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

^a Geosciences Dep., Wellesley College, 21 Wellesley College Rd, Wellesley, MA 02481
^b Wellesley College, 21 Wellesley College Rd, Wellesley, MA 02481

View larger version (22K): [in a new window]   Fig. 1. The environmental Pb cycle is unique in the urban environment. This flow chart, modified from Litt et al. (2002), includes urban produce, which has not been quantified as a sink or a pathway of exposure.

View larger version (23K): [in a new window]   Fig. 2. Regional Pb contamination has been measured by field-portable X-ray fluorescence (FP-XRF) and the distribution of Pb can be illustrated by (a) GIS mapping and (b) a histogram of frequencies of observed soil Pb concentrations (Pbsoil).

View larger version (13K): [in a new window]   Fig. 3. The Pbsoil and plant Pb uptake (Pbplant) in Brassica rapa (mustard) tissue analyzed by XRF. Mustards were grown in both the greenhouse (n = 4) and in situ in the test plots (n = 8). Each point represents an average of 2 to 4 Pbsoil measurements and 5 to 8 Pbplant measurements.

View larger version (20K): [in a new window]   Fig. 4. Sources of Pb were identified using (a) trace element ratio and (b) isotopic ratio (measured by inductively coupled plasma mass spectrometry (ICP–MS)) analysis techniques. Both graphs represent data (n = 4) from a nonurban residence with a known and isolated Pb-based paint Pb source. The data in (b) is compared to the isotope ratio range for Pb-based paint and a leaded gasoline signature measured by Rabinowitz (1986).

View larger version (24K): [in a new window]   Fig. 5. Isotope/isotope ratios of size-fractioned (4 to 0.037 mm) samples measured by inductively coupled plasma mass spectrometry (ICP–MS) from four of the urban phytoremediation test plots and the nonurban residence with an isolated Pb-based paint source. Error bars represent analytical uncertainty. The proposed end-member isotopic compositions for Pb-based paint and leaded gasoline are from Rabinowitz (1986). The plotted symbols represent the mean and the shaded ellipses represent the standard deviation. Ayuso et al. (2004) represents the atmospheric Pb composition in the USA in the 1970s and Mississippi Valley Type ore.