An eight-month study of Vancouver garden and agricultural soils has found levels of lead and other metals above the most stringent Canadian standards for human health.

Samples taken from the 16 Oaks community garden averaged 219 parts per million of lead, which exceeds the standard of 70 to 140 ppm for agricultural, residential and park land set by the Canadian Council of Environment Ministers.

Levels of lead — a potent neurotoxin — are five times higher than those measured at UBC Farm, a site remote from urban activity just a few kilometres away.

Samples of soil, dust and Kentucky bluegrass were collected from UBC Farm, the community garden (which was once a parking lot and restaurant), and a former scrap yard at East Hastings and Glen Drive and analyzed for five metals of interest: zinc, lead, manganese, nickel and copper.

Levels of all the metals measured in soil from UBC farm were close to normal, expected concentrations. Zinc and lead were several times higher than normal at the community garden, located at West 16th And Oak, and levels of zinc, lead and copper were elevated at the Hastings site, a so-called “brownfield” located between a busy roadway and railroad tracks.

A brownfield is land assumed to be contaminated due to industrial use.

Dust samples suggest contamination on the urban sites is likely the result of decades of accumulation of metal-contaminated particles from automobile, train and marine traffic, according to the study’s author Gladys Oka, a graduate student at the University of B.C.

Although lead was removed from most fuels in the late 1980s, it continues to accumulate in dust on the urban test sites at twice the rate as on UBC Farm, the study found.

Lead can persist in soil for many years, but because the dust is heavy it doesn’t travel far from its source, so soil contamination could be managed in community gardens with buffer zones between gardens and transportation corridors, she said.

The levels of metals found in the roots and shoots of the bluegrass samples closely mirrored the elevated levels of metals in the soils on the urban sites and were much lower at UBC Farm. Bluegrass samples from 16 Oaks contained approximately 400 ppm of lead, while the Hastings site samples contained 172-253 ppm.

Plants grown on uncontaminated soil typically have lead concentrations between 0.1 ppm and about 10 ppm, with an average concentration of 2 ppm.

Canada sets a limit on the lead content for apples and pears at 7.0 ppm and 0.2 ppm for fruit juices, according to a report issued by the World Health Organization and the Food and Agriculture Organization of the United Nations. Health Canada is proposing to further reduce the acceptable levels of lead in fruit juices and nectars.

Urban gardeners should consider Kentucky bluegrass the “canary in the mine shaft” for foods grown in the city, especially near busy roads and transportation corridors, according to Oka’s thesis adviser Les Lavkulich, a professor emeritus at the faculty of land and food systems.

How much lead is accumulated by a growing plant varies widely by species, weather and soil type.

“We don’t eat Kentucky bluegrass, but the results are an indication that there is something wrong,” he said.

The soil samples from the urban test sites exceeded most government and international standards for metal pollution, said Lavkulich, adding, “These numbers are higher than is commonly acceptable for growing vegetables and food crops.”

Oka’s findings may call into question the City of Vancouver’s enthusiasm for urban agriculture.

“You want to be conservative. According to the precautionary principle, if you aren’t sure what you are dealing with, you have a moral and ethical responsibility to go slowly,” said Lavkulich. “We aren’t saying don’t grow food, but you want to be sure what the impacts are on human health before you start advocating for urban agriculture.”

The city encourages would-be gardeners to have their soil tested and, barring that, to grow vegetables in lined boxes with clean soil rather than in the native soil, said Coun. Andrea Reimer.

“This city has a long industrial history and they didn’t always have the environmental standards that we have today,” she said.

Vancouver is in the process of developing a plan to deal with environmental toxins, including those in soil, as part of the Healthy City Strategy passed by council in October, Reimer said.

Toronto and Montreal already have guidelines to assess potential sites for urban agriculture and community gardens for contamination, according to the study.

The study, Soil Assessment for Urban Agriculture: A Vancouver Case Study, is published in the peer-reviewed Journal of Soil Science and Plant Nutrition.

rshore@vancouversun.com

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