Remediation of contaminated soil using soil washing and biopile methodologies at a field level

Background, Aims and Scope  An out-of-service oil distribution and storage station (ODSS), which operated from 1966 to 2000 in Mexico, is contaminated mainly by gasoline and diesel, showing the presence of methyl-tert-butyl-ether, benzene, toluene, ethyl benzene, and xylenes. Nine of the 16 polycyclic aromatic hydrocarbons were found, as well as Fe, Pb, V, and Zn. The health risk assessment suggested the necessity of reducing of three PAHs [benzo(a)anthracene, benzo(a)pyrene, and benzo-(b)fluoranthene], and vanadium. The aim of this work is to show that soil washing (on-site) and biopiles are excellent remediation methodologies to treat soils contaminated with petroleum derivates and metals. Applying them, it is possible to reach the goal value of 2,000 mg TPH/kg in a few months, as requested by Mexican legislation. Methods  More than 140 m³ were excavated from the ODSS. Three soil-washing dishes were built. 1540 m³ were treated by soil washing using a nonionic surfactant. A 100 m³ biopile was built to study the system capabilities in the biodegradation of around 4,500 mg/kg of TPH using the autochthonous microflora. Results and Discussion  The soil washing, average TPH-removal value was 83%, but values up to ca. 93% were observed. Removal values resulted in a function of the TPH initial values. Biopile (100 m³) worked during 66 days, reaching a TPH-removal value of 85%. At the end of the processes, no PAHs were detected. The contaminated soil was treated successfully, reaching the legislation limits (TPH values under 2,000 mg/kg, and a significant reduction in PAH concentrations). Conclusion and Recommendation  Both systems are suitable for remediation purposes, achieving high removal efficiencies at short and medium stages. It is highly recommended to proceed with soil washing studies, identifying new products, and mixtures, which could reduce costs and assure optimum operation.     

Oil residuals in lowland forest soil after pollution with crude oil

Research on oil residuals in lowland forest soil was carried out in 6 sample plots in the lowland forest ecosystem located in an oil field. Four plots were differently affected in terms of discharged oil and the time lapsed after the accident, as well as in terms of micro-relief terrain features. One plot was established in a reclaimed mud ditch site, while the control plot was set up in a micro-relief elevation outside the influence of oil pollution. Total petroleum hydrocarbon (TPH) concentrations were measured at three soil depths at the beginning and the end of the vegetation period. The analysis of the results revealed significant differences in petroleum hydrocarbon concentrations among the sites. Increased TPH concentrations were recorded in several plots, while the values measured in some other plots indicated very low quantities of residual TPH in the soil. The highest average TPH concentrations (200–400 mg kg¹) were recorded in the mud ditch site. In one of the plots exposed to oil pollution after an oil pipe rupture, there was the constant presence of increased TPH concentration in the surface soil part (≥200 mg kg¹ on average). The sporadic presence of increased TPH concentrations in micro-depressions that cannot be attributed to a local accident indicates seasonal soil pollution with petroleum carbohydrates from floodwater. The soil in the sample plots is not contaminated with soluble salts or heavy metals. Low values of TPH concentrations in the soil water eluate indicate that the soil does not represent a source of hydrospheric pollution with petrol hydrocarbons.     

Total petroleum hydrocarbons and heavy metals in road-deposited sediments in Tijuana,Mexico

Purpose

A study was carried out to evaluate the concentration of heavy metals (Pb, Cu, Cr, Cd, and Hg) and total petroleum hydrocarbons (TPH) in road-deposited sediments (RDS) from Tijuana, Mexico, and identify their possible sources.

Materials and methods

Thirty RDS samples were randomly collected during the dry season using a brush and dustpan and classified according to construction material, traffic intensity, and land use. Soil samples were collected from a nonurban area and their concentrations were used as background values. For TPH, the samples were quantified gravimetrically after Soxhlet extraction, whereas heavy metals were extracted by acid digestion and their concentrations were measured by atomic absorption spectrometry.

Results and discussion

The mean TPH concentrations for RDS were 4208 mg kg^?1 and ranged from 1186 to 9982 mg kg^?1. For heavy metals, mean concentrations were 31.8, 50.2, 17.1, 0.1, and 0.1 mg kg^?1 for Pb, Cu, Cr, Cd, and Hg, respectively. The Igeo results showed that RDS from Tijuana are moderately to strongly polluted with Pb and Cu and moderately polluted with Cr. Principal component analysis (PCA) showed that Pb, Cu, and Cr could have their origin in tire wear, brake pads, bearings, and bushings.

Conclusions

The findings of this study revealed that RDS from Tijuana are polluted with TPH and heavy metals and that their principal sources are anthropogenic activities.

     

中国原油污染区重金属空间分布模式及其潜在来源研究

Twenty-two soil samples were collected at the subregional scale （50 km2） around Gudao Town, a typical oil-producing region of the Shengli Oilfield in the Yellow River Delta, China to determine the spatial distribution patterns and potential sources of heavy metals in soils of crude oil-polluted regions. The concentrations of total petroleum hydrocaxbons （TPHs） and heavy metals as well as other soil properties were determined and the enrichment factor values were calculated for the heavy metals measured. Principal component analysis （PCA） and cluster analysis （CA） were used to estimate potential sources contributing to the concentrations of heavy metals in the soils. The results revealed that the soils were slightly alkaline （pH = 7.33-8.05） and high in salinity （1.43-41.30 g kg-1）, TPHs （0.51 28.40 g kg-1） and organic matter （1.74-31.50 g kg-1）. The mean concentrations of the measured heavy metals Cu, Zn, Pb, Cd, Cr, Ni and V were 18.4, 78.2, 20.8, 0.19, 56.6, 26.3 and 62.1 mg kg-1, respectively. Although the concentrations of all the metals measured in this study were not high enough to exceed the national control standards, there was a significant enrichment of Cd in the study area and Zn and Ni were in the category of deficiency to minimal enrichment. The spatial distribution patterns of Cu, Cr, Ni and V were similar and partially affected by oil exploitation and petroleum hydrocarbon spills. Potential sources of Cr, Ni, V and Cu in the soils were both natural sources and petroleum hydrocarbon spills, while Zn, Pb and Cd were probably from anthropogenic sources such as farming activities and traffic.     

Use of the BCR three-step sequential extraction procedure for the study of the partitioning of Cd, Pb and Zn in various soil samples

A slightly modified three-step sequential extraction procedure proposed by the Community Bureau of Reference (BCR) for analysis of sediments was successfully applied to soil samples. Contaminated soil samples from the lead and zinc mining area in the Mezica valley (Slovenia) and natural soils from a non-industrial area were analysed. The total concentrations of Cd, Pb and Zn and their concentrations in fractions after extraction were determined by flame or electrothermal atomic absorption spectrometry (FAAS, ETAAS). Total metal concentrations in natural soils ranged from 0.3 to 2.6 mg kg^-1 for Cd, from 20 to 45 mg kg^-1 for Pb and from 70 to 140 mg kg^-1 for Zn, while these concentrations ranged from 0.5 to 35 mg kg^-1 for Cd, from 200 to 10000 mg kg^-1 for Pb and from 140 to 1500 mg kg^-1 for Zn in soils from contaminated areas. The results of the partitioning study applying the slightly modified BCR three-step extraction procedure indicate that Cd, Pb and Zn in natural soils prevails mostly in sparingly soluble fractions. Cd in natural soils is bound mainly to Fe and Mn oxides and hydroxides, Pb to organic matter, sulphides and silicates, while Zn is predominantly bound to silicates. In contaminated soils, Cd, Pb and Zn are distributed between the easily and sparingly soluble fractions. Due to the high total Cd, Pb and Zn concentrations in contaminated soil close to the smelter, ! and their high proportions in the easily soluble fraction (80% of Cd, 50% of Pb and 70% of Zn), the soil around smelters represents an environmental hazard.     

Effects of Distance and Depth on Total and Bioaccessible Lead Concentrations in Soils from Two Farmhouses in Beltsville,Maryland

Movement of soil lead (Pb) has been studied, but Pb bioaccessiblity as a function of distance and depth from houses with histories of lead paint use needs to be investigated. This study investigated the effect of distance and depth on total and bioaccessible Pb near two houses with histories of lead paint use. Soil samples were collected at four distances and four depths. Total and bioaccessible Pb were extracted using 1 N ammonia nitrate and 0.4 m glycine, respectively. Bioaccessible Pb ranged from 27 to 886 mg kg^?1 and from 187 to 4796 mg kg^?1 for houses 1 and 2, respectively. Total and bioaccessible Pb concentrations were greatest at the 0.5 m distance and 2.5 cm depth for both houses. Percentage of total Pb that was bioaccessible at lower horizons was greater than or equal to that of the surface soil. Soil Pb reduction with increasing distance and depth makes it amenable to soil remediation.     

Fractionation of chromium in tannery sludge-amended soil and its availability to fenugreek plants

Purpose

Fenugreek (Trigonella foenum-graecum L.) is a medicinal plant with antidiabetic effects. Chromium has been related to better glucose tolerance in humans. The objective of this study was to determine whether tannery sludge could be used for Cr biofortification of fenugreek.

Materials and methods

Soil was mixed with tannery sludge containing 6.03 g Cr kg^?1. All Cr was in the form of Cr(III). Three treatments were disposed: control without sludge, and two treatments with 10 and 20 g sludge kg^?1, respectively. Control and the 10 g sludge kg^?1 treatments received NPK fertilizer to adjust the concentrations of major mineral nutrients to similar levels in all treatments. Soils were potted and planted with fenugreek. Plants harvested at the initial flowering stage were analysed for total Cr, Fe, Zn and Pb. Sequential soil extraction was applied to obtain operationally defined soil Cr fractions.

Results and discussion

Total Cr in all treatments was below or within the allowable range for agricultural soils (100–150 mg kg^?1). In control soils, most Cr was in the residual fraction (HF/HClO₄ digest). Tannery sludge-amended soils incorporated most Cr into the moderately reducible fraction (oxalic acid/ammonium oxalate extract). In fenugreek shoots, Cr concentrations reached 3.2 mg Cr kg^?1, a higher concentration than that reported for other leafy vegetables. Lead concentrations in plant shoots from this treatment were enhanced but hardly exceeded 1 mg Pb kg^?1.

Conclusions

Tannery sludge-amended soils containing Cr within the range of permissible concentrations can increase shoot Cr in fenugreek. Only sludge with low Pb concentrations should be used for Cr biofortification of fenugreek.     

Application of Organic Wastes in a Soil Polluted with Different Rates of Cr-Pb: Effects on Soil Biological Properties

An experiment was performed to determine the effects of adding municipal solid waste (MSW) and poultry manure (PM) to a soil polluted with chromium (Cr), lead (Pb), and Cr + Pb on the biological parameters of the soil. Soil was mixed with two solutions of Cr(NO₃)₃ and/or Pb(NO₃)₂ to give three concentrations (0, 100, and 250 mg Cr kg^?1 soil and 0, 100, and 250 mg Pb kg^?1 soil) and treated with MSW or PM. When the soil was contaminated with the metals without combining, the greatest adenosine triphosphate (ATP), urease, and phosphatase inhibition percentages occurred for 250 mg Pb kg^?1 soil. When the heavy metals were mixed, the inhibition of the biochemical parameters increased. The application of MSW and PM decreased the inhibition of the biochemical parameters and microbial population in the polluted soils. The inhibition percentage was greater for the soil amended with MSW than with PM, possibly due to the high humic acid concentration.     

Distribution of Heavy Metals in Near-Shore Sediments of the Swan River Estuary,Western Australia

Estuarine systems adjacent to urban areas are at risk of contamination by contaminants from anthropogenic sources, such as heavy metals. We anticipated that the sediments of the Swan River estuary, which runs through metropolitan Perth in Western Australia, would show metal contamination related to industrialization and inputs of stormwater. Total Cu, Pb and Cd concentrations, and Cu, Pb, Cr and Zn inoperationally-defined fractions, were determined inseparate sampling exercises in near-shore sediments ofthe upper Swan River estuary.Total metal concentrations in sediments were not high (maximum values of 297 mg kg^-1 for Cu, 184 mg kg^-1 for Pb and 0.9 mg kg^-1 for Cd) when compared with Australian environmental assessmentguidelines for soils. On the basis of linear regressions between sediment metal concentrations andphysicochemical properties of the sediments (pH, organic carbon, particle size distribution), no single parameter could explain the variation in metal concentrations for all metals. Sediment organic carbon content was positively correlated with Cu concentration; Cu concentrations also increased significantly with increasing clay content anddecreasing sand content. Pb concentrations showed a significant increase with increasing sediment pH, and were approximately three-fold higher in sediments adjacent to stormwater drain outfalls than in sediments remote from drains; no such effect was observed for Cu or Cd. No effect of distance downstream was observed. Sequential extraction of sediments showed that most of the metals were in relatively immobile forms, for example bound to Feoxides, or only extractable by aqua regia. The enhanced concentrations of Pb near stormwater outfalls suggest that vehicle-derived Pb may be an important contributor of Pb to the estuary.     

Chemical characterization of heavy-metal contaminated soil in southeast Kansas

A tri-state mining region, including parts of Missouri, Oklahoma, and Kansas, was the site of intense lead and zinc mining and smelting activity until the 1950's. A study was initiated to characterize the heavy-metal contamination of soils in this area. Water-soluble, an index of plantavailable, total, and sequentially extractable metals; organic, and total carbon; and saturated paste pH were determined for mine tailings and soil samples. Mine tailings contained 81 to 89 mg kg^?1 total Cd, 1 150 to 1 370 mg kg^?1 total Pb, and 11 400 to 13 700 mg kg^?1 total Zn. Total concentrations in soil samples were 15 to 86 mg kg^?1 Cd, 35 to 1 620 mg kg^?1 Pb, and 99 to 18 500 mg kg^?1 Zn; and, DTPA extractable concentrations ranged from 0.6 to 10 mg kg^?1 Cd, 7.8 to 68 mg kg^?1 Pb, and 33 to 715 mg kg^?1 Zn. Samples were sequentially extracted to approximate the proportions of the metals in the sulfide, carbonate, organic, sorbed, and exchangeable fractions. For Zn and Cd, concentrations were greatest in the sulfide fraction followed by carbonate, organic, sorbed, and exchangeable. Lead followed the same pattern, except higher concentrations were observed in the sorbed than the organic fractions.     

Removal of Lead from Contaminated Soils by Typha Angustifolia

A greenhouse study was demonstrated for removal of lead (Pb) from contaminated soil by the narrow — leaved cattail, Typha angustifolia. The plants were grown in sandy loam soil containing various concentrations of Pb(NO₃)₂ (53.3, 106.7, 160, 213.3, and 266.7 mg Pb kg^-1 soil). Most lead was accumulated in roots and then transported to leaves. In soil contaminated with 266.7 mg kg^-1 of lead, the plants accumulated 7492.6 mg Pb kg^-1 dry weight in the roots and 167 mg Pb kg^-1 dry weight in the leaves. Yet, no growth retardation from lead was detected. T. angustifolia has high potential as a plant to clean up lead contaminated soil due to its vigorous growth, high biomass productivity, and because it is a perennial in nature. Further work is required to study on the iron plaque formation and its role in metal immobilization.     

Arsenic and Heavy Metal Pollution of Soil,Water and Sediments in a Semi-Arid Climate Mining Area in Mexico

The environmental impact of arsenic and heavy metals on a 105 km² area of the historical and recent mining site of Villa de la Paz-Matehuala, San Luis Potosí (Mexico) was evaluated. Results of soil samples reported concentrations between 19–17 384 mg kg^-1 As, 15–7200 mg kg^-1 Cu, 31–3450 mg kg^-1 Pb and 26–6270 mg kg^-1 Zn, meanwhile, the concentrations in dry stream sediment samples were found to vary between 29–28 600 mg kg^-1 As, 50–2160 mg kg^-1 Pb, 71–2190 mg kg^-1 Cu, and 98–5940 mg kg^-1 Zn. The maximum arsenic concentration in pluvial water storage ponds (265 μg L^-1), near the main potential sources of pollution, exceed by 5 times the Mexican drinking water quality guideline (50 μg L^-1). The arsenic concentrations in water storage ponds and stream sediments decrease as distance from the potential sources increase. A special case is the `Cerrito Blanco' area located 5 km east of Matehuala, where the highest arsenic concentration in water was found (>5900 μg L^-1), exceeding by 100 times the established guideline, thus representing a severe health risk. The results suggest that arsenic and heavy metal dispersion from their pollution sources (historical and active tailings impoundments, waste rock dumps and historical slag piles), is mainly associated in this site with: (1) fluvial transportation of mine waste through streams that cross the area in W–E direction; and (2) aeolian transportation of mineral particles in SW–NE direction. Finally, control measures for pollution routes and remediation measures of the site are proposed.     

Accumulation of lead and arsenic by peanut grown on lead and arsenic contaminated soils amended with broiler litter ash or superphosphate

Accumulation of lead (Pb) and arsenic (As) in peanut grown on Pb/As-contaminated soils amended with two sources of phosphorus (P) was investigated. An urban soil and an orchard soil with Pb concentrations of 1120 and 272, and As concentrations of 6.9 and 90 mg kg^-1, respectively, were amended with three rates (0, 56, and 112 kg ha^-1) of P supplied as broiler litter ash or superphosphate and planted with peanuts. At harvest, peanut kernel As concentration was 2.9 mg kg^-1 on the orchard soil and 0.003 mg kg^-1 on the urban soil. Kernel As was not significantly affected by P source and was not significantly different between the normal and high P rates. Kernel Pb concentration was below the instrument detection limit in all cases. Land with history of arsenic or lead-arsenate application should be tested for As before used for peanut production.     

三峡库区土壤重金属背景值研究

在大规模、系统采样的基础上,通过不同均值计算方法的比较,提出了三峡库区土壤重金属含量背景值：As为5．835mg·kg^-1,Cd为0．134mg·kg^-1,Cr为78．03mg·kg^-1,Cu为25．00mg·kg^-1,Hg为0．046mg·kg^-1,Ni为29．47mg·kg^-1,Pb为23．88mg·kg^-2,Zn为69．88mg·kg^-1。与全国土壤背景值比较,三峡库区As、Hg背景含量低于全国背景值,Pb、Zn含量略低于全国背景值,Cd、Cr含量高于全国土壤背景值,Cu、Ni含量略高于全国背景值。根据本研究成果进行三峡库区环境质量评价,将能更加真实地反映三峡库区的实际情况,有利于库区土壤环境质量管理。     

Removal of Heavy Metals from Calcareous Contaminated Soils by EDTA Leaching

The performance of EDTA for the treatment of calcareous soils contaminated with heavy metals from mining and smelting activities was evaluated in this study. Soil samples containing variable levels of contamination, from 500 to 35 000 mg kg^-1 Pb and 700 to 20 000 mg kg^-1 Zn, were subjected to EDTA treatment and the extraction of heavy metals was found to vary, ranging between 50 and 98% for Pb and 50 to 100% for Zn. Total residual concentrations were above the limits set by regulatory authorities; leachable metals, however, were efficiently removed and treated soils were all acceptable in terms of toxicity. The effect of EDTA concentration and pulp density was studied on a soil sample containing 12 000 mg kg^-1 Pb and 10 000 mg kg^-1 Zn. Heavy metals removal was improved at low pulp densities and when EDTA concentration was increased from 0.025 to 0.25 M. The tetrasodium salt Na₄-EDTA was found to be less effective for metals removal compared to the disodium salt Na₂-EDTA, though applied at higher concentrations. This experimental work has also demonstrated the great importance of soil matrix for the overall evaluation of the EDTA leaching as a cost effective remedial option. The simultaneous dissolution of calcite was found to consume approximately 90% of the available EDTA. It was thus concluded that for the treatment of calcareous soils the design criteria and cost estimations should be based on the calcite content of the soil.     

Glutamic acid decomposition as a sensitive measure of heavy metal pollution in soil

The effect of added heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) on the rate of decomposition of glutamic acid was studied in four Dutch soil types in order to determine if such measurements would serve as sensitive indicators of heavy metal pollution in soil. The time required to reach the maximum respiration rate (referred to as the decomposition time) with glutamic acid was linearly related to increasing concentrations of Ni in a sandy loam soil.Changes in decomposition time were measured 18 months after addition of 55, 400 or 1000 mg kg^? of Cd, Cr, Cu, Ni, Pb or Zn respectively to sand, silty loam, clay and sandy peat soils. A significant increase in the decomposition time occurred with a concentration of 55 mg kg^?1 of Cd, Cu or Zn in the sand soil. At 400mgkg^?1 adverse effects in the various soils are distinct. The sensitivity of the decomposition time of glutamic acid as a method to measure soil pollution is discussed.     

Modeling Water Quality Impacts of Petroleum Contaminated Soils in a Reservoir Catchment

Soil contamination due to spills or leaks of crude oils andrefined hydrocarbons is a common problem. Estimation of spillvolume is a crucial issue in order to determine the expectedcontaminating life span of contaminated soils. The directprocedure to determine the amount of hydrocarbon in soil is to measure the concentration of total petroleum hydrocarbon (TPH) in soil samples. The primary objective of this study was toassess the potential effects of oil contaminated soils on thewater quality of Devegecidi dam reservoir. For this purpose,limited spill data available were evaluated and soil samplingstudies were conducted in the Beykan oil field to analyze forTPH on oil contaminated soils. Available spill and measured soilTPH data were used in a subsequent modeling study to assess thereservoir water quality impacts due to dissolved mass leachingfrom hydrocarbon contaminated soils. Evaluation of availablespill data between 1989 and 1995 revealed that a total of 252recorded spills resulted in a net spill of 395 tons. The majortypes of oil spills were identified as well heads (WH), returnlines/flow lines (RL/FL), and power oil lines (POL). A total of211 soil samples was collected at selected well heads andanalyzed for TPH in the laboratory. TPH results revealed aconcentration range between 600 and 115 500 mg kg^-1 with a meanconcentration of 20 300 mg kg^-1. Modeling studies focused onbehavior assessment and involved two major components. The firstcomponent is a soil-leaching submodel for estimating theleachate concentration and contaminant mass leaching out of thecontaminated soil body. The second component is a reservoirwater quality submodel assuming complete-mix conditions forestimating the changes of hydrocarbon concentration in thereservoir water as a function of time. These two components arecoupled via a mass inflow term present in the reservoir waterquality model, accounting for contaminant mass loadingcontributed by the leaching of contaminated soil. Simulation runs performed under conservative conditions assuming an annualaverage oil spill volume of 95 tons and the minimum reservoirvolume of 7.3 × 10⁶ m³ revealed that there isno imminent threat to reservoir water quality from the dissolved phase contaminants soils. Limited amount of availablemeasurements of TPH concentrations in soil samples and benzeneconcentrations in reservoir water samples supported model results.     

Critical Toxic Ranges of Chromium in Spinach Plants and in Soil

ABSTRACT

Long-term irrigation with untreated industrial sewage effluents causes accumulation of high concentrations of chromium (Cr) and other heavy metals in soil and subsequently in crop plants (especially leafy vegetables), which can be phytotoxic to plants and/or a health hazard to animals and humans. Greenhouse experiments were conducted to determine the effects of Cr application on the growth of spinach (Spinacia oleracia L.) and to develop critical toxic ranges of Cr in plants and in soil. The study involved growing of spinach variety ‘Punjab Green’ in a greenhouse on silty clay loam and sandy soils equilibrated with different levels of applied Cr (0, 1.25, 2.5, 5, 10, 20, 40, 80, 160, and 320 mg Cr kg^{? 1} soil). Plants were harvested at: three growth stages 45, 60, and 90 days after sowing (DAS). Critical toxic ranges were estimated by regressing and plotting data on ammoniumbicarbonate-diethylenetriaminepenta-acetic acid (AB-DTPA) extractable Cr in soil or Cr concentration in plants versus dry-matter yield (DMY) of spinach at the three growth stages. Toxic ranges, i.e., slightly toxic (80%–90%), moderately toxic (70%–80%), and extremely toxic (< 70%) in terms of DMY relative to the attainable maximum DMY, were established for both soils and for plants at all three growth stages. There was no germination of spinach with applied Cr at 320 mg Cr kg^{? 1} rate in silty clay loam soil and at 40 mg Cr kg^{? 1} rate in sandy soil due to Cr toxicity. Roots accumulated more Cr in comparison with shoots. Chromium concentrations of 0.47–1.93 mg Cr kg^{? 1} soil in silty clay loam soil, 0.13–0.94 mg Cr kg^{? 1} soil in sandy soil, 1.08–5.40 mg Cr kg^{? 1} plant DM in silty clay loam soil and 0.54–11.7 mg Cr kg^{? 1} plant DM in sandy soil were found to be toxic. The critical toxicity ranges of Cr thus established in this study could help in demarcating Cr toxicity in soils and in plants such as spinach and other leafy vegetables due to irrigation of soils with untreated sewage water contaminated with chromium.     

Distribution and Mobility of Trace Elements in Soils and Vegetation Around the Mining and Smelting Areas of Tharsis, Ríotinto and Huelva, Iberian Pyrite Belt, SW Spain

Trace elements may present an environmental hazard in the vicinity of mining and smelting activities. However, the factors controlling their distribution and transfer within the soil and vegetation systems are not always well defined. Total concentrations of up to 15,195 mg . kg ^–1 As, 6,690 mg . kg^–1 Cu, 24,820 mg . kg^–1 Pb and 9,810 mg . kg^–1 Zn in soils, and 62 mg . kg^–1 As, 1,765 mg . kg^–1 Cu, 280 mg . kg^–1 Pb and 3,460 mg . kg ^–1 Zn in vegetation were measured. However, unusually for smelters and mines of a similar size, the elevated trace element concentrations in soils were found to be restricted to the immediate vicinity of the mines and smelters (maximum 2–3 km). Parent material, prevailing wind direction, and soil physical and chemical characteristics were found to correlate poorly with the restricted trace element distributions in soils. Hypotheses are given for this unusual distribution: (1) the contaminated soils were removed by erosion or (2) mines and smelters released large heavy particles that could not have been transported long distances. Analyses of the accumulation of trace elements in vegetation (median ratios: As 0.06, Cu 0.19, Pb 0.54 and Zn 1.07) and the percentage of total trace elements being DTPA extractable in soils (median percentages: As 0.06%, Cu 15%, Pb 7% and Zn 4%) indicated higher relative trace element mobility in soils with low total concentrations than in soils with elevated concentrations.     

Predicting heavy metal transfer from soil to plant: potential use of Freundlich‐type functions

Soil‐plant transfer of metals is a nonlinear process. We therefore aimed at evaluating the potential of Freundlich‐type functions (c_Plant = b × c_Soil^a) to predict Cd, Cu, Pb, and Zn concentrations in wheat (Triticum aestivum L.) grain and leaf (c_Plant) from soil concentrations (c_Soil). Wheat plants and soil A horizons, mainly developed from Holocene sediments, were sampled at 54 agricultural sites in Slovakia. Metals were extracted from soils with 0.025 M EDTA at pH 4.6 and concentrated HNO₃/HClO₄ (3:1); plant samples were digested with concentrated HNO₃. Total metal concentrations of soil samples were 0.07—25 mg Cd kg^—1, 9.3—220 mg Cu kg^—1, 14—1827 mg Pb kg^—1, and 34—1454 mg Zn kg^—1. On average, between 20 % (Zn) and 80 % (Cd) of the total concentrations were EDTA‐extractable. The total metal concentrations of grain samples were < 0.01—1.3 mg Cd kg^—1, 1.3—6.6 mg Cu kg^—1, < 0.05—0.30 mg Pb kg^—1, and 8—104 mg Zn kg^—1. The leaves contained up to 3.2 mg Cd kg^—1, 111 mg Cu kg^—1, 4.3 mg Pb kg^—1, and 177 mg Zn kg^—1. Linear regression without data transformation was precluded because of the nonnormal data distribution. The Freundlich‐type function was suitable to predict Cd (grain: r = 0.71, leaf: 0.86 for the log‐transformed data) and Zn concentrations (grain: 0.69, leaf: 0.68) in wheat grain and leaf from the EDTA‐extractable metal concentrations. The prediction of Cu and Pb concentrations in grain (Cu: r = 0.44, Pb: 0.41) was poorer and in leaf only possible for Pb (0.50). We suggest to use the Freundlich‐type function for defining threshold values instead of linear regression because it is more appropriate to simulate the nonlinear uptake processes and because it offers interpretation potential. The results suggest that the coefficient b of the Freundlich‐type function depends on the intensity of metal uptake, while the coefficient a reflects the plants' capability to control the heavy metal uptake. The latter is also sensitive to metal translocation in plants and atmospheric deposition.<?show $6#>