How Safe Is Your Soil? 

Urban farming has become hugely popular in the East Bay, but lead and other heavy metals in the soil pose potential health risks. Meanwhile, there's little consensus on what to do about it.

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Even with a standardized testing procedure and a focus on sites that could support urban farming, he encountered a huge range of results. Lead values spanned from as low as 50 parts per million in the hills to as high as 980 in West Oakland. Residential lots in West Oakland averaged about 360 — still below the US Environmental Protection Agency's action level of 400, but nearly double that of the regional water quality control board and more than twice as high as average values throughout the rest of the city.

The gist of McClintock's data, if not the exact values, is corroborated by Calanog's research for the EPA. Calanog is in the midst of administering a program that will provide free lead remediation services to West Oakland's Prescott neighborhood, one of the city's oldest and most polluted. His results put West Oakland's lead levels even higher than do McClintock's — much higher. Based on one hundred samples taken from sixty yards, Calanog says levels average around 800 parts per million and reach as high as 2,700.

The discrepancy is due to differences in testing protocols and site selection. But there's evidence that these base lead-content counts may not actually be very helpful. Both McClintock and Calanog suggest that the more important number, which is costly to gather, measures the lead content that is bioavailable. The distinction is essential, since many lead compounds are bound with phosphorous, calcium, or other organic matter in the soil, making them inert and harmless to humans.

The cornucopia of screening levels proposed by various public agencies muddies the water even more. The California Office of Environmental Health puts its hazard assessment level at 80 parts per million for ingested soil, while the California Department of Toxic Substances Control says soil becomes hazardous material when lead surpasses 1,000 parts per million. Between them is a bevy of guidelines and limits for lead exposure in food, water, and soil in a variety of contexts. They tend to provide more confusion than guidance.

But there's a simple bottom line, said Alameda County Lead Poisoning Prevention Program communications manager Julie Twichell: "No level of lead is safe. You don't need any lead in your body, and studies have shown that even minor levels of lead can cause harm." This is particularly true for children, who are most susceptible to lead poisoning through ingestion of lead dust, paint, and soil. Lead is the most common source of heavy metal poisoning in children and can cause irreversible problems in growth and development affecting behavior, hearing, and learning.

In adults, lead poisoning can cause high blood pressure and damage to the brain, nervous system, kidneys, thyroid, and blood. The body mistakes heavy metals like lead, arsenic, and mercury for essential nutrients such as calcium and iron and stores them in tissue, where they bind with cells and are readily absorbed. What's more, there's no cure beyond simply removing the source of contamination and allowing the body to clean itself out.

Diagnosing lead poisoning is tricky. Symptoms are unreliable, onset is gradual, and in children developmental problems may not surface until years later. The only way to know for sure is to get tested. US Centers for Disease Control and Prevention defines the condition as lead levels at or beyond 10 micrograms per deciliter of blood, but effects in children have been found at levels as low as 5 micrograms.

In 2009, the last year for which statistics are available, of 16,870 Alameda County children screened for lead, 3.2 percent tested positive for unsafe exposure, according to the Alameda County Lead Poisoning Prevention program. The rate in Oakland was more than double the county average, a worrisome 6.6 percent of all children tested.


When a group of West Oakland neighbors came together a few years ago to plan a community vegetable garden for a vacant lot at the corner of 39th Street and Martin Luther King Jr. Way, they knew they'd be contending with contaminated soil. But they had no idea just how much trouble it would cause.

In early 2009, the group sent away for a soil test that put the plot's lead level at 219 parts per million — well under the EPA's limit. But to eliminate any risk of ingestion, they designed a garden that would use landscape fabric and a heavy layer of mulch to cover the contaminated soil. They'd also grow vegetables in clean soil in 22 raised beds, rather than directly in the earth. With $340,000 pledged in support from Oakland's Redevelopment Agency and City Council, the project seemed ready to go.

Except for one thing. Since the city would be holding title to the newly purchased property and therefore technically liable, it wanted to conduct soil tests of its own. These were far more involved than the low-cost mail-away test ordered by the neighbors. Instead, the city hired a professional firm to perform elaborate soil testing and analysis at a cost of more than $5,000.

The results showed lead levels ranging between 300 and 790 parts per million, all of which exceeded the applied standard of 200 parts per million. The testing agency recommended that the top two feet of soil be removed and disposed of as hazardous waste, at a cost of approximately $170,000. But there wasn't enough money in the budget, and just like that the Crossroads Community Garden was shot. The site has since been sold to a developer looking to pour a parking lot.

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