Testing and educating on urban soil lead: A case of Chicago community gardens

Chicago has many urban agricultural projects that provide a source of local food for city dwellers. Urban garden soil, however, may contain lead pollution, and soil quality can vary dramatically from location to location. Soil testing and access to information should improve gardeners' abilities to grow food safely in urban soils, and to know if time-consuming or expensive measures to avoid lead exposure or enrich the soil are really necessary for their gardens. Soil quality including lead levels was profiled in 10 Chicago gardens. Gardens growing food within raised beds were compared to gardens growing food without raised beds. We also quantified lead in adjacent areas of bare soil or where children might play. Soil lead was measured in two ways: through acid digestion with the Environmental Protection Agency (EPA) 3050B method and a Mehlich-III extraction. The overall mean soil lead level reported through the EPA method was 135 parts per million (n=86), with a range from 10 parts per million to 889 parts per million in individual soil samples. The average for the Mehlich-III method was 63 parts per million. Lead levels in most gardens were not a concern, although gardens contained excessive fertility. Use of raised beds reduced lead levels and thus the potential risk of lead ingestion from plant uptake, but further study comparing the use of raised beds with a greater number of gardens is required. Higher lead levels in soil from nearby areas suggest the possibility of contamination to raised beds and supports the notion that areas with bare soil adjacent to gardens may be an equal or greater source of risk. Our results suggest that the Mehlich-III soil test was positively correlated with the more costly EPA test and could be developed as less expensive test easily conducted by commercial soil-testing labs. Additionally, a training program about urban garden safety with live and online options was created and evaluated with questionnaires given to Master Gardeners. Both live-trained and online-trained groups' quiz scores improved significantly after the trainings, demonstrating that education about urban soil management can be effective.