Testing and Interpreting Soil Pb Concentration and Bioavailability.

Large scale urban redevelopment and demolition of abandoned housing has created large areas of vacant land in old industrial cities in the U.S. City planners, community groups and other stakeholders seek to convert some of the newly created vacant land into urban agriculture and gardening, parks, playgrounds and other common areas. Because this type of land use involves high amounts of exposure to the soil, it is important to assess historical legacy soil contaminants, such as Pb, in these areas prior to redevelopment. Urban children are the most vulnerable to Pb exposure through the ingestion of household dust as well as the ingestion of soil. Required regulatory testing measures total Pb content of soil However, risk to children exposure by soil ingestion depends on Pb bioavailability not total Pb. Bioaccessibility methods are available to predict bioavailable Pb associated with soil ingestion. However, most urban soils are not tested for Pb because of the high costs associated with laboratory analysis of total soil Pb and bioaccessible Pb. Several university soil testing labs use Mehlich 3 as a screening tool to estimate soil Pb. Recent research shows potential for Mehlich 3 to estimate both total Pb and bioaccessible Pb. Use of the Mehlich soil test to predict total and bioaccessible Pb, as well as plant nutrients, would increase soil testing of urban soils. In vitro bioaccessible Pb tests and possibly the Mehlich 3 soil test can be used to evaluate urban soil treated with soil amendments to reduce Pb bioavailability. Limitations of these Pb methods to predict bioavailable Pb in treated soils will be presented. A risk-based and bioavailability-based decision framework for soil Pb and other metal contaminants in urban vacant residential lots will be presented.