A Field Evaluation of Lead Transfer From Urban Soils to Vegetables.

Urban gardening improves primary food production and nutritional status of urban residents; however, development of urban gardens can be complicated by the presence of contaminants in urban soils. Lead (Pb), originated from Pb based gasoline and paint, is one of the most abundant inorganic contaminant in urban soils. A field experiment was conducted on a community gardening site in Kansas City, Missouri to assess potential risk from both direct and indirect exposure to soil Pb. Three vegetable crops (tomato, swiss chard and carrot) were grown to evaluate plant Pb uptake.  The experimental design was a randomized complete block with split plot arrangement. The main plot factor was compost addition (28 kg/m²). Lead in edible portions was determined after following two cleaning procedures which represent two sub plot factors: cleaning with (1) tap water only (to mimic “kitchen style washing”) (2) 5 g/L sodium lauryl sulfate, followed by deionized water (laboratory cleaning). Lead concentration in soils ranged from 60 to 385 mg/kg. Compost addition diluted soil Pb concentration by ~59%. In compost added plots, Pb uptake was 59% lower in swiss chard and 20% lower in carrot compared to the swiss chard and carrot grown in control soils, respectively. However, Pb concentration in tomato was not significantly affected by the compost addition. Laboratory cleaned swiss chard and tomato had 67 and 73% lower Pb concentration, respectively compared to swiss chard and tomato cleaned with tap water. Cleaning method was not significant for Pb concentration in carrot. Compost addition did not reduce bioaccessible Pb as determined by physiologically based extraction test at pH 2.5. Addition of compost and thorough cleaning of vegetables reduce potential for Pb transfer from soil-plant-human.  

Keywords: urban gardening, Lead, compost, vegetables, cleaning method