Potential human inhalation exposure to soil contaminants in urban gardens on brownfields sites: A breath of fresh air?

Urban gardening has been experiencing increased popularity around the world. Many urban gardens are located on sites that may be contaminated by trace elements or organic compounds due to previous use. The three main exposure pathways to the human body for soil contaminants are (a) ingestion of soil directly, (b) consumption of produce containing or superficially contaminated with a contaminant, (c) and inhalation of soil dust. The first two modes have received much attention; however, the contribution of the inhalation route has not been investigated adequately. Two inhalation risk studies were carried out in urban gardens located in Kansas City, MO, by collecting dust while 25-m2 plots were rototilled. Microclimatic variables were monitored, and total inhalable dust mass was determined using a personal sampling train including a small pump and air filter. Soil lead (Pb) concentration was assessed at both sites. For Study 1, particle size distribution of collected particles was estimated through analysis of scanning electron microscope images of filters. Little dust was collected at either site. Most particles captured, however, appeared to be <4 µm in diameter. The amount of dust emitted was correlated with soil moisture. Tilling reduced soil aggregate size and blended soil, resulting in a more homogeneous distribution of Pb. Dust inhalation while tilling is likely not a major Pb exposure risk for gardeners, but given the preponderance of very small particles in what was captured, care should be taken to prevent dust from entering the respiratory system.

Dust emission source characterization for visibility hazard assessment on Lordsburg Playa in Southwestern New Mexico, USA.

In drylands around the world, ephemeral lakes (playas) are common. Dry, wind-erodible playa sediments are potent local and regional sources of dust and PM10 (airborne particles with diameters less than 10 µm). Dust clouds often cause sudden and/or prolonged loss of visibility to travelers on downwind roadways. Lordsburg Playa, in southwestern New Mexico, USA is bisected by Interstate Highway 10. Dust storms emanating from the playa have been responsible for numerous visibility-related road closures (including 39 road closures between 2012 and 2019) causing major economic losses, in addition to well over a hundred dust-related vehicle crashes causing at least 41 lost lives in the last 53 years. In order to improve understanding of the surfaces responsible for the dust emissions, we investigated the critical wind friction velocity thresholds and the dust emissivities of surfaces representing areas typical of Lordsburg Playa's stream deltas, shorelines, and ephemerally flooded lakebed using a Portable In-Situ Wind ERosion Laboratory (PI-SWERL). Mean threshold friction velocities for PM10 entrainment ranged from less than 0.30 m s- 1 for areas in the delta and shoreline to greater than 0.55 m s- 1 for ephemerally flooded areas of the lakebed. Similarly, we quantified mean PM10 vertical flux rates ranging from less than 500 µg m- 2 s- 1 for ephemerally flooded areas of lakebed to nearly 25,000 µg m- 2 s- 1 for disturbed delta surfaces. The unlimited PM10 supply of the relatively coarse sediments along the western shoreline is problematic and indicates that this may be the source area for longer-term visibility reducing dust events and should be a focus area for dust mitigation efforts.

Blowing dust and highway safety in the southwestern United States: Characteristics of dust emission "hotspots" and management implications.

Despite the widespread media attention of chain-reaction traffic incidents and property damage caused by windblown dust in the U.S. and elsewhere in the world, very few studies have provided in-depth analysis on this issue. Remote sensing and field observations reveal that wind erosion in the southwestern U.S. typically occurs in localized source areas, characterized as "hotspots", while most of the landscape is not eroding. In this study, we identified the spatial and temporal distribution patterns of hotspots that may contribute dust blowing onto highways in the southwestern U.S. We further classified the hotspots for the potential of blowing dust production based upon field observations and wind erosion modeling. Results of land use and land cover show that shrubland, grassland, and cropland accounted for 42%, 31%, and 21% of the overall study area, respectively. However, of the 620 total hotspots identified, 164 (26%), 141 (22%), and 234 (38%) are located on shrubland, grassland, and cropland, respectively. Barren land represented 0.9% of the land area but 8% of the dust hotspots. While a majority of these hotspots are located close to highways, we focused on 55 of them, which are located <1km to adjacent highways and accessible via non-private roads. Field investigations and laboratory analysis showed that soils at these hotspot sites are dominated by sand and silt particles with threshold shear velocities ranging from 0.17-0.78m s-1, largely depending on the land use of the hotspot sites. Dust emission modeling showed that 13 hotspot sites could produce annual emissions >3.79kg m-2, yielding highly hazardous dust emissions to ground transportation with visibility <200m. Results of location, timing, and magnitude of the dust production at the hotspots are critical information for highway authorities to make informed and timely management decisions when wind events strike.