Toxic Soil: Assessing Heavy Metal Contamination in Urban Gardens across the San Francisco Bay Area- Using Soil Biogeochemistry to Combat Environmental Injustice

EJ @ Stanford
EJ @ stanford
Published in
4 min readNov 4, 2021


By Alexis Wilson

This blog post was written by a recipient of our Summer 2021 Environmental Justice Graduate Student Research Fellowship.

When I began my PhD program at Stanford in 2019, I had previous research experience working on issues related to forest ecology, drought, and climate change. I loved the research I did in those areas but was looking for other ways to expand my knowledge and impact in the field of environmental science. As I took courses such as “Science of Soils” and “Shades of Green”, my research interests expanded to include soil biogeochemistry and environmental justice. I began thinking of ways I could combine my interest in soil science with my desire to pursue research that was relevant to frontline communities which experience the biggest impacts of climate change and environmental injustices.

Photo of Alexis standing in the Florence Fang Community Farm in SF after volunteering (PC: David Gonzalez)

While volunteering at a community farm in San Francisco during January of 2020, I began thinking about the garden’s location and possible soil contamination because of past land uses and/or present sources of pollution. I wondered, what risk did working in contaminated soil pose to garden users? What about the safety of the food grown in this soil? When speaking with garden leaders, I learned about the many benefits the garden provided for community members such as fresh, culturally relevant produce and a space for community building. I then wondered if urban soil contamination was a threat to this garden and many others like it.

From here, I began learning more about urban soil contamination, food insecurity, urban agriculture and the connections between them. Through my research, I found that the combination of urban food insecurity and soil contamination becomes an environmental justice issue because research indicates that communities of color (Black, Indigenous, Latino/Hispanic, Asian/Pacific Islander) and low-income communities disproportionality face food insecurity and exposure to environmental pollution. Through urban gardens, I had successfully found a way that I could use soil biogeochemistry to examine and solve an environmental justice problem facing frontline communities. The overall goal of my PhD research is to use an interdisciplinary approach, using Environmental Justice and Community-Based Participatory Research as foundational frameworks, to advance our understanding of the threat of soil contamination to urban gardens across the San Francisco Bay Area, specifically focusing on marginalized communities.

Photo of Alexis using a shovel to collect soil and place it in a bucket. (PC: Alexis Wilson)
Photo of Alexis holding a handful of collected soil samples in Ziplock bags from the field site (PC: Alexis Wilson)

To begin this work, I have been building a partnership with a community organization over the past year based in Oakland, CA that runs an educational urban garden program (The organization will remain unnamed at this stage). We have worked together to create projects that align with my research goals and their identified needs. Conducting research in partnership with this organization has made this work more meaningful in that it is directly in line with what they need and want, we have a reciprocal and respectful relationship, and our goal is for this work to benefit the community. Our first project together is transforming an empty urban field into an educational community farm. Part of the initial steps in this process is to assess the site for soil contamination; this is where I come in.

In October 2021, I traveled to the site in Oakland and collected over 120 soil samples with help from the partner. I transported the samples back to Stanford to determine the total concentration (amount) of heavy metals (specifically lead, arsenic, cadmium, and chromium which are common urban soil contaminants) in the sample using an X-ray Fluorescence Spectrometer. After analyzing the results, I will compare them to soil screening levels used by the State of California in assessing sites for soil contamination and present the results to the partner. From there, we will discuss remediation options, if necessary, and continue the process of transforming this space into a safe, thriving community farm.

Photo of Alexis working with the soil samples in the lab back at Stanford. (PC: Alexis Wilson)

This is the first of many projects that I will be conducting over the next few years. I will be conducting qualitative interviews of garden users, managers, and community organizers to learn more about their perspectives on urban agriculture and soil contamination. I will also be collecting soil samples from community, school, and home gardens across the Bay Area and analyzing them for heavy metal contamination. If you are interested in learning more about this work or getting involved, I can be reached via email at Thank You.

Alexis Wilson (she/her) is a third year PhD candidate in the Department of Earth System Science. Her passion lies in understanding and combating environmental racism and climate injustices on local and global scales. Alexis’ current research focuses on identifying and remediating soil contamination in urban gardens, particularly in marginalized communities in the Bay Area. She is pursuing this work in partnership with local environmental organizations and centering community-identified needs in the research process. You can contact her at to learn more.



EJ @ Stanford
EJ @ stanford

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