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-m 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.