Lability of Pb in soil: effects of soil properties and contaminant source

Abstract

Environmental context There is growing concern that lead in the environment may cause adverse health effects in human populations. We investigated the combined use of isotopic abundance and isotopic dilution to show how the origins of soil Pb and soil characteristics affect lability. Soil pH and soil Pb content are the dominant controls on Pb lability; the lability of recent petrol-derived Pb is similar to that of other sources in urban soils but greater than geogenic Pb in rural roadside topsoils. Abstract Lability of lead in soils is influenced by both soil properties and source(s) of contamination. We investigated factors controlling Pb lability in soils from (i) land adjacent to a major rural road, (ii) a sewage processing farm and (iii) an archive of the geochemical survey of London. We measured isotopically exchangeable Pb (E-values; PbE), phase fractionation of Pb by a sequential extraction procedure (SEP) and inferred source apportionment from measured Pb isotopic ratios. Isotopic ratios (206Pb/207Pb and 208Pb/207Pb) of total soil Pb fell on a mixing line between those of petrol and UK coal or Pb ore. The main determinant of the isotopically exchangeable Pb fraction (%E-value) was soil pH: %E-values decreased with increasing pH. In rural roadside topsoils, there was also evidence that petrol-derived Pb remained more labile (35%) than Pb from soil parent material (27%). However, in biosolid-amended and London soils, %E-values were low (~25%), covered a restricted range and showed no clear evidence of source-dependent lability.

Bioaccessibility of As and Pb in orchard and urban soils amended with phosphate, Fe oxide and organic matter

“…The Pb bioaccessibilities of the urban garden soils measured here are lower than bioaccessibilites reported for other Pb-contaminated urban and industrial sites (Lamb et al, 2009;Roussel et al, 2010;Sialelli et al, 2011). However, the results are consistent with studies indicating that the high organic matter content of urban garden soils may account in part for low Pb bioaccessibilities (Atkinson et al, 2011;Mao et al, 2014;Walraven et al, 2015). Nevertheless, these same cited studies have also indicated that the original physical-chemical form of the Pb in anthropogenicially contaminated soils maintains a strong residual effect on lability and bioaccessibility of Pb.…”

Variation in soil chemistry related to different classes and eras of urbanisation in the London area

“…Atmospheric particles deposited onto the soil can be recycled into the atmosphere. Mao et al (2014) suggested that other markers of road traffic sources such as Sb and Cu from brake liners may assist with contamination source identification, but there is no significant correlation between any of the Pb isotope ratios and other indicators including As, Ca, Cu, Sb, Sn and Zn in the 50 soil samples used by both Mao et al (2014) and 3.5. Other sources of contamination P enrichment within the GLA as the result of fertilizer application is supported by the strong correlation between P and Cd.…”

“…Equally, the narrow range of isotopically exchangeable Pb (16-26%) suggested a consistent assimilation and 'aging' of Pb from a wide range of sources, and this could reflect mixing of Pb over many decades (Mao et al, 2014). Mao et al (2014) also concluded that whilst the Pb isotope data for London soils are impacted by petrol Pb they are likely to be most impacted by non-petrol Broken Hill Type Pb ( 206 Pb/ 207 Pb 1.04) which was widely used in industrial application, including paint manufacture in the 20th century, as suggested by the sample with the lowest 206 Pb/ 207 Pb located close to an early 20th century 'White Lead Works' that possibly used BHT or Canadian Pb (Mao et al, 2014).…”

“…The data in this study do not indicate a concomitant rise in Fe, Mn or Ti with Pb, Ca and associated elements with data grouped over the range 0-24 m to > 200 m (Supplementary materials Table SM-4) reducing the likelihood of contamination related to brake dust from vehicles being a dominant factor. Mao et al (2014) demonstrated that London soils have a relatively narrow range of 206 Pb/ 207 Pb falling on a mixing line between geogenic (UK coal and UK Pb ore; Shepherd et al, 2016) and UK leaded petrol (1.06-1.09 Shepherd et al, 2016;Chenery et al, 2012;Sangster et al, 2000) suggesting multiple sources of Pb contamination including petrol, paint, water pipes, coal ash. Whereas Total Pb does not correlate with 206 Pb/ 207 Pb, it is the primary determinant of isotopically exchangeable Pb (Mao et al, 2014) as it is for bioaccessible Pb .…”

“…Mao et al (2014) demonstrated that London soils have a relatively narrow range of 206 Pb/ 207 Pb falling on a mixing line between geogenic (UK coal and UK Pb ore; Shepherd et al, 2016) and UK leaded petrol (1.06-1.09 Shepherd et al, 2016;Chenery et al, 2012;Sangster et al, 2000) suggesting multiple sources of Pb contamination including petrol, paint, water pipes, coal ash. Whereas Total Pb does not correlate with 206 Pb/ 207 Pb, it is the primary determinant of isotopically exchangeable Pb (Mao et al, 2014) as it is for bioaccessible Pb . Equally, the narrow range of isotopically exchangeable Pb (16-26%) suggested a consistent assimilation and 'aging' of Pb from a wide range of sources, and this could reflect mixing of Pb over many decades (Mao et al, 2014).…”