Publication Date

Spring 2012

Degree Type


Degree Name

Master of Science (MS)


Environmental Studies


Rachel O'Malley


Environmental Justice, Heavy Metals, Lead, Soil Contamination, Urban Gardens, Vegetables

Subject Areas

Environmental science; Agriculture; Environmental justice


As urban dwellers prioritize eating locally grown foods to reduce environmental impacts, benefit the local economy, and bring fresh produce to the table, urban gardening has emerged as a popular approach to improving food security. Researchers have shown previously that urban landscapes can accumulate environmental toxins at levels that may be unsafe for human health, with socioeconomically disadvantaged communities often shouldering an unequal burden of exposure. In order to identify and predict likely risk to gardeners, in this study, soil samples from 91 vegetable gardens in the city of San Francisco were analyzed for 16 heavy metals. A majority of the gardens exceeded the California Human Health Screening Level for arsenic (74%), cadmium (84%), and lead (62%), including nine gardens with lead levels above the hazardous toxic waste threshold for California. Cadmium and lead concentrations increased with home age, suggesting that older house paint is a major source of these metals. Contrary to findings in many other cities, the majority of gardens with hazardous lead levels in San Francisco were located in higher income and predominantly White neighborhoods, with no associations found with existing industrial contamination. Encouragingly, community gardens and raised beds had significantly lower average metal concentrations than backyard and in-ground gardens, respectively. Overall, the goal of this study is to illustrate the importance of providing access to soil testing and related education in order to support urban gardeners in their efforts to grow and consume healthy produce.