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“The road dust found in mining areas is composed of dust from multiple sources, including wind transported mineral dust from mines and tailings as well as uncovered trucks leakage. Collectively, these are then distributed via wind and traffic activity, becoming an important source of particulate matter (PM) and subsequently inhaled by pedestrians. A common practice in previous road dust risk assessments has regarded them as soil, which likely led to a significant underestimation of the actual inhaled amount. To more accurately understand the inhalation risk presented by road dust in mining areas, the study applied a detailed pollution analysis and dust dispersion model to assess the inhaled amount of road dust. Road dust samples located at different distances to the mine and tailings were collected and sieved to 10?µm (RD10). Enrichment factors (EFs) of Ce, As, Cd, and Mo exceeded 20 across most sampled sites, suggesting extreme pollution. Source analysis indicated that most of the collected RD10 had greater
than half of its mass originating from the mine. To assess the risk presented by inhalation exposure to local populations, we built a method using Gaussian diffusion model and two exposure scenarios for both adults and children were considered. The level of simulated particle concentrations was comparable to that described in the literature; the inhalation of potential toxic elements (PTEs) in RD10 led to health risks for both adults and children (adult and child HI?>?1, with adults CR in industrial areas >10-4). Results also indicated that a ten-fold reduction of silt load resulted in a >4-fold decrease in risk. Collectively, the results suggest that fine road dust is a potential hotspot for mineral exposure in populations living around a mine and its tailings; moreover, that effective prevention measures like road cleaning and truck regulation are urgently needed.
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Mining operations are one of the most notable anthropogenic activities in terms of the quantity of dust and aerosol emissions, the globally extensive area affected, and the contents of potential toxic elements (PETs) (Csavina et al., 2012). Developing countries face a particular severe set of challenges, where effective management and prevention measures are largely absent, allowing large quantities of dust containing heavy metals (HMs) and radioactive materials to be released into the atmosphere during mining and other related operational processes. As a result, these activities pose a great threat to the population living around mines and even populations that leave farther from such areas—since fine particles have a longer atmospheric half-life and are capable of migrating across large distances away (Ni et al., 2018).
Measurements of road dust can serve as a comprehensive indicator of urban pollution levels, and a host of studies have focused on such urban road dust pollution, particularly in large metropolitan areas. The PTEs and organic matters were found to be derived primarily from urban traffic and demolition activities (Amato et al., 2009). However, scarce work has examined the pollution levels and health risks of road dust in mine-polluted areas. Our previous work found that in the surrounding areas of Bayan Obo, coarse road dust (diameters =100?µm and 100–2000?µm) contained more REEs and HMs than local PM10; moreover, that REE and HM concentrations increased with decreasing diameter (Tian et al., 2018; Wang et al., 2014a). The high concentrations may indicate the influence of a variety of polluting pathways in addition to atmospheric transmission directly from the mine pit—for instance, leakage from ore transportation.
There are reasons to believe that the fine road dust around mining areas presents a higher pollution level and, thus, an even greater pollution challenge. More specifically, this type of road dust not only consists of more pollutants from different sources, but also likely serves as a notable source of pollutants itself. The important role played by road dust with smaller grain size in diffuse urban pollution has been highlighted by past work (Zhao et al., 2010), and the resuspension of fine road dust likely considerably contributes to PM10 as one of the biggest parts of non-exhaust, traffic-derived emissions (Wang et al., 2014b). Amato et al. (2014) summarized PM sources apportionment studies conducted in European countries and found that 12–90% of atmospheric particulates originated from non-exhaust sources or road dust. To this end, many vehicle emission inventory models account for exhaust emissions, while ignoring non-exhaust emissions, which is especially true for road dust resuspension (Thouron et al., 2018).
The particulates inhaled during an individual’s commute comprises a major part of the total particulates inhaled, and thus, different combinations of residential locations and travel modes may cause distinct exposure amounts of air pollutants (de Nazelle et al., 2012; Karanasiou et al., 2014). Recently, concerns have developed related to the influence of the non-uniformity of pollutant distribution on a given road, different commuting vehicles and paths, and overall commuting time on the exposure dose and its attendant health risk on individual level (Fajardo and Rojas, 2012; Soulhac et al., 2009; Tiwary et al., 2011). Despite this, the inhalation risks presented by the various non-exhaust emissions—especially road dust contaminated by specific sources— remain understudied. Of the work that has been done, particulates dominated by minerals with larger sizes when relative to diesel exhaust particles also induced hazardous effects (Baron et al., 2002; Puledda et al., 1999). Thus, better assessment of the health risks posed by resuspended road dust especially in mining areas is urgently needed. When considering the mobility and inhalation risk, particle size is a key factor. In addition to the longer suspension time, RD10 is also assumed to have the potential to directly interact with PM10, which is thought to be the ‘inhalable’ size that can enter the respiratory tract, resulting in toxicological complications (Jin et al., 2016).
Up until this point, a common practice in health risk assessments regarding the amount of road dust inhalation was to categorize it as soil using a particulate emission factor (PEF) (Ma et al., 2017). However, this approach runs a high risk of underestimating the amount inhaled since it neglects the intense disturbance of traffic. Instead, Zhao et al. (2016) estimated the spatial variations of pollutants contributed by road dust to atmospheric particulate matter considering size-specific mobility. However, wind erosion but not traffic was considered; moreover, the resuspension was not quantified. Similarly, Amato et al. (2009) also assessed the resuspension amount of RD10 and the incident metals emissions (µg/m2) in an urban environment. However, they failed to estimate the concentration, leaving the inhalation risk unknown. On the other hand, comprehensive and mature models have been developed in the field of air pollution simulation including NORTRIP and AERMOD. While valuable, these approaches require numerous topographical, climatic, and traffic parameters, and have large computational costs. These constraints limit their applications for the quick assessment of road dust emissions. With this in mind, it would be beneficial to apply a simple Gaussian diffusion model to obtain a relatively accurate estimate without the need for such cumbersome modeling.”
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