Bioavailable Fraction Of Heavy Metals Research Articles

Application of Microbial Biosensors to Complement Geochemical Characterisation: a Case Study in Northern China

There are significant concerns about the impact of heavy metal contamination in soils as a consequence of urbanisation and industrialisation in developing countries. Routine chemical analysis of soils is used to measure the total concentration of metals from point source or diffuse activities, but this fails to put in context the bioavailability of the analyte or the potential toxicity of multiple contaminants. Bacterial biosensors provide a useful tool for assessing the toxicity of the bioavailable fraction of heavy metals in soils and for complementing chemical analysis. There are few examples of genuine environmental applications of biosensors for pollutant diagnosis. This study applied constitutively marked biosensors (which were comprehensively characterised) to soils collected from across Northern China (60,000 km2). The biosensors were responsive to soils impacted by As, Cd, Cr, Cu, Hg, Pb, and Zn when compared to ‘uncontaminated controls’. The response of the biosensor correlated with individual (or groups of) metals related to their concentration and source. The geo-accumulation index (I geo) assisted in explaining the biosensor response. The constitutively marked biosensors offered a focussed understanding of analyte bioavailability and placed in a relevant context the elemental analysis. When matrix-matched control samples can be collected, then such a biosensor procedure (as adopted here) is applicable to contrasting soils exposed to a wide range of contaminants. Biosensor applications complemented routine soil chemical analysis for this regional-scale study.

Concentration, Distribution and Comparison of Total and Bioavailable Heavy Metals in Top Soils of Bonab District in Zanjan Province

Heavy metal contamination of soils is a widespread problem in Zanjan province located in North West Iran due to natural pedo geochemical background and anthropogenic sources. The province is highly polluted by some heavy metals due to the presence of mineral resources notably Lead and Zinc, their improper utilization, and also the development of a number of related industries. Bonab district was selected for detail study and the objectives of the study were set to evaluate the total as well as bioavailable fraction of heavy metals in surficial soils within the studied area. 72 soil samples were collected and analyzed for heavy metal contamination by Atomic Absorption Spectrometry (AAS). The obtained results when compared with WHO and USEPA standards show a very high concentration of some toxic metals. Soils were basically polluted by Pb, Zn, Cu, and Cd. Bioavailable fraction of studied metals were also measured with formation of metal complex with Diethylene tri amine penta acetic acid (DTPA) agent. To find the share of the anthropogenic sources in the contamination of soils, the Enrichment factor (EF) and Geological Accumulation Index were measured and the distribution maps were drawn using Arc GIS (9.3). Highest concentrations of some toxic metals were found as isolated patches around the Bonab Industrial Town as well as within and around the most populated areas of the district notably Zanjan city indicating its anthropogenic origin.

Levels of arsenic and heavy metals in the rural soils of Beijing and their changes over the last two decades (1985–2008)

Heavy metal levels in the rural soils are associated with the quality of agricultural products. In this study, soil samples were collected from the rural soils of Beijing; distribution of As, Co, Cr, Cu, Hg, Mn, Ni, Pb, V, Zn and their changes over the last two decades have been investigated. The results indicated that the concentrations of Co, Cr, Mn, Ni, and V were primarily controlled by the parent materials of soils, while concentrations of Hg, As, Cu, Pb, and Zn were affected by anthropogenic activities. Hg concentration in the surface soils was 2–3 times the subsurface soils; slight accumulations of As, Cu, Pb, and Zn in the top soils were also observed. The bioavailable fractions of heavy metals including exchangeable and carbonate-bounded fraction were lower than 10% except for Cr, Mn and Zn. In general, the concentrations of heavy metals in the rural soils of Beijing met environmental quality standard (grade II) for soils of China. Although some elements such as Hg and As have increased significantly in several sample sites, the average concentrations of all heavy metals had no significant change over the past 20 years due to effective environmental protection for many years in Beijing.

Concentrations and Availability Indicators of Soil Heavy Metals; the Case of Children’s Playgrounds in the City of Athens (Greece)

This study reports on the concentrations, distribution, and availability of heavy metals in the children’s playground soils of Athens. Playgrounds were chosen because they are open city areas; they show relatively even spatial distribution within the district of Athens and are used by a great number of young children and their escorts on a regular basis. Samples were collected from 70 playground surface soils, representing more than 70% of the city’s playgrounds. Cu, Zn, Pb, Cr, Ni, Co, Mn, and Fe were extracted by aqua regia and by diethylene triamine pentaacetic acid (DTPA) to estimate total and available metal forms, respectively. Their mean total concentrations were 43, 174, 110, 80, 82, 22, 312, and 17 × 103 mg kg−1, respectively. The DTPA-extracted fraction showed much lower values, with means of 2.5, 7.8, 5.8, 1.5, 1.3, 0.4, 8.4, and 2.0 mg kg−1 respectively, which, however, should be carefully monitored since they relate directly to the bioavailable fraction of heavy metals. Though mean values of metal concentrations are not particularly high, the calculated enrichment factors indicate site-specific cases of high enrichment with heavy metals. Considering that the bioavailable fraction of a metal is possibly a more appropriate indicator for the recent soil pollution history, availability ratios were calculated and their distribution was visualized over the entire city profile using the appropriate GIS software. It was shown that recent metal pollution events appear to have affected mostly playground sites in the southern and eastern part of the municipality.

Concentration, Distribution and Comparison of Total and Bioavailable Metals in Top Soils and Plants Accumulation in Zanjan Zinc Industrial Town-Iran

Heavy metal contamination of metal-mined soils is a widespread problem in parts of Zanjan province. The province located in North West of Iran is highly polluted by heavy metals due to the presence, improper utilization of its mineral resources notably Lead and Zinc, and also the development of a number of related industries. Soils are basically polluted by Pb, Zn and Cd and their concentrations in top soils are very high exceeding European and USEPA standards. The main objective of this study is to evaluate heavy metals concentration and bioavailable fractions of heavy metals and accumulation of such toxic metals in native plants growing naturally on the polluted sites. The information obtained from this study is of great value to obtain bioavailability of the toxic metals and their potential harmful effects for plants, animals and humans.

Heavy Metal Displacement by Exchangeable Bases (Ca, Mg, K, Na) in Soils and Sediments

The extractability of heavy metals with exchangeable bases is of particular importance for two reasons: (i) Ca, Mg, K, and Na form the predominant electropositive elements in the soil solution (on molar basis) and can interact with adsorbed fractions of heavy metals; and (ii) single extractions aimed at ascertaining soil mobile or bioavailable fractions of heavy metals in the soils are for a major part based on these interactions. This article assesses metal extractability by Ca(NO3)(2), Mg(NO3)(2), KNO3, and NaNO3, and competitiveness for adsorption to the soil matrix between the exchangeable bases and the metals Cu, Cd, Cr, Ni, and Pb. To this end, experiments were performed in which a moderately contaminated soil was extracted with varying doses of extractant: 0, 0.05, 0.1, 0.25, 0.5 M of NaNO3, 0, 0.05, 0.1, 0.2, 0.4 M of KNO3, 0, 0.05, 0.1, 0.2 M of Ca(NO3)(2), and 0, 0.05, 0.1, 0.2 M of Mg(NO3)(2). In addition, differences in metal extractability between 0.01 M of Ca(NO3)(2) and 0.01 M of CaCl2 and between 1 M Of MgCl2 and 1 M of Mg(NO3)(2) were evaluated in six soils with varying soil composition and pollution level to assess the effect of the counter ion (Cl- vs. NO3-). Finally, in a third experiment, heavy metal desorption in the presence of increasing concentrations of Ca(NO3)(2) (0-0.1 M) was evaluated in four polluted soils. Total, soil content of a given metal does not suffice to assess its environmental impact and bioavailability. Therefore, the study of metal exchangeability with Ca 21 is proposed to grant additional and complementary insight for soil metal analysis. Extraction with sufficiently high ionic strength, such as 0.1 M of Ca(NO3)(2), can be used to give an estimate of the total exchangeable pool, whereas weaker extractions at around the ionic strength of the soil solution (similar to 0.0 1 M of CaCl2) allow for the estimation of the quantitative responsiveness of metal release as a function of increasing Ca2+ in the extractant solution at around relevant soil solution conditions.

The Use of Bioassays for the Risk Assessment of Toxic Leachates: An Experimental Study

Solid wastes from the oil-shale industry produce leachates containing toxic compounds such as heavy metals and persistent polycyclic aromatic hydrocarbons (PAH). The hazard to the environment represented by waste leachates depends not only on their chemical composition, but also on the mobility and bioavailability of toxic contaminants in soils. We evaluated the applicability of bioassays for toxicity assessment of the bioavailable fraction of heavy metals and PAH in soils, in experiments with samples of four different soil types (Rendzina, Brown pseudopodzolic, Typical brown, Sodpodzolic), the pH of which ranged from 6.2 to 7.2. The toxicity of the bioavailable fraction of the soil contaminants was assessed with the dehydrogenase enzyme activity assay, and with a Toxkit microbiotest with the crustacean, Thamnocephalus platyurus, after treatment of the soil samples with an artificial solution containing chromium (III), lead (II), copper (II), cadmium (II) and pyrene. The test results confirm those of earlier experiments, which characterised the sorption potential of investigated soils for the same compounds. Both tests turned out to be sufficiently sensitive, and hence can be recommended as effective and useful tools for the assessment of the bioavailable fraction of soil contaminants.

Distribution of arsenic and copper in sediment pore water: an ecological risk assessment case study for offshore drilling waste discharges.

Due to the hydrophobic nature of synthetic based fluids (SBFs), drilling cuttings are not very dispersive in the water column and settle down close to the disposal site. Arsenic and copper are two important toxic heavy metals, among others, found in the drilling waste. In this article, the concentrations of heavy metals are determined using a steady state "aquivalence-based" fate model in a probabilistic mode. Monte Carlo simulations are employed to determine pore water concentrations. A hypothetical case study is used to determine the water quality impacts for two discharge options: 4% and 10% attached SBFs, which correspond to the best available technology option and the current discharge practice in the U.S. offshore. The exposure concentration (CE) is a predicted environmental concentration, which is adjusted for exposure probability and bioavailable fraction of heavy metals. The response of the ecosystem (RE) is defined by developing an empirical distribution function of predicted no-effect concentration. The pollutants' pore water concentrations within the radius of 750 m are estimated and cumulative distributions of risk quotient (RQ=CE/RE) are developed to determine the probability of RQ greater than 1.

Construction and use of specific luminescent recombinant bacterial sensors for the assessment of bioavailable fraction of cadmium, zinc, mercury and chromium in the soil

Recombinant luminescent bacterial sensors for the detection of zinc [MC1061(pzntRluc)] and chromate [AE104(pchrBluc)] were constructed. The sensors carry firefly luciferase gene as a reporter under the control of zinc-inducible regulatory unit from Zn resistance system in chromosomal DNA of Escherichia coli or chromate-inducible unit from Ralstonia metallidurans CH34 megaplasmid pMOL28. The response of the sensors was calibrated using Zn 2+, Cr 2O 7 2− and CrO 4 2−, respectively. The detection limit of the zinc sensor for zinc was 40 μM (2.6 mg l −1 of Zn) and that of chromate sensor for dichromate 30 nM (1.6 μg l −1 of Cr) and for chromate 50 nM (2.6 μg l −1 of Cr), respectively. The specificity of the two above-mentioned sensors constructed in this study and a mercury-inducible bacterial sensor MC1061(pmerBR BSluc) constructed by us earlier [Anal. Chem. 73 (2001) 5168] was determined by using different heavy metal compounds. The zinc and mercury sensors were not completely specific to the target metals. The zinc sensor was co-inducible with cadmium and mercury and the mercury sensor with cadmium. The chromate sensor was inducible not only by chromate but also with Cr 3+. The bacterial sensors constructed were used for the estimation of bioavailable fraction of heavy metals in soils spiked with different amounts of zinc, cadmium, mercury and chromate. Both soil–water suspensions and soil–water extracts were analyzed. The results showed that the majority of heavy metals remained adsorbed to soil particles: only 0.6% of Cd, 1.3% of Hg, 2% of Zn and 46% of Cr (VI) were available to the bacterial sensors in soil–water extracts. However, when the soil–water suspensions were analyzed, approximately 20 times more cadmium and 30 times more mercury (12 and 40%, respectively) was available for the sensor bacteria whereas the available fractions of zinc and chromate in soil–water extract and suspension were similar. Thus, this study showed that in case of cadmium and mercury (but not zinc and chromium) the particle-bound metals were also partially bioavailable.

Biomarkers and trace metals in the digestive gland of indigenous and transplanted mussels, Mytilus galloprovincialis, in Venice Lagoon, Italy

The aim of this study was to investigate the cellular and biochemical response of mussels, Mytilus galloprovincialis, transplanted from a relatively pristine site to a polluted one and vice versa in the Lagoon of Venice (northeast of Italy) and to apply auto-metallography, a rapid and sensitive histochemical technique, to determine the bio-available fraction of heavy metals accumulated in the body tissues of organisms. Animal digestive glands have been used for morphological analyses (lysosomal volume, surface and numerical density, mean epithelial thickness, mean diverticular and luminar radius), autometallographical black silver deposits quantification and biochemical assays (superoxide dismutase and catalase activity). Furthermore, heavy metal content was determined by atomic absorption spectrophotometry (AAS) using standard procedures. The overall results indicate a direct influence of the environment in the thinning of the digestive cells and in the increasing number of lysosomes in mussels from the more polluted site. These data are in agreement with the metal content in digestive cell lysosomes as determined by autometallography, whereas AAS measurements show less significant differences.