D. Distribution of Metals

Three of the five zip codes were found to have elevated levels of lead, with two of these three zip codes consistently having higher levels of metals than the other 3 zip codes.  The following tables and maps show the distribution of some of the heavy metals that were tested for.  Note that locations of some gardens were slightly changed on the maps so that garden locations remain confidential.

Average Levels in Existing Soil (In-Ground Gardens)

Since in-ground gardens are often planted directly into the existing soil, they are more likely to reflect the amount of metals in the soil of the surrounding area than a raised bed garden.  The table below shows average concentrations of metals in in-ground gardens by zip code.  Potrero Hill (94107) and Noe Valley/Castro (94114) have either the highest or second highest average concentration for 5 of the metals of most concern.  In addition, the Mission (94110) has the third highest concentration for each of these metals, with Visitation Valley/Portola (94134) & Bayview/Hunters Point (94124) having the lowest averages for these metals.

The maps below show the levels of lead, arsenic and cadmium by individual garden, and includes in-ground, raised beds, backyard, community and school gardens.  Other maps can be found on the Environmental Justice page that show potential relationships to income & race/ethnicity.

Lead in San Francisco Gardens

Three of the five zip codes in the study area (94107, 94114, & 94110) have at least one garden with lead levels that are higher than 1,000ppm, the threshold for hazardous toxic waste in the state of California. The two remaining zip codes (94124 & 94134) each had approximately equal numbers of gardens with "Safe" and "Unsafe" levels.


Cadmium & Arsenic in San Francisco Gardens

No gardens had levels of cadmium or arsenic that would be considered hazardous waste by the State of California, however many of the gardens do have levels that are higher than what the California Office of Environmental Health Hazard Assessment considers safe for human health.  These levels are 1.7ppm for cadmium and 0.07 for arsenic.  The U.S. EPA has published that they believe that soil is safe for vegetable gardens with a cadmium concentration of up to 39ppm or an arsenic concentration up to 41ppm. It is unclear, however, why the U.S. EPA levels are higher than the California levels, when the federal levels include consuming soil and produce, when the California levels only include eating soil.  (Note: The range of naturally existing levels for cadmium is 0.01-2.0 ppm and 5-10 ppm for arsenic. (Gardea-Torresdey, et al., 2005; Gadepalle, et al., 2008))


(Click on maps to enlarge)

More Project Details:

A.  Project Summary

B.  Project Demographics

C.  Raised Beds vs. In-Ground Gardens

D.  Distribution of Metals by Zip Code

E.  Addressing Environmental Justice