A team of researchers at the University of British Columbia has found a way to assess the cleanliness of a city and identify sources of pollution by analyzing the honey produced by urban bees.
The researchers, from UBC’s Pacific Centre for Isotopic and Geochemical Research (PCIGR), tested honey from hives across the Vancouver area, from the downtown core to outlying agricultural areas, for the presence of trace metals. Worker bees fly through the air and land on a variety of surfaces in the process of gathering nectar to make honey, picking up dust and other particulate matter from their surroundings along the way.
“What we found was that certain trace elements, like lead, copper, cadmium, zinc and titanium all had elevated concentrations in honey from areas of greater urban density relative to honey from rural areas around here,” says Kate Smith, lead author of the study, published last month in the journal Nature Sustainability.
The study was made possible by a partnership with Hives for Humanity, a non-profit organization that aims to encourage urban beekeeping. Chief beekeeper Julia Common was often asked about the cleanliness of the honey produced on Vancouver’s downtown eastside, so Dominique Weis, director of the PCIGR, offered to analyze it.
“That collaboration facilitated a bit of a citizen-science project, because there are bee hives all over the city,” says Smith, referring to the more than 17,000 registered hives in the metro Vancouver area. Members of the beekeeping community were invited to contribute honey samples for analysis.
To analyze the honey samples, the researchers used inductively coupled plasma mass spectrometry (ICP-MS), a technique that can detect even trace amounts of metal in any substrate.
The team then used lead isotopic fingerprinting to compare their findings to the local geology, such as particulate from the Fraser River and rock from the Garibaldi Volcanic Belt, to determine the source of the elements.
“What we found in the honey downtown is that the lead isotopic composition does not match that of the local geology,” says Smith. The honey from rural areas is closer to the local geochemical signature, but it doesn’t match perfectly either.
Smith attributes the difference in geochemical signatures to a range of human sources. Leaded gasoline, for example, was used in North America for decades before it was banned in the 1990s, and those lead emissions are still present in the urban environment today. Vehicle emissions from stop-and-go traffic are likely another contributor of pollutants, as is Vancouver’s busy shipping port.
“Most of our ships — more than 70 per cent — come from Asia,” says Smith. “They are bunkering there with fuels presumably derived from Asian geologic sources. There are Asian petroleum products that have a different lead isotopic signature than what we observe here in North America.”
Smith, however, emphasizes that the presence of these trace elements does not mean the honey from Hives for Humanity is dangerous to humans. The lead is measured in parts per billion — equivalent to one drop of water in an Olympic-size swimming pool.
“The honey from metro Vancouver is well below the worldwide reported average for lead in honey,” says Smith.
Weis adds that this methodology could be applied in many other Canadian cities as a relatively cheap and easy way to monitor levels and sources of pollution over time. Her team is now using a similar process to analyze salmon while reconstructing their migration journeys.