Bumblebees are exposed to significantly higher levels of toxic heavy metals than honeybees, even when they forage in the same environment, according to new research from the University of Cambridge.
The study found bumblebees collected pollen containing between two and seven times more heavy metals than honeybees and accumulated around three times higher concentrations of the metals in their bodies.
Researchers say the findings raise concerns about the impact of pollution on wild pollinators, which play a vital role in biodiversity and food production.
Published in the journal Ecological Entomology, the study examined honeybees and bumblebees living side by side in Cambridgeshire, an area considered to have relatively low levels of soil contamination.
Scientists analysed pollen and bee samples for six heavy metals – arsenic, cadmium, chromium, cobalt, lead and tin – and found marked differences between the two species despite them foraging across the same landscapes.
Heavy metals can enter the environment through industrial activity, mining, traffic pollution and agriculture before being deposited in soil, dust and plants. Bees can inadvertently collect these pollutants while gathering nectar and pollen.
Although the levels detected were generally too low to kill the insects, researchers say long-term exposure could still affect their health.
Dr Sarah Scott, who carried out the research at the University of Cambridge and is now based at Newcastle University, said: ‘Most metal levels we found were not high enough to kill bees, but even low levels can still harm bee health and colony success in subtle but important ways, such as affecting their ability to forage and reproduce.’
The researchers believe the differences are linked to the bees’ behaviour and biology. Bumblebees tend to forage closer to their nests and collect pollen from fewer plant species, making them more vulnerable if those plants are contaminated. They are also hairier than honeybees, allowing them to pick up more dust particles that may contain heavy metals.
Honeybees, by contrast, travel much greater distances to forage and collect pollen from a wider variety of flowers, which may dilute their exposure to contaminants.
Professor Lynn Dicks, the study’s senior author from the University of Cambridge’s Department of Zoology, said: ‘Even in areas that we usually consider safe or lower risk for heavy metals – typically rural areas, away from industrial or mining areas – bees can pick up toxic metals. Bumblebee colonies tend to have fewer workers available to perform tasks, so the loss of individuals can have a big impact on overall colony function.’
The researchers say the findings also suggest honeybees may not always provide an accurate picture of pollution levels affecting other pollinating insects, despite often being used to monitor environmental contamination.
Dr Scott said the results should not discourage people from creating habitats for bees: ‘Bees play a critical role in both biodiversity and food security, so we’d still encourage people to plant flowers to help them, even if you live in an area more likely to be contaminated. At the end of the day, bees still need food. Even if it carries traces of heavy metals, having some food is better than having no food.’
The full research can be read here.
Photo: Philipp Pilz
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