Monday, July 9, 2012

Know your soil

Public health message: lead hazards in urban farming

According to SF Department of Public Health (DPH) Children’s Environmental Health Promotion Program, one of the major sources of lead exposure to children in SF is bare soil in gardens with lead contamination from house paint or previous use of leaded gasoline. Though lead has been banned in house paint since 1979 and in auto fuel since 1996, lead does not break down over time, but remains in the environment. Most urban gardens in SF are located near residential buildings, of which more than 90% have at one time been covered with lead-based paint. Because safe work practices disturbing paint on building exteriors were not required until 1998, migration of lead paint dust into the soil was common.

(A few months ago, the apartment buildings adjacent to The Free Farm were painted. It’s good to know standards exist to prevent lead paint migration, including requirement that property owner or contractor post “Lead Work in Progress” sign or provide written notice to adjacent neighbors; see

While gardening, we can get lead into our body from our hands contaminated with lead soil, eating lead-contaminated soil or paint dust on unwashed produce, or eating produce that has lead uptake. Lead toxicity can cause serious health problems: impair brain development, damage the nervous system, cause iron deficiency/anemia, interfere with calcium uptake, harm kidneys and reproductive health (fetus at risk because lead easily crosses placenta).
At workshop host site Garden For the Environment (, Janet collects soil samples for lead testing, while her DPH colleagues Joe and Karen look on. DPH recommends getting soil analysis done by a local company like Micro Analytical Laboratories, Inc., 5900 Hollis St., Suite M, Emeryville, CA 94608, 510-653-0824,  SF residents can get a special rate of $25 if they note “SFDPH Partner” on the documentation sent to this lab with the samples, and if the lab does not have to explain the results; instead, for lab results interpretation, call SF DPH at 415-252-3956. (DPH conducted lead testing for Alemany Farm

Children are at most risk because of their still developing brains and bodies. Because daily contact with 80 ppm lead in soil can raise a child’s blood lead level by one unit, 80 ppm is the precautionary standard in risk assessment (i.e., soils with lead levels greater than 80 ppm should not be used for gardening unless remediated).
SFGTV Channel 26 films workshop participant washing hands after gardening.

DPH recommends the following best practices for reducing lead exposure from gardening: practice good personal hygiene (wear gloves while gardening, wash hands frequently, wash produce well before consuming), garden on low-leaded soil (< 80 ppm) when possible, and prevent further soil contamination by looking for surrounding risks. Other best practices include amending soil with organic matter (clean compost) and maintaining neutral pH (add limestone if soil is too acidic). More information at

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