Elevated levels of toxic metals at a Vancouver community garden site raise questions about the city’s approach to promoting urban agriculture, say UBC researchers.
In research outlined last month in the Journal of Soil Science and Plant Nutrition, lead author Gladys Oka detected elevated levels of zinc and lead in soil from a community garden site at 16th Avenue and Oak Street.
“My intention is not to say don’t plant, don’t do community gardens,” says Oka, an MSc candidate in soil science. “But I don’t think it’s necessarily in the best interest of Vancouver to push something without informing people of all the considerations they need to make.”
Native soil sampled from the garden site was found to have concentrations of 456 parts per million (ppm) of zinc, and 219 ppm of lead—exceeding background soil levels in the Lower Mainland of 200 ppm and 60 ppm respectively. Kentucky bluegrass, used as an indicator plant, was found to absorb the metals: the shoots of those grown on the garden site contained 1,330 ppm of zinc and 387 ppm of lead. The European Scientific Commission on Food recommends no more than 25 mg per day of zinc and no more than 0.03 mg per day of lead be ingested by a 60 kg person.
While the use of raised beds could mitigate contamination from the soil, Oka says readings of metals in the air are also a concern. Compared to the UBC Farm site, which the researchers also tested, there was eight times as much zinc and twice as much lead and copper in the air around the community garden.
“You can fix the problem of what’s happening in your surface soils by using compost, but if you’re growing in that for five years, you might be accumulating a lot of metals,” she notes.
Co-author Les Lavkulich, program director of the UBC Master of Land and Water Systems, calls for a measured approach to urban gardening. “Our research has shown that the potential for metal contamination is a concern. Before we start promoting things, we should make sure we have a relatively good idea of what we’re promoting.”
Oka recommends that the City of Vancouver follow the lead of other Canadian cities like Toronto, and adopt a framework to investigate the health of soil at urban farming sites.
The study, Soil assessment for urban agriculture: a Vancouver case study, can be found here.
Excessive zinc can cause nausea, vomiting, loss of appetite, abdominal cramps, diarrhea and headaches.
Symptoms of lead poisoning in children can include developmental delays, learning difficulties, irritability, fatigue, and hearing loss. In adults, symptoms of lead poisoning can include high blood pressure, declines in mental functioning, joint and muscle pain, headache, mood disorders, and miscarriage or premature birth in pregnant women.
Urban gardening framework:
The city of Toronto adopted GrowTO: An Urban Agriculture Action Plan in 2012. The city also has a Supervisor of Community Gardens Program.
According to the city of Vancouver’s official website, none of the community gardens in Vancouver are run or overseen by city staff.