Neighborhood-scale lead (Pb) speciation in Akron, Ohio (USA) soils: primary sources, post-deposition diagenesis, and high concentrations of labile Pb

Abstract

Lead (Pb) poses a significant risk to infants and children through exposure to contaminated soil and dust. However, there is a lack of information on Pb speciation and distribution at the neighborhood-scale. This work aimed to determine: (1) the distribution of acid-extractable (labile) Pb and other metals ([M]_AE) in two neighborhoods in Akron, Ohio (USA) (Summit Lake and West Akron; n = 82 samples); and (2) Pb speciation and potential sources. Total metal concentration ([M]_T) and [M]_AE was strongly correlated for Pb and Zn (R² of 0.66 and 0.55, respectively), corresponding to 35% and 33% acid-extractability. Lead and Zn exhibited a strong positive correlation with each other (R² = 0.56 for M_T and 0.68 for M_AE). Three types of Pb-bearing phases were observed by electron microscopy: (1) galena (PbS)-like (5-10 μm); (2) paint chip residuals (10-20 μm); and (3) Pb-bearing Fe-oxides (20 μm). Isotope ratio values for Pb_AE were 1.159 to 1.245 for ²⁰⁶Pb/²⁰⁷Pb, and 1.999 to 2.098 for ²⁰⁸Pb/²⁰⁶Pb, and there was a statistically significant difference between the two neighborhoods (p = 0.010 for ²⁰⁶Pb/²⁰⁷Pb and p = 0.009 for ²⁰⁸Pb/²⁰⁶Pb). Paint and petrol are the dominant sources of Pb, with some from coal and fly ash. Lead speciation and distribution is variable and reflects a complex relationship between the input of primary sources and post-deposition transformations. This work highlights the importance of community science collaborations to expand the reach of soil sampling and establish areas most at risk based on neighborhood-dependent Pb speciation and distribution for targeted remediation.

Keywords: Lead; Metal contamination; Pb isotopes; Urban soil.

Fig. 1

A location of Akron, OH (USA); B map of Akron (in blue) with the locations of the West Akron and Summit Lake neighborhoods outlined in dashed lines. Each circle represents the location where a soil sample was collected; the symbol size corresponds to the amount of total Pb (Pb_T) and the symbol color corresponds to the amount of nitric acid-extractable Pb (Pb_AE)

Fig. 2

Box-and-whisker plots (left) for [M]_T and [M]_AE for M = Ti, Cr, Mn, Cu, Zn, and Pb (n = 82), and scatter plots (right) showing the relationship between [M]_T and [M]_AE

Fig. 3

Representative SEM images and EDS element maps for two samples showing Pb–S-rich phases consistent with the composition and morphology of galena. Values for [Pb]_T and [Pb]_AE were 263 mg/kg and 26 mg/kg, respectively (A) and 762 mg/kg and 114 mg/kg, respectively (B)

Fig. 4

Representative SEM images and EDS maps of Pb-Ti–O-rich phases consistent with paint particles. Values for [Pb]_T and [Pb]_AE were 544 mg/kg and 123 mg/kg, respectively (A) and 517 mg/kg and 102 mg/kg, respectively (B)

Fig. 5

Representative SEM images and EDS maps of Pb-Fe–O-rich phases consistent with Pb associated with Fe-oxides. Values for [Pb]_T and [Pb]_AE were 435 mg/kg and 260 mg/kg, respectively (A) and 139 mg/kg and 79 mg/kg, respectively (B)

Fig. 6

Isotopic composition of acid-extractable Pb (Pb_AE) for all Akron soil samples separated by neighborhood (red triangles for Summit Lake; and blue circles for West Akron). Also included are average data and ranges for US soil (natural Pb, gray area), paint (short dash-lined area), petrol (solid-lined region), and coal and fly ash (long dashed-line area) (Wang et al., 2019). Error bars (representing instrumental error based on reference standards collected in between samples) are smaller than the data symbols