Investigating the Geochemical Controls on Pb Bioaccessibility in Urban Agricultural Soils to Inform Sustainable Site Management

Entwistle, Jane, Bramwell, Lindsay, Wragg, Joanna, Cave, Mark, Hamilton, Elliott, Gardner, Amanda and Dean, John (2020) Investigating the Geochemical Controls on Pb Bioaccessibility in Urban Agricultural Soils to Inform Sustainable Site Management. Geosciences, 10 (10). p. 398. ISSN 2076-3263

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The solid-phase speciation of contaminants in soil plays a major role in regulating both the environmental mobility of contaminants and their bioavailability in biological receptors such as humans. With the increasing prevalence of urban agriculture, in tandem with growing evidence of the negative health impacts of even low levels of exposure to Pb, there is a pressing need to provide regulators with a relevant evidence base on which to build human health risk assessments and construct sustainable site management plans. We detail how the solid-phase fractionation of Pb from selected urban agricultural soil samples, using sequential extraction, can be utilised to interpret the bioaccessible fraction of Pb and ultimately inform sustainable site management plans. Our sequential extraction data shows that the Pb in our urban soils is primarily associated with Al oxide phases, with the second most important phase associated with either Fe oxyhydroxide or crystalline FeO, and only to a limited extent with Ca carbonates. We interpret the co-presence of a P component with the Al oxide cluster to indicate the soils contain Pb phosphate type minerals, such as plumbogummite (PbAl3(PO4)2(OH)5·H2O), as a consequence of natural “soil aging” processes. The presence of Pb phosphates, in conjunction with our biomonitoring data, which indicates the lack of elevated blood Pb levels in our gardeners compared to their non-gardening neighbours, suggests the (legacy) Pb in these soils has been rendered relatively immobile. This study has given confidence to the local authority regulators, and the gardeners, that these urban gardens can be safe to use, even where soil Pb levels are up to ten times above the UK’s recommended lead screening level. The advice to our urban gardeners, based on our findings, is to carry on gardening but follow recommended good land management and hygiene practices.

Item Type: Article
Additional Information: Funding information: J.E. and L.B. kindly acknowledge funding from the Institutes for Sustainability and Social Renewal, Newcastle University and the Society of Brownfield Risk Assessment (SoBRA).
Uncontrolled Keywords: Risk assessment; urban gardens; lead; source apportionment
Subjects: C700 Molecular Biology, Biophysics and Biochemistry
F600 Geology
F800 Physical and Terrestrial Geographical and Environmental Sciences
Department: Faculties > Engineering and Environment > Geography and Environmental Sciences
Faculties > Health and Life Sciences > Applied Sciences
Depositing User: Elena Carlaw
Date Deposited: 05 Oct 2020 12:10
Last Modified: 27 Aug 2021 14:47

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