Environmental Risk Assessment of Heavy Metals by Exploring Chemical Fractions, Leachability, Bioavailability in Road Dusts from Steel-Industrial City (Anshan), Northeastern China

This study evaluated chemical fractions, potential leachability, and bio-accessibility of heavy metals (Cr, Cu, Cd, Ni, Pb, and Zn) in road dusts from the steel-industrial city (Anshan), Northeastern China. Chemical fractions of heavy metals were determined using Tessier sequential extraction method. The environmental risk assessment was evaluated using short-term extraction tests: TCLP, PBET, and CaCl2. Sequential extraction analysis reveals that Cr and Ni primarily existed in residual form. The non-residual fraction of heavy metals decreased in the order of Zn (average 57.78%)> Cu (39.16%)> Pb (30.73%)≈ Cd (30.67%)> Ni (19.06 %)> Cr (8.7%%). The results showed that Cd, Cu, Zn and Pb, which were extremely concentrated in potentially mobile fractions, had highly potential environmental risks. The mobility of Cd and Zn was usually higher than those of Cr, Cu, Pb and Ni, which means that Cd and Zn have higher hazardous to ecosystem. The order of bioavailability identified by PBET method was generally Zn>Cd>Pb>Ni>Cu>Cr. There was a significantly relationship between PBET, TCLP-test and bioavailable parts (F1+F2+F3+F4, SUM4) of sequential extraction, respectively. Multiple linear regression analysis indicated that toxicity and bioavailability of heavy metals were not only depended on RDs properties, but also lied on the total heavy metals.

Metal(loids) Bioaccessibility in Road Dusts from the Surrounding Villages of an Active Mine

Aiming the characterization of road dusts on the surrounding villages of an active mine and to assess metal(loids) bioaccessible fractions, a dust samples survey was undertaken. To achieve these objectives, pseudototal element concentration, mineralogical composition, Enrichment factor and in vitro extraction UBM assay for both gastric (G) and gastrointestinal (GI) phases, were determined. Results obtained revealed that arsenic represents the higher risk to humans, with mean pseudototal values higher than the maximum reference value range. Enrichment factor points to As significant to very high enrichment in all villages. Particles enriched in As, Ca, Fe, Cu, Al, Ti were identified by SEM-EDS in weathered agglomerates, linked to mine wastes and long-distance transport, both by wind and/or traffic. Arsenic bioaccessibility fraction (%BAF) presents low values in the studied samples, possibly due to low Fe complexes solubility with adsorbed As, limiting arsenic release and reducing its bioaccessibility. Concentrations of Cd bioaccessible G and GI phases are within the reference values range, while for Cu are above and for Pb are lower, than reference value range. Results show that the pseudototal fraction risk is overestimated when comparing to BAF (bioaccessible fraction), nevertheless, total G and GI risk are above the carcinogenic target risk (1.00E-06) in most samples. Carcinogenic risk of the bioaccessible contaminants shows that As is the element that represents higher risk for developing cancer over a lifetime, being ingestion the main risk route.