I wanted to start a vegetable garden in my backyard. But my yard is in Brooklyn, a land of street garbage, truck exhaust, and stray cats. So I decided to figure it out: Was it really safe to grow food there? I had no idea that the rabbit hole I burrowed in urban gardens would lead to dead cows in Georgia, a global contamination meeting in Sweden, and the strange price we pay to make sure kids don’t catch on fire.

I started by calling Murray McBride, a professor at Cornell University who researches contamination, to find out if city gardens are really safe. According to McBride, I should be worried about one main thing:

“We found lead to be the biggest problem,” he told me. “There can be high concentrations of lead even in the garden beds.”

Making things with this toxic metal is a bit passé, but lead doesn’t go away. The lead painted in houses and used in gasoline and industry is still floating around in dust and landing in backgrounds. But there’s a twist: plants don’t generally take this lead up through their roots.

“It’s not in the lettuce. It’s in the dirt that may stick to the lettuce,” another scientist named Sally Brown would tell me later. So I should use compost and wash my plants before eating them, McBride explained. I had my answer. Or so I thought.

“So I should just buy compost at the gardening store?” I asked.

“Well ... a lot of soil in those stores isn’t well regulated,” McBride told me. “Don't trust topsoil. And make sure you’re not buying sewer sludge.”

“... What?”

© Devan King/The Nature Conservancy

McBride told me that sanitation plants take sewage sludge, clean it up a bit, and sell it as fertilizer. One popular brand of fertilizer, for instance, is sewer sludge from Milwaukee that’s sold around the country. These “biosolids,” as they’re called, can have pharmaceuticals, lead, toxic metals, and fire retardants in them. Safe amounts ... maybe.

Hundreds of people who live near places where farmers dump biosolids have complained that the biosolids made them sick. Andy McElmurray, a dairy farmer in Georgia, fertilized his fields with biosolids. He grew hay in the fields and fed it to his cattle. Hundreds of cows got sick and died. McElmurray said the biosolids must have been tainted with industrial waste from nearby factories, poisoning the cows. He argued his case in court ... and won.

“The administrative record contains evidence that senior EPA officials took extraordinary steps to quash scientific dissent, and any questioning of the EPA's biosolids program,” the court ruled.

I officially wanted to know more. Are these biosolids really that dangerous?

“You should talk to Robert Hale about it,” McBride told me. “He’s one of the world experts on a lot of these chemicals.”

So I called Hale, an environmental chemistry professor at the College of William & Mary who researches pollution.

USDA/Public Domain

Hale told me that he’s analyzed biosolids and found all kinds of contaminants.

“They found flame retardants in this stuff in 2000,” he said. “And they’re still in there.” These chemicals are used to make stuff not catch on fire, and a lot of people are worried about their health and environmental effects. The EPA says they may cause learning disorders, thyroid disorders, and cancer.

And this stuff isn’t just in gardens. Most biosolids are spread over farmland. In fact, about half the sewage sludge in the country is applied to farmland (though generally farmland used to grown stuff like soybeans for fuel and animal chow rather than human food). Hale has even found flame retardants in Antarctica.

“Is that ... a problem?” I asked. “Are biosolids safe?”

“That’s kind of the six million dollar question,” he answered. Nobody’s done enough research to know for sure how these chemicals affect people, or how many chemicals is too many. It wasn't really the answer I was hoping for.

“Should I be worried?” I asked. “Should the government step in?”

“The government is part of this,” Hale answered.

© From water to trees to bees, there are a lot of natural elements that go into making our food that aren't listed on nutrition labels. Chris Helzer/TNC

The government actually makes a lot of these biosolids; they sell them and give them to farmers. “We’ve got this viewpoint in this country that things are safe until proven dangerous,” he added.

Hale says that other countries are more concerned. He once gave a talk in Sweden where experts from around the world met to discuss contamination. They were banning a particular flame retardant.

“They were congratulating themselves on how they solved the problem on a global basis,” Hale said. “I stood up and said, “Uh guys? All you have to do is look at the production statistics. We use 95 percent of it in North America, and we’re still using it.” A few jaws in the audience dropped.

I wasn’t concerned about urban gardens anymore. Instead, I was feeling the weight of yet another massive global problem settling onto my shoulders. Did I really have to live in a contaminated world now?

Still, something itched. This all seemed so extreme and, I don’t know, oddly cinematic. Was the situation really so dire? Was there something oddly familiar about this storyline? And would it make for a good Mr. Robot meets Farmville style show?

I wanted to talk to another expert before I made up my mind. So I called up Sally Brown, a University of Washington professor who, you guessed it, also researches this stuff.

We chatted about urban gardens as I wondered how I’d bring up biosolids. Fortunately, she started telling me about a great urban gardening program in Washington and mentioned that it used biosolids.

“Yeah,” I said, trying not to sound too excited. “I heard biosolids are dangerous.”

“They’re not,” she said flatly. “People always think they are, but they’re not.”

I wasn’t convinced.

“I talked to Robert Hale,” I said.

“He’s made a lot of his fame and fortune by telling people they’re going to die if they eat biosolids,” she said. “You can make a name for yourself screaming the sky is falling.”

© K Martinko

Brown didn’t exactly disagree with Hale’s research. She told me that, yes, there are flame retardants and other chemicals in sewage sludge, but the levels are kept low (Hale isn't so sure about that), they aren’t going into the plants, and nobody really knows if they can make people sick. Besides, the chemicals in sewage come mostly ... from our houses.

“They’re in our TVs, they’re in our furniture, they’re in our laptops,” she said. “They used to be in kids’ pajamas. The concentration of this stuff in dust in your home is much higher than in biosolids.”

Brown pointed out that if your kid chews on his flame retardant pajamas, he’s getting exposed to “several million times” more of the stuff than is in biosolids. Hale actually told me something similar: a couple decades ago, a study found that flame retardants in Swedish women’s breast milk have been increasing exponentially over a ten year period. Then someone tested American women.

“The levels were ten times higher,” Hale said. The flame retardants probably came from indoor dust. Hale agrees that there are generally more of these contaminates inside than in biosolids; he's just worried about them everywhere.

I was not feeling particularly reassured.

“Wait, so should I be worried about all these chemicals in my house?” I asked Brown.

“It’s really, really hard to say,” she answered. “Just because chemicals are there doesn’t mean they can hurt you.” Besides, even if these chemicals are questionable, they might be worth the risk.

“It’s much better to have a kid exposed to flame retardants than for the kid to catch on fire,” Brown said.

So there you have it: We’re putting sewage with flame retardants, toxic metals, and other surprise stuff in it over our gardens and farmland. But that’s largely because sewage comes from the buildings we live and work in, which have even more of these chemicals in them. And the jury’s still out on whether these chemicals in these amounts are dangerous contaminates or harmless specks of dust. Or somewhere in between. But hey, at least we don’t paint our walls with lead anymore.

On the bright side, the scientists all seemed to agree on one thing: As long as I use compost and wash my vegetables, I can totally start an urban garden.