Bees can make an outstanding contribution to detailed and comprehensive environmental monitoring, which is why scientists around the world regularly recruit them as hard-working members of their research teams. The insects forage in well-defined regions, where their bodies pick up minute samples of elements that may be present. Back in the hive, as they groom one another to round up any stray pollen grains, this other material is also collected and captured, providing a reference collection of the surrounding landscape.
“Not only are they sampling for us, but the ultimate hive products — the honey included — reflect a chemical snapshot of the environment immediately around the hive,” says Kate Smith, a PhD student with the University of British Columbia’s Pacific Centre for Isotopic and Geochemical Research.
That snapshot can offer fascinating insights, as Smith and her supervisor Dr. Dominique Weis discovered. Weis, who holds UBC’s Canada Research Chair in the Geochemistry of the Earth’s Mantle, was approached in 2014 by a Vancouver network of beekeepers, Hives for Humanity. The group wanted to confront the notion that even though its honey was produced by bees in the middle of one of Canada’s most densely populated cities, it was clean and safe to eat.
Weis brought some extremely sophisticated equipment to the task, including a single-collector, high-resolution inductively coupled plasma mass spectrometer. “That’s what made the difference,” she explains. “It’s one thing to measure very low levels of trace elements, it’s another thing to be able to measure isotopic composition.”
The good news for the beekeepers was that levels of lead were in fact on the order of parts per billion, far below any amount of concern and orders of magnitude lower than the macronutrients found in the honey. But with the ability to look closely at isotopes, Weis saw the making of a compelling PhD project for Smith as Hives for Humanity continued to expand their operation throughout the city.
“Closer to downtown we see elevated levels of vanadium, which is found in heavy fuel distillates that you would have in a busy harbour area,” says Smith.
There was also lead, she adds, but its isotopic “fingerprint” did not match that of locally occurring sources, such as lichens, river sediment, or regional bedrock. Instead, it more closely resembled lead found in the aerosols around Asian cities with coal-fired plants and ore smelters. Since a majority of the ships in Vancouver harbour come from just such cities, this finding pointed to an industrial source for the minute amounts of lead found in the honey.
Smith and Weis co-authored a recent paper in Nature Sustainability that outlines the viability of this technique as a way of tracking lead in the environment and confirming its origin. They also suggest how further work could build on these preliminary findings.
“Only a detailed investigation of Pb isotopic compositions of diesel exhausts (non-marine), power station fuels and marine industrial sources (fuel oils, paints and exhausts near the Port of Vancouver), coupled with receptor modelling, will confirm the source(s) and determine the extent of their relative contributions to the final observed Pb isotopic signature of the downtown honey,” the authors conclude.
Smith notes that this kind of work can also be combined with more conventional air sampling stations, as is done routinely in cities around the world, where the introduction of isotopic fingerprinting would add a powerful new dimension.
“It supplements and complements what we saw in the suite of trace elements, which is really exciting,” she says.