Bioaccessibility Of Trace Metals Research Articles

Geochemical Contamination, Speciation, and Bioaccessibility of Trace Metals in Road Dust of a Megacity (Guangzhou) in Southern China: Implications for Human Health

Road dust has been severely contaminated by trace metals and has become a major health risk to urban residents. However, there is a lack of information on bioaccessible trace metals in road dust, which is necessary for an accurate health risk assessment. In this study, we collected road dust samples from industrial areas, traffic intersections, and agricultural fields from a megacity (Guangzhou), China, and conducted a geochemical enrichment, speciation, and bioaccessibility-based health risk assessment of trace metals. In comparison with local soil background values, the results revealed a significant accumulation of trace metals, including Zn, Cd, Cu, and Pb in the road dust, which is considered moderate to heavy pollution. Sequential extraction indicated that most trace metals in the road dust were primarily composed of a Fe/Mn oxide-bound fraction, carbonate-bound fraction, and residual fraction, while the dominant fraction was the organic matter-bound fraction of Cu, and the residual fractions of As, Cr, and Ni. The in vitro gastrointestinal (IVG) method revealed that high percentages of Zn, Cd, Cu, and As were bioaccessible, suggesting the possible dissolution of trace metals from adsorbed and carbonate-associated fractions in road dust exposed to the biological fluid matrix. The IVG bioaccessibility-based concentration largely decreased the noncarcinogenic health risk to a negligible level. Nevertheless, the entire population is still exposed to the cumulative probability of a carcinogenic risk, which is primarily contributed to by As, Cd, Cr, and Pb. Future identification of the exact sources of these toxic metals would be helpful for the appropriate management of urban road dust contamination.

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.

Comparison of In Vitro PBET and Phosphoric Acid Extraction as an Approach to Estimate Selenite and Selenate Bioaccessibility from Soil

Several approaches have been used to estimate the bioaccessibility of trace metals from soils. Here, we applied phosphoric acid extraction and the in vitro test physiologically based extraction (PBET) to soils containing selenium (Se) and compared their performance in estimating the bioaccessibility of Se. For this purpose, we used two soil samples and two Certified Reference Material soil samples with a range of Se concentrations. The total Se contents were measured in the samples and in the extracts by hydride generation–atomic fluorescence spectroscopy. Moreover, we also measured selenite and selenate in the soil extracts (from phosphoric acid and from the PBET) using the coupled techniques liquid chromatography–UV photooxidation–atomic fluorescence spectroscopy and liquid chromatography–mass spectrometry with inductively coupled plasma. From the results obtained in the present study, the PBET showed that the selenium bioaccessible fraction was mainly attributed to the gastrointestinal step. When comparing the results from PBET with those of the phosphoric acid extraction, similar values of Se (IV) and Se (VI) were obtained for both extraction systems. An estimation of the bioaccessibility percentage of Se is also reported.

Bioaccessibility of trace metals in boat paint particles

A ground composite of paint fragments collected from a leisure boatyard has been analysed for total and bioaccessible trace metal concentrations. The sample contained concentrations of Cu and Zn of about 1% due to their use in antifouling formulations, and significant quantities of Ba, Cd, Cr, Ni, Pb, Sb and Sn. In a simulated stomach phase (pH 2.5), bioaccessible concentrations relative to respective total concentrations ranged from ≤10% for Ba, Cr, Ni and Sn to 80–90% for Cu and Zn. Under subsequently simulated intestinal conditions (pH 7), metal accessibility was either reduced or maintained. Increasing pH of the stomach phase from 1 to 4.5 resulted in a reduction in bioaccessibility, an effect that was propagated, in most cases, into the intestinal phase. These results are critical to the formulation of risk assessments for individuals exposed to paint particles during vessel maintenance or in home environments subjected to particulate track-in.

Levels and Bioaccessibilities of Metals in Dusts from an Arid Environment

The elemental composition and bioaccessibility of trace metals have been determined in a variety of geosolids (soils, road dusts and house dusts) from an arid, coastal region (Dhahran, Saudi Arabia). Concentrations of many elements reflected those of the local geology, ascertained by analysis of desert sand. Several trace metals (e.g. Cu, Sb, Zn, Pb, Tl and Sn) were moderately enriched in both road and house dusts, reflecting external and internal (household) anthropogenic sources. For a given trace metal, bioaccessibilities, assessed using a physiologically based extraction test, were broadly similar across the range of geosolids. Median values for a simulated gastric phase ranged from less than 10% (Ba, Cu, Cr, Ni and V) to more than 50% (As, Cd, Sb, Sn and Tl), and for a subsequently simulated intestinal phase from less than 15% (Ba, Cr, Cu, Ni, V and Zn) to more than 50% (As, Cd, Sb, Tl and U). Results suggest that the levels and bioaccessibilities of trace metals in dusts from arid environments are controlled by the dilution of anthropogenic particulates by variable (but significant) proportions of fine, baseline sand.