Sources, Sinks, and Exposure Pathways of Lead in Urban Garden Soil

Abstract

The chemistry of Pb in urban soil must be understood in order to limit human exposure to Pb in soil and produce and to implement remediation schemes. In inner-city gardens where Pb contamination is prevalent and financial resources are limited, it is critical to identify the variables that control Pb bioavailability. Field-portable X-ray fluorescence was used to measure Pb in 103 urban gardens in Roxbury and Dorchester, MA, and 88% were found to contain Pb above the USEPA reportable limit of 400 mug g(-1). Phosphorus, iron, loss on ignition, and pH data were collected, Pb-bearing phases were identified by X-ray diffraction, and Pb isotopes were measured using inductively coupled plasma mass spectrometry. Four test crops were grown both in situ and in Roxbury soil in a greenhouse, and plant tissue was analyzed for Pb uptake by polarized energy-dispersive X-ray fluorescence. Variation at the neighborhood scale in soil mineralogical and chemical characteristics suggests that the bioavailable fraction of Pb in gardens is site specific. Based on Pb isotope analysis, two historical Pb sources appear to dominate the inventory of Pb in Roxbury gardens: leaded gasoline ((207) Pb/(206) Pb = 0.827) and Pb-based paint ((207)Pb/(206) Pb = 0.867). Nearly 70% of the samples analyzed can be isotopically described by mixing these two end members, with Pb-based paint contributing 40 to 80% of the mass balance. A simplified urban human exposure model suggests that the consumption of produce from urban gardens is equivalent to approximately 10 to 25% of children's daily exposure from tap water. Furthermore, analysis of over 60 samples of plant tissue from the four test species suggests that in these urban gardens unamended phytoremediation is an inadequate tool for decreasing soil Pb.

A városi talajok szennyezettségének hatása a közösségi kertekre

“…A talajok toxikuselem-tartalmát a talajképző kőzet, a feltöltések, a korábbi területhasználat, az ipari és bányászati tevékenység, a közlekedés befolyásolja. Szennyezést okozhat a nö-vényvédő szerek, a műtrágyák, a szennyvizek és a szennyvíziszapok nem szakszerű al- (CSATHÓ, 1994;ALLOWAY, 2004;CLARK et al, 2006). SÄUMEL és munkatársai (2012) szerint a városi környezetben termesztett növényekben a nyomelemek feldúsulása leginkább három módon jöhet létre: a talaj szennyezettségéből adó-dóan, a szennyvízzel való öntözéssel és a közlekedési vagy ipari eredetű emisszióból származó levegőszennyezés miatt.…”

Total and Bioavailable Pb Content in Urban Paddy Rice Soils in Niger State, Nigeria

“…In urban areas, Pb contamination is generally higher in high traffic zones, concentrated industrial areas and older housing stock with lead containing paint (USEPA, 1998). Since Pb does not biodegrade or decay, concern for its significant role as a primary contributor in soil contamination in urban areas still persist, despite the fact that the addition of lead to gasoline and paint has been phased out in the 1970s ( Clark et al, 2006). In urban gardens, fruits and vegetables grown in contaminated soils may also become contaminated as a result of plant uptake of Pb from soils or direct deposition of leaded dust onto plant surfaces (Rahlenbeck et al, 1999).…”

An Analysis of the Potential Risk Exposure to Lead (Pb) through Urban Community Gardens

“…Many practices result in the discharge of toxic fumes and dust, such as: the smelting of Pb, the manufacture of pesticides, insecticides, paint, and gasoline containing fuel additives, sewage sludge, mining practices, and from shooting ranges (Duffus, 1980;Xiong, 1998;Siegel, 2002;Zia et al, 2011;Ming et al, 2012). The use of Pb in paints and gasoline has been phased out, but this Pb still persists in soil and water (Clark et al, 2006). The United States banned the use of lead (Pb)-based paint in 1978 and Pb as a gasoline additive in 1986, however both had been used since the 1920s (Gasana et al, 2006).…”

“…The exposure risk is higher for children and pregnant women than for adults; however, everyone can experience the effects of Pb poisoning (Mielke et al, 2008;Clark et al, 2006). In children, Pb poses a particular threat because it inhibits their growth and development (Clark et al, 2006).…”

“…Lead (Pb) is consumed by inhalation or ingestion of contaminated soil particles, or by consumption of foods grown on contaminated soils, which have bioaccumulated Pb in their tissues (Sharma et al, 2008;Zia et al, 2011;Pandey et al, 2012). Exposure to Pb from soil contamination is an environmental justice issue, since it has been observed those affected typically live in urban areas, which include a large portion of lower socioeconomic and minority communities (Clark et al, 2006).…”