Working dirt: Community based research on lead, gardens, and place

Background/Question/Methods

Urban sustainability goals often include increasing local food production through urban gardening.  Growing food in cities poses specific challenges; one being potential exposure to elevated levels of lead in soil from legacy sources such as paint, gasoline, and industry.  Soil lead can become a source of lead to humans when inhaled or ingested.  Researchers from three universities are working in partnership with Ubuntu Green, a non-profit organization based in Sacramento, CA, to support healthy urban gardening by studying how lead is distributed across the landscape and how experiences of urban gardening and soil lead testing shape community.  Collectively the project seeks to understand both the biological and social implications of elevated soil lead on urban gardening activities.  This talk will focus on the biogeophysical research questions which are organized by three spatial scales – city, parcel, and garden – and address the fine scale heterogeneity of soil lead, correlations with land cover, and change over time.  Soil lead was quantified in two neighborhoods of Sacramento, CA using handheld x-ray fluorescence.  We will share findings from the parcel and garden scale sampling and discuss how these data will be used to model soil lead concentrations at the city scale.

Results/Conclusions

At the parcel scale, none of the properties have average soil lead concentrations that exceed the US EPA Federal guideline of 400 ppm; however, 27% of properties demonstrate soil lead concentrations that exceed 400 ppm in some areas – 36% have average lead concentrations that exceed the California Office of Environmental Health Hazard Assessment screening level of 80 ppm with 82% exceeding that level in some areas.  Raised-bed gardens were expected to have much lower lead concentrations compared to the property in which they are embedded because they contain imported soil.  Average lead concentrations in all of the raised-bed gardens falls below EPA and CA limits and only 3% demonstrate some areas that exceed 80 ppm.  Measurements at the parcel scale allow us to explore the fine scale heterogeneity of soil lead and potential correlations with land cover.  Continued monitoring at the garden scale allows us to determine whether soil lead concentrations change over time.  This is especially important in Sacramento where dry windy conditions could redistribute lead in the form of re-suspended fine particulates.  Together parcel and garden scale data will be used to understand soil lead concentrations at the city scale in order to identify areas of concern.