Extractability of Pb in urban gardens and orchards linked to soil properties

Abstract

Summary The hypothesis that lability and bioavailability of lead (Pb) in strongly contaminated soil is limited by interaction with phosphate and organic matter was tested on soil from urban gardens and orchards by extracting available Pb and P with the modified Morgan's extractant (ammonium acetate, pH 4.8) and measuring organic matter by loss‐on‐ignition. The extractable fraction of total Pb was larger in general in the urban garden than orchard soil, which indicates greater lability in urban garden soil than was expected if insoluble Pb phosphates such as pyromorphite were limiting Pb extractability. The extractable Pb fraction was generally larger in soil with greater total Pb, an indication that soil with large Pb concentrations contained Pb in more labile forms than soil with small concentrations. Larger organic matter contents in garden soil reduced the extractable fraction of Pb, but large available phosphate concentrations did not have this effect. The results indicate that soil organic matter has an important role in limiting Pb extractability in strongly contaminated soil, whereas a large soil phosphate concentration does not, despite the expectation that formation of insoluble Pb phosphates would reduce Pb lability. Nevertheless, a spatial association of P with Pb in Pb‐rich particles identified in urban garden soil with the electron microprobe suggests that Pb phosphates have formed in such soil from more reactive forms of Pb. The hypothesis is that a small fraction only of the total Pb in the urban soil occurs in a phosphate phase, and more acid‐labile forms of Pb co‐exist with insoluble phosphates for long time periods. Highlights Lead bioavailability in soil can potentially be reduced with phosphate. Hypothesis is that soil Pb availability is limited by available phosphate or total organic matter. Large soil organic matter content correlated with reduced Pb extractability, but not large available phosphorus content. Lead‐phosphate phases did not appear to limit soil Pb extractability.

Heavy metal pollution in soils and urban-grown organic vegetables in the province of Sevilla, Spain

“…The problem of lead pollution in urban soils due to paints has already reported in the U.S.A (Datko- Williams et al 2014;Mitchell et al 2014;McBride 2016)…”

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

“…The association of Pb and P in this and other urban garden soil studied in our lab suggests that Pb phosphates may have formed owing to the high phosphate status of many of these soils (McBride, 2016). Conversely, while Pb in the orchard soil appears to be distributed heterogeneously, an association with As, Fe and P was also observed as displayed in the EDS spectra ( Figure 3) and in the elemental maps presented in Fleming et al (2013).…”

“…Previous investigations using the electron microprobe have revealed a strong tendency for Pb in anthropogenically contaminated soils to be spatially distributed in a highly heterogeneous manner (Cotter-Howells, 1996;Fleming et al, 2013;Tai et al, 2013;McBride, 2016). This characteristic was observed in the soils of the present study, with the EDS X-ray spectra of selected Pb-rich regions within the (Albany) urban soil and orchard soil in Figure 3 showing a clearer indication of a Pb phosphate phase in the former soil, as the Pb "peak" has greater intensity than the P "peak", consistent with the measured X-ray spectrum of pyromorphite (not shown here).…”

“…Recent research has shown that a larger fraction of total soil Pb is extracted by 1M NH 4 Ac (pH 4.8) from urban garden soils than orchard soils (McBride, 2016), leading to the conclusion that some fraction of the Pb in urban garden soils is more labile than Pb in the orchard soils. However, the bioaccessibility results in Figure 1 would seem to support the opposite conclusion.…”

Tracing Pb Pollution Penetration in Temperate Podzols

“…This is in agreement with the Pb EFs (Figure c) in ACB1 and ACB2 soils, which illustrate a substantial vertical mobility of Pb. Furthermore, the fact that the highest loadings on LV1 ext correspond to variables related to the metal–organic complex content is in agreement with previous research studying lead binding to organic compounds and its effect on lead mobility and bioavailability (Gustafsson et al ., ; Kaste et al ., ; Kaste et al ., ; McBride, ). According to Gangloff et al .…”