Biogeochemical characterization of municipal compost to support urban agriculture and limit childhood lead exposure from resuspended urban soils

Abstract

Chronic low-level lead exposure among low-income minority children is an urgent environmental justice issue. Addressing this ubiquitous urban public health crisis requires a new transdisciplinary paradigm. The primary goals of this work are to inform best practices for urban gardeners working in lead contaminated soils and to reimagine urban organic waste management schemes to produce compost, which when covering or mixed with urban soil, could minimize lead exposure. We investigate bulk and bioaccessible lead from five types of compost used in urban gardens in Boston, MA. We categorized them by feedstock and measured bulk elemental concentrations and physical characteristics. Our results show that different feedstocks exhibit unique geochemical fingerprints. While bulk lead concentrations in compost are a fraction of what is typical for urban soils, the bioaccessible lead fraction in compost is greater than the default parameters for the Integrated Exposure Uptake Biokinetic (IEUBK) model. The lack of geochemical differences across feedstocks for lead sorption to carbon indicates a similar sorption mechanism for all compost. This suggests that municipal compost would be suitable for capping lead contaminated urban soils. Risk assessment models should consider lead bioaccessibility, to prevent the underprediction of exposure risk, and should include compost along with soils as urban matrices. Based on the observed bioaccessibility in our compost samples, 170 mg/kg total lead in compost will yield the same bioaccessible lead as the IEUBK model predicts for the 400 mg/kg EPA soil lead benchmark. Local logistical challenges remain for interdisciplinary teams of city planners, exposure scientists, and urban agricultural communities to design organic waste collection practices to produce compost that will support urban agriculture and primary lead exposure prevention.

Lead (Pb) Bioaccessibility and Mobility Assessment of Urban Soils and Composts: Fingerprinting Sources and Refining Risks to Support Urban Agriculture

“…Other studies have also found a linear relationship between total and bioaccessible Pb, though the slope of the regression line varies by study location (Fitzstevens et al, 2017). Other studies have also found a linear relationship between total and bioaccessible Pb, though the slope of the regression line varies by study location (Fitzstevens et al, 2017).…”

“…Previous studies have shown that compost dilutes total soil Pb concentrations Clark et al, 2008;Clarke et al, 2015;Fitzstevens et al, 2017). Since total Pb is directly proportional to bioaccessible Pb and compost binds Pb more effectively than soil, compost application also reduces urban gardeners' exposure to bioaccessible Pb through dilution and limiting Pb solubility (Table 1).…”

“…Composts are the nutrient-rich product of accelerated degradation of organic matter, primarily food, yard, and park waste (Fitzstevens et al, 2017). Though each sample is unique due to urban environment heterogeneity, they can be grouped into four categories.…”

“…Aligning with Fitzstevens et al (2017), composts have significantly lower Pb concentrations than soils. Aligning with Fitzstevens et al (2017), composts have significantly lower Pb concentrations than soils.…”

“…Since Pb bioavailability in urban soils can vary significantly (Zia et al, 2011), recent studies are framing soil exposure risk in terms of bioavailable Pb instead of the total soil Pb Clarke et al, 2015;Fitzstevens et al, 2017;Henry et al, 2015). Since Pb bioavailability in urban soils can vary significantly (Zia et al, 2011), recent studies are framing soil exposure risk in terms of bioavailable Pb instead of the total soil Pb Clarke et al, 2015;Fitzstevens et al, 2017;Henry et al, 2015).…”