Ecological vulnerability: seasonal and spatial assessment of trace metals in soils and plants in the vicinity of a scrap metal recycling factory in Southwestern Nigeria

The concentrations of selected heavy metals in the soil and vegetation in the immediate vicinity of a metal scrap recycling factory were determined in the dry and wet seasons using the Atomic Absorption Spectrophotometer. The results showed that the soil pH in all the sites indicated slight acidity (from 5.07 to 6.13), high soil organic matter content (from 2.08 to 5.60 %), and a well-drained soil of sandy loam textural composition. Soil heavy metal content in the dry season were 0.84–3.12 mg/kg for Pb, 0.26–0.46 mg/kg for Cd, 9.19–24.70 mg/kg for Zn, and 1.46–1.97 mg/kg for Cu. These values were higher than those in the wet season which ranged from 0.62–0.69 mg/kg for Pb, 0.67–0.78 mg/kg for Cd, 0.84–1.00 mg/kg for Zn, and 1.26–1.45 mg/kg for Cu. Except for cadmium in the dry season, the highest concentrations occurred in the northern side of the factory for all the elements in both seasons. An increase in the concentrations of the elements up to 350 m in most directions was also observed. There was no specific pattern in the level of the metals in the leaves of the plant used for the study. However, slightly elevated values were observed in the wet season (Pb 0.53 mg/kg, Cd 0.59 mg/kg, Cu 0.88 mg/kg) compared with the dry season values (Pb 0.50 mg/kg, Cd 0.57 mg/kg, Cu 0.83 mg/kg). This study showed that the elevated concentrations of these metals might be associated with the activities from the recycling plant, providing the basis for heavy metal pollution monitoring and control of this locality that is primarily used for agricultural purposes.     

Characteristics and distribution of analyzed metals in soil profiles in the vicinity of a postflotation waste site in the Bukowno region, Poland

The lead–zinc industry in the Bukowno region of southern Poland has polluted the surface layer of the surrounding soils mainly with lead (Pb), cadmium (Cd), zinc (Zn), arsenic (As), and thallium (Tl). Analysis of six soil profiles, taken on the east side of the postflotation waste site of the Mining and Metallurgical Plants ZGH "Boles?aw" in Bukowno, showed that they were podzol soils, taking form of loose sands with neutral pH and reducing conditions. Concentration of organic matter in the horizons ranged from 2 to 80 %. The main components of the mineral soil were quartz, carbonates, K-feldspars, plagioclases, and micas (sericite). The highest total concentrations of metals were found in the O, A, and B horizons. Over 90 % of the Cd content, 80 % of the Pb content, 60 % of the Zn content, ～60 % of the Tl content, and 20 % of the As content occurred as mobile forms. The corresponding total concentrations were 10 mg/kg Cd, 922 mg/kg Pb, 694 mg/kg Zn, <1 mg/kg Tl, and <5 mg/kg As. This can potentially be taken up from the soil and transported in the trophic chain. Comparing the total metal content with the legal limits in Poland, it is observed, that the investigated soils exceeded the permissible levels of Cd, Pb, and Zn for agricultural soils. Arsenic and Tl are not reflected in the chemical quality of soil classifications.     

Heavy metal concentration in deepwater rose shrimp species (Parapenaeus longirostris,Lucas, 1846) collected from the Marmara Sea Coast in Tekirdağ

Zn, Cd, Cr, Hg, As (total), Cu, Pb, and Ni levels of the deepwater rose shrimp (Parapenaeus longirostris, Lucas 1846), which were collected from the Tekirda? coast of the Marmara Sea, were evaluated. The Marmara Sea is the recipient of discharges from both land-based sources and the Black Sea Bosphorus stream. There are large numbers of anthropogenic activities in the coastal region of the northern Marmara Sea that include urban effluent, discharges from touristic resorts, agricultural runoff, fishing, and transportation. Heavy metal contamination of water resources may cause critical health problems for the people living around these water bodies. In deepwater rose shrimp (P. longirostris), the highest concentration level detected for Zn was 22.4?±?24.4 mg/kg in winter 2012, Cd 0.106?±?0.01 mg/kg in summer 2012, Cr 0.77?±?0.05 mg/kg in winter 2012, Hg 0.18?±?0.04 mg/kg in summer 2011, As 9.93?±?1.4 mg/kg in spring 2012, Cu 25.48?±?0.3 mg/kg in winter 2012, Pb 2.12?±?0.8 mg/kg in spring, and Ni 19.25?±?7.1 mg/kg in spring. The values of heavy metal analysis were compared to both the Turkish Food Codex (TFC) limits and international standards for human consumption. The Pb, As, and Cu levels were found to be higher than the maximum allowable limits.     

Enhanced uptake of heavy metals in municipal solid waste compost by turfgrass following the application of EDTA

Enhancement of multiple heavy metal uptake from municipal solid waste (MSW) compost by Lolium perenne L. in a field experiment was investigated with application of EDTA. EDTA was added in solution at six rates (0–30 mmol kg^???1) after 50 days of plant growth. Two weeks later, plants were harvested for the first crop and then all the turfgrasses were mowed. After another 30 days of growth, EDTA was added again at above six rates to the corresponding sites and the second crop was harvested 2 weeks later. The results showed that EDTA significantly increased heavy metal accumulation in both crops of L. perenne. For the first crop, the concentrations of Mn, Ni, Cd, and Pb in the shoots increased remarkably with increasing EDTA supply, peaked at 25 mmol kg^???1 EDTA, and shoots of 0–5 cm height (shoots from medium surface to 5 cm height) had higher metal concentrations than 5–10 cm and >10 cm shoots. The highest concentration of Mn, Ni, Cd, and Pb was 2.3-, 2.3-, 2.6-, and 3.2-fold, respectively, in 0–5 cm shoots higher than control. For the second crop, the concentrations of Mn, Cu, and Pb in shoots were, in general, less than those in the first crop. However, the second crop was significantly higher (P?< 0.05) than the first crop in dry biomass, so the total amount of metals removed by the second crop was more than the first crop. In addition, EDTA significantly increased the translocation ratios of most heavy metals from roots to shoots. For the first crop, 38% of the total Zn, 51% of Cd, 49% of Pb, 60% Mn, 55% Ni, and 45% Cu taken up by the plant was translocated in the shoots of 0–5 cm height. Turfgrass would have potential for use in remediation of heavy metals in MSW compost or contaminated soils.     

Effect of wastewater irrigation on vegetables in relation to bioaccumulation of heavy metals and biochemical changes

The present study was conducted to determine the heavy metal contamination in soil with accumulation in edible parts of plants and their subsequent changes in biochemical constituents due to wastewater irrigation. Though the wastewater contains low levels of the heavy metals (Fe, Mn, Pb, Cd, and Cr), the soil and plant samples show higher values due to accumulation. The trend of metal accumulation in wastewater-irrigated soil is in the order: Fe > Pb > Mn > Cr > Cd. Of the three species Colocasia esculentum, Brassica nigra, and Raphanus sativus that are grown, the order of total heavy metal accumulation in roots is Raphanus sativus > Colocasia esculentum, while in shoots the order is Brassica nigra > Colocasia esculentum > Raphanus sativus. The enrichment factor (EF) of the heavy metals in contaminated soil is in the sequence of Cd (3) > Mn (2.7) > Cr (1.62) > Pb (1.46) > Fe (1.44), while in plants EF varies depending upon the species and plant part. C. esculentum and R. sativus show a higher EF for Cr and Cd. All plants show a high transfer factor (TF > 1) for Cd signifying a high mobility of Cd from soil to plant whereas the TF values for Pb are very low as it is not bioavailable. Results of the biochemical parameters show decrease in total chlorophyll and total amino acid levels in plants and an increase in amounts of soluble sugars, total protein, ascorbic acid, and phenol except B. nigra for protein in plants grown in soil irrigated with wastewater as compared to control site.     

Spatial distribution and potential ecologic risk assessment of heavy metals in the sediments of the Nansi Lake in China

The contamination levels and ecological risks of heavy metals in the sediments of the Nansi Lake were investigated. The contents of Cd, Cr, Cu, Pb, Zn, Ni, and Co in the surface sediments collected at 20 sites ranged from 0.08 to 1.12, 58.92 to 135.62, 38.09 to 78.65, 24.51 to 53.95, 110.51 to 235.36, 11.30 to 65.40, and 4.12 to 20.14 mg/kg, respectively. The results of partitioning analysis revealed that the proportions of soluble and exchangeable fraction were less than 1 %, the proportions of carbonate, amorphous oxides, organic matter, and crystalline oxides fraction were less than 10 %, and 10.52 % of Cd was associated with carbonate. The average proportions in the residual fraction ranged from 48.62 % for Cu to 73.76 % for Ni, indicating low mobility and bioavailability. The geoaccumulation index (I _geo), relative enrichment factor (REF), sediment pollution index (SPI), and potential effect concentration quotient (PECQ) values of the heavy metals in the sediments were not in agreement with each another. The average REF values of Cd and Zn were higher than those of other metals. However, the average PECQ values were higher for Cr and Ni than those of other metals, indicating that these two metals would cause higher adverse biological effects. Therefore, it is suggested that future management and pollution control might focus on Cd, Zn, Cr, and Ni in the sediments of the Nansi Lake.     

Determination of heavy metal contents in water,sediments, and fish tissues of Shizothorax plagiostomus in river Panjkora at Lower Dir,Khyber Pakhtunkhwa,Pakistan

The present study was conducted to investigate the contamination of water, sediments, and fish tissues with heavy metals in river Panjkora at Lower Dir, Khyber Pakhtunkhwa, Pakistan. Water, sediments, and fish (Shizothorax plagiostomus) samples were collected from September 2012 to January 2013 at three different sites (upstream site at Sharigut, sewage site at Timergara, and downstream site at Sadoo) of river Panjkora. The concentrations of heavy metals in water were in the order Zn?>?Cu?≈?Pb?>?Ni?≈?Cd with mean values of 0.30, 0.01, 0.01, 0.0 and 0.0 mg/l, respectively, which were below the maximum permissible limits of WHO for drinking water. In sediments, heavy metals were found in the order Cu?>?Zn?>?Ni?>?Pb?>?Cd with mean concentrations of 50.6, 38.7, 9.3, 8, and 0.4 mg/kg, respectively. Ni and Cd were not found in any fish tissues, but Zn, Cu, and Pb were detected with the mean concentration ranges of 0.04–1.19, 0.03–0.12, and 0.01–0.09 μg/g, respectively. The present study demonstrates that disposal of waste effluents causes a slight increase in the concentration of heavy metals in river Panjkora as revealed by variation in metal concentrations from upstream to downstream site. Sewage disposal was also found to change physicochemical characteristics of Panjkora water. At present, water and fish of river Panjkora are safe for human consumption, but the continuous sewage disposal may create problems in the future.     

Distribution and fractionation of cadmium, copper, lead, nickel, and zinc in a calcareous sandy soil receiving municipal solid waste

This study was conducted to evaluate the degree of mobility and fractionation of cadmium (Cd), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn) after the addition of municipal solid sewage sludge (MSS) in a sandy calcareous soil. Treatments were (1) soil application of MSS, (2) soil application of enriched municipal solid waste compost (EMSS), and (3) control soil. The MSS application represented a dose of 200 Mg dry weight per hectare. Soil columns were incubated at room temperature for 15 days and irrigated daily with deionized water to make a total of 505 mm. At the end of leaching experiments, soil samples from each column were divided into 14 layers, each being 1 cm down to 10 and 2.5 cm below that and analyzed for diethylenetriaminepentaacetic acid (DTPA)-extractable Cd, Cu, Pb, Ni, and Zn. The fractionation of the heavy metals in the top five layers of the surface soil samples was investigated by the sequential extraction method. All soil layers of the columns receiving MSS and EMSS had significantly higher concentrations of DTPA-extractable heavy metals than control soil. The maximum concentration of heavy metals in treated soil was in the surface layer and declined significantly with depth. Sequential extraction results showed that in the treated soil, a major proportion of Cd, Pb, and Ni was associated with organic matter (OM) and exchangeable (EXCH) fractions, and a major proportion of Cu and Zn was associated with residual (RES) and OM fractions. Based on relative percent, Pb, Cd, and Ni in the EXCH fraction was higher than Cu and Zn in soil leached with MSS and EMSS, suggesting that application of this MSS to a sandy calcareous soil, at the loading rate used here, may pose a risk in terms of groundwater contamination with Pb, Cd, and Ni.     

Accumulation of heavy metals in Spinacia oleracea irrigated with paper mill effluent and sewage

The present study on heavy metal contamination in soil and their accumulation in edible part (leaves) and roots of Spinacia oleracea (Spinach) on irrigation with paper mill effluent (PME)/sewage revealed that there was significant increase in the nickel (Ni, +227.17 %) content of the soil irrigated with PME, whereas in the soil irrigated with sewage chromium (Cr, +274.84 %), iron (Fe, +149.56 %), and cadmium (Cd, +133.39 %), contents were increased appreciably. The value of enrichment factor (EF) for Ni (3.27) indicated moderate enrichment in PME-irrigated soil. The EF of Fe, zinc (Zn), Cd, and Cr were <2 in PME effluent-irrigated soil which showed deficiency of minimal enrichment. In sewage irrigated soil, EF value for Cr, Fe, and Cd indicated moderate enrichment, while the values for Zn and Ni indicated deficiency of minimal enrichment. Among various metallic concentrations, the maximum concentration of Fe was observed in leaves (400.12?±?11.47 mg/kg) and root (301.41?±?13.14 mg/kg) of S. oleracea after irrigation with PME, whereas the maximum concentrations of Fe was found in leaves (400.49?±?5.97 mg/kg) and root (363.94?±?11.37 mg/kg) of S. oleracea after irrigation with sewage for 60 days. The bioaccumulation factor value was found maximum for Cd (2.23) in the plants irrigated with PME while that of Fe (0.90) in the plants irrigated with sewage. The undiluted use of PME/sewage for irrigation increased the concentration of Cr, Cd, Zn, Ni, and Fe metals which were accumulated in S. oleracea, posing a potential threat to human health from this practice of irrigation.     

Contamination assessment of arsenic and heavy metals in a typical abandoned estuary wetland—a case study of the Yellow River Delta Natural Reserve

Coastal and estuarine areas are often polluted by heavy metals that result from industrial production and agricultural activities. In this study, we investigated the concentration trait and vertical pattern of trace elements, such as As, Cd, Ni, Zn, Pb, Cu, and Cr, and the relationship between those trace elements and the soil properties in coastal wetlands using 28 profiles that were surveyed across the Diaokouhe Nature Reserve (DKHNR). The goal of this study is to investigate profile distribution characteristics of heavy metals in different wetland types and their variations with the soil depth to assess heavy metal pollution using pollution indices and to identify the pollution sources using multivariate analysis and sediment quality guidelines. Principal component analysis, cluster analysis, and pollution level indices were applied to evaluate the contamination conditions due to wetland degradation. The findings indicated that the concentration of trace elements decreased with the soil depth, while Cd increases with soil depth. The As concentrations in reed swamps and Suaeda heteroptera surface layers were slightly higher than those in other land use types. All six heavy metals, i.e., Ni, Cu, As, Zn, Cr, and Pb, were strongly associated with PC1 (positive loading) and could reflect the contribution of natural geological sources of metals into the coastal sediments. PC2 is highly associated with Cd and could represent anthropogenic sources of metal pollution. Most of the heavy metals exhibited significant positive correlations with total concentrations; however, no significant correlations were observed between them and the soil salt and soil organic carbon. Soil organic carbon exhibited a positive linear relationship with Cu, Pb, and Zn in the first soil layer (0–20 cm); As, Cr, Cu, Ni, Pb, and Zn in the second layer (20–40 cm); and As, Cr, Cu, Ni, Pb, and Zn in the third layer (40–60 cm). Soil organic carbon exhibited only a negative correlation with Cd (P?I _geo values), which averaged less than 0 in the three soil layers, this finding indicates that the soils have remained unpolluted by these heavy metals. The mean concentrations of these trace elements were lower than Class I criteria. The degradation wetland restoration suggestions have also been provided in such a way as to restore the reserved flow path of the Yellow River. The results that are associated with trace element contamination would be helpful in providing scientific directions to restore wetlands across the world.     

Trace metals in soil and vegetables and associated health risk assessment

The objective of this study was to assess the contamination level of trace metals in soil and vegetables and health risk to the urban population in Bangladesh. The range of Cr, Ni, Cu, As, Cd, and Pb in agricultural soils was 158–1160, 104–443, 157–519, 41–93, 3.9–13, and 84–574 mg/kg, respectively. Sequential extraction tests revealed that the studied metals were predominantly associated with the residual fraction, followed by the organically bound phase. Concerning Cu, Ni, Cd, and Pb in vegetables, more than 50 % samples exceeded the FAO/WHO recommended permissible limits. Considering the transfer of metals from soil to vegetables, Cu and Cd exhibited higher transfer factor (TF) values than the other metals. Target hazard quotient (THQ) for individual metal was below 1, suggesting that people would not experience significant health hazards if they ingest a single metal from vegetables. However, total metal THQ signifies the potential non-carcinogenic health hazard to the highly exposed consumers. The carcinogenic risk (TR) of As (1.9?×?10^?4) and Pb (2.3?×?10^?5) through consumption of vegetables were higher than the USEPA threshold level (10^?6), indicating potential cancer risks.     

The influence of chemical protection on the content of heavy metals in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) growing on the soil enriched with granular sludge

The presence of heavy metals in Triticum aestivum L. growing on the soil enriched with granular sludge after chemical protection was observed. The five variants of treatments using herbicide (Chwastox Turbo 340SL) and four fungicides (Topsin M 500SC, Amistar 250SC, Artea 330EC, and Falcon 460EC) were performed. On control and experimental plots, the concentration of Ni, Pb, Cr, and Cu in wheat leaves were in the range 0.32–0.99, 0.92–1.57, 0.89–6.31, and 7.08–12.59 mg/kg and in grains 0.03 to 0.11, 0.14–0.25, 0.11–0.76, and 1.06–1.46 mg/kg, respectively. The concentration of Pb in grain protected by MCPA and 2,4-D with thiophanate-methyl and azoxystrobin was higher than the maximum levels of 0.20 mg/kg D.M. The bioconcentration factor (BCF) differed and depended on chemical protection. The highest value of BCF was achieved for Cd. The statistical analysis showed a significant correlation between concentration of metals and quality parameters of wheat. One observed significant negative correlations between Ni/Zeleny sedimentation value (r = ?0.51) and between Pb/starch content (r = ?0.57). Positive correlations were observed between Cd/yield, the number of grains/ergosterol concentration (respectively, r = 0.41, r = 0.55, r = 0.56), and Zn/thousand grain weight (r = 0.50) at a p ≤ 0.05.     

Small mammals as biomonitors of metal pollution: a case study in Slovenia

The transfer of lead, cadmium, zinc, mercury, copper and molybdenum from soil to the tissues of small mammals inhabiting differently polluted areas in Slovenia was investigated. Metals were determined in soil samples and in the livers of 139 individuals of five small mammal species, collected in 2012 in the vicinity of a former lead smelter, the largest Slovenian thermal power plant, along a main road and in a control area. The area in the vicinity of former lead smelter differs considerably from other study areas. The soil from that area is heavily polluted with Pb and Cd. The mean metal concentrations in the liver, irrespective of species, varied in the following ranges—Pb: 0.40–7.40 mg/kg fw and Cd: 0.27–135 mg/kg fw and reached effect concentrations at which toxic effects can be expected in a significant proportion of the livers of the small mammal specimens (Pb 40 %, Cd 67 %). These findings indicate that the majority of small mammals trapped in the area of the former lead smelter are at risk of toxic effects due to the very high bioaccumulation of Pb and Cd in the organism. On the contrary, Pd and Cd concentrations in the livers of small mammals sampled in the vicinity of the thermal power plant and along the main road were comparable with reference values and considerably lower than effect concentrations. Additionally, the study suggests that Apodemus flavicollis and Myodes glareolus are very suitable biomonitors of metal pollution.     

Heavy metal contamination of urban soils and dusts in Guangzhou, South China

The heavy metal concentrations of soil and dust samples from roadside, residential areas, parks, campus sport grounds, and commercial sites were studied in Guangzhou, South China. Heavy metals in samples were determined by inductively coupled plasma atomic emission spectrophotometer following acidic digestion with HClO₄ + HF + HNO₃. High concentrations, especially of Cd, Pb, and Zn, were found with mean concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in the urban dusts being 4.22?±?1.21, 62.2?±?27.1, 116?±?30, 31.9?±?12.6, 72.6?±?17.9, and 504?±?191 mg/kg dry weight, respectively. The respective levels in urban soils (0.23?±?0.19, 22.4?±?13.8, 41.6?±?29.4, 11.1?±?5.3, 65.4?±?40.2, and 277?±?214 mg/kg dry weight, respectively), were significantly lower. The integrated pollution index of six metals varied from 0.25 to 3.4 and from 2.5 to 8.4 in urban soils and dusts, respectively, with 61 % of urban soil samples being classified as moderately to highly polluted and all dust samples being classified as highly polluted. The statistical analysis results for the urban dust showed good agreement between principal component analysis and cluster analysis, but distinctly different elemental associations and clustering patterns were observed among heavy metals in the urban soils. The results of multivariate statistic analysis indicated that Cr and Ni concentrations were mainly of natural origin, while Cd, Cu, Pb, and Zn were derived from anthropogenic activities.     

Assessment of cadmium content of potato grown in Weining County,Guizhou Province,China

A total of 54 soil and 54 potato samples have been collected from Weining County to evaluate the accumulation of cadmium in potatoes. The concentrations of the total Cd and the available Cd in the soil samples have been detected. The total concentrations of Cd were from 0.41 to 10.0 mg/kg with an average value of 2.60 mg/kg in soil. The concentrations of available Cd in the soil were 0.07 to 3.47 mg/kg with an average value of 0.59 mg/kg. The concentration of the available Cd showed a good linear positive correlation with the total Cd content in the soil. For the 54 potato samples, the Cd concentrations were from 0.023 to 0.18 mg/kg with an average value 0.083 mg/kg (fresh weight).The bioconcentration factor (BCF) values of Cd in potatoes, based on dry weight, were from 0.02 to 0.96 with an average value 0.24. The uptake of cadmium by plants is dependent on various soil and environmental factors. A regression model to predict the concentration of cadmium in Weining potatoes based on soil properties and elevation was developed. The results showed the elevation and the soil pH played an important role and had a negative influence on the uptake of Cd by potato in Weining County. The mean intake of Cd by adults through consumption of potato from Weining would be 5.9 μg/day, and it is well below the provisionally tolerable daily intake for Cd (70 μg/day).     

Vertical distribution of heavy metals in soil profile in a seasonally waterlogging agriculture field in Eastern Ganges Basin

The accumulation of heavy metals in soil and water is a serious concern due to their persistence and toxicity. This study investigated the vertical distribution of heavy metals, possible sources and their relation with soil texture in a soil profile from seasonally waterlogged agriculture fields of Eastern Ganges basin. Fifteen samples were collected at ～0.90-m interval during drilling of 13.11 mbgl and analysed for physical parameters (moisture content and grain size parameters: sand, silt, clay ratio) and heavy metals (Fe, Mn, Cr, Cu, Pb, Zn, Co, Ni and Cd). The average metal content was in the decreasing order of Fe?>?Mn?>?Cr?>?Zn?>?Ni?>?Cu?>?Co?>?Pb?>?Cd. Vertical distribution of Fe, Mn, Zn and Ni shows more or less similar trends, and clay zone records high concentration of heavy metals. The enrichment of heavy metals in clay zone with alkaline pH strongly implies that the heavy metal distributions in the study site are effectively regulated by soil texture and reductive dissolution of Fe and Mn oxy-hydroxides. Correlation coefficient analysis indicates that most of the metals correlate with Fe, Mn and soil texture (clay and silt). Soil quality assessment was carried out using geoaccumulation index (I _geo), enrichment factor (EF) and contamination factor (CF). The enrichment factor values were ranged between 0.66 (Mn) and 2.34 (Co) for the studied metals, and the contamination factor values varied between 0.79 (Mn) and 2.55 (Co). Results suggest that the elements such as Cu and Co are categorized as moderate to moderately severe contamination, which are further confirmed by I _geo values (0.69 for Cu and 0.78 for Co). The concentration of Ni exceeded the effects-range median values, and the biological adverse effect of this metal is 87 %. The average concentration of heavy metals was compared with published data such as concentration of heavy metals in Ganga River sediments, Ganga Delta sediments and upper continental crust (UCC), which apparently revealed that heavy metals such as Fe, Mn, Cr, Pb, Zn and Cd are influenced by the dynamic nature of flood plain deposits. Agricultural practice and domestic sewage are also influenced on the heavy metal content in the study area.     

Predicting bioavailability of metals from sludge-amended soils

We attempted to develop a protocol for fixing the maximum permissible limit of sludge in agricultural lands based on transfer of metals from sludge-amended soils to human food chain. For this purpose, spinach was grown as a test crop on acid and alkaline soils with graded doses of sludge (0, 1.12, 2.24, 4.48, 8.96, 17.9, 35.8, 71.6, 142 and 285 g kg^?1 of soil) in a pot experiment. Biomass yield of spinach was increased due to sludge application in both acid and alkaline soils. Among the chemical extractants, EDTA extracted the highest amount of metals from sludge-amended soil followed by diethylenetriaminepentaacetic acid (DTPA) and CaCl₂. Elevated levels of Zn, Cu, Fe, Mn, Ni, Cd and Pb in spinach were observed due to sludge application over control. Application of sludge was more effective in increasing metal content in spinach grown on acid soil than alkaline soil. Solubility-free ion activity model as a function of pH, organic carbon and extractable metal was far more effective in predicting metal uptake by spinach grown on sludge-amended soils as compared to that of chemical extractants. Risk in terms of hazard quotient (HQ) for intake of metals through consumption of spinach by humans grown on sludge-treated soils was computed for different metals separately. In a 90-day pot experiment, safe rates of sludge application were worked out as 4.48 and 71.6 g kg^?1 for acid and alkaline soils, respectively.     

The high potential of Pelargonium roseum plant for phytoremediation of heavy metals

The major objective of this investigation was to evaluate the potential of scented geraniums, Pelargonium roseum, to uptake and accumulate heavy metals nickel (Ni), cadmium (Cd), or lead (Pb). For this, plants were grown in an artificial soil system and exposed to a range of metal concentrations over a 14-day treatment period. Then, metals from the entire biomass were extracted. The results showed that scented geranium plants accumulated in excess of 20,055 mg of Ni kg^?1 dry weight (DW) of root and 10,889 mg of Ni kg^?1 DW of shoot, and in excess of 86,566 mg of Pb kg^?1 DW for roots and 4,416 mg of Pb kg^?1 DW for shoots within 14 days. Also, the uptake and accumulation of cadmium in roots of scented geranium plants increased with the exposure at low (250, 500 mg?L^?1) and medium level (750 mg?L^?1) followed by a decline at the highest level (1,000 mg?L^?1). The highest accumulation in roots (31,267 mg?kg^?1 DW) was observed in 750 mg?L^?1 cadmium treatment. In the shoots of scented geraniums, the highest amount of metal accumulation (1,957 mg?kg^?1 DW) was detected at 750 and 1,000 mg?L^?1 of cadmium in the culture solution. Finally, since the high concentrations of Ni or Pb accumulated in shoots of scented geranium has far exceeded 0.1 % DW and for Cd has far exceeded 0.01 % DW, P. roseum is a new hyperaccumulator species for these metals and can be used in phytoremediation industry.     

Effect of citric acid on metals mobility in pruning wastes and biosolids compost and metals uptake in <Emphasis Type="Italic">Atriplex halimus</Emphasis> and <Emphasis Type="Italic">Rosmarinus officinalis</Emphasis>

To assess metal mobility in pruning waste and biosolids compost (pH?6.9 and total concentration of metals in milligram per kilogram of Cd 1.9, Cu 132, Fe 8,513, Mn 192, Pb 81, and Zn 313), shrubs species Atriplex halimus and Rosmarinus officinalis were transplanted in this substrate and irrigated with citric acid (4 g?L^?1, pH?2.9) and nutrient solution daily for 60 days. Citric acid significantly increased the concentrations of soluble Mn and Fe in the nutrient substrate solution measured by suction probes, while other metals did not vary in concentration (Cu and Zn) or were not observed at detectable levels (Cd and Pb). In plants, citric acid significantly increased the concentrations of Cu (2.7?±?0.1–3.3?±?0.1 mg?kg^?1), Fe (49.2?±?5.2–76.8?±?6.8 mg?kg^?1), and Mn (7.2?±?1.1–11.4?±?0.7 mg?kg^?1) in leaves of R. officinalis, whereas the concentration of only Mn (25.4?±?0.3–42.2?±?2.9 mg?kg^?1) was increased in A. halimus. Increasing Fe and Mn solubility by citric acid addition indicates the possibility of using it to improve plant nutrition. The mobility of metals in this substrate was influenced for the concentration of the metal, the degree of humification of organic matter and its high Fe content.     

Associations of cadmium, zinc, and lead in soils from a lead and zinc mining area as studied by single and sequential extractions

An exploratory study of the area surrounding a historical Pb?CZn mining and smelting area in Zawar, India, detected significant contamination of the terrestrial environment by heavy metals. Soils (n?=?87) were analyzed for pH, EC, total organic matter (TOM), Pb, Zn, Mn, and Cd levels. The statistical analysis indicated that the frequency distribution of the analyzed parameters for these soils was not normal. The median concentrations of metals in surface soils were: Pb 420.21 ?? g/g, Zn 870.25 ?? g/g, Mn 696.70 ?? g/g, and Cd 2.09 ?? g/g. Zn concentrations were significantly correlated with Cd (r?=?0.867), indicating that levels of Cd are dependent on Zn. However, pH, electrical conductivity and total organic matter were not correlated significantly with Cd, Pb, Zn, and Mn. To assess the potential mobility of Cd, Pb, and Zn in soils, single (EDTA) as well as sequential extraction scheme (modified BCR) were applied to representative (n?=?23) soil samples. The amount of Cd, Pb, and Zn extracted by EDTA and their total concentrations showed linear positive correlation, which are statistically significant (r values for Cd, Pb, and Zn being 0.901, 0.971, and 0.795, respectively, and P values being <0.001). The correlation coefficients indicate a strong relation between EDTA-extractable metal and total metal. These results appear to justify the use of ??total?? metal contents as a useful preliminary indicator of areas where the risks of metal excess or deficiency are high. The EDTA extractability was maximum for Cd followed by Pb and Zn in soils from all the locations. As indicated by single extraction, the apparent mobility and potential bioavailability of metals in soils followed the order: Cd ?? Pb >?> Zn. Soil samples were sequentially extracted (modified BCR) so that solid pools of Cd, Zn, and Pb could be partitioned into four operationally defined fractions viz. acid-soluble, reducible, oxidizable, and residual. Cadmium was present appreciably (39.41%) in the acid-soluble fraction and zinc was predominantly associated (32.42%) with residual fraction. Pb (66.86%) and Zn (30.44%) were present mainly in the reducible fraction. Assuming that the mobility and bioavailability are related to solubility of geochemical forms of metals and decrease in the order of extraction, the apparent mobility and potential metal bioavailability for these contaminated soil samples is Cd > Zn > Pb.