Industrial fumes, old paint and now-banned gasoline additives are all culprits, putting toxic metals like lead in Philadelphia's soil for generations.
Sampling twenty-four sites in parks across the city, Temple University master's student Stephen Peterson found lead in higher than expected concentrations throughout the park system.
What does that mean exactly? Lead is a basic element – so it's normal to find small amounts in soil. According to the United States Geological Survey, lead in the soil naturally occurs at a level of 33 parts per million in the Philadelphia region. The national average is 19 ppm, and industrial East Coast cities pull that number up with higher concentrations due to longer industrial use.
Taking all of this into consideration, Peterson was still surprised by how much lead he found and where.
"It turns out only one percent of my samples were at or below that geologic background level," said Peterson. "Sixteen percent of the soil samples were above the EPA soil saturation limit for residential use, which is 400 ppm." In a few sites, he found extremely hig levels of lead – with one in North Philadelphia clocking in at 10,000 ppm, roughly one percent of the entire soil makeup. "I took that sample next to an old building, so the lead probably came from layers and layers of paint scraping off over the years," said Peterson.
Peterson also found elevated lead levels in remote parts of the Wissahickon, and other areas with no history of industrial or even residential use.
Lead is a neurotoxin, meaning it can cause brain damage if concentrations in the blood get too high. Lead typically enters the body through accidental ingestion or inhalation.
GROWING FOOD IN A POST-INDUSTRIAL CITY
Gardening or farming in contaminated soil presents two ways to accidentally take in lead: exposure through working in the soil itself, and eating food that absorbed the metal from its environment.
Around one in five of Philadelphia's community gardens is in a park, so testing for lead in these areas became a focal point of Peterson's research.
"Everywhere that I saw an urban garden, I made sure I tested," said Peterson. In all of those soil samples, "the level was super low or not even detectable."
Peterson says urban gardeners like who use raised beds — bringing in clean soil — are taking the right steps.
Mary Seton-Corboy, co-founder of urban farm Greensgrow, says in some ways the Environmental Protection Agencies guidelines are unrealistic for a city with as long an industrial history as Philadelphia's.
"If you look at the standards set by the EPA, we'd have to dig up the Liberty Bell. There's crap on everything and in everything," said Seton-Corboy.
Seton-Corboy's farm is on the site of a former steel mill. Greensgrow's farm beds sit on top of a three foot thick concrete slab to prevent chemicals from leeching in.
NEW URBAN GARDENING GUIDELINES
Peterson's research led him to work closely with the Philadelphia Department of Parks and Recreation, which oversees the entire Fairmount Park system.
Joan Blaustein, Director of Urban Forestry and Ecosystem Management for the City, said Peterson's findings are not surprising. "It does confirm what we suspect is in most urban areas, and it's good to have that confirmation so we can feel it's appropriate to caution people about being careful about where they're growing and how they're growing."
Parks and Recreation already makes recommendations for gardeners and people with yards to test their soil and to plant in raised beds. Colleges such as the University of Delaware, the University of Pittsburgh and the University of Massachusetts all offer soil testing for common contaminants, for as little as $10. Blaustein recommends shopping around and says that the city plans to do even more to educate people about soil contamination.
"We are in the process of creating guidelines for gardeners to grow plants safely," said Blaustein. For example, don't use treated lumber in your raised bed, or if a site may have been contaminated make sure that you mulch the walkways, things like that."
"We want people to have a level of assurance that what they're growing is going to be healthy," said Blaustein.