The rise of foodies and of locavore cuisine has also brought the return of the backyard chicken coop. But this boom in popularity has also brought a surge of news stories fretting about the risks of raising food on contaminated city soils.
The worries are not unfounded, and, actually, they kind of make sense. Soil contamination from things like lead is prevalent in urban centers. According to a new study led by Henry Spliethoff, with the New York State Department of Health, “soils in urban yards, and in vacant lots and brownﬁelds often considered as sites for urban community gardens and farms, may contain chemical contaminants.”
Lead, for example, which has a median background concentration of 23 mg/kg in New York State rural soils (NYSDEC 2006), can be found at concentrations of several hundred or even thousands of mg/kg in soil in NYC and other cities, due to historical sources such as lead-based paint, leaded gasoline combustion emissions, and point sources such as waste incinerators and metal smelters.
Last year the New York Times ran a story on Spliethoff's preliminary research after he found elevated levels of lead in eggs from urban hens. The big question left by the Times is what those lead concentrations actually mean, health-wise.
A year later, Spliethoff's results are ready, published recently in the journal Environmental Geochemistry and Health. The result? Everybody can calm down.
All but one of the eggs in our study had less than 100 μg/kg lead, suggesting that, in general, they contained lead at concentrations were not higher than those in foods considered acceptable for commercial distribution.
The scientists did find detectable levels of lead in roughly half of the urban eggs they tested, while store-bought and rural-raised eggs had no detectable lead. They found that the amount of lead in chickens' eggs depended on the amount of lead in the soil.
As a worst-case scenario, the scientists calculated lead exposure if a small child ate an egg from the highest measured concentration, “every day, all year.” At these extreme levels the lead exposure would top the recommended daily maximum intake, but just barely.
These evaluations implied that, overall, the lead concentrations we found in eggs from NYC community gardens were not likely to signiﬁcantly increase lead exposure or to pose a signiﬁcant health risk. However, frequent consumption of eggs with the highest lead concentration we found could signiﬁcantly increase lead exposure, and chickens exposed to higher concentrations of lead in soil are likely to produce eggs with higher concentrations of lead. This exposure pathway could potentially be signiﬁcant in some gardens, and it should not be ignored.
So, if you're set on raising chickens in the city this is something to keep in mind and deal with, but it's not really worth freaking out about.
If you do raise chickens in the city, Spliethoff has some tips on how you can help minimize the amount of lead flowing into your chicken's eggs.
- Add clean soil, mulch, or other clean cover material to existing chicken runs to help reduce chickens’ contact with and ingestion of contaminated soil. Use clean soil when constructing new chicken runs. Inspect the clean cover material regularly, and add or maintain material as needed to help keep chickens from coming in contact with underlying soil that may have higher concentrations of lead.
- Provide chickens’ regular feed in feeders, and avoid scattering feed, including scratch grains and food scraps, on bare ground in areas where soil has higher concentrations of lead, or where lead concentrations are not well characterized.
- Evaluate gardens for potential sources of lead. Do not allow chickens to forage near these sources. For example, keep chickens away from structures painted with lead-based paint and out of areas where the soil has higher concentrations of lead.
- Avoid feeding chickens unwashed garden scraps from areas where the soil has higher concentrations of lead.
- Consider providing a calcium supplement, which may help to reduce the amount of lead that gets into chickens’ eggs.
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