Significant progress has been made worldwide over the past half century in reducing child Pb poisoning rates. In the US, for example, estimates of children and pregnant women with high blood Pb levels have dropped significantly in recent decades [1]. Despite this progress, about 250,000 children in the US have blood lead levels over the current Level of Concern of 10 µg/dL [2]. This number is likely to double as the U.S. Centers for Disease Control and Prevention (CDC) considers the recommendation of its advisory body to lower the Level of Concern from 10 µg/dL to 5 µg/dL [3]. This major change in national policy is based on a large and growing body of evidence showing that even single-digit blood Pb levels have significant impacts on Intelligence Quotients, Attention Deficit Hyperactivity Disorder risks, cardiovascular disease, and kidney function [4,5,6,7,8]. If CDC finalizes this change, the World Health Organization will likely consider a similar move, potentially impacting the Pb regulatory environment worldwide and improving the prospect of reducing the Pb burden on millions of impacted children.

The most common Pb exposure pathways for children are ingestion or inhalation of Pb-bearing particulate matter, whether in the household or outdoor environment [9,10,11]. The most common sources of Pb are paint (typically as lead chromate, PbCrO₄ or lead carbonate, PbCO₃) [12,13] and gasoline containing tetraethyl lead. In many settings, mining and smelting operations remain major sources as well [14]. Chronic exposure is a long-term legacy, even in jurisdictions where lead releases were minimized or eliminated long ago, because Pb persists in near-surface soil environments [15,16]. In the US, socio-economic analyses have shown that the exposure burden is disproportionately carried by lower-income and minority communities, although significant risks to upper income and non-minority populations are found as well [1].

Numerous studies have shown the importance of the soil Pb reservoir in the cycling of Pb in the urban environment [16,17,18,19,20,21]. Depending on climate, soil Pb can be seasonally resuspended, leading to predictable quantitative exposure rates among children [15,16]. In highly urbanized environments, however, assessing soil Pb content can be difficult because of high spatial variability and confounding factors such as landscaping, erosion, and the presence of impervious surfaces. In a number of cities, studies of road dust have also been undertaken, as this material is present in significant quantities and is also susceptible to resuspension [21,22,23,24].

The purpose of this paper is to report the preliminary results of analyses of road dust metal contents in two urban neighborhoods of Atlanta, GA, USA [25]. The working hypotheses of the study are that: (1) despite strict controls on emissions, Pb persists in Atlanta road dust; and (2) physical and social processes in different neighborhoods produce different geospatial patterns in metal load.

In May, 2011, two neighborhoods were sampled near the heart of the urban core of Atlanta. The first area is known locally as “Downtown”, and is comprised largely of high-rise buildings in a commercial setting. The second area is comprised of the western two thirds of Atlanta’s Neighborhood Planning Unit V (NPU-V). The neighborhood is within 1 km of Downtown, and is a residential neighborhood with mostly early to mid-20th century construction; the neighborhood has a history of mixed residential and light commercial use. Both neighborhoods are adjacent to major transportation arteries. Seventy two (72) samples of road dust were collected by sweeping a 1 m × 1 m square area and collecting the dust in plastic bags. The two neighborhoods were selected because they are in the urban core of Atlanta, but they have different land uses. Individual sample sites were located randomly in a grid across the area, with added complexity of problems of access and several samples that did not contain enough fine material for analysis. These samples were excluded from the analysis. All analyzed samples are reported here.

In the lab, samples were sieved at 250 µm, and shipped to ALS Chemex (Reno, NV, USA) for geochemical analysis. Samples were pulverized and digested in nitric, perchloric, hydrofluoric, and hydrochloric acid, and analyzed by inductively coupled plasma atomic emission spectrometry. Analytical precision is in all cases less than 10% of the reported values. Metal abundances were treated as non-parametric data; correlations among the analytes were determined by Spearman Rank Correlation coefficent calculated using SPSS (v. 18). Geospatial analysis of the results was done using the Geostatistical Analysis tool in ArcGIS Desktop.

Road dust in the NPU-V and Downtown Atlanta neighborhoods has median Pb concentrations of about 85 mg/kg. Values in the northwest of the Downtown area reach a high of 278 mg/kg Pb, whereas high samples in the southern part of NPU-V reach 972 mg/kg Pb. These results suggest that despite the complexities of resuspension and transport of Pb-bearing particulates by wind and water in the road environment, substantial Pb remains in road dust decades after Pb-containing gasoline was banned, just as it is well known to persist in urban soils. This may be due to limits on rates of Pb removal from road dust, or other continuing sources of Pb in the urban environment. Geospatial variation can be observed at the scale of tens to hundreds of meters, and probably at even finer scales. Very high resolution of sampling is therefore required to adequately assess Pb exposure risks due to road dust, as well as other sources of Pb in the urban setting.