Sustainable Gardening Initiatives in Previously Used Urban Soils

The objective of the project was to evaluate the uptake of soil contaminants, specifically lead (Pb) by food crops grown on a community garden in the Southern California urban area. Test plots were established in mildly contaminated urban garden soils. The plants used for testing (carrots, beets, lettuce, and radish) all had different uptake and growing characteristics. They were grown for four growing seasons with and without site-specific soil amendments. Compost, lime, and compost +lime were used as soil amendments to reduce the availability of Pb in soil. Soils were tested before and after, gardening and harvesting activities. Produce samples were tested for Pb concentration. Moreover, to assess lead bioaccessibility due to accidental human ingestion of Pb contaminated soil, the soil lead bioaccesssibility was measured using physiologically based extraction test (PBET in vitro method). Results showed that the manure treatment did not have a significant effect in the plant uptake of lead. The lead concentrations in the root crops were above 1.5 mg kg -1 dry-weight basis, which is the maximum allowable limit of Pb established by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) for root crops. However, the uptake of leafy crops (grown above ground surface) was below 5.0 mg kg -1 dry weight, which is the maximum allowable limit of Pb established by the FAO/WHO for leafy vegetables. Bioaccessible lead concentrations ranged from about 11.9% (in the control soil and lime treated plots) to 12.8% (in both lime and compost added plots) indicating that bioavailability of lead in these soils is lower compared to the EPA's default soil Pb relative bioavailability (RBA) of 60%.