Heavy Metals Bioconcentration from Soil to Vegetables and Assessment of Health Risk Caused by Their Ingestion

The present study was undertaken to assess the non-carcinogenic human health risk of heavy metals through the ingestion of locally grown and commonly used vegetables viz. Raphanus sativus (root vegetable), Daucus carota (root vegetable), Benincasa hispida (fruit vegetable) and Brassica campestris leaves (leafy vegetable) in a semi-urbanized area of Haryana state, India. Heavy metal quantification of soil and vegetable samples was done using flame atomic absorption spectrophotometer. Lead, cadmium and nickel concentration in vegetable samples varied in range of 0.12–6.54 mg kg^?1, 0.02–0.67 mg kg^?1 and <0.05–0.41 mg kg^?1, respectively. Cadmium and lead concentration in some vegetable samples exceeded maximum permissible limit given by World Health Organization/Food and Agriculture Organization and Indian standards. Much higher concentrations of Pb (40–190.5 mg kg^?1), Cd (0.56–9.85 mg kg^-1) and Ni (3.21–45.87 mg kg^?1) were reported in corresponding vegetable fields’ soils. Correlation analysis revealed the formation of three primary clusters, i.e. Cu–Cd, Cd–Pb and Ni–Zn in vegetable fields’ soils further supported by cluster analysis and principal component analysis. Bioconcentration factor revealed that heavy metals’ uptake was more by leafy vegetable than root and fruit vegetables. Hazard index of all the vegetables was less than unity; thus, the ingestion of these vegetables is unlikely to pose health risks to the target population.     

Health Risk Assessment of Heavy Metals in Urban Soil of Karachi,Pakistan

The potential health risk due to lifetime exposure to copper, lead, chromium, zinc, and iron in urban soil of Karachi, Pakistan, was evaluated. Mean concentrations of Cu, Pb, Cr, Zn, and Fe in topsoil samples were 33.3 ± 12.8, 42.1 ± 55.8, 9.6 ± 4.2, 99.5 ± 37.3, and 908.4 ± 57.8 mg kg^?1, respectively. A U.S. Environmental Protection Agency model was adopted for the carcinogenic and non-carcinogenic risk assessment from different exposure pathways. Risk assessment indicated that the overall results for the carcinogenic risk were insignificant. However, the carcinogenic risk from Pb due to oral ingestion of soil exceeded the value of 1 × 10^?6, in some areas of the city. It indicates that the exposure to Pb-contaminated soil may cause adverse health effects in humans, especially in children. The Hazard Quotient (HQ) for different metals through ingestion and dermal pathways was also found to be less than 1. The combined Hazard Index (HI) for children through different routes of exposure was 8.9 times greater than for adults. It indicates that the children are more susceptible to non-carcinogenic health effects of trace metals compared to adults. Particularly, non-carcinogenic risk of Pb to children via oral ingestion needs special attention.     

Enhanced Methane Production from Anaerobic Digestion of Disintegrated and Deproteinized Excess Sludge

To improve biogas yield and methane content in anaerobic digestion of excess sludge from the wastewater treatment plant, the sludge was disintegrated by using various methods (sonication, alkaline and thermal treatments). Since disintegrated sludge contains a high concentration of soluble proteins, the resulting metabolite, ammonia, may inhibit methane generation. Therefore, the effects of protein removal from disintegrated sludge on methane production were also studied. As a result, an obvious enhancement of biogas generation was observed by digesting disintegrated sludge (biogas yield increased from 15 to 36 ml/g COD_added·day for the raw excess sludge and the sonicated sludge, respectively). The quality of biogas was also improved by removing proteins from the disintegrated sludge. About 50% (w/w) of soluble proteins were removed from the suspension of disintegrated sludge by salting out using 35 g MgCl₂·6H₂O/l and also by isoelectric point precipitation at pH 3.3. For deproteinized sludge, methane production increased by 19%, and its yield increased from 145 ml/g COD_removed to 325 ml/g COD_removed. Therefore, the yield and quality of biogas produced from digestion of excess sludge can be enhanced by disintegrating the sludge and subsequent protein removal. Revisions requested 14 November 2005; Revisions received 13 January 2006     

Health Risk Assessment of Consumption of Heavy Metals in Market Food Crops from Sialkot and Gujranwala Districts,Pakistan

This study was performed to investigate the potential health risk of heavy metals (HMs) through consumption of market food crops (MFCs) in the Sialkot and Gujranwala districts, Pakistan. Both study areas are located in industrialized regions of the country, where atmospheric pollution is a problem and irrigation of food crops is mostly practiced on the use of wastewater/contaminated water. For the purpose of this study, MFCs samples were collected and assessed for HMs (Cr, Ni, Cd, Pb, Mn, Cu, Zn, and Fe) by using flame atomic absorption spectrophotometry. Concentration of HMs such as Pb and Cd exceeded the Food and Agriculture/World Health Organization's recommended limits in all MFCs, while Cr in most of the vegetables of the Sialkot and Gujranwala districts also exceeded that limit. The health risk index was >1 in Triticum aestivum for Pb and Cd intake in the Sialkot district and only Pb in the Gujranwala district. Therefore, this study suggests pretreatment of wastewater and its utilization for lawns and green belts irrigation, rather than for food crops. This study also suggests a regular monitoring of HMs in the irrigation water, subsequent soil, air, and MFCs in order to prevent or reduce health hazards.     

Health Risk Assessment of Heavy Metals in Soils and Vegetables from a Typical Greenhouse Vegetable Production System in China

There is growing concern about food safety and environmental contamination due to potential health risks to consumers. The aims of this study are to elucidate the accumulation status, influencing factors, and potential risk of selected heavy metals in soils and vegetables from a typical greenhouse vegetable production system in China. The potential health risks of heavy metals through soil contact and vegetable consumption were evaluated for greenhouse and corresponding open field production. The results indicated that the mean concentrations of Hg, Pb, Cu, and Zn in greenhouse vegetable soils were greater than those in open field soils. Leaf vegetables had relatively higher concentrations and transfer factors of heavy metals than root and fruit vegetables, especially for Cd. The target hazard quotient of heavy metals through vegetable consumption was greater than 1 for leaf vegetables, and was also higher for greenhouse vegetables than those from open field. The risk of exposure to heavy metals through direct contact with soil and vegetable consumption was higher for children than for adults and seniors. Planting patterns with different vegetable types and soil properties can affect bioavailability and crop accumulation of heavy metals.     

EDTA-Facilitated Phytoremediation of Soil with Heavy Metals from Sewage Sludge

The objective of this research was to determine the effect of the chelate EDTA (ethylenediaminetetraacetic acid), which is used in phytoremediation, on plant availability of heavy metals in liquid sewage sludge applied to soil. Sunflower (Helianthus annuus L.) was grown under greenhouse conditions in a commercial potting soil; the tetrasodium salt of EDTA (EDTA Na₄) was added at a rate of 1 g kg^-1 to half the pots. Immediately after seeds were planted, half of the pots with each soil (with or without EDTA) were irrigated with 60 ml sludge, and half were irrigated with 60 ml tap water. For the subsequent five irrigations, plants in soil with EDTA received either sludge or tap water containing 0.5 g EDTA Na₄ per 1000 ml, and plants in soil without EDTA received sludge or tap water without EDTA. Of the four heavy metals whose extractable concentrations in the soil were measured (Cu, Fe, Mn, and Zn), only Zn had a higher concentration in sludge-treated soil with EDTA compared to sludge-treated soil without EDTA. The concentrations of Fe, Cu, and Mn were similar in sludge-treated soil with and without EDTA. Of the three heavy metals whose total concentrations in the soil were measured (Cd, Pb, Cr), Pb (<10 mg kg^-1) and Cd (< 1 mg kg^-1) were below detection limits, and Cr was unaffected by treatment. The concentration of all measured elements in plants (Cd, Cu, Fe, Zn, Pb) was higher than the concentrations measured in the soil. With no EDTA, sludge-treated plants had a higher concentration of the five heavy elements than plants grown without sludge. Cadmium was lower in sludge-treated plants with EDTA than plants with EDTA and no sludge. After treatment with EDTA, the concentrations of Cu, Fe, and Zn were similar in plants with and without sludge. Lead was higher in plants with EDTA than plants without EDTA, showing that EDTA can facilitate phytoremediation of soil with Pb from sewage sludge.     

重金属诱导细胞凋亡的分子机制

重金属诱导的细胞凋亡是一个十分复杂的过程,不同种类的重金属以及同类重金属离子的不同价态所诱导的凋亡效应及其分子机制不尽相同。目前的研究表明,重金属与DNA形成加合物而导致DNA损伤可能是引发细胞凋亡的重要步骤：多种重金属能通过激活内质网、线粒体钙通道,使Ca^2 释放进入细胞质而引发凋亡;重金属还能使细胞中ROS升高,在直接导致DNA损伤的同时,启动与线粒体相关的细胞凋亡信号通路。此外,ROS还能通过MAPKs增强JNK介导的：FasL和Fas表达,最终使caspase-3和caspase-7激活,从而促进凋亡的发生。重金属诱导细胞凋亡还涉及一系列重要基因和蛋白质的参与,包括促进凋亡的Src家族酪氨酸激酶、bax、fas和p53等基因及相关蛋白,抑制凋亡的Sp1锌指转录因子、bcl-2和myc等基因及相关蛋白。部分重金属如镉、锌等对细胞凋亡具有诱导和拮抗双重效应,其中拮抗效应主要是通过与自由钙离子协同进行的,而诱导效应则可能是通过调节caspase-3活性而实现的。     

Health Risk Assessment of Metals in Surface Water from Freshwater Source Lakes,Pakistan

This study investigated the concentrations of selected metals (Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Pb, Sr, and Zn) in freshwater source lakes in Pakistan and assessed the preliminary health risks associated with them. Water samples were collected from Khanpur and Simly Lakes and analyzed for the metals using flame atomic absorption spectrophotometry. Major contributions were noted for Ca, K, Mg, and K; however, the measured levels of Cd, Co, Cr, and Pb were many times higher than the permissible national/international guideline values. The risk characterization revealed that hazard quotient (HQ_ing) and hazard index (HI_ing) values exceeded the acceptable limit unity, indicating non-carcinogenic risk to the recipients via oral intake of contaminated water. The carcinogenic risk (CR_ing) via ingestion route for Cd, Cr, and Pb was found much greater than the acceptable limit (10^–6). Overall, Cd, Co, Cr, and Pb were the major contributors to potential adverse health risk to the inhabitants. Multivariate analysis demonstrated anthropogenic intrusions of the metals in both lakes. The study clearly indicated that there was gross contamination of water in both lakes, so special attention should be paid to manage the pollution sources of metals.     

Sister Chromatid Exchanges Induced by Heavy Metals in Vicia Faba

The induction of sister chromatid exchanges (SCE) by chloride and nitrate salts of nickel, cobalt, cadmium and zinc were studied in meristematic root cells of Vicia faba. Salts of nickel, cobalt and cadmium significantly increased the frequency of SCE, whereas chloride and nitrate salts of zinc did not increase the frequency of SCE significantly above the spontaneous level. The reported data demonstrate that the induction of SCE in Vicia faba may represent a valuable bioindicator for detecting the cytogenetic damage of heavy metals.     

Risk Assessment of Heavy Metals in Street Dust Particles to a Stream Network

Runoff with contaminated urban soil has an environmental risk to the aquatic environment. An assessment of heavy metals in street dust particles from a small town and their risks to the township stream network were conducted at Yangtze River delta. This assessment is based on measurement of heavy metal contents in dust particles with different particle sizes, river sediments, and suspended solids of urban runoff. The ranges of heavy metal content were 0.8–4.3, 16–380, 69–240, 9.3–350, 9.6–863 and 67–1170 mg/kg dry street dust, for Cr, Cu, Ni, Pb and Zn, respectively. Approximately 63%-71% of heavy metals were associated with particles less than 250 μ m; this particle size accounted for 40% of the total mass of street dusts. Of the five land use areas, the industrial areas had the highest heavy metal level. The smaller particle size fraction has a higher heavy metal content, low density, high mobility in runoff, and thus is a higher risk to the stream network. The topographical and hydrological features of the landscape also influence the transport of the contaminated street dusts to the aquatic environment.     

Precautionary Health Risk Assessment: Case Study of Biological Insecticides

In conventional risk assessment approaches, experts define the scientific questions that can legitimately be asked and the burden of proof is on the potentially exposed community to show that a proposal is unsafe. Here I propose an alternative approach, precautionary health risk assessment, in which the scientific questions to be addressed are defined by community consultation. I illustrate the approach with a case study of exposure to biological insecticides. This illustrates how community consultation can have a critical influence on the outcome of a health risk assessment. Government agencies may be reluctant to involve stakeholders in health risk assessments because this involves a loss of political control of the process. However, precautionary approaches are likely to lead to better health outcomes where decision stakes and scientific uncertainty are both high.     

Health Risk Assessment of Exposure to Metals in a Nigerian Water Supply

This article reports the health risk associated with chronic intake of metals in the municipal water supplies of Eleyele and neighboring towns in the Ibadan metropolitan area of Nigeria. A total of 42 composite samples, consisting of treated water from the water treatment facility and residential areas receiving personal-use water (i.e., tap water) directly from the facility, as well as raw water from the treatment facility's water supply dam were sampled twice every month for 7 months. Concentrations of the metals were determined by atomic absorption spectrophotometry. Among the metals studied, Cd, Co, Cr, and Pb were detected at concentrations higher than maximum regulatory limits. Cd, Co, Cr, and Pb concentrations in treated water at the treatment facility ranged from 0.08–0.10, 0.14–0.16, 0.04–0.22 and 0.07–0.36 mg L^?1, respectively, while personal-use water ranged from 0.08–0.11, 0.15–0.29, 0.02–0.29, and 0.12–0.65 mg L¹, respectively. Likewise, concentrations of the metals at the dam ranged from 0.06–0.08, 0.17–0.20, 0.13–0.37, and 0.03–0.15 mg L¹, respectively. It is estimated that exposure to the metals in the water supply results in oncological and non-oncological systemic health risks higher than is generally acceptable for drinking water.     

Effect of Iron Hydroxide on Phosphate Removal during Anaerobic Digestion of Activated Sludge

The addition of iron (III) hydroxide during methanogenic digestion of activated sludge by anaerobic sludge displaying an iron-reducing activity resulted in a microbial reduction of iron (III) with the formation of iron (II), capable of precipitating phosphates. The feasibility of eliminating 66.6 to 99.6% of the dissolved phosphate at initial concentrations of 1000 to 3500 mg PO^3- ₄/l by adding 6420 mg/l iron (III) hydroxide into a reactor for anaerobic fermentation of activated sludge was analyzed. The optimal ratio of iron (III) added to dissolved phosphate removed (mg) providing a 95% removal amounted to 2 : 1. These results may be used in new technology for anaerobic wastewater treatment with phosphate removal.     

Methanosarcinaceae and Acetate-Oxidizing Pathways Dominate in High-Rate Thermophilic Anaerobic Digestion of Waste-Activated Sludge

This study investigated the process of high-rate, high-temperature methanogenesis to enable very-high-volume loading during anaerobic digestion of waste-activated sludge. Reducing the hydraulic retention time (HRT) from 15 to 20 days in mesophilic digestion down to 3 days was achievable at a thermophilic temperature (55°C) with stable digester performance and methanogenic activity. A volatile solids (VS) destruction efficiency of 33 to 35% was achieved on waste-activated sludge, comparable to that obtained via mesophilic processes with low organic acid levels (<200 mg/liter chemical oxygen demand [COD]). Methane yield (VS basis) was 150 to 180 liters of CH₄/kg of VS_added. According to 16S rRNA pyrotag sequencing and fluorescence in situ hybridization (FISH), the methanogenic community was dominated by members of the Methanosarcinaceae, which have a high level of metabolic capability, including acetoclastic and hydrogenotrophic methanogenesis. Loss of function at an HRT of 2 days was accompanied by a loss of the methanogens, according to pyrotag sequencing. The two acetate conversion pathways, namely, acetoclastic methanogenesis and syntrophic acetate oxidation, were quantified by stable carbon isotope ratio mass spectrometry. The results showed that the majority of methane was generated by nonacetoclastic pathways, both in the reactors and in off-line batch tests, confirming that syntrophic acetate oxidation is a key pathway at elevated temperatures. The proportion of methane due to acetate cleavage increased later in the batch, and it is likely that stable oxidation in the continuous reactor was maintained by application of the consistently low retention time.     

Biochemical and RAPD Analysis of Hibiscus rosa sinensis Induced by Heavy Metals

The present study was designed to assess the effects of three different metals (cadmium, lead, and zinc) at the same concentrations on Hibiscus rosa sinensis during metal uptake. The effects of different metals at the same concentrations were assessed on biomass, root-shoot length, and biochemical parameters like chlorophyll and antioxidant enzymes like SOD and CAT to establish the tolerance potential and toxic effects on plants in different metals. The accumulation of metals by plants was found to be in the following order: Zn > mixed metals > Cd > Pb, where Zn was accumulated approximately 79.6% in plant tissues. Plants removed from Cd showed more enzyme activities than the other two metals. DNA stability was investigated by a Random Amplified Polymorphic DNA (RAPD) technique, which demonstrated that the samples in Cd and mixed metal showed similar trends, whereas samples in Zn and Pb showed similar band intensity to the control. Results suggested that Cd and/or heavy metal stress influences antioxidant status and also induces DNA changes during remediation. Therefore, these studies could be a useful biomarker assay for better treatment for metals’ remediation from soil by means of phytoremediation.     

Uncertainties in the Environmental Risk Assessment of Metals

As life has evolved in the presence of metals, the assessment of the potential adverse effects of metals on ecosystems requires a different approach than those presently used for man-made organic substances. This article provides a brief review of applications and limitations of current techniques and presents, based on recent research results, suggestions for improving the scientific relevance and accuracy of environmental risk assessments of metals. The importance of the following factors responsible for major uncertainties in current environmental risk assessments of metals are discussed: factors affecting metal bioavailability and toxicity, the potential importance of deficiency effects (for essential metals), and field extrapolation of laboratory toxicity data. Possible (regulatory) consequences of inaccurately assessing the natural background concentrations of metals and acclimatization/adaptation potential of laboratory organisms and resident communities are illustrated using examples of recent research, hypothesis development, and a probabilistic environmental risk assessment.     

Distribution and Risk Assessment of Heavy Metals in Sediments of the Pearl River Estuary,Southern China

Sediment cores collected at six freshwater discharge outlets of the Pearl River Estuary were analyzed for metal (Al, Fe, Cr, Pb, and Cd) concentration and risk assessment. The contents of Cr, Pb, Fe, and Al in these samples were measured by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), and Cd was measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The result showed that the concentration ranged (in mg/kg dry weight) as follows: Al, 7,880–97,700; Fe, 30,100–51,900; Cd, 0.23–1.09; Cr, 48.7–109; Pb, 22.3–70.2; respectively. The sediments of different particle size were measured and the result showed that the pelitic fraction (< 0.05 mm) was more enriched in heavy metals. Cd and Pb showed a similar spatial distribution in the sediment, which reflected similar anthropogenic origins. In addition, the temporal distribution of Cr, Pb, and Cd showed a light increase from the 1970s to the 2000s. Furthermore, the enrichment factor (EF) and the geo-accumulation index (I_geo) were used to comprehensively evaluate the pollution degree of heavy metals. The findings will be useful in proposing measures for strategic environmental control in estuaries.     

Aquatic Risk Assessment of Metals in Sediment from South Florida Canals

A major watershed restoration effort is underway in south Florida, yet there are significant gaps in scientific information on exposure and risks of contaminants to its natural resources. We conducted a two-tier aquatic screening-level ecological risk assessment for metals that were monitored in sediment at 32 sampling sites in south Florida freshwater canals from 1990–2002. For tier 1, the chemicals (or metals) of potential ecological concern (COPECs) were identified as arsenic, cadmium, chromium, copper, lead, nickel and zinc based on their exceedences of Florida sediment quality guidelines at 10 sites. For tier 2, we used a probabilistic risk assessment method to compare distributions of predicted pore water exposure concentrations of seven metal COPECs with distributions of species response data from laboratory toxicity tests to quantify the likelihood of risk. The overlap of pore water concentrations (90th centile for exposure) for metal COPECs and the effects distributions for arthropods (10th centile of LC50s) and all species (10th centile of chronic NOECs) were used as a measure of potential acute and chronic risks, respectively. Arsenic (25%) in the Holey Land tracts, in Broward County north of Everglades National Park (ENP), and chromium (25%) in the C-111 freshwater system, at the east boundary of ENP, were the most frequently detected COPECs in sediment. Antimony (6%), zinc (6%) and lead (5%) were the least frequently detected COPECs in sediment. The 90th centile concentrations for bulk sediment were highest for zinc (at S-178) and lead (at S-176) in the C-111system. The 90th centile concentration for pore water exposure was highest for arsenic in the Holey Land tracts and lowest for cadmium and chromium. The estimated acute 10th centile concentration for effects was lowest for copper and arthropods. The probabilities of pore water exposures of copper exceeding the estimated acute 10th centile concentration from the species sensitivity distributions (SSD) of acute toxicity data (for arthropods) were 57 and 100% for copper at S-177 and S-178 in the C-111 system, respectively. The probability of pore water exposures of copper exceeding the estimated NOEC 10th centile concentration from the SSD of chronic toxicity data (for all species) was 93 and 100% for copper at S-177 and S-178, respectively. Uncertainties in exposure and effects analysis and risk characterization are identified and discussed. The study presents a straightforward approach to estimate exposure and potential risks of metals detected in sediment from south Florida canals.     

Carcinogenic and Non-carcinogenic Risk Assessment of Heavy Metals in Groundwater Wells in Neyshabur Plain,Iran

The present work reports the As, Cr, Cu, Pb, Zn, and Fe concentrations of drinking water samples in Neyshabur Plain, Iran. This study aimed also to ascertain the potential consumers’ health risk of heavy metal intake. Heavy metal concentrations were analyzed by inductively coupled plasma optical emission spectrometry. The highest and lowest average values in the analyzed water samples were observed for Fe (9.78 ± 5.61 μg/L) and As (1.30 ± 2.99 μg/L), respectively. These values were well below the limits recommended by the World Health Organization and the Iranian national standard. Heavy metal pollution index and heavy metal evaluation index were used to evaluate drinking water quality. The risk index was calculated by chronic daily intake and hazard quotient according to the United States Environmental Protection Agency approach. Heavy metal pollution index in all the samples was less than 100, indicating that it is a low-level heavy metal. The total risk of all heavy metals in the urban environment varied from 40.164 × 10⁻⁷ to 174.8 × 10⁻⁷. In this research, the maximum average of risk belonged to lead and copper with the respective values of 60.10 × 10⁻⁷and 33.99 × 10⁻⁷ from the selected wells. However, considering the toxic effect of some elements, including Pb and As, in the chronic exposure of consumers, we suggest a continuous evaluation and monitoring of drinking water resources.

     

Effect of Microwave Radiation on Immobilization of Heavy Metals in Sediment Sludge

In order to evaluate the effect of microwave radiation on immobilization of heavy metals (Cu ^{2 +} , Cr ^{6 +} , Zn ^{2 +} and Pb ^{2 +} ) in sediment sludge, leaching tests were run under different test conditions to compare microwave radiation with conventional blast heating and drying process for their effectiveness in immobilizing heavy metals within sediment sludge. Experimental results indicate that microwave radiation can decrease the concentration of heavy metals in leachate by 63% ～ 70% more than conventional blast heating and drying process in an aclinic shake leaching test. Under the same simulated natural water conditions, the concentration of heavy metals in the leachate using microwave radiation is well below the concentration of heavy metals in leachate using conventional blast heating and drying process. It is therefore concluded that microwave radiation is much more effective than conventional blast heating and drying process in immobilizing heavy metals in sediment sludge.