Bioaccessibility Of Metals In Soils Research Articles

Heavy metals in homestead soil: Metal fraction contents, bioaccessibility, and risk assessment

Rapid urbanization in China has led to the disappearance of countless villages and the transformation of homestead land into cultivated land or grassland. The quality of homestead soil (HS) plays a pivotal role in land-use conversion and reuse strategies, so the current state of heavy metal pollution in HS deserves attention. This study determined the fraction contents, bioaccessibility, risks, and affecting factors of Hg, As, Cd, Pb, Cu, and Zn in HS by comparing them with soil in cultivated land (CS), grassland (GS), homestead-converted cultivated land (HCS), and homestead-converted grassland (HGS). Results demonstrate that the contents of the six metals exceed background values, especially for Cd and Hg, resulting in significant pollution and elevated ecological risk. Distinct from the dominant residual fraction of other metals, the extractable fraction of Cd shows the highest proportion, which also contributes most to the high values of the Risk Assessment Code and extreme pollution conditions in HS, GS, and CS. Moreover, pH shows predominantly negative relations with the effective available and potentially available contents, while the effects of organic carbon fractions are notably the opposite. Furthermore, CS and GS suggest higher non-carcinogenic and carcinogenic risks than in the converted soil. This study indicates that HS has a lower metal accumulation risk compared with cultivated land and grassland, and homestead conversion seems to restrict the bioaccessibility of metals in soil.

Bioaccessibility of Metals in Soils at Typical Legacy Industrial Sites: In Vitro Evaluation Using Physiologically-Based Extraction.

Risk assessment of soil metal pollution based on total metal contents might give overestimates by neglecting the bioaccessibility of the pollutants to soil biota. Physiologically-based extraction tests (PBET) are in vitro methods for evaluation of bioaccessibility of soil pollutants. A total of 27 soil samples collected from four types of legacy industrial site representing metal smelting, lead-acid battery factories, chemical plants and steel plants were analyzed for the bioaccessibility of six potentially toxic metals using a PBET method. The metal pollutants at the industrial sites depended on the former industrial processes and emissions. The highest proportions of gastric phase and intestinal phase in these soil samples were 43.9% for Cd and 27% for Cu, respectively. Factors affecting metal bioaccessibility included type of industry and soil properties. The soils at a lead-acid battery factory showed relatively high bioaccessibility of Pb, Zn and Cd and those at the steel plant showed relatively low metal bioaccessibility. Soil organic matter and clay contents were positively related to metal bioaccessibility but soil pH and CEC showed negative relationships. Further studies are recommended to determine the speciation of the bioaccessible metals in these soils.

Bioaccessibility of metals in soils surrounding two dismissed mining sites in Northern Italy

Mining activities are one of the main contributors to metals contamination of soils, most often due to the inappropriate management of the mining residues. In Italy, hundreds of small mining sites are scattered around the mountainous areas, near small villages with fragile environments. Here, wastes and residues may have polluted the surrounding soils and become a threat to living organisms. We investigated two dismissed sites in Northern Italy with extractive wastes in unmanaged areas close to villages using bioaccessibility and size fractionation methods, focussing on particles that can potentially be eroded and/or ingested (< 10 µm and < 200 µm). In the Campello Monti site, Co, Cu and Ni showed high values in soils near the landfills, with the highest concentrations in the < 10 µm particles around the landfills and along the valley bottom. Lead and Ni were the most bioaccessible metals. In the Plassa site, Cd and Zn were the most important contaminants, with an average content of 118 and 34,000 mg/kg. They originated from mining wastes scattered through the slope and had a particularly high bioaccessible fractions, close to the 100% for Zn and above 80% for Cd in the fine particles. The study of the fine, more reactive and mobile particles offered a close insight into the lability of contaminants, as in both sites, a dispersion of metal contaminants through very fine particles in surrounding and downhill areas was observed, resulting in an increased risk to all living organism and for the environment.

Factors influencing the heavy metal bioaccessibility in soils were site dependent from different geographical locations.

A soil survey was conducted in urban areas from five sites, including Beijing, Baotou, Datong, Fuyang, and Xiantao in China. The objective was to explore the most significant factors that may impact the bioaccessibility of heavy metals (Bio-HMs), including As, Cr, Cu, Pb, and Zn, in soils. Twenty to 30 composite soil samples were collected at each site. The various soil properties, including pH, particle size, Fe/Mn, and organic matter contents, were analyzed. The chemical operated forms of HMs in soils were measured by the Bureau of Reference (BCR) sequential extraction scheme, while the Bio-HMs were determined by the simple bioaccessibility extraction test (SBET) procedure. The concentrations of total heavy metals (T-HMs) in soils from different sites (cities) were in the range as As (5.69-9.86), Cr (77.42-230.20), Cu (15.68-36.54), Pb (14.12-58.93), and Zn (38.66-183.46) mg/kg. Cu and Pb had higher relative bioaccessibilities (48-70%) than those of As and Cr (6-15%), indicating higher health risks of the former than the latter two HMs. The Bio-HMs for various HMs were comparable to the first two or three combined BCR extracted fractions, with an exception of Cu, whose Bio-HMs were larger than the combined three BCR fractions, indicating that Cu was highly accessible in soils as compared with other HMs. Factor analysis showed that all variables, including soil property parameters and BCR extracted fractions, could be represented by three common factors extracted with higher than 0.5 loadings and ∼80% cumulative contribution to the total variance. Among the three common factors, factor 1, containing mainly pH, texture, and Fe/Mn variables, and factor 3, containing mainly organic matter variable, could be attributed to geographical regions, while factor 2, containing mainly BCR extracted fractions, could be ascribed to relative bioaccessibility of HMs (R-Bio-HMs). Interactive mapping of the main factors and cluster analysis were consistent, which supported the "site gathering" of the soil sample pools, suggesting that the Bio-HMs in soils in different geographical localities were site dependent.

Bioaccessibility of metals in soils: comparison between chemical extractions and in vitro tests

It is well-known that the total metal content in soils is not a good indicator of their harmful effects, leading to an overestimation of risks. Toxicological and environmental hazards depend on the chemical species and on its bioavailability to target organisms. Because a good estimation of bioavailability is difficult, a good compromise is to assess bioaccessibility, defined as the maximum amount of a pollutant which is potentially absorbable by a target organism. This study presents a comparison of different strategies to measure metal bioaccessibility in soils. Three procedures were applied to real soil samples with different levels of metal contamination: pseudo-total metal attack, selective sequential extractions and in vitro tests (deliberately developed to simulate human or mammals digestion). Considering the first step of the selective extraction procedure, which can provide the bioaccessible fraction for deposit-feeder organisms, data obtained for each metal were lower than those obtained from in vitro tests. Therefore, it is possible to highlight that this extraction tends to underestimate metal bioaccessibility in soils for humans, while in vitro tests certainly will overestimate bioaccessibility for organisms as invertebrates. If the sum of first and second step of sequential procedure is considered, results are quite similar to those obtained from in vitro tests, but this kind of procedure would require two days of work rather than a few hours required to perform an in vitro test. Results highlight the diversity among the differently defined bioaccessible fractions and the need to apply the most suitable procedure depending on the target organism.

Assessment of potential health risk for inhabitants living near a former lead smelter. Part 2: site-specific human health risk assessment of Cd and Pb contamination in kitchen gardens

Metal contamination of urban soils and homegrown products has caused major concern. In Part 1, we investigated the long-term effects of a former smelter on the degree of kitchen garden-soil contamination and the quality of the homegrown vegetables from these gardens. The results showed that the soils retained a high level of contamination and that a large proportion of the vegetables produced did not comply with the legislation on the levels of metals allowed for human consumption. The present study aims to assess the associated potential health risk to local inhabitants through consumption of homegrown vegetables and ingestion of soil particles using a land use-based approach. For lead (Pb), the standard hazard quotient (HQ)-based risk assessment method was used to determine the HQ. For cadmium (Cd), the approach consisted of calculating the HQs and then deriving site-specific assessment criteria (SSAC) using the SNIFFER method. The results suggested that the exposure pathways considered should not engender any form of deleterious health effects for adults. For children, Pb was the main concern and induced a relatively high health risk through soil particle ingestion, and most total soil Cd concentrations exceeded the derived SSAC, in particular, through consumption of vegetables. The metal bioaccessibility in soils was incorporated into the methods to establish more realistic risk assessment measures. This study proposes an approach to integrate different human health risk assessment methods. Further investigations should complete the assessment to improve risk determination, e.g., the determination of metal bioaccessibility in vegetables.

Mobility and bioaccessibility of trace metals in soils assessed by conventional extraction procedures and passive diffusive samplers

Our objective was to verify the use of the diffusive gradient in thin films technique (DGT) for assessment of metal mobility and bioaccessibility in soil and to compare the results with classical extraction procedures. Non-contaminated natural grassland and arable land soil samples from the South Moravian district, Czech Republic, both homogenised and undisturbed, were studied. DGT applied to soil cores gave information about the vicinity of the sampling probe related predominantly to the local structure and heterogeneity of the soil. However, measurement of mobile and kinetically labile metal species in the soil slurry could provide an approximation of the average information on plant accessible metals pools in soils, that was several orders of magnitude lower in comparison with results obtained by extraction procedures. Most DGT measured metals occurred in low molecular labile forms as demonstrated by using the diffusive gels with different pore size. Concentration of metals measured in soil solution was used for R-value (cDGT/csol) calculation. The R-values (0.6–1.1) indicated high lability of Cd species at both sampling sites. In contrast to Cu and Ni (R=0.11–0.15), Pb was relatively labile in nature grassland near the highway with heavy traffic density (R= 0.45-0.75) in agreement with results obtained by extraction procedures.

Development of a simulated earthworm gut for determining bioaccessible arsenic, copper, and zinc from soil

Soil physicochemical characteristics and contamination levels alter the bioavailability of metals to terrestrial invertebrates. Current laboratory-derived benchmark concentrations used to estimate risk do not take into account site-specific conditions, such as contaminant sequestration, and site-specific risk assessment requires a battery of time-consuming and costly toxicity tests. The development of an in vitro simulator for earthworm bioaccessibility would significantly shorten analytical time and enable site managers to focus on areas of greatest concern. The simulated earthworm gut (SEG) was developed to measure the bioaccessibility of metals in soil to earthworms by mimicking the gastrointestinal fluid composition of earthworms. Three formulations of the SEG (enzymes, microbial culture, enzymes and microbial culture) were developed and used to digest field soils from a former industrial site with varying physicochemical characteristics and contamination levels. Formulations containing enzymes released between two to 10 times more arsenic, copper, and zinc from contaminated soils compared with control and 0.01 M CaCl2 extractions. Metal concentrations in extracts from SEG formulation with microbial culture alone were not different from values for chemical extractions. The mechanism for greater bioaccessible metal concentrations from enzyme-treated soils is uncertain, but it is postulated that enzymatic digestion of soil organic matter might release sequestered metal. The relevance of these SEG results will need validation through further comparison and correlation with bioaccumulation tests, alternative chemical extraction tests, and a battery of chronic toxicity tests with invertebrates and plants.

Bioaccessibility of metals in soils and dusts contaminated by marine antifouling paint particles

Fragments of antifouling paint and environmental geosolids have been sampled from the island of Malta and analysed for total and bioaccessible metals. Total concentrations of Ba, Cd, Cu, Pb, Sn and Zn were two to three orders of magnitude higher in spent antifouling composites relative to respective values in background soils and road dusts. Paint fragments were visible in geosolids taken from the immediate vicinity of boat maintenance facilities and mass balance calculations, based on Ba as a paint tracer, suggested that the most contaminated soils, road dusts and boatyard dusts contained about 1%, 7% and 9%, respectively, of antifouling particles. Human bioaccessibilities of metals were evaluated in selected samples using a physiologically based extraction technique. Accessibilities of Cd, Cu, Pb and Zn in the most contaminated solids were sufficient to be cause for concern for individuals working in the boat repair industry and to the wider, local community.

Health Canada Approaches and Activities With Respect to Bioavailability of Contaminants in Soil

MS1-06 Abstract: Under the Canadian Federal Contaminated Sites Action Plan (FCSAP), Health Canada is responsible for the provision of guidance, training, and advice on human health risk assessment (and related topics) to federal departments with custodial responsibilities for contaminated sites. This presentation provides an overview of Health Canada-funded research into the relevance and applicability of in vitro simulated lung fluid solubility assays, in vitro dermal penetration of various soil-borne contaminants using viable human skin, and factors affecting oral bioavailability. One way to improve human health exposure estimates is to apply an increasingly realistic understanding of the fate of particulates and the substances they carry. A review of in vitro studies for the pulmonary tract indicated that given the complexity of particulate distribution, clearance, dissolution, and interaction with macrophages in the pulmonary tract, there is insufficient experimental evidence for other types of solubility assessments to allow for the confident use of in vitro assays as estimates of in vivo contaminant bioavailability. Based on the currently available studies, any arguments for decreased bioavailability of substances derived from inhaled particulates are necessarily accompanied by a very low level of confidence. Ongoing in vitro studies are being conducted at Health Canada to examine bioavailability through viable excised skin. It is anticipated that this will provide more relevant data for human exposures than studies with cadaver skin or animal studies. Contaminated soils are applied to the tissue for various durations as well as soils spiked with chemicals. A database of these results will be compiled for a variety of chemicals that are commonly found at contaminated sites. With regard to oral bioavailability, Health Canada has funded numerous studies to evaluate oral bioavailability of soil-borne contaminants. Health Canada is working toward having a standardized in vitro test that can be used to evaluate site-specific bioaccessibility of metals in soils because the soil characteristics and chemical speciation can have a significant impact on the bioavailability. Each of these pathways can have significant influence in the estimates of exposures in human health risk assessment, including childhood exposures to metals in soils and house dust in residential environments. This presentation provides information on these studies and recommendations toward regulatory approaches with respect to bioavailability of contaminants in soils and housedust.

Environmental contamination and bioaccessibility of arsenic and metals around the Dongjeong Au–Ag–Cu mine, Korea

The objectives of this study were to investigate the level of arsenic and metal contamination of soils, crop plants and waters around the Dongjeong Au–Ag–Cu mine, and to assess bioaccessibility of metals in soil and plant using the EHS (extraction of heavy metals in stomach and small intestine) test. The EHS test was used to simulate the conditions in the human stomach and small intestine. In tailings, the mean concentrations of elements from the mine area were As 4070 mg kg −1 , Cd 6 mg kg −1 , Cu 380 mg kg −1 , Mn 7760 mg kg −1 , Pb 19 150 mg kg −1 , Zn 2590 mg kg −1 and Hg 2.8 mg kg −1 . Mountain soils adjacent to the tailings and waste rock piles were significantly contaminated by these elements. Farmland soils contained higher concentrations of As, Cd, Hg, Mn, Pb and Zn than soils at the control area, especially As and Pb which were over permissible levels. Metals were accumulated in crop plants grown on farmland soil near the mine area. The concentrations of metals were higher in leafy plants than in grain plants such as rice grain and red pepper. The concentrations of SO 4 2− , Mn and Zn were elevated in stream water and were influenced by effluents from the tailings and waste rock piles. The concentrations of Cd and Pb in groundwater were higher than the permissible levels for drinking water in Korea. The results of the EHS test showed c. 60% of Cd, 10% of As and 30–40% of Cu, Pb, Mn and Zn were present as a bioaccessible fraction in farmland soils. In crop plants, high percentages of total concentrations of metals except Pb were extracted as bioaccessible concentrations. Bioaccessible concentrations of metals may be valuable for providing the input data for risk assessment at sites subject to anthropogenic soil contamination.

In Vitro Bioaccessibility of Metals in Soils from a Superfund Site in Puerto Rico

In Vitro Bioaccessibility of Metals in Soils from a Superfund Site in Puerto Rico

Bioaccessibility of Metals in Soils for Different Liquid to Solid Ratios in Synthetic Gastric Fluid

The bioaccessible fraction of metals in the stomach has been estimated for two soil materials using laboratory synthesized gastric juice. Heavy metals present in each soil matrix were extracted and measured, as a technique to simulate metal solubilization processes that occur in the human stomach. The results from the synthetic gastric juice extraction were compared to values obtained using a modified EPA concentrated acid extraction procedure, method 3051, on the same soils. The experiments evaluated the effect of varying the liquid to solid ratio on gastric juice extraction efficiency for arsenic (As), chromium (Cr), nickel (Ni), cadmium (Cd), and lead (Pb). Soil samples employed were a National Institute of Standards and Technology (NIST) standard soil (Montana SRM 2710) and a composite hazardous waste contaminated soil from Jersey City, NJ. The current work demonstrates that bioaccessibility is not the same for each metal within a given soil, nor between the soils. Estimates of the bioaccessible fraction of the metals studied ranged from 2 to 61% of the NIST certified values for Montana soil, and from 3% to 58% of EPA method 3051 values in contaminated Jersey City soil. The experiments indicated that the bioaccessibility of metals in the soils extracted by the in vitro synthetic gastric juice will only be affected slightly by changes in gastric fluid liquid to solid ratios for the range 100:1 to 5000:1 (mL/g). Further, the masses of each soil (0.05 or 0.5 g) used did not affect the bioaccessibility at the 1000:1 ratio.