Dirt and plant in handCross-posted from East Bay Express.

When Laura Blakeney moved into her house in West Oakland, Calif. last year, she was thrilled to have a backyard. Her young daughter loved playing in the dirt. And all that space seemed perfect for a vegetable and herb garden. What she didn’t see was the danger lurking in her soil.

To help get the garden started, a neighbor suggested Blakeney contact City Slicker Farms, a West Oakland nonprofit that advocates for urban agriculture and installs backyard gardens in homes throughout the Bay Area. After Blakeney called to request a garden, City Slicker visited her house to take four soil samples — standard protocol for every garden they install. The results were surprising: nearly 500 parts per million (ppm) of lead, more than twice the level deemed safe by the San Francisco Bay Regional Water Quality Control Board.

Built in 1889, the two-story Victorian was covered in layers of lead paint that had flaked off and seeped into the soil. Other environmental factors that likely contributed to the contamination included nearby industry and exhaust from leaded gasoline.

The organization opted to cover all of the exposed dirt in Blakeney’s yard with cardboard and wood chips — a process known as sheet mulching — and build raised beds for the garden. On a recent Thursday afternoon, 20 young volunteers from City Slicker and Urban Adamah, a nonprofit based in Berkeley, arrived at the house with four truckloads of mulch, hundreds of empty cardboard boxes, a few cubic yards of soil and compost, and materials to construct two four-by-eight-foot raised beds on the small concrete patio.

The workers spent an entire day on the project, leaving Blakeney, her roommates, and her daughter with a safe yard, pre-planted garden beds, and a young lemon tree. That’s no small victory in a neighborhood notorious for its lack of fresh and affordable produce. “One little thing turned into all this, and we just wanted some vegetables to cook with,” she said. “It really turned into this wonderful thing.”

Blakeney said she’s glad to have discovered the lead contamination before anyone ate produce grown in the soil, and has scheduled a meeting with Alameda County’s lead abatement program to further address the source of the problem. “If we hadn’t done this, we never would’ve known,” she said. “Who thinks of lead in their dirt?”

As backyard gardening continues to explode in popularity, many new farmers may be ignorant of the fact that urban topsoil, particularly throughout the East Bay flatlands, contains a cocktail of heavy metal pollutants, including zinc, nickel, and cadmium, that can be consumed by humans and pets through contaminated plants and soil dust. Lead, in particular, is virtually ubiquitous.

At the same time, spurred by citizen demand, municipalities across the country are embracing urban agriculture. In Oakland, efforts are underway to modify the city’s outdated zoning code to be more permissive of urban farming. A planning commission meeting on July 21 that officially initiated the process attracted more than 300 enthusiastic residents. Chicago, Cleveland, Seattle, and San Francisco are among the many cities that have already enacted similar changes.

While all share the common goal of encouraging sustainable local food production, no two cities have approached the issue of soil contamination in quite the same way. Not only is there no agreement about how to encourage — or even require — urban farmers to handle soil safely, there’s also a lack of consensus among regional, state, and federal agencies as to what actually qualifies as safe.

Untangling these issues won’t be easy, especially in Oakland. On one hand, the city must protect citizens from the dangers of lead poisoning, and on the other, it’s tasked with supporting urban agriculture in areas known to contain contaminated soil. Striking the proper balance will mean the difference between disease, disappointment, and a thriving 21st-century city.

Lead in urban soils is commonly referred to as a legacy pollutant. It is most closely correlated with two sources: lead paint and leaded gasoline. Neither is still in use; lead paint was outlawed in 1978, and leaded gasoline’s six-decade run ended in 1986. But their effects remain, especially in older neighborhoods near historic freeway corridors. Lead contamination in soil can also result from lead plumbing and prior commercial and industrial land uses.

In the East Bay, the epicenter of old homes, freeways, and industry is West Oakland. There, due to a confluence of factors, including cheaper rents and land values, more vacant lots, fewer grocery stores, and more low-income residents in need of fresh produce, urban agriculture is thriving in some of the most polluted soil in the East Bay.

But there’s no reason urban gardens shouldn’t grow there. Lead doesn’t move around once it’s in the soil, so levels near the perimeter of a home are often much higher than in the middle of the yard. A single paint chip in a one-cup soil sample can elevate its lead level 10-fold.

The same applies to lead from leaded gasoline. According to Environmental Protection Agency (EPA) lead expert Steve Calanog, elevated levels of lead are present throughout the East Bay along the Interstate 80 corridor, yet deposition may vary from one yard to the next, and even between front and backyards of the same home. The question of where you plant — and where you test — is of utmost importance.

Likewise, quantifying lead contamination is at best complex and at worst Sisyphean. Perhaps no one knows this better than Nathan McClintock, a UC Berkeley Ph.D. candidate in geography who is completing a dissertation on urban agriculture that has led him to collect and analyze more than 120 soil samples throughout Oakland.

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 ppm in the hills to as high as 980 ppm in West Oakland. Residential lots in West Oakland averaged about 360 ppm — still below the EPA’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 the ones McClintock found — much higher. Based on 100 samples taken from 60 yards, Calanog says levels average around 800 ppm and reach as high as 2,700 ppm.

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 ppm for ingested soil, while the California Department of Toxic Substances Control says soil becomes hazardous material when lead surpasses 1,000 ppm. 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. U.S. 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 five 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.