Effects of Road Dust Particle Size on Mineralogy, Chemical Bulk Content, Pollution and Health Risk Analyses.

Because of the rising environmental and health concerns associated with atmospheric pollution caused by potentially toxic elements (PTEs), several road dust studies have been performed across the world in recent decades. This paper illustrates the effects of particle size on the PTE contents, mineralogical composition, environmental pollution and health risk assessments in road dust from Barcelona (Spain). The samples were sieved into five size fractions ranging from <45 to 500-800 µm. Although the major mineral contents (tectosilicates, phyllosilicates, and carbonates) were profuse in all fractions, the identified inhalable PTE particles (e.g., Fe, Cr, Cu, Zn, Ni, and REE), with size < 10 µm, were more pervasive in the finest fraction (<45 µm). This is consistent with the concentrations measured: the finest fractions were richer in PTEs than the coarser ones, resulting in a direct correlation with the enrichment factor (EFx), geo-accumulation (Igeo), and non-carcinogenic (HI) and carcinogenic (CRI) values. Igeo and EFx values can be appropriate tracers for some common elements (e.g., Zn, Sb, Sn, Cu, and Cr), but they do not seem adequate for anthropogenic particles accumulated at concentrations similar to the geogenic background. Overall, the HI and CRI values obtained in Barcelona were acceptable, reflecting no serious health impacts in the study area, except for Cr. Our results suggest that fine dust particles are a more suitable fraction to conduct pollution and health risk assessments than coarser ones, although the EFx, Igeo, HI, and CRI threshold values should be redefined in the future to include all emergent pollutants as well. In summary, monitoring programs should include at least the road dust evaluation of <45 µm particles, which can be performed with a simple sieving method, which is both time- and cost-effective.

Quantifying the potential seepage from porphyry copper tailing impoundments using a multi-isotopic approach.

Porphyry-style copper deposits are characterized by low Cu grades and high tonnages, resulting in large mine tailing volumes disposed in impoundments. Due to the mining tailing sizes, waterproofing techniques cannot be applied along the dam base. Therefore, to minimize seepage towards the aquifers, pumping wells are usually installed as hydraulic barriers. Currently, there is a controversy over whether or not the water extracted from hydraulic barriers should be counted as the use of new water rights. Consequently, a growing interest to develop tools to trace and quantify the tailing impacts in groundwater and to determine the water pumped amount subjected to water rights exist. In the present study, isotope data (δ2H-H2O, δ18O-H2O, δ34S-SO42- and δ18O-SO42-) are proposed as a tool to quantify tailings seepage towards groundwater and to assess hydraulic barriers effectiveness. To illustrate this approach usefulness, the Quillayes porphyry Cu tailing impoundment (Chile) case study is presented. The multi-isotopic approach revealed that tailing waters are highly evaporated showing high SO42- content (~1900 mg L-1) derived from primary sulfate ore dissolution, whereas freshwaters, derived from recharge water, have low SO42- contents (10-400 mg L-1) resulting from the interaction with geogenic sulfides from barren host rock. The δ2H and δ18O values of groundwater samples collected downstream from the impoundment suggest a mixing at different proportions of highly evaporated water from the mine tailing waters and non-evaporated regional fresh groundwater. Cl-/SO42-, δ34S-SO42-/δ18O-SO42-, δ34S-SO42-/ln(SO42-) and δ2H-H2O/δ18O-H2O mixing models allowed to determine that groundwater located closer to the impoundment had a mine tailing water contribution from 45 to 90 %, whereas those located farther away had lower contribution (5-25 %). Results confirmed the stable isotope usefulness to determine the water origin and to calculate the hydraulic barrier efficiencies and the pumped water proportions unrelated to the mining tailing subject to the water rights.