Chemical Speciation Of Heavy Metals Research Articles

Chemical Speciation of Heavy Metals with Contaminated Sediment by Hydrothermal Technology

Chemical Speciation of Heavy Metals with Contaminated Sediment by Hydrothermal Technology

Optimization of liquefaction process based on global meta-analysis and machine learning approach: Effect of process conditions and raw material selection on remaining ratio and bioavailability of heavy metals in biochar

<abstract> <p>Although liquefaction technology has been extensively applied, plenty of biomass remains tainted with heavy metals (HMs). A meta-analysis of literature published from 2010 to 2023 was conducted to investigate the effects of liquefaction conditions and biomass characteristics on the remaining ratio and chemical speciation of HMs in biochar, aiming to achieve harmless treatment of biomass contaminated with HMs. The results showed that a liquefaction time of 1–3 h led to the largest HMs remaining ratio in biochar, with the mean ranging from 84.09% to 92.76%, compared with liquefaction times of less than 1 h and more than 3 h. Organic and acidic solvents liquefied biochar exhibited the greatest and lowest HMs remaining ratio. The effect of liquefaction temperature on HMs remaining ratio was not significant. The C, H, O, volatile matter, and fixed carbon contents of biomass were negatively correlated with the HMs remaining ratio, and N, S, and ash were positively correlated. In addition, liquefaction significantly transformed the HMs in biochar from bioavailable fractions (F1 and F2) to stable fractions (F3) (<italic>P</italic> < 0.05) when the temperature was increased to 280–330 ℃, with a liquefaction time of 1–3 h, and organic solvent as the liquefaction solvent. N and ash in biomass were positively correlated with the residue state (F4) of HMs in biochar and negatively correlated with F1 or F2, while H, O, fixed carbon, and volatile matter were negatively correlated with F4 but positively correlated with F3. Machine learning results showed that the contribution of biomass characteristics to HMs remaining ratio was higher than that of liquefaction factor. The most prominent contribution to the chemical speciation changes of HMs was the characteristics of HMs themselves, followed by ash content in biomass, liquefaction time, and C content. The findings of this meta-analysis contribute to factor selection, modification, and application of liquefied biomass to reducing risks.</p> </abstract>

Comparative Pollution Toxicity and Chemical Speciation of Heavy Metals in MSWI Fly Ash with Different Particle Size Distribution

Comparative Pollution Toxicity and Chemical Speciation of Heavy Metals in MSWI Fly Ash with Different Particle Size Distribution

Ecological Risk Assessment and Source Identification of Heavy Metals in Soils from Shiyang River Watershed in Northwest China.

Shiyang River Watershed is an important ecological barrier and agricultural production area in Northwest China, and the study of soil heavy metal content, distribution, and sources is important for agricultural product safety, pollution control, and ecosystem health. In this paper, 140 soil samples were collected from 28 stations to assess the level of heavy metal (Arsenic (As), Copper (Cu), Lead (Pb), Cadmium (Cd), Chromium (Cr), Mercury (Hg), Nickel (Ni), Zinc (Zn)) contamination, pollutant sources and influencing factors of soil in Shiyang River Watershed through determination of the metal contents and statistical analysis. The results indicated that the soils in the study area are typical saline soils in arid zones. The enrichment factors (EF) of As, Cr, Cu, Ni, Zn, and Pb indicate no contamination, and the EFs of Cd and Hg suggested minor contamination. Although the concentrations of Cd and Hg in soil are lower than others, they are more biotoxic and exhibit a moderate-high ecological risk. The index of geoaccumulation (Igeo) values reflect that most of the stations, especially the three groups of samples from depths of 10-20 cm, 20-40 cm, and 40-80 cm, are below the contamination threshold for all heavy metals. The chemical speciation of heavy metals, principal component analysis, and correlation analysis showed that Cr, Cu, Pb, Cd, Ni, and Zn mainly come from the natural accumulation upon weathering of soil-forming matrices. Hg and As mainly come from anthropogenic contributions. The effect of agricultural crop cultivation on soil heavy metal contamination is mainly through farm irrigation and crop-soil interactions, which accelerate the release of heavy metals through the weathering of soil-forming parent material and irrigation, which transports the heavy metals below the surface. The results of this study can provide a scientific basis for the involved authorities to formulate reasonable policies on environmental protection and pollution control.

Spatio-temporal variation and hazard assessment of potentially toxic metal element contamination in sediments and water before and after a water-level fluctuation cycle in the Three Gorges Reservoir, Wanzhou, China.

Previous investigations on heavy metals in the water-sediment compartment focused on their spatial distribution, and the influence of sediment pH and organic matter (OM) on metal environmental occurrences. However, there are limited studies on the effects of physicochemical properties on the migration and transformation of heavy metals in the water-sediment compartments. This study investigated the relationship between the physicochemical properties of sediments and the distribution and chemical speciation of heavy metals, and the potential environmental risk of heavy metals in water and sediment using Risk Assessment Code (RAC) values and the Tessier five-step extraction method. Adsorption and desorption experiments showed that the sediment had weak adsorption and the strongest desorption capacity for Cd. Results of the pH, OM, surface element content, and X-ray diffraction (XRD) patterns suggested that cadmium (Cd) was more likely to partition into the water phase from the sediment during the flooding and water storage periods. When pH was 7-8 and OM content was 3.6-5.9%, the sediment-water distribution coefficient of Cd was low due to its large ionic radius, and the surface adsorption sites were saturated by other elements. These studies can provide a theoretical basis for the management and pollution control of the Three Gorges Reservoir.

Chemical Speciation Distribution and Thermal Stability of Heavy Metals along Flue Gas Cleaning Systems in a Hazardous Waste Incinerator

Hazardous heavy metals may release from incineration residues in the utilization concerning heat treatment or landfills, which would cause great harm on the environment. The evaluation of chemical speciation and thermal stability of heavy metals are of great significance for the control of heavy metal pollution during heat treatments. In this study, chemical speciation distribution and thermal stability of heavy metals (As, Cd, Cr, Cu, Pb, Se, Zn, and Hg) along flue gas cleaning systems were investigated in a hazardous waste incinerator located in Zhejiang, China. The chemical speciation and thermal stability of heavy metals, environmental risk evaluation, and morphological and mineralogical characteristics of incineration residues were assessed before and after heat treatments. Results indicated that the chemical speciation of heavy metals in the bottom slag, burn-out chamber ash, boiler ash, and bag filter ash varied significantly. The thermal stability of heavy metals in the incineration residues was significantly influenced by chemical speciation, and the thermal stability of the chemical speciation decreased basically in the order of residual form > reducible form > oxidizable form > acid soluble form. As, Cr, and Se showed high thermal stability due to the fact that they were involved in the crystallization reaction, and heat treatment would promote the transformation from mobile fractions into the residual fraction. Hg and Cd displayed the worst thermal stability, and high-temperature heat treatment would contribute to secondary volatilization from the incineration residues. More attention should be paid to the secondary volatilization of Hg and Cd during thermal disposal. Cu, Pb, and Zn had moderate thermal stability, and heat treatment would cause the volatilization of mobile fractions and the transformation from mobile fractions into the residual fraction. Pretreatments such as water-washing or adding a chemical stabilizer would be conducive to reducing the volatilization of heavy metals during thermal disposal.

An investigation on mobility of heavy metals for assessing the reusability of soil-like material reclaimed from mining of municipal solid waste dumpsites

Landfill mining, often referred to as “bio-mining”, enables the recovery of resources, including combustible, compostable, and recyclable fractions from landfills. However, most of the materials mined from old landfills mainly consist of soil-like materials (SLM). The reuse of SLM depends on the concentration of contaminants, such as heavy metals, soluble salts, etc. A sound risk assessment requires sequential extraction to determine the bioavailability of heavy metals. This study focuses on the mobility and chemical speciation of heavy metals in SLM from four old municipal solid waste dumpsites in India by performing selective sequential extraction. Additionally, the study compares the results with those of four previous investigations to identify international similarities. It has been observed that Zn was mainly available in the reducible phase (average 41%), whereas Ni and Cr proved to have the highest distribution in the residual phase (64% and 71%, respectively). Pb analysis showed a large portion in the oxidizable phase (39%), while Cu was mainly present in the oxidizable (37%) and residual (39%) phases. Similarities with previous investigations were observed for Zn (primarily reducible 48%), Ni (residual 52%), and Cu (oxidizable 56%). Correlation analysis showed that Ni correlated with all heavy metals (ρ = 0.71–0.78), except with Cu. The present study suggested that Zn and Pb are associated with a high risk of pollution due to their maximum distribution in the bioavailable phase. The findings of the study can be used to assess the heavy metal contamination potential of SLM prior to its reuse in offsite applications.

Effects of sulfur on variations in the chemical speciation of heavy metals from fly ash glass

Effects of sulfur on variations in the chemical speciation of heavy metals from fly ash glass

Immobilization of Pb and Zn in Contaminated Soil Using Alumina–Silica Nano-Amendments Synthesized from Coal Fly Ash

To apply coal fly ash to the remediation of heavy-metal-contaminated soil, an alumina-silica nano-amendment (ASNA) was synthesized from coal fly ash and was used for the immobilization of lead and zinc in contaminated soil. The investigation on the synthesis of the ASNA shows that the ASNA can be obtained under a roasting temperature of 700 °C, a ratio of alkali to coal fly ash of 1.2:1, and a molar ratio of silicon to aluminum of 1:1. The ASNA could increase the soil pH and cation exchange capacity (CEC) and decrease the bioavailability of Pb and Zn. When the ASNA addition increased from 0 to 2%, the bioavailability (extracted by CaCl2) of Pb and Zn decreased by 47% and 72%, respectively. Moreover, the addition of the ASNA facilitated the transformation of Pb from a reducible fraction to oxidizable and residual fractions and Zn from an exchangeable fraction to a residual fraction. The correlation analysis and cluster analysis verify that the ASNA modulates the chemical speciation of heavy metals by increasing the soil's CEC and pH, thereby immobilizing heavy metals. It is expected that this study can provide a new method for the remediation of Pb- and Zn-contaminated soil.

Zero-valent iron drives the passivation of Zn and Cu during composting: Fate of heavy metal resistant bacteria and genes

Livestock and poultry manures usually contain substantial heavy metals, especially Cu and Zn, which may induce the enrichment of heavy metal resistant genes (HMRGs) and heavy metal resistant bacteria (HMRB). This study aims to clarify the relationship among heavy metal bioavailability, HMRB and HMRGs during composting, so as to assess and alleviate potential ecological risks of manure application to land. In this study, zero-valent iron (ZVI) was used as passivator, and HMRGs and their host microorganisms were investigated by metagenomic analysis. The results showed that ZVI effectively promoted the passivation of Zn and Cu, and the bioavailability of Zn and Cu decreased by 8.25% and 19.84%, respectively. Proteobacteria was the main HMRB in composting, among which Escherichia, Pseudomonas and Salmonella contained abundant HMRGs, and the succession of these bacteria was closely related to the fate of HMRGs. Spearman correlation analysis showed that metal exchangeable and reducible fractions were positively correlated with the abundance of most HMRGs. Furthermore, structural equation model showed that heavy metal passivation can also indirectly reduce the abundance of HMRGs by regulating the succession of HMRB. These results suggested that the fate of HMRGs is closely related to the chemical speciation of heavy metals in composting habitats.

Microplastics can affect soil properties and chemical speciation of metals in yellow-brown soil

Although the influence of microplastics (MPs) in different soil environments has been investigated, their effects on the physiochemical properties and chemical speciation of heavy metals in yellow-brown soil remains unknown. This study aimed to determine the effects of various concentrations of linear low-density polyethylene (LLDPE), polyamide (PA), polyurethane (PU), polystyrene (PS), and low-density polyethylene (LDPE) MPs on the yellow-brown soil environment and chemical speciation of the heavy metals cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn). MPs influenced the physicochemical properties and chemical speciation of heavy metals in yellow-brown soil. The physicochemical properties of yellow-brown soil can be altered by changing the concentrations of LDPE MP. The relationship between changes in field capacity (FC) and LDPE concentrations was approximately linear. The physiochemical properties of yellow-brown soil containing added PA, PU, and LDPE MPs were substantially improved (control vs. MPs): FC, 39 % vs. 42.50 % for PU, cation exchange capacity (CEC) 45.77, 56.65, and 57.44 cmol.kg−1 for PA, PU, and LDPE respectively, and organic matter (OM) content, 40.16 vs. 51.68 g.kg−1 for PA. The LLDPE and PU MPs also simultaneously affected the chemical speciation of heavy metals in yellow-brown soil. The LLDPE MPs increased the acid-soluble (45.17–54.67 % (Cd-F1), 7.24–11.30 % (Cu-F1), 4.20–7.23 % (Pb-F1), 21.21–31.47 % (Zn-F1)) and reducible (24.02–29.41 % (Cd-F2), 25.69–34.95 % (Cu-F2), 74.29–81.07 % (Pb-F2), 28.77–34.19 % (Zn-F2)) fractions of heavy metals, which increased their bioavailability. However, PU MPs reduced the ecological risk of heavy metals in yellow-brown soil by increasing the content of the residual fraction (26.11–40.21 % (Cd-F4), 47.63–59.67 % (Cu-F4), 17.25–26.76 % (Pb-F4), 32.63–50.46 % (Zn-F4)). Changes in the properties of yellow-brown soil and the impact of MPs on heavy metals, might change the chemical speciation of heavy metals. The impact of MPs on heavy metals in yellow-brown soil requires further investigation.

Co-hydrothermal carbonization of sewage sludge and swine manure: Hydrochar properties and heavy metal chemical speciation

Alleviating the risk of heavy metals while improving fuel properties is one of the important challenges of sewage sludge (SS) disposal. In this work, ferric chloride (FeCl3) was chosen as a typical additive (0.005–0.02 mol) to analyse its effect on the co-hydrothermal carbonation (co-HTC) of SS and swine manure (SM). During co-HTC, SS was converted into hydrochar with SM at different mixing ratio (30–70 %) at 230 °C. Chemical speciation of heavy metals (HMs) in hydrochars, along with fuel properties, were evaluated. The results showed that co-HTC was beneficial for the decline of weakly fractions of Cr, Ni, Mn, and Zn. Furthermore, FeCl3 further decreased the risk of Mn and Zn without significantly expanding the pollution of Ni. More importantly, the risk of Cu was dramatically alleviated by the addition of 0.02 mol FeCl3. Compared with the hydrochar produced from SS, the fuel ratio, higher heating values (9.75–13.09 MJ/kg), and combustion behavior of the hydrochar derived from co-HTC were upgraded and improved. The FeCl3 could notably promoted the dehydration and decarboxylation reaction and prevented the reservation of N content. This study suggested that co-HTC with FeCl3 was a promising strategy to produce superior solid fuel with lower risk of HMs.

Contamination and ecological risk assessment of heavy metals, and relationship with organic matter sources in surface sediments of the Cross River Estuary and nearshore areas

Chemical speciation of heavy metals (Zn, Pb, Cu, and Cd) was studied to evaluate the contamination status and associated risks and to constrain the sources of heavy metals in relation to sedimentary organic matter (OM) sources in surface sediments of the Cross River Estuary (CRE) and nearshore areas surrounded by a degrading mangrove ecosystem (typical C3 plants). The contamination factor (CF) and geo-accumulation (Igeo) indicated that Cd and Zn were the most polluted heavy metals. High percentages of Zn (63.78%), Pb (64.48%), Cd (76.72%) and the considerable amount of Cu (48.57%) in non-residual fractions indicated that these heavy metals are bioavailable. Cd showed moderate to high ecological and bioavailability risk based on the ecological risk (Er) and risk assessment code (RAC). Significant positive correlations occurred among the heavy metals, fine-grained sediments, and sedimentary OM from terrestrial C3 sources. These correlations, together with high percentages of heavy metals in the oxidizable fraction (~33–50%), indicated that the erosive washout of OM and fine sediments ladened with heavy metals from the adjoining degraded mangrove ecosystem contributed significantly to the increased contents of heavy metals in surface sediments of the study area.

Mobility and environmental fate of heavy metals in fine fraction of dumped legacy waste: Implications on reclamation and ecological risk

The study evaluates mobility and chemical speciation of heavy metals (HMs) in fine fraction (<4 mm) collected from municipal solid waste dumpsite located in Mumbai, India to assess its reclamation feasabilty. A total of fifteen samples were collected from five zones (named chronologically, zone A to zone E, with the increasing waste age) at 1-m depth interval to understand temporal variation in mobility and potential pollution risk of heavy metals. The results depicted that Zn had the highest concentration in the fine fraction, followed by Cu > Cr > Pb > Ni > Cd. Furthermore, HMs concentration showed increasing trend with the waste age. According to hiererachial cluster analysis, two cluster were observed in the analyzed samples which could be differentiated with age of the waste. Further, the chemical speciation differed for all assessed HMs and had a significant change with age. HMs were dominant in non-bioavailable forms, except for Cd that had significant distribution in all forms. In addition, Cd (23%) and Zn (17%) showed high mobility amongst all analyzed HM, while Cr (0.4%) had the least. According to pollution assessment and chemical speciation results, Cd was identified as the most polluting and mobile HM. The study shows that the mobile form of HMs is low and needs to be considered while deciding the remediation routes and environment hazards.

Assessing mobility and chemical speciation of heavy metals during rotary drum composting of Ageratum conyzoides

Ageratum conyzoides, a goat weed that has invaded the world with its disparate behaviour through the inherence of heavy metal against the cultivated crops. The present study enrapt on composting of this disparate weed by assessing the heavy metal virulent throughout the composting process. A 550 L rotary drum composter (an In-vessel composting technique) was used for managing Ageratum conyzoides biologically by blending with inoculum and sawdust. It was evident that the substrate’s volatile solids and biological parameters were high and decreased in the final compost product. The first-order decay model was used for biological parameters and volatile solids through adjusted R2 ksBOD (R2=0.975), ksCOD (R2=0.974 and kV S (R2=0.941) respectively. The mass balance concept was utilised to evaluate the dynamics of the rotary drum composting process. The heavy metal virulent was assessed through bioavailable forms, and leachable heavy metals with chemical speciation fractions were carried out in the composting process. Ni and Cd were found predominantly in residual fractions with 99.7% and 99.5% in final day compost. Pb, Cr, Mn, Fe, Cu and Zn were moderately leached in mobile fractions throughout the composting process. The study stipulates the dynamics of heavy metals in the rotary drum composting process and indicates the compositions of every metal in various distinguished chemical fractions.

Measurement and modeling of heavy metal behaviors during the incineration of RDF in a pilot-scale kiln incinerator-Part 1: Modeling using multizonal thermodynamic equilibrium calculation

Multizonal thermodynamic equilibrium calculation is one of the methods used in estimating or explaining the fate of elements such as heavy metals during waste incinerations and probably only one method that can estimate the fate of trace elements, but the ability of the calculation as a fate-estimation tool was not fully examined. This study examines the performance of multizonal thermodynamic equilibrium calculation applied to waste incineration by comparing the calculated results with the results from the incineration test and literature information. High temperature behaviors of the heavy metals were also reviewed to correctly understand their gas phase speciation in the incinerator, and the thermodynamic data of gaseous Cd species were modified to better reproduce the high temperature vaporization behavior. The calculation represented the high volatility of Hg, Cd, Pb, and low volatility of Cr in the incineration, whereas the measured high volatility of Zn and As could not be obtained by the calculation. The calculation succeeded in reproducing the possible gas phase chemical speciation of heavy metals in the incinerator expected from the review on the high temperature properties, whereas the calculated fly ash speciation does not match with the measured speciation. Possible reasons for these inconsistencies were considered.

Performance of Chlorella Vulgaris Exposed to Heavy Metal Mixtures: Linking Measured Endpoints and Mechanisms.

Microalgae growth inhibition assays are candidates for referent ecotoxicology as a fundamental part of the strategy to reduce the use of fish and other animal models in aquatic toxicology. In the present work, the performance of Chlorella vulgaris exposed to heavy metals following standardized growth and photosynthesis inhibition assays was assessed in two different scenarios: (1) dilutions of single heavy metals and (2) an artificial mixture of heavy metals at similar levels as those found in natural rivers. Chemical speciation of heavy metals was estimated with Visual MINTEQ software; free heavy metal ion concentrations were used as input data, together with microalgae growth and photosynthesis inhibition, to compare different effects and explain possible toxicity mechanisms. The final goal was to assess the suitability of the ecotoxicological test based on the growth and photosynthesis inhibition of microalgae cultures, supported by mathematic models for regulatory and decision-making purposes. The C. vulgaris algae growth inhibition test was more sensitive for As, Zn, and Pb exposure whereas the photosynthesis inhibition test was more sensitive for Cu and Ni exposure. The effects on growth and photosynthesis were not related. C. vulgaris evidenced the formation of mucilaginous aggregations at lower copper concentrations. We found that the toxicity of a given heavy metal is not only determined by its chemical speciation; other chemical compounds (as nutrient loads) and biological interactions play an important role in the final toxicity. Predictive mixture effect models tend to overestimate the effects of metal mixtures in C. vulgaris for both growth and photosynthesis inhibition tests. Growth and photosynthesis inhibition tests give complementary information, and both are a fast, cheap, and sensitive alternative to animal testing. More research is needed to solve the challenge of complex pollutant mixtures as they are present in natural environments, where microalgae-based assays can be suitable monitoring tools for pollution management and regulatory purposes.

Relationships between soil properties and the accumulation of heavy metals in different Brassica campestris L. growth stages in a Karst mountainous area

The speciation and activity of heavy metals in farmland were changed with the different soil properties and flooded environment, especially in the complex and rainy environment in soil of Guizhou Province. The objective of this study was to explore the concentrations of a variety of heavy metal activity and the speciation of those heavy metals in rhizosphere soil at different growth stages of Brassica campestris L. in a Karst mountainous area. Tessier's five-stage sequential extraction procedure, the potential ecological risk index, a Bayesian network, accumulation factors, translocation factors and a laboratory simulation experiment were applied in this study. The results showed that (1) no heavy metal concentrations (except the Cd concentration) exceeded the limits of the soil environmental quality risk control standards for soil contamination of agricultural land in China (GB15618-2018). (2) The orders of the accumulation factor and translocation factor values were Zn > Cd > Cu > Pb > Cr and Cd > Cu > Zn > Pb > Cr, respectively. The order of the heavy metal contents of different tissues during the whole growth period was roots > leaves > stems. (3) The indoor simulation test exhibited that the dry-wet alternation and flooding can reduce Cd activity in soil. (4) Redox potential (Eh), rather than pH or organic matter, was the main factor impacting the total content and chemical speciation of heavy metals in the soil, based on a dynamic Bayesian network. Based on the results, we suggest that the activity of heavy metals should be improved by using dry-wet alternation, whereas the proportions of ion-exchangeable forms of heavy metals are relatively low in the study area (except for Cd). Several measures may be taken to enhance soil acidity and reduce the Cd activity during Brassica campestris L. cultivation.

The Ecological Risk Assessment and the Chemical Speciation of Heavy Metals in Ash after the Incineration of Municipal Sewage Sludge

Popular incineration of sewage sludge results in the increase in heavy metals content in ash. The knowledge of the total content of heavy metals in sewage sludge ash does not demonstrate a potential hazard. The toxicity of heavy metals in great measure depends on the form of their occurrence. The prevailing norms do not require the ecological risk assessment of the environmental burden with heavy metals for the choice of the method of the utilization of sewage sludge ash. The paper presents the research results on the mobility of heavy metals in sewage sludge ash after its incineration. The geo-accumulation index (IGAI), the potential ecological risk index (PERI) and the risk assessment code (RAC) were used for the evaluation of the potential soil contamination with heavy metals. The authors also suggested a new formula, which took into consideration more factors influencing the risk of the contamination of a water-soil environment with heavy metals—the water and soil environment risk index (WSERI). The calculated indices for sewage sludge ash indicate the risk of soil contamination with heavy metals.

Chemical speciation and mobility of heavy metals in soils of refuse dumpsites in some urban towns in the Niger Delta of Nigeria

Abstract Refuse dumpsites often contain materials which are capable of polluting surrounding soils especially if the dumpsites are not adequately shielded from the surrounding area. This study examined chemical speciation and mobility of heavy metals in three urban towns in the Niger Delta. Soil samples were collected from three dumpsites in each of the three selected urban towns at 0-15 cm, 15-30 cm and 30-45 cm depths. The chemical speciation of the heavy metals in the soils was determined using the Tessier’s sequential extraction procedure. The results showed that on the average, the residual fraction was the predominant fraction of all the metals except Pb which was dominant in the organic fraction. The mobility factor followed the order Zn &gt; Fe &gt; Pb &gt; Cr &gt; Ni &gt; Cd &gt; Cu. The study indicates that the metals studied do not pose environmental risk considering their relatively low concentrations and the chemical forms they are associated with. It is however recommended that the sites be continuously monitored because of the deleterious health effects of exposure to heavy metal pollution in the events of reclaim.