Using Mehlich III Soil Test As An Inexpensive Screening Tool to Estimate Total and Bioaccessible Pb in Urban Soils.

Urban redevelopment has created vacant land in many industrial cities.  Use of urban land for food production, including gardening, involves human exposure to soil. This can be a human health issue if the soil contains historical contaminants such as Pb. Most urban soils are not tested for Pb because of the high costs associated with sampling and laboratory analysis of soil contaminants. However, soil testing for plant nutrients is inexpensive and routinely performed for agricultural soils used for food production. The objectives of this study are to evaluate the ability of the Mehlich III to predict both total Pb and bioaccessible Pb in urban soils.  Total and bioaccessible Pb was determined from 65 urban residential vacant lots being considered for urban gardens and food production in Cleveland, OH. Extractable Pb was determined using Mehlich III extraction. The results of this study show Mehlich III was strongly correlated with total and bioaccessible Pb. Most commercial and university soil testing labs use Mehlich III to measure available plant nutrients. These laboratories are more likely to use their existing Mehlich III soil test to estimate Pb. They are unlikely to add a new soil test (Modified Morgan or 1M HNO₃) solely for estimating Pb. The Mehlich III soil test could be used as a screening tool to not only estimate total Pb (slope 1.83, r² = 0.959) but also to estimate bioaccessible Pb when using RBALP at pH 1.5 (slope 1.47, r² =0.965) and RBALP at pH 2.5 (slope 0.92, r² = 0.943). Because Mehlich III is currently the most widely used test to evaluate available plant nutrients and because it is relatively inexpensive (< $15/soil) it can easily be adopted by soil testing laboratories to screen samples for Pb. Our results show that total Pb can be conservatively estimated by the following equation Total Pb (mg kg^-1) = Mehlich III Pb (mg kg^-1) x 2