentration of Cd and Pb in soils irrigated with wastewater, even though these levels were below the permissible limits in water and soil matrices. The pollution index for Cd was mostly greater than 1 at the selected sites, indicating its accumulation in soil over time due to wastewater irrigation. Conversely, the pollution index for Pb was below 1 at all sites. Among the plants, Zea mays accumulated the highest concentration of Cd and Pb. The translocation factor from soil to root was highest for Brassica olearecea (7.037 for Cd) and Zea mays (6.383 for Pb). The target hazard quotient (THQ) value of Cd exceeded the non-carcinogenic limit for most vegetables. The highest value was found in Allium cepa (5.256) and the lowest in Allium sativum (0.040). In contrast, the THQ level of Pb was below the non-carcinogenic limit for most vegetables, except for Allium cepa (1.479), Solanum lycopersicum (1.367), and Solanum tuberosum (1.326). The study highlights that Allium cepa poses the highest health risk for humans, while Medicago sativa poses the highest risk for animals due to Cd and Pb contamination. These results underscore the urgent need for effective measures to mitigate the health risks associated with HM contamination in crops and soils.

Assessment of heavy metal distribution and bioaccumulation in soil and plants near coal mining areas: implications for environmental pollution and health risks

Monitoring heavy metals (HMs) across source distance and depth distribution near coal mining sites is essential for preventing environmental pollution and health risks. This study investigated the distribution of selected HMs, cadmium (Cd2+), chromium (Cr2+), copper (Cu2+), manganese (Mn2+), nickel (Ni2+), lead (Pb2+), and zinc (Zn2+), in soil samples collected from ten sites (S-1-S-10) at two different depths (0-15 and 15-30 cm) and distances of 50, 100, and 200 m from a mining source. Additionally, three plant species, Prosopis spp., Justicia spp., and wheat, were collected to assess HM bioavailability and leaf accumulation. Coal mine activities' impact on soil properties and their HM associations were also explored. Results reveal HM concentrations except for Cr2+ exceeding World Health Organization (WHO) limits. In surface soil, Cd2+ (58%), Cu2+ (93%), Mn2+ (68%), Ni2+ (80%), Pb2+ (35%), and Zn2+ (88%) surpassed permissible limits. Subsurface soil also exhibited elevated Cd2+ (53%), Cu2+ (83%), Mn2+ (60%), Ni2+ (80%), Pb2+ (35%), and Zn2+ (77%). Plant species displayed varying HM levels, exceeding permissible limits, with average concentrations of 1.4, 1.34, 1.42, 4.1, 2.74, 2.0, and 1.98 mg kg-1 for Cd2+, Pb2+, Cr2+, Cu2+, Mn2+, Ni2+, and Zn2+, respectively. Bioaccumulation factors were highest in wheat, Prosopis spp., and Justicia spp. Source distance and depth distribution significantly influenced soil pH, electrical conductivity (EC), and soil organic carbon (SOC). Soil pH and EC increased with an increase in soil depth, while SOC decreased. Pearson correlation analysis revealed varying relationships between soil properties and HMs, showing a considerably negative correlation. Concentrations of HMs decreased with increasing depth and distance from mining activities, validated by regression analysis. Findings suggest crops from these soils may pose health risks for consumption.

Source apportionment and risk assessment of heavy metals in typical greenhouse vegetable soils in Shenyang, China

In this study, the concentrations of Cr, Cu, Ni, Pb, Zn, Cd, As, and Hg in the typical greenhouse vegetable soils in Shenyang, Northeast of China, were determined, and the pollution characteristics and primary sources of heavy mental pollution in soil were analyzed. Results showed that the sum of the mean values of eight typical heavy metals in the soil of the greenhouse soils was 219.79 mg/kg. According to the "Chinese Environmental Quality Evaluation Standard for Farmland of Greenhouse Vegetables Production" (HJ/T 333-2006), the concentrations of Cu (33.50 ± 11.99 mg/kg), Cd (0.246 ± 0.156 mg/kg), and Hg (0.214 ± 0.177 mg/kg) exceeded the limit values in 14.29%, 39.29%, and 39.29% of sampling points, respectively. The single factor pollution index and the Nemerow comprehensive pollution index of heavy metal elements showed that most greenhouse soils were at safety, alert, or light pollution levels. The potential ecological risk index (RI = 505.19) showed that 42.86% of the samples were at high or very high risk and Cd and Hg were the main ecological risk factors. Based on the result of correlation analysis, the Positive Matrix Factorization (PMF) differentiated sources of heavy metal pollution in the study area into four components, including fertilizer input, soil parent material, pesticide spraying and raw coal combustion, and plastic film mulching, which accounted for 36.76%, 22.64%, 20.89%, and 19.71%, respectively, of the total sources of heavy metals.

Essential role of multi-element data in interpreting elevated element concentrations in areas impacted by both natural and anthropogenic influences

Background

This article presents a detailed analysis of a dataset consisting of 27 elements found in soils, soil eluates, and vegetables from private gardens in a region with a long history of coal mining and burning. With coal being one of the world's most significant energy sources, and previous studies highlighting elevated element levels in vegetables from this region, the objective of this study was to identify the factors that impact soil geochemistry and metal(loid) uptake in plants.

Methods

Total major and trace element concentrations were analyzed in soils, soil eluates and vegetables by high resolution inductively coupled plasma mass spectrometry. The vegetable samples included six species: fennel, garlic, lettuce, parsley, onion, and radicchio. Each plant was divided into roots, stems, leaves, and/or bulbs and analyzed separately. In addition, the soil pollution status, bioavailable fractions and transfer factors from soil and soil eluates to different plant parts were determined.

Results

The comprehensive dataset revealed that, apart from the substrate enriched with various elements (Al, As, Co, Cr, Mo, Ni, Pb, Sb, Sn, Ti, U, V, and Zn), other anthropogenic factors such as the legacy of coal mining and combustion activities, associated industries in the area, transport, and agricultural practices, also influence the elevated element concentrations (Cd, Cu, Fe, Mn, and Se) in locally grown vegetables. The transfer factors based on element concentrations in aqueous soil eluates and element bioavailable fractions confirmed to be an effective tool for evaluating metal uptake in plants, emphazising to some extent the effects of plant species and revealing unique patterns for each pollution source within its environmental context (e.g., Cd, Mo, S, and Se in this case). The study highlights the crucial importance of utilizing comprehensive datasets that encompass a multitude of factors when interpreting the impacts of element uptake in edible plants.

Concentrations and health risk appraisal of heavy metals and volatile organic compounds in soils of automobile mechanic villages in Ogun State, Nigeria

This report presents the findings of the concentrations, distributions and health risks assessment of heavy metals (HMs) and volatile organic compounds (VOCs) in topsoils of two typical automobile mechanic villages (MVs) situated within Ogun State, Nigeria. One of the MVs is located in basement complex terrain (Abeokuta), while the second is in the sedimentary formation (Sagamu). Ten composite samples were collected at depth of 0-30 cm with the aid of soil auger from spent oil-contaminated spots within the two MVs. The chemical parameters of interest were Pb, Cd, benzene, ethylbenzene, toluene, total petroleum hydrocarbon (TPH) as well as oil and grease (O&G). In addition, soil pH, cation exchange capacity (CEC), electrical conductivity (EC) and particle size distribution were also evaluated in order to find out their impacts on assessed soil pollutants. Results revealed that the soils in both MVs are of sandy loam texture, slight acidic to neutral pH, mean CEC < 15 cmol/kg and mean EC > 100 μS/cm. The mean concentration of each of analyzed HMs and VOCs in soils from the two MVs was < 5 mg/kg, while the mean values of TPH and O&G content were > 50 mg/kg. The mean Cd values in soils of both MVs were higher than the national soil screening level of 0.8 mg/kg, but lower than the Canadian and Italian guidelines. There is no significant correlation between each of HMs/VOCs and any of assessed soil physicochemical variables. The non-cancer risk expressed in terms of hazard index (HI) was > 1 via oral ingestion route for adults and children at the two MVs, indicating adverse non-carcinogenic health risk. The HI > 1 value was obtained for adults only through the dermal absorption pathway in Abeokuta MV. However, HI values for the two age groups at the two MVs via inhalation route were < 1, indicating no likelihood of any non-carcinogenic effects via the breathing exposure. The potential of non-cancer risk via oral ingestion route in both MVs was derived from the contributive ratios of HMs and VOCs in the order: Cd > benzene > Pb > toluene. The carcinogenic risk (CR) values due to ingested Cd, benzene and Pb for both age groups at the two MVs exceed the safe limit range of 10-6 to 10-4. Cadmium, benzene and lead made considerable contributions to the estimation of CR through dermal exposure for adults only in Abeokuta MV. The CR values via inhalation pathway for adults and children in both MVs were within the threshold range. Artisans and children should circumvent accidental ingestion of contaminated soils in addition to wearing of protective clothes during routine vehicle maintenance activities.

Determination of Heavy Metal Levels and Health Risk Assessment of Raw Cow Milk in Guelma Region, Algeria

During the recent decades, adverse effects of unexpected contaminants, such as heavy metals on raw cow milk quality, have threatened human health. The objective of this study was to determine heavy metal levels in raw milk collected from autochthonous bovine breeds in the eastern region of Algeria. Eighty-eight pooled milk samples were analyzed using atomic absorption spectrometry for Pb, Cd, Cr, Cu, Ni, Fe, and Zn, and dietary risks were estimated for infants, children, and adults with minimum, average, and maximum milk consumption scenarios. Results revealed that Pb (0.94 ± 0.49 mg/kg), Cd (0.03 ± 0.01 mg/kg), and Cu (0.14 ± 0.08 mg/kg) levels in all analyzed samples were higher than their corresponding maximum residue levels (MRLs). The task hazard quotient (THQ) values suggest potential risk for infants in the three scenarios from Pb, Cd, and Cr; for children in the three scenarios from Pb and in the high scenario from Cr; and for adults in the medium and high scenarios from Pb. The hazard index (HI) values were higher than 1, and the contributions of each metal to the overall HI followed a descending order of Pb, Cr, Cd, Ni, Zn, Cu, and Fe with values of 68.19%, 15.39%, 6.91%, 4.94%, 3.42%, 0.88%, and 0.28%, respectively. Our results indicated that there may be a potential risk of heavy metals, especially Pb, for infants through raw cow milk consumption. Moreover, data actualization and continuous monitoring are necessary and recommended to evaluate heavy metal effects in future studies.

Anthropogenic activities affecting metal transfer and health risk in plastic-shed soil-vegetable-human system via changing soil pH and metal contents

Accumulation and concomitant risk of metals in plastic-shed soil (PSS)-vegetable system around industrial areas have attracted growing public concern recently, while limited studies have focused on human bioaccessible metals in various plastic-shed vegetables and health risk calculated using bioaccessible metals. Previous studies showed that intensive farming and industrial activities could prominently affect metal migration from PSS to vegetables via altering PSS pH, total and bioavailable metal contents. In contrast, whether changes in PSS pH and metal contents control bioaccessible metals in vegetables and health risk is still unknown. For PSS management and sustainable plastic-shed vegetable production in the areas with rapid industrialization, 41 PSS and 32 plastic-shed vegetable samples were sampled from the industrial areas of Yangtze River Delta, China to systematically clarify the specific connections among anthropogenic activities, soil pH and metal contents, and metal transfer and health risk in PSS-vegetable-human system. The results indicated that Cr and Cd contents in 15.6% and 9.38% of vegetable samples exceeded the allowable limits in China. Tolerable cancer risk existed and was mainly induced by bioaccessible Cr in vegetables. Decreased PSS pH mainly caused by heavy use of nitrogen fertilizers increased bioavailable Ni, Cd, Zn, Pb, and Cu in PSS and subsequently enhanced their total and bioaccessible contents in vegetables. Prominent Cr accumulation in PSS induced by industrial wastewater irrigation exacerbated Cr uptake by vegetables, which increased bioaccessible Cr in vegetables and contributed greatly to cancer risk. To reduce transfer and health risk especially of Cd and Cr in the food chain, some appropriate measures related to source control and remediation should be proposed for preventing and mitigating PSS acidification and Cr accumulation.

Inconsistent effects of a composite soil amendment on cadmium accumulation and consumption risk of 14 vegetables

Organic and inorganic mixtures can be developed as immobilizing agents that could reduce heavy metal accumulation in crops and contribute to food safety. Here, inorganic materials (lime, L; zeolite, Z; and sepiolite, S) and organic materials (biochar, B, and compost, C) were selectively mixed to produce six composite soil amendments (LZBC, LSBC, LZC, LZB, LSC, and LSB). Given the fact that LZBC showed the best performance in decreasing soil Cd availability in the incubation experiment, it was further applied in the field condition with 14 vegetables as the test crops to investigate its effects on crop safety production in polluted greenhouse. The results showed that LZBC addition elevated rhizosphere soil pH by 0.1-2.0 units and reduced soil Cd availability by 1.85-37.99%. Both the biomass and the yields of edible parts of all vegetables were improved by LZBC addition. However, LZBC addition differently affected Cd accumulation in edible parts of the experimental vegetables, with the observation that Cd contents were significantly reduced in Allium fistulosum L., Amaranthus tricolor L., and Coriandrum sativum Linn., but increased in the three species of Lactuca sativa. Further health risk assessment showed that LZBC application significantly decreased daily intake of metal (DIM), health risk index (HRI), and target hazard quotient (THQ) for Cd in Allium fistulosum L., Amaranthus tricolor L., and Coriandrum sativum Linn., whereas increased all the indexes in Lactuca sativa. Our results showed that the effect of a composite amendment on Cd accumulation in different vegetables could be divergent and species-dependent, which suggested that it is essential to conduct a pre-experiment to verify applicable species for a specific soil amendment designed for heavy metal immobilization.

Heavy metal and nutrient concentrations in top- and sub-soils of greenhouses and arable fields in East China - Effects of cultivation years, management, and shelter

Although greenhouse vegetable production in China is rapidly changing, consumers are concerned about food quality and safety. Studies have shown that greenhouse soils are highly eutrophicated and potentially contaminated by heavy metals. However, to date, no regional study has assessed whether greenhouse soils differ significantly in their heavy metal and nutrient loads compared to adjacent arable land. Our study was conducted in Shouguang County, a key region of greenhouse vegetable production in China. Soil samples down to soil depths of 3 m were taken from 60 greenhouse vegetable fields of three different ages (5, 10, and 20 years) and from 20 adjacent arable fields to analyze the concentrations of heavy metals, nutrients, and soil physio-chemical parameters. A comparison of greenhouse soils with adjacent arable fields revealed that for greenhouses, (a) micro (heavy metals: Cu, Zn, and Mn) and macronutrients (Nmin, Olsen-P, available K) were significantly higher by a factor of about five, (b) N:P:K ratios were significantly imbalanced towards P and K, and (c) topsoil (0-30 cm) concentrations of the above-mentioned micro- and macronutrients increased with years of vegetable cultivation. In contrast, the soil concentrations of the heavy metals Cr and Pb were lower in greenhouse soils. Heavy metal concentrations did not vary significantly with soil depth, except for the micronutrients Cu and Zn, which were between 1- and 3-fold higher in the topsoil (0-30 cm) than in the subsoil (30-300 cm). The Nemerow pollution index (P_N) was 0.37, which was below the recommended environmental threshold value (P_N < 1). Structural equation model analysis revealed that soil nutrient concentrations in greenhouse soils are directly related to the input of fertilizers and agrochemicals. Lower values of soil Pb and Cr concentrations in greenhouses were due to the sheltering effect of the greenhouse roof, which protected soils from atmospheric deposition due to emissions from nearby industrial complexes.

Bioaccumulation characteristics, transfer model of heavy metals in soil-crop system and health assessment in plateau region, China

This study investigated the bioaccumulation and transfer of heavy metals including Cd, Cr, Cu, Mn, Ni, Pb and Zn in soil-crop system in Lhasa, and assessed the health risks of the edible part of the crops. The results showed that the average values of Cd, Cr, Cu, Mn, Ni, Pb and Zn were 0.15, 44.55, 24.68, 532.40, 22.47, 38.18 and 73.99 mg kg^-1 in natural soil, and 0.16, 46.93, 38.45, 559.13, 23.23, 40.03 and 83.29 mg kg^-1 in cultivated soil, respectively. Highland barley and wheat had the strongest ability to accumulate Zn in grain, the BCF values were 0.24 and 0.27, respectively, significant differences in the distribution of metal contents in crop root, stem, leaf and grain were observed. Root presented larger accumulation capacity in most metals, Zn and Cu was easily transferred in the plant organs, most metals in this study presented difficult to migrate from root to grain. The transfer peak of most metals in soil-crop system appeared from stem to leaf. The concentrations of Cr and Mn in crop grains could be predicted according to the multiple linear regression models. THQ and HI values of heavy metals in edible parts of both highland barley and wheat were below the safety threshold of 1, indicating no detrimental effects posed to adults health. This study helps to understand the accumulation and transfer of heavy metals in soil-crop system in plateau region.

Long-Term Fertilizer Reduction in Greenhouse Tomato-Cucumber Rotation System to Assess N Utilization, Leaching, and Cost Efficiency

Technology-oriented approaches to reduce chemical fertilization in agroecosystems without influencing the vegetable yield is a proficient method for sustainable agriculture and environmental safety. However, short-term studies are not capable to indicate the effects of various inputs in a long run; therefore, a six-year experiment was conducted in Ningxia, China. The experimental units were: no fertilizer control (CK: 0 kg N ha−1), chicken manure (M: organic N 362 kg ha−1), reduced chemical fertilizer (RCF: chemical N 992 kg ha−1 + organic N 362 kg ha−1), and conventional fertilizer (CF: chemical N 1515 kg ha−1 + organic N 362 kg ha−1). The study aimed to assess the effects of reduced fertilization on yield, nitrogen (N) use efficiency (NUE), N leaching, and the economic benefits. The results achieved herein indicate that RCF has significantly improved the NUE, reduced N leaching (23.7%), and improved the N economic benefit (NEB, 41.8%) as compared to the CF. Based on yield, net benefit, and NUE conditions, the optimum N application range was 634–821 kg N ha−1 for tomato and 556–778 kg N ha−1 for cucumber. The study concluded that reduced chemical application of N is an important factor to control environmental pollution and improve fertilizer use efficiency. Further experiments are suggested to examine the optimum N rate provision from chemical fertilizer and its ratio with organic fertilization.

Bioaccumulation and phytotoxicity of ZnO nanoparticles in soil-grown Brassica chinensis L. and potential risks

Zinc oxide nanoparticles (ZnO NPs) widely used have caught the attention of researchers, nevertheless, phytotoxicity, bioaccumulation, and potential risks thereof to the green leafy still have knowledge defects. A pot experiment was intended to cultivate pakchoi (Brassica chinensis L.) following root exposure to ZnO NPs and Zn²⁺. ZnO NPs promoted plant growth and Zn accumulation, formed a dose-dependent effect on chlorophyll and carotenoids, and induced fluctuations in antioxidant enzyme activities and alleviated the oxidative damage of pakchoi. Particularly, 1000 mg kg^-1 ZnO NPs resulted in malondialdehyde (MDA) content of pakchoi shoots that was 87% higher than control. TEM was used to observe ZnO NPs of root cells and found that its possible way to enter the plant was endocytosis. Research on the content of several co-existing nutrients showed that 100 mg kg^-1 ZnO NPs significantly (p < 0.05) promoted the absorption of Ca, P and Fe by pakchoi shoots. In parallel, the hazard quotient (HQ) was used to assess the potential health risk of ZnO NPs.

Potentially Toxic Metals in the High-Biomass Non-Hyperaccumulating Plant Amaranthus viridis: Human Health Risks and Phytoremediation Potentials

Human health risk and phytoremediation of potentially toxic metals (PTMs) in the edible vegetables have been widely discussed recently. This study aimed to determine the concentrations of four PTMs, namely Cd, Fe, Ni, and Zn) in Amaranthus viridis (leaves, stems, and roots) collected from 11 sampling sites in Peninsular Malaysia and to assess their human health risk (HHR). In general, the metal levels followed the order: roots > stems > leaves. The metal concentrations (µg/g) in the leaves of A. viridis ranged from 0.45 to 2.18 dry weight (dw) (0.05−0.26 wet weight (ww)), 74.8 to 535 dw (8.97−64.2 ww), 2.02 to 7.45 dw (0.24−0.89 ww), and 65.2 to 521 dw (7.83−62.6 ww), for Cd, Fe, Ni, and Zn, respectively. The positive relationships between the metals, the plant parts, and the geochemical factions of their habitat topsoils indicated the potential of A. viridis as a good biomonitor of Cd, Fe, and Ni pollution. With most of the values of the bioconcentration factor (BCF) > 1.0 and the transfer factor (TF) > 1.0, A. viridis was a very promising phytoextraction agent of Ni and Zn. Additionally, with most of the values of BCF > 1.0 and TF < 1.0, A. viridis was a very promising phytostabiliser of Cd and Fe. With respect to HHR, the target hazard quotients (THQ) for Cd, Fe, Pb, and Zn in the leaves of A. viridis were all below 1.00, indicating there were no non-carcinogenic risks of the four metals to consumers, including children and adults. Nevertheless, routine monitoring of PTMs in Amaranthus farms is much needed.

Contamination characteristics, source analysis and health risk assessment of heavy metals in the soil in Shi River Basin in China based on high density sampling

To explore the contamination of heavy metals in the Shi River Basin soil in China, a high density sampling of surface soil was conducted. In this study, an absolute principal component scores multiple linear regression model (APCS-MLR) was used to identify the sources of heavy metals in the soil and quantify their amounts. The methods to assess the heavy metals included a fuzzy synthetic evaluation, index and health risk assessment. The results show that heavy metals are relatively rich southwest of the study area. Their levels may be affected by natural sources, such as parent materials. The pollution caused by human factors cannot be ignored, and it is primarily influenced by traffic emissions and processing sources, which contribute 62.6%, followed by agricultural sources, such as pesticides and fertilizers, that contribute 21.1%. The risk assessment indicated that the study area was slightly to moderately polluted. All heavy metals pose higher carcinogenic and other health risks to children than adults, and ingestion is the main way that these pollutants enter the body. The carcinogenic risk of children owing to Cr from natural sources merits further study, while the carcinogenic risk to adults and the non-carcinogenic risk to both adults and children are at acceptable levels. Transportation and industrial processing sources are the main cause of the non-carcinogenic risk. The results could provide reference for reducing heavy metal pollution in the soil.

RNA-Seq Identification of Cd Responsive Transporters Provides Insights into the Association of Oxidation Resistance and Cd Accumulation in Cucumis sativus L

Greenhouse vegetable production (GVP) has grown rapidly and has become a major force for cucumber production in China. In highly intensive GVP systems, excessive fertilization results in soil acidification, increasing Cd accumulation and oxidative stress damage in vegetables as well as increasing health risk of vegetable consumers. Therefore, enhancing antioxidant capacity and activating the expression level of Cd transporter genes seem to be feasible solutions to promote plant resistance to Cd stress and to reduce accumulated Cd concentration. Here, we used transcriptomics to identify five cucumber transporter genes (CsNRAMP1, CsNRAMP4, CsHMA1, CsZIP1, and CsZIP8) in response to cadmium stress, which were involved in Cd transport activity in yeast. Ionomics, gene expression, and REDOX reaction level association analyses have shown that the transcript of CsNRAMP4 was positively correlated with Cd accumulation and antioxidant capacity of cucumber roots. The expression level of CsHMA1 was negatively correlated with Cd-induced antioxidant capacity. The overexpression of CsHMA1 significantly relieved Cd stress-induced antioxidant activities. In addition, shoots with high CsHMA2 expression remarkably presented Cd bioaccumulation. Grafting experiments confirmed that CsHMA1 contributed to the high antioxidant capacity of cucumber, while CsHMA2 was responsible for the transport of Cd from the roots to the shoots. Our study elucidated a novel regulatory mechanism for Cd transport and oxidative damage removal in horticultural melons and provided a perspective to regulate Cd transport artificially by modulating Cd accumulation and resistance in plants.

Source and Health Risk Assessment of Heavy Metals in Soil-Ginger System in the Jing River Basin of Shandong Province, North China

This study investigated the characteristics and sources of heavy metals in a soil-ginger system and assessed their health risks. To this end, 321 topsoil samples and eight soil samples from a soil profile, and 18 ginger samples with root-soil were collected from a ginger-planting area in the Jing River Basin. The average concentration of heavy metals in the topsoil followed the order: Cr > Zn > Pb > Ni > Cu > As > Cd > Hg. In the soil profile, at depths greater than 80 cm, the contents of Cr, Ni, and Zn tended to increase with depth, which may be related to the parent materials, whereas As and Cu contents showed little change. In contrast, Pb content decreased sharply from top to bottom, which may be attributable to external environmental and anthropogenic factors. Multivariate statistical analysis showed that Cr, Ni, Cu, Zn, and Cd contents in soil are affected by natural sources, Pb and As contents are significantly affected by human activities, and Hg content is affected by farmland irrigation. Combined results of the single pollution index (Pi), geo-accumulation index (Igeo), and potential ecological risk assessment (Ei and RI) suggest that soil in the study area is generally not polluted by heavy metals. In ginger, Zn content was the highest (2.36 mg/kg) and Hg content was the lowest (0.0015 mg/kg). Based on the bioconcentration factor, Cd and Zn have high potential for enrichment in ginger. With reference to the limit of heavy metals in tubers, Cr content in ginger exceeds the standard in the study area. Although Cr does not accumulate in ginger, Cr enrichment in soil significantly increases the risk of excessive Cr content in ginger.

Cyclocarya paliurus for Phytomanagement of Lead-Contaminated Soils

Cyclocarya paliurus seedlings were cultivated in three types of lead (Pb)-contaminated soils with Pb concentration of 305 ± 17 mg/kg (T1), 1964 ± 59 mg/kg (T2) and 3502 ± 107 mg/kg (T3), respectively. The results showed that after 180 days of cultivation, the contents of exchangeable and carbonate-bound Pb fractions significantly decreased in T1 and T2, but increased in T3. The growth indices of C. paliurus seedlings decreased with increasing Pb concentration; however, no difference was found between that in T1 and in Pb-free soil. The Pb concentration in the roots was an order of magnitude higher than that in the stems and in the leaves. The bioconcentration factor (BCF) of the leaves was the lowest among the three tissues investigated, and decreased with the higher concentration of Pb in the soils. These results suggest that C. paliurus can be used as a sustainable and profitable plant for the phytomanagement of Pb-contaminated soil.

Multivariate linear regression models for predicting metal content and sources in leafy vegetables and human health risk assessment in metal mining areas of Southern Jharkhand, India

The present study was intended to investigate the metal concentrations in the leafy vegetables, irrigation water, soil, and atmospheric dust deposition in the iron and copper mining areas of Southern Jharkhand, India. The study aimed to develop a multivariate linear regression (MVLR) model to predict the concentration of metals in leafy vegetables from the metals in associated environmental factors and assessment of the risk to the local population through the consumption of leafy vegetables and other allied pathways. The developed species-specific MVLR models were well fitted to predict the concentration of metals in the leafy vegetables. The coefficient of determination values (R²) was greater than 0.8 for all the species-specific models. Risk assessment was carried out considering multiple pathways of ingestion, inhalation, and dermal contact of vegetables, soil, water, and free-fall dust. Consumption of leafy vegetables was the major route of metal exposure to the local population in both the metal mining areas. The average hazard index (HI) value considering all the metals and pathways was calculated to be 5.13 and 12.1, respectively for iron and copper mining areas suggesting considerable risk to the local residents. Fe, As, and Cu were the major contributors to non-carcinogenic risk in the Iron mining areas while in the case of copper mining areas, the main contributors were Co, As, and Cu.

Plastic shed production systems: The migration of heavy metals from soil to vegetables and human health risk assessment

Plastic shed production system (PSPS) provide abundant vegetable products for human consumption. Comprehensive and accurate heavy metal (HM) risk assessment of soil and vegetable under plastic sheds is crucial for human health. Pollution assessment, bioavailability and mobility evaluation and health risk assessment of Cd, Cr, Cu, Zn Ni, Pb, and As were performed in a presentative Plastic shed production system. The concentrations of the Cd, Cu and Zn exceeded their background value. Positive I_geo values suggested that soil under plastic sheds was widely contaminated with Cd. The bioavailability of heavy metals in soils was evaluated using DTPA extraction and DGT methods. The results of both methods demonstrated that Cd, Cu, and Zn have high bioavailability, especially Cd. Analogically, the results of mobility assignment based on DIFS showed that Cd has a high migration risk due to the large available pool. Based on specific cultivation and management patterns of plastic shed production system, pH reduction and salt and nutrient accumulation may increase the heavy metals migration risk in soil under plastic sheds, while a high organic matter content may reduce the heavy metals migration risk. The average concentrations of Cd, Cr, Cu, Zn, Ni, Pb, and As in vegetables were 0.023, 0.226, 0.654, 2.984, 0.329, 0.041, and 0.010 mg/kg, respectively. All samples were well below the threshold. The order of target hazard quotient of different heavy metals caused by vegetable consumption was Cd > Cr > As > Cu, Ni, Pb, Zn, and the average total hazard index value was below 1, which demonstrated that risk of vegetable consumption in the study area. However, due to its high concentration and transfer coefficient in spinach, Cd might pose a health risk to humans, which requires special attention. In this study, Cd caused a significant issue than other HMs, whether pollution level, health risk and migration risk. DGT and DIFS can be used as an effective evaluation tool in the research of controlling heavy metals migration in soil-crop systems.

A phytoremediation coupled with agro-production mode suppresses Fusarium wilt disease and alleviates cadmium phytotoxicity of cucumber (Cucumis sativus L.) in continuous cropping greenhouse soil

Cadmium (Cd) contamination and continuous cropping obstacle often coexist in greenhouse soil and seriously restrict cucumber production. In this study, hyperaccumulator Sedum alfredii Hance was intercropped with spring cucumber (Cucumis sativus L.), then rotated with low accumulator water spinach and autumn cucumber under rational water regime, composited amendment was applied to soil before transplanting autumn cucumber. The results showed that, compared with conventional crop rotation system (Chinese cabbage and cucumber rotation), superposition management practice suppressed Fusarium wilt disease by 28.4 and 57.4% and increased yield by 35.2 and 383% for spring and autumn cucumbers, respectively. Meanwhile, photosynthetic characteristics, antioxidant system and fruit quality were significantly improved. Furthermore, this mode modified soil microbial community structure, enhanced soil enzyme activities, and simultaneously reduced soil total and phytoavailable Cd by 30.3 and 47.7%, respectively. These results demonstrated a feasible technical system to achieve phytoremediation coupled with argo-production in Cd contaminated greenhouse soil with continuous cropping obstacle and provided useful information for further revelation of interaction mechanisms between multicropping and comprehensive biofortification measurements.

Transfer of heavy metals in fruits and vegetables grown in greenhouse cultivation systems and their health risks in Northwest China

Due to the high cropping index and substantial agricultural inputs in greenhouse cultivation systems (GCS) compared to traditional farming methods, the environmental problems caused by heavy metals in GCS are becoming increasingly serious. The concentration of the heavy metals As, Cd, Cr, Cu, Pb and Zn in soil and food crops were analyzed and assessed in two study areas. There were greater accumulation of heavy metals in soils from Central Shaanxi (CS) than that from Northern Shaanxi (NS). However, heavy metal concentrations in leafy vegetables were higher in NS compared to CS, particularly Cr accumulation in leafy vegetables. Overall, leafy vegetables contained higher concentrations of heavy metals than fresh fruits and fruit vegetables from both areas. The heavy metal transfer factors (TF) for fresh fruits and fruit vegetables were as follows: Cu > Zn > Cd > Cr > As > Pb. However, in leafy vegetables, Cd had a higher TF value than the other metals tested. The target hazard quotient (THQ) values were less than 1 for fruits and vegetables, except for As in leafy vegetables from NS. The THQ values indicated that As contamination was the most serious concern, followed by Cu > Zn > Cd > Pb > Cr in both areas. The soil threshold value (STV) based on THQ showed that the level of As in leafy vegetables grown in alkaline soil was 10.85, which was inferior to the current standards. This study demonstrates the health risks associated with the heavy metal content of fruits and vegetables grown in GCS and suggests that necessary measures should be taken to reduce the accumulation of heavy metals in GCS crops in northwest China.

Effects of exogenous sulfur on maize (Zea mays L.) growth and Cd accumulation in Cd-contaminated plastic shed soil

Cadmium (Cd) pollution in plastic shed soils has become increasingly severe, posing a great threat to human health and social stability. Phytoremediation of cadmium pollution is an environmentally friendly and inexpensive remediation method. In this study, maize (Zea mays L.) was selected as the phytoremediation crop by a potted method, and the bioavailability of cadmium was investigated by adding exogenous elemental sulfur. The relationships among the sulfur content, maize growth, cadmium accumulation, and soil parameters were systematically studied. The results showed that, with the supplement of sulfur, the soil pH and activities of soil enzymes (urease, catalase, and sucrase) decreased gradually, and the available heavy metals (Cd, Cr, Zn, and Cu) in soil showed an upward trend. The optimal cadmium enrichment was achieved under T2 by increasing both the biomass of the maize plant and the cadmium concentration in roots and stems. However, T3 and T4 significantly inhibited the growth of maize roots and shoots, leading to a much lower plant biomass compared with that of CK (sulfur-free treatment) and T2. In addition, the cumulative cadmium was not increased because of the low accumulation of cadmium in some parts of the plant. Correlation analyses showed that the sulfur content was negatively correlated with soil pH and maize biomass (P < 0.01), and the cadmium content of whole maize was positively correlated with the dry weight of maize (P < 0.05) and the cadmium content in roots and stems (P < 0.01). In summary, to optimize cadmium phytoremediation of the plastic shed soil, an appropriate concentration of sulfur should be selected in practical applications to ensure that the biomass of the maize is maximized, and the cadmium concentration in different parts of the maize is increased or stabilized.

The Availability and Accumulation of Heavy Metals in Greenhouse Soils Associated with Intensive Fertilizer Application

In China, greenhouse agriculture, which provides abundant vegetable products for human consumption, has been rapidly developed in recent decades. Heavy metal accumulation in greenhouse soil and products obtained have received increasing attention. Therefore, the availability and accumulation of cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) and their association with soil pH, soil organic matter (SOM), inorganic nitrogen (IN), total nitrogen (TN), available phosphorus (AP), and planting year (PY) in greenhouse soils were analyzed. The results showed that the mean concentrations of available Cd, Cu, Ni, Pb, and Zn were 17.25 μg/kg, 2.89, 0.18, 0.36, and 5.33 mg/kg, respectively, while their suggested levels in China are 0.6, 100, 100, 120, and 250 mg/kg. Cd, Cu, and Zn might be mainly originated from fertilizer application. A lower soil pH significantly increased the available Cu, Ni, and Zn concentrations and reduced Cd, Cu, Ni, and Zn accumulation. A higher AP significantly increased the proportions of available Cu, Ni, and Zn and elevated Cd, Cu, and Zn accumulation. There was a strong positive correlation between Cd, Pb, and Zn availability and TN, while IN was negatively related to the availability and accumulation of Cu and Zn. It was concluded that chemical fertilizer application increased the availability of Cu, Ni, Pb, and Zn and the accumulation of Cd, Cu, and Zn. Manure application clearly elevated the accumulation and availability of Cd and Zn in greenhouse soil.

Using pXRF to assess the accumulation, sources, and potential ecological risk of potentially toxic elements in soil under two greenhouse vegetable production systems in North China

Intensive greenhouse vegetable production (GVP) has increased the pollution risk of potentially toxic elements (PTEs) in soils. This study examined the accumulation, sources, and potential ecological risk of six PTEs (Cu, Zn, As, Ni, Pb, and Cr) in soil under two GVP (solar greenhouse (SG) and round-arched plastic greenhouse (RAPG)) systems by portable X-ray fluorescence spectroscopy (pXRF) and conventional laboratory analysis. The results indicated that all PTE concentrations were lower than their corresponding thresholds in GVP soils, presenting a low potential ecological risk in both GVP soils according to risk indices (RI ≤ 40.67). As, Ni, Pb, and Cr were not significantly accumulated in both GVP soils. Although Cu and Zn accumulated in both GVP soils, their accumulation extents in SG soil were both greater than that in RAPG soil. Cu and Zn were mainly originated from anthropogenic activities based on multivariate statistical analysis, which were greatly associated with excessive manure application. Overall, pXRF can identify the accumulation difference of PTEs between the two GVP soils, which is generally consistent with conventional laboratory analysis. Hence, pXRF can be a promising alternative to conventional laboratory analysis for rapid assessment of PTEs accumulation, sources, and the potential ecological risk in the two GVP soils. Although PTEs had a low ecological risk, Cu and Zn accumulation in SG soil was increased with the planting years. Therefore, rational application of livestock manure containing high levels of Cu and Zn should inspire strategies to mitigate the environmental risk in GVP soils, especially in SG soil.

Bioavailability of cadmium to celery (Apium graveolens L.) grown in acidic and Cd-contaminated greenhouse soil as affected by the application of hydroxyapatite with different particle sizes

Cadmium contamination in greenhouse vegetable fields greatly limited the sustainable production especially of leafy vegetables. Hydroxyapatite (HAP), as a common soil amendment, has been widely used in the remediation of Cd-contaminated soils, while its remediation efficiency greatly depends on its particle sizes. In this study, a rhizobag pot experiment was conducted to investigate the effects of HAP (<60 nm, <12 μm and <80 μm) on bioavailability of Cd to celery grown in acidic and slightly Cd-contaminated greenhouse soil. The results suggested that HAP with the largest particle size (<80 μm) had the best effectiveness in reducing Cd uptake especially by the edible part of celery. Specifically, the increase in HAP (<80 μm) addition from 0.5% to 3% prominently reduced Cd concentrations in celery shoot by 19.6%-76.8% as compared with the untreated group. Also, adding HAP (<80 μm) especially at 3% significantly decreased translocation factor (TF) of Cd from celery root to shoot by 30.6% and reduced bioconcentration factor (BCF) of Cd from rhizosphere soil to celery shoot by 76.4%. These were predominantly associated with the significantly increased soil pH and the subsequently decreased soil CaCl₂-Cd concentration after adding HAP (<80 μm). Overall, although rhizosphere soil pH was the key factor in controlling Cd uptake by edible celery and regulating BCF and TF of Cd, insignificant root-induced acidification had limited effect on the immobilization efficiency of Cd by HAP (<80 μm). In conclusion, HAP (<80 μm) has good potential for the remediation of Cd-contaminated greenhouse soils.

Assessment of the health risks of heavy metals in soils and vegetables from greenhouse production systems in Iran

Overuse of chemical and organic fertilizers in greenhouse (GH) crop production may cause the accumulation of heavy metals in soils and risks to human health. The aims of this study were to compare physical and chemical properties of GH with open-field (OF) soils, to clarify the buildup of heavy metals and phosphorus (P) in soils, and to assess the risks of selected heavy metals in soils and cucumber (Cucumis sativus L.) and tomato (Lycopersicon esculentum Mill.) from GH vegetables in Hamedan, western Iran. The average total and Olsen P of GH soils were significantly higher than the OF soils for both vegetables. The order of total and available heavy metal content in tomato GH soils has been set as zinc (Zn) > nickel (Ni) > chromium (Cr) > lead (Pb) > copper (Cu) > cadmium (Cd) and Zn > Cr > Cu > Pb > Ni > Cd, respectively. The same order was found for cucumber GH soils, except that the position of Pb and Cu was changed. The results indicated that in both GH cucumber and tomato soils, the mean content of total and available Zn, available Cu, Ni, and Pb, was extra than in OF soils. There were no significant differences between average total Cr, Cu, Ni, and Pb in GH and OF soils. Tomato vegetables had higher heavy metal content and transfer factors, particularly for Cr than cucumber vegetables. According to the health risk indices, Cr and Pb represented a high potential risk for health through cucumber and tomato consumption. There were limited Cd, Cu, Pb, and Zn inputs from the irrigation waters, while the input of Cr and Ni may be important. However, the amount of manure application and heavy metal content of the manures was significant.

Differences in cadmium absorption by 71 leaf vegetable varieties from different families and genera and their health risk assessment

Leaf vegetables have strong capabilities to take up cadmium (Cd) compared to other vegetable varieties. Until now, the differences in Cd uptake and accumulation by leaf vegetables from different families and genera and the related health risks were unknown. To remedy this, we studied 71 leaf vegetables (multiple genotypes within 17 categories of vegetables) in soil cultivation experiments (3 Cd treatment levels). Results showed that at 2.12 mg kg^-1 Cd treatment, the dry weight of only five genotypic varieties from the families Brassicaceae and Asteraceae significantly decreased compared to the control, suggesting their weak Cd tolerances. Vegetables from the Brassicaceae, Asteraceae, Apiaceae, and Convolvulaceae families had stronger Cd absorption capabilities, whereas those from the Liliaceae and Amaranthaceae families had weaker ones. Cluster analysis found that the 17 vegetable categories could be divided into three groups: vegetables with high Cd accumulation capabilities were Lactuca sativa L.var. ramosa Hort. and Lactuca sativa var. longifoliaf. Lam. Vegetables with moderate Cd accumulation capabilities were bok choy, napa cabbage, choy sum, leaf mustard, Lactuca sativa L., Sonchus oleraceus L., celery, coriander, and water spinach. Vegetables with low Cd accumulation capabilities were cabbage, crown daisy, garlic chive, Allium ascalonicum, Gynura cusimbua, and edible amaranth. Estimated daily intake (EDI) and target hazard quotient (THQ) analysis results showed that 100% genotypes of vegetables from the Apiaceae and Convolvulaceae families had health risks; 100% genotypes of Lactuca sativa L., Sonchus oleraceus L., Lactuca sativa L. var. ramosa Hort., and Lactuca sativa var. longifoliaf. Lam from the Asteraceae family carried high risks. Of vegetables in the Brassicaceae family, 42.9% showed risks. Vegetables from the Amaranthaceae and Liliaceae families, Gynura cusimbua and crown daisy from the Asteraceae family, and cabbage from the Brassicaceae family all displayed relatively low risks (all 100%).

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

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

Risk assessment and prediction for toxic heavy metals in chestnut and growth soil from China

BACKGROUND

Toxic heavy metals (THMs) cause severe environmental hazards and threaten human health through various consumption of food stuff. However, little is known of THMs in chestnuts. In this study, the risk assessment and prediction of THMs [lead (Pb), arsenic (As), chromium (Cr), cadmium (Cd) and mercury (Hg)] in chestnuts and growth soils from China were investigated.

RESULTS

The main detected THMs in chestnuts and growth soils were As and Cd. The total pollution levels of the five THMs (Nemerow pollution indexes, NPIs) were 0.062 and 1.06, respectively. The dietary risks for children were higher than those of adults, especially short-term non-carcinogenic risk. The main combined risks from the relationships between THMs were Pb-Cr (r = 0.85, P < 0.01) in chestnuts and Pb-As (r = 0.59, P < 0.01) in growth soils. The risk source was found to be the uptake effect of THMs from soil to chestnut, with the highest bioaccumulation factors (BCFs) of Cd (0.254). Several comprehensive risk models were established with the highest coefficient of determination (R² ) of 0.79. In addition, the main contribution rates of different soil parameters to comprehensive risk of THMs uptake were 49.8% (Cd), 23.4% (pH), 13.8% (Cr) and 13.0% (organic carbon).

CONCLUSION

The total pollution levels of THMs fell outside of the safety domain in growth soils. Furthermore, more attention needs to be paid to Cd pollution owing to its low environment background value and high accumulation ability. Three main soil parameters (Cr content, pH, organic carbon) played important roles in the formations and accumulations of THMs in chestnuts. © 2019 Society of Chemical Industry.

Heavy metals in food crops: Health risks, fate, mechanisms, and management

Food security is a high-priority issue for sustainable global development both quantitatively and qualitatively. In recent decades, adverse effects of unexpected contaminants on crop quality have threatened both food security and human health. Heavy metals and metalloids (e.g., Hg, As, Pb, Cd, and Cr) can disturb human metabolomics, contributing to morbidity and even mortality. Therefore, this review focuses on and describes heavy metal contamination in soil-food crop subsystems with respect to human health risks. It also explores the possible geographical pathways of heavy metals in such subsystems. In-depth discussion is further offered on physiological/molecular translocation mechanisms involved in the uptake of metallic contaminants inside food crops. Finally, management strategies are proposed to regain sustainability in soil-food subsystems.

Heavy metal and soil nutrient accumulation and ecological risk assessment of vegetable fields in representative facilities in Shandong Province, China

Shandong is one of the main areas for protected vegetable cultivation in China. A total of 88.5% of the facility soil samples had a pH between 7.0 and 8.4, indicating the majority of the soils were alkaline. Key properties, including total nitrogen (TN), organic matter (OM), electrical conductivity (EC), available phosphorus (AP), and available potassium (AK), showed an increasing trend with the number of years. The geoaccumulation index (I_geo) indicated that the Cd and Hg contents ranged from uncontaminated to moderate contaminated, while the risk of Hg and Cd reached the class of considerable risk as indicated by the potential ecological risk factor ([Formula: see text]). The mean of Hakanson potential ecological risk index (RI) was 234.00, with the highest contribution from Hg (55.26%), followed by Cd (38.81%). It indicated that the survey area was at the moderate-risk level and Hg had the highest potential ecological risk factor, followed by Cd.

Occurrence, speciation, and risks of trace metals in soils of greenhouse vegetable production from the vicinity of industrial areas in the Yangtze River Delta, China

The effect of industrial activities on trace metals in farmland of rapidly industrializing regions in developing countries has increasingly been a concern to the public. Here, soils were collected from 13 greenhouse vegetable production (GVP) farms or bases near industrial areas in the Yangtze River Delta of China to investigate the occurrence, speciation, and risks of Cr, Cu, Zn, Cd, Ni, and Pb in GVP soil. The results revealed that the main metal elements causing GVP soil pollution were Cd, Zn, Ni, and Cu, of which contamination levels were generally unpolluted to moderately polluted. Zinc pollution was mainly attributed to heavy fertilization, while Cd, Ni, and Cu pollution may be greatly ascribed to industrial effluents and coal combustion. Metal speciation studies showed that most of Cr, Ni, Cu, and Zn was present in residual fraction while more than half of Cd and Pb was present in non-residual fractions. Additionally, pollution of Cd, Cu, Ni, and Zn in GVP soil increased their corresponding mobile fractions. Risk assessment using potential ecological risk index and risk assessment code showed that Cd was the major risk contributor. Specifically, Cd generally posed moderate or considerable ecological risk as well as displayed medium or high mobility risk in GVP soil. Thus, great attention should be paid to the contribution of both industrial discharges and intensive farming to soil pollution by trace metals, especially Cd, because of its high mobility risk.

A comprehensive mitigation strategy for heavy metal contamination of farmland around mining areas - Screening of low accumulated cultivars, soil remediation and risk assessment

A three-year field test was conducted in an area surrounding past mining activity (mining area) to investigate the value of a novel comprehensive remediation strategy for Cd and Pb contamination, which included screening of low accumulated vegetable cultivars that take up Cd and Pb less than normal cultivars, in situ soil remediation using different soil amendments, and health risk assessment that evaluates the possibility of safe consumption for the vegetables. Results showed that cultivar Huoqing 91-5C of which vegetable was selected as a low accumulator of Cd and Pb in a soil contaminated with 0.5 mg kg^-1 and 8180 mg kg^-1 total Cd and Pb concentrations, respectively. Addition of 20 t ha^-1 of biochar with 2 t ha^-1 of calcium superphosphate in 10 cm depth could decrease available Cd and Pb by 70% and 85% after 1 year, respectively. Following treatments, hazard quotients for adults and children were below 1, indicating that the vegetables grown were safe for human consumption. The total cost of remediation was $3885 ha^-1, so the cost of the remediation of the combination of Cd and Pb was economic in this mining area.

Probabilistic risk assessment (Monte Carlo simulation method) of Pb and Cd in the onion bulb (Allium cepa) and soil of Iran

Recently, the exposure to heavy metals through the consumption of vegetables has become a global concern. In this regard, the current study was aimed to measure the concentrations of lead (Pb) and cadmium (Cd) in the collected onion bulb samples as well as the surrounded soil using a flame atomic absorption spectrometer (FAAS). Additionally, the target hazard quotient (THQ) for males and females in all age groups of consumers were estimated by using Monte Carlo Simulation (MCS) method. Furthermore, the soil threshold values (STVs) were evaluated to investigate the heavy metal contents in the soil based on the established standard limits. In this context, 45 onion bulbs (HashtBandi region, 25 and Ravang region, 20) and 41 soil (HashtBandi region, 21 and Ravang region, 20) samples were collected (March-May of 2016). The average concentrations of Pb in the onions from HashtBandi and Ravang regions were determined as 0.0052 ± 0.0011 and 0.0061 ± 0.0022 mg/kg, and for Cd were 0.0095 ± 0.0024 and 0.0011 ± 0.0035 mg/kg, respectively. The average concentration of Pb in the soil from HashtBandi and Ravang regions were measured as 3.99 ± 3.77 and 2.03 ± 0.69 mg/kg, and for Cd, the corresponding values were determined as 2.21 ± 3.17 and 2.22 ± 0.92 mg/kg, respectively. The average concentration of Pb and Cd in both investigated onion bulb and soil were lower than Iranian national (onion bulb: Pb = 0.1 mg/kg, Cd = 0.05 mg/kg) and FAO/WHO (onion bulb: Pb = 0.3 mg/kg, Cd = 0.1 mg/kg; soil: Pb = 50 mg/kg, Cd = 0.3 mg/kg) standard limits. Moreover, the THQ and total target hazard quotient (TTHQ) for males and females in all age groups were less than 1 value. Therefore, no risk of the exposure to Pb and Cd as result of onion bulb consumption was reported. STVs for Pb and Cd in the HashtBandi region were calculated as 3.99 and 2.21 mg/kg, and Ravang as 2.03 and 2.22 mg/kg, respectively. Due to the higher calculated STVs for Cd while compared with the established standard limit for the soil, the further revisions regarding the heavy metal standard limits in the soil were recommended.

Source Contribution Analysis and Collaborative Assessment of Heavy Metals in Vegetable-Growing Soils

Source quantification of heavy metals in farmland is essential for developing and implementing restoration strategies. We used various data analyses to identify and quantify sources of arsenic, cadmium, chromium, copper, mercury, nickel, lead, and zinc in vegetable-growing soils. A new method of collaborative assessment, combining soil environmental quality and agricultural product safety, showed that approximately 5.20% of cultivation systems were multi-contaminated by heavy metals. The nonlinear relationship between pollution sources and the comprehensive contamination situation was established, deriving from a fitted bivariate model. The model revealed that anthropogenic sources and natural origins accounted for 65.8-86.0 and 34.2-14.0% of the comprehensive pollution, respectively. These results suggested that both human activities and natural factors contributed to the decline of local soil quality and the influence of the former was more substantial than that of the latter.

Soil threshold values for cadmium based on paired soil-vegetable content analyses of greenhouse vegetable production systems in China: Implications for safe food production

Greenhouse vegetable production (GVP) is the major type of vegetable production in China. However, dietary exposure of heavy metals through vegetable consumption has been identified as a potential risk to human health. To ensure safety of vegetables, soil threshold values (STVs) of cadmium (Cd) in GVP systems were assessed based on analysis of soil-vegetable Cd contents in relation to human health risk. Contents of Cd were determined in 324 sampled soil-vegetable pairs from five GVP systems in three Chinese provinces. Soil Cd contents ranged from 0.07 to 1.32 mg kg^-1, with 17.9% of sampled soils exceeding current Chinese threshold values. Vegetable Cd contents ranged from 0.0003 to 0.546 mg kg^-1, with 8.6% exceeding permissible maxima. Vegetable type and soil pH significantly affected Cd transfer from soil to vegetable with lower transfer at neutral (6.5 < pH ≤ 7.5) to alkaline (pH > 7.5) soils and uptake decreasing in the order: Leafy > rootstalk > fruit. Consequently, both soil pH and vegetable type should be taken into consideration as suggested when revising current STVs for Cd in GVP systems in order to capture the health risk correctly and ensure safe vegetable consumption.

Citrus Epicarp-Derived Biochar Reduced Cd Uptake and Ameliorates Oxidative Stress in Young Abelmoschus esculentus (L.) Moench (okra) Under Low Cd Stress

Due to the important role of biochar (BC) in reducing metal-toxicity in plants, this study was aimed at assessing the potential of citrus epicarp-derived BC in ameliorating Cd toxicity in young Abelmoschus esculentus (okra) under low Cd toxicity. Okra was grown in soil amended with BC at four treatment levels for 49 days as follows: control (A), sole 1.4 mg Cd/kg-spiked soil (B), 1.4 mg Cd/kg-spiked soil + 1% BC (C) and 1.4 mg Cd/kg-spiked soil + 3% BC (D). The results showed a dose-dependent reduction in shoot accumulation of Cd due to the BC application. In addition, compared to control and sole Cd-amended soil, BC treatments (both at 1% and 3% w/w) decreased the oxidative stress, and enhanced activities of enzymatic and non-enzymatic antioxidants in the young okra. Generally, the application of BC to the soil was effective in ameliorating the Cd-induced oxidative stress in okra with limited shoot bioaccumulation of Cd.

Bioaccumulation and sources of metal(loid)s in lilies and their potential health risks

Dietary intake of metal(loid)s can seriously affect human health, but the levels, the bioaccumulation, sources and related health risks of As, Cd, Cr and Pb in cultivated lilies, particularly for Lilium davidii var. unicolor, remain unresolved. We collected 35 lily samples aged 1-6 years from farmlands of two types of soil (heilu soils and loessal soils) in Qilihe district in 2016 and analysed the concentrations of As, Cd, Cr and Pb in bulbs, the soil-bulb bioaccumulation and the potential sources of these elements in bulbs. Non-carcinogenic and carcinogenic risks by consuming lilies were also assessed. Concentrations of four elements decreased in the order of Cr > Pb > Cd > As, and soil-bulb BCFs in the order of BCF_Cd > BCF_Cr > BCF_Pb > BCF_As. The Cd concentration of bulbs of lilies which grew in heilu soils was statistically higher than that of bulbs of lilies which grew in loessal soils, and the Cd concentration of bulbs of lilies aged 1-3 years was statistically higher than that of bulbs of lilies aged 4-6 years. Levels and soil-bulb BCFs of Cr and Pb of two-bulbed lilies were statistically higher than those of one-bulbed lilies. Farmyard manure may be a primary source of Cd in soil. There existed overall potential non-carcinogenic effects by exposure to the combination of four elements. Dietary intake of Cr posed carcinogenic risks to both adults and children. Non-carcinogenic and carcinogenic risks were higher for adults than children. Concluding, the edible parts of lily were significantly polluted by Cr and Pb but not by As and Cd. The number of bulbs significantly impacted concentrations and soil-bulb BCFs of Cr and Pb, but the reason for which needs further studies. Non-carcinogenic and carcinogenic risks caused by lily consumption should not be neglected.

Heavy metal contamination in soils and vegetables and health risk assessment of inhabitants in Daye, China

Objective

This study was performed to evaluate the state of heavy metal contamination in soil and vegetables and assess the health risk of inhabitants in the mine-affected area and area far from the mine (reference area) in Daye, China.

Methods

The heavy metal concentrations in soil and vegetable samples were detected by inductively coupled plasma mass spectrometry. Residents’ exposure parameters were obtained through a questionnaire survey. A health risk assessment model recommended by the United States Environmental Protection Agency was used to evaluate the residents’ risk of oral exposure.

Results

The copper, lead, cadmium, and arsenic concentrations in soil and in vegetables were higher in the mine-affected area than in the reference area. The health risk of residents in the reference area was within the acceptable range (hazard index < 1, carcinogen risk < 10⁻⁴). In the contaminated area, however, the mean hazard index was 2.25 for children and 3.00 for adults, and the mean carcinogen risk was 4.749 × 10⁻⁴ for children and 0.587 × 10⁻⁴ for adults.

Conclusions

Potential health risks exist for inhabitants near the mine area. Cadmium and arsenic should be paid more attention as risk sources.

Derivation of reliable empirical models describing lead transfer from metal-polluted soils to radish (Raphanus sativa L.): Determining factors and soil criteria

Reliable models describing Pb transfer from soils to food crops are useful in the improvement of soil protection guidelines. This study provides mechanistic insights from in-situ soil solution measurement on the Pb uptake in the root tissues (RF) of radish, grown in 25 representative Pb-contaminated agricultural soils. Lead speciation and regression analysis indicate that >88.6% of the variation in RF Pb is attributable to free Pb²⁺ activity (aPb²⁺) in the soil solution, which is predominantly controlled by pH and DOC. Higher DOC would increase the total dissolved Pb (C_Sol-Pb) in the soil solution but reduce the bioavailability of Pb to radish. C_Sol-Pb performs poorly in predicting RF Pb unless pH and DOC are included. However, 0.01M CaCl₂ extractable Pb (C_CC-Pb) alone can satisfactorily predict RF Pb, attributable to the fact that C_CC-Pb is consistent with aPb²⁺. C_CC-Pb can be predicted using C_Sol-Pb and pH. Total soil Pb (C_T-Pb), or 0.43M HNO₃ extractable Pb (C_NA-Pb) has a strong, non-linear correlation with C_Sol-Pb or C_CC-Pb and it is therefore not surprising that C_T-Pb or C_NA-Pb, together with pH and CEC, can also satisfactorily predict RF Pb. Derived models are effective in identification of soils where RF Pb exceeds the food quality standard (FQS). Soil Pb criteria based on C_T-Pb, C_NA-Pb and C_CC-Pb are derived by inverse use of empirical models. The derived Pb criterion (target value) based on C_CC-Pb is 0.02mgkg^-1 and the stricter criterion (safe value) is 0.01mgkg^-1, which allows a 5% probability for RF Pb to exceed FQS. Safe values based on C_T-Pb and C_NA-Pb ranged from 26 to 1036mgkg^-1 and 9 to 745mgkg^-1, respectively.

Assessment of edibility and effect of arbuscular mycorrhizal fungi on Solanum melongena L. grown under heavy metal(loid) contaminated soil

Arbuscular mycorrhizal fungi (AMF) aids in plant establishment at heavy metal(loid) (HM) contaminated soils, strengthening plant defense system along with promoting growth. A pot experiment was carried out to evaluate the effect of AMF on eggplants grown under HM stress. Further, the potential health risks of HM exposure to the humans via dietary intake of eggplant were also estimated. Results showed that AMF application improved growth, biomass and antioxidative defense response of plants against HM stress. Significant difference (p ≤ 0.001) in parameters under study was found on increasing metal dose and on application of AMF. Among metal(loid)s maximum uptake was recorded for Pb (29.64mgkg^-1 in roots; 23.08mgkg^-1 in shoot) followed by As (3.84mgkg^-1 in roots; 8.20mgkg^-1 in shoot) and, Cd (0.96mgkg^-1 in roots; 2.12mgkg^-1 in shoot). Based on the accumulation of HM in edible part, Hazard Quotient (HQ) was calculated. HQ was found to be > 1 for Pb, which highlights the risks associated with consumption of Eggplants grown on Pb contaminated soil. However this potential, which was further enhanced by application of AMF, can be harnessed for on-site remediation of Pb contaminated soils. The content of Cd and As in the edible part was found to be within safe limits (HQ < 1) when compared to chronic reference dose stated by USEPA.

Multiple factors impact the contents of heavy metals in vegetables in high natural background area of China

A field survey was conducted to investigate the concentrations of chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb) in vegetables, corresponding cultivated soils and irrigation waters from 36 open sites in high natural background area of Wuzhou, South China. Redundancy analysis, Spearman's rho correlation analysis and multiple regression analysis were adopted to evaluate the contributions of impacting factors on metal contents in the edible parts of vegetables. This study concluded that leafy and root vegetables had relatively higher metal concentrations and adjusted transfer factor values compared to fruiting vegetables according to nonparametric tests. Plant species, total soil metal content and soil pH value were affirmed as three critical factors with the highest contribution rate among all the influencing factors. The bivariate curve equation models for heavy metals in the edible vegetable tissues were well fitted to predict the metal concentrations in vegetables. The results from this case study also suggested that it could be one of efficient strategies for clean agricultural production and food safety in high natural background area to breed vegetable varieties with low heavy metal accumulation and to enlarge planting scale of these varieties.

Accumulation, sources and health risks of trace metals in elevated geochemical background soils used for greenhouse vegetable production in southwestern China

Greenhouse vegetable cultivation with substantive manure and fertilizer input on soils with an elevated geochemical background can accumulate trace metals in soils and plants leading to human health risks. Studies on trace metal accumulation over a land use shift duration in an elevated geochemical background scenario are lacking. Accumulation characteristics of seven trace metals in greenhouse soil and edible plants were evaluated along with an assessment of the health risk to the consumers. A total of 118 greenhouse surface soils (0-20cm) and 30 vegetables were collected from Kunming City, Yunnan Province, southwestern China, and analyzed for total Cd, Pb, Cu, Zn, As, Hg, and Cr content by ICP-MS and AFS. The trace metals were ordered Cu>Cd>Hg>Zn>Pb>As>Cr in greenhouse soils accumulation level, and the geo-accumulation index suggested the soil more severely polluted with Cd, Cu, Hg and Zn. The greenhouse and open-field soils had significant difference in Cd, Cr and Zn. The duration of shift from paddy to greenhouse land-use significantly influenced trace metal accumulation with a dramatic change during five to ten year greenhouse land-use, and continuous increase of Cd and Hg. A spatial pattern from north to south for Cd and Hg and a zonal pattern for Cu and Zn were found. An anthropogenic source primarily caused trace metal accumulation, where the principal component analysis/multiple linear regression indicated a contribution 61.2%. While the assessment showed no potential risk for children and adults, the hazard health risks index was greater than one for adolescents. The extended duration of land use as greenhouses caused the trace metal accumulation, rotation in land use should be promoted to reduce the health risks.

Soil environmental quality in greenhouse vegetable production systems in eastern China: Current status and management strategies

Greenhouse vegetable production (GVP) has become an important source of public vegetable consumption and farmers' income in China. However, various pollutants can be accumulated in GVP soils due to the high cropping index, large agricultural input, and closed environment. Ecological toxicity caused by excessive pollutants' accumulation can then lead to serious health risks. This paper was aimed to systematically review the current status of soil environmental quality, analyze their impact factors, and consequently to propose integrated management strategies for GVP systems. Results indicated a decrease in soil pH, soil salinization, and nutrients imbalance in GVP soils. Fungicides, remaining nutrients, antibiotics, heavy metals, and phthalate esters were main pollutants accumulating in GVP soils comparing to surrounding open field soils. Degradation of soil ecological function, accumulation of major pollutants in vegetables, deterioration of neighboring water bodies, and potential human health risks has occurred due to the changes of soil properties and accumulation of pollutants such as heavy metals and fungicides in soils. Four dominant factors were identified leading to the above-mentioned issues including heavy application of agricultural inputs, outmoded planting styles with poor environmental protection awareness, old-fashion regulations, unreasonable standards, and ineffective supervisory management. To guarantee a sustainable GVP development, several strategies were suggested to protect and improve soil environmental quality. Implementation of various strategies not only requires the concerted efforts among different stakeholders, but also the whole lifecycle assessment throughout the GVP processes as well as effective enforcement of policies, laws, and regulations.

Accumulation of trace elements in edible crops and poplar grown on a titanium ore landfill

Urban gardening has recently experienced rapid development; however, the risk of the transfer of toxic elements from neighboring industry needs to be evaluated. We performed a multi-elemental analysis with several common edible crops (cucumber, pepper, cabbage, and lettuce) and poplar grown directly on a titanium ore landfill as a maximized scenario of exposure. Despite elevated concentrations of soil Ca, Fe, Mn, and Ti resulting from the industrial process, we did not register higher accumulation of these elements in the edible parts of crops or in poplar leaves grown on red gypsum compared with the control soil. Only S concentrations were higher in plants grown on the red gypsum, especially for cabbage. The principal component analysis among elements for plants grown on red gypsum indicated that S and Mn were accumulated by different plant species than Cd, Cu, and Zn. The poplar clone had a significantly higher transfer of S and Cr than the control and is a suitable tree species for monitoring element transfer to vegetation in this industrial context. By comparing our data with tolerable daily intake (TDI) recommendations, we demonstrated the low risk of cultivating edible crops directly on an industrial substrate in a maximized scenario of exposure, except for Cr, for which the toxicity depends on the bioavailable form. However, we did not consider the cumulative effects of the various elements because there are no current guidelines, and further research is needed to address this question.

Heavy metals in intensive greenhouse vegetable production systems along Yellow Sea of China: Levels, transfer and health risk

Recently, greenhouse vegetable production (GVP) has grown rapidly and counts a large proportion of vegetable production in China. In this study, the accumulation, health risk and threshold values of selected heavy metals were evaluated systematically. A total of 120 paired soil and vegetable samples were collected from three typical intensive GVP systems along the Yellow Sea of China. Mean concentrations of Cd, As, Hg, Pb, Cu and Zn in greenhouse soils were 0.21, 7.12, 0.05, 19.81, 24.95 and 94.11 mg kg^-1, respectively. Compared to rootstalk and fruit vegetables, leafy vegetables had relatively high concentrations and transfer factors of heavy metals. The accumulation of heavy metals in soils was affected by soil pH and soil organic matter. The calculated hazard quotients (HQ) of the heavy metals by vegetable consumption decreased in the order of leafy > rootstalk > fruit vegetables with hazard index (HI) values of 0.61, 0.33 and 0.26, respectively. The HI values were all below 1, which indicates that there is a low risk of greenhouse vegetable consumption. Soil threshold values (STVs) of heavy metals in GVP system were established according to the health risk assessment. The relatively lower transfer factors of rootstalk and fruit vegetables and higher STVs suggest that these types of vegetables are more suitable for cultivation in greenhouse soils. This study will provide an useful reference for controlling heavy metals and developing sustainable GVP.

Determination and evaluation of heavy metals in soils under two different greenhouse vegetable production systems in eastern China

The evaluation of heavy metals (HMs) in greenhouse soils is crucial for both environmental monitoring and human health; thus, it is imperative to determine their concentrations, identify their sources and assess their potential risks. In this study, eight metals (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in 167 surface soils were investigated in two representative greenhouse vegetable systems of China: perennial solar greenhouse (SG) and seasonal plastic greenhouse (PG). The results indicated accumulations of Cd, Cu, Hg and Zn in the SG soils and Cd, Pb, Hg and Zn in the PG soils, with higher concentrations than the background values. In particular, Cd and Hg exhibited high levels of pollution under both GVP systems due to their positive Igeo values. Principle component analysis (PCA) and correlation analysis suggested that Cd, Cu, Hg and Zn in the SG soils and Cd, Hg and Zn in the PG soils were mainly related to intensive farming practices; Pb in the PG soils was significantly affected by atmospheric deposition. The results showed that soil characteristics, in particular soil organic matter, total nitrogen and total phosphorus, exerted significant influence on Hg, Cu, Cd, and Zn under the SG system. However, the HMs in the PG soils were weakly affected by soil properties. Overall, this study provides comparative research on the accumulation, potential risks and sources of HMs in two typical greenhouse soils in China, and our findings suggest that, Cd and Hg in both greenhouse soils could potentially represent environmental problems.