Making sense of the buzz behind biomonitoring of environment by bees
Bees are most sensitive and effective markers of smelter contamination
When it comes to understanding contamination, honey bees can do the hard work for us. While foraging for nectar, pollen and water, bees are constantly picking up contaminants from their environment. As we are aware of their lifespan and approximate foraging range, it is fair enough to believe that chemical analysis can provide a snapshot of the levels of their contaminants.
With the help of backyard beekeepers, our two studies traced toxic metals and antimicrobial resistance genes across two urban centres: Sydney and Nouméa in New Caledonia.
European honey bees have long been used as sentinel species to monitor for pests and diseases, including varroa mites and chemicals at airports. Bees can also be used as biomonitors to understand contaminants across our urban environments.
As the popularity of urban beekeeping has grown, there has been more research on honey bee biomonitoring of a range of contaminants, including metals, pesticides and so-called “forever chemicals”, known as PFAS, in honey.
In Nouméa, honey bees map impacts from the local nickel smelter. The levels of metals associated with the smelter – nickel, chromium and cobalt – were elevated next to the smelter and decreased farther away.
This might not sound surprising given the smelter is a major source of pollution. However, comparing the data from bees to soil and dust samples revealed that bees were the most sensitive and effective marker of smelter contamination.
By mapping trace metals in honey bees in Sydney specific factors contributing to metal pollution within their foraging range. For the neurotoxic metal lead, residential and industrial activities were key influences, especially in heavily populated inner-city areas.
In contrast, less populated locations and larger areas of parks or farms had higher levels of manganese. This likely came from natural soil sources and pesticide use.
Bees can help us understand emerging concerns such as the spread of antimicrobial resistance (AMR) genes. It’s a key concern in urban areas, driven by the misuse and overuse of antibiotics.
AMR genes were common across Sydney – 83% of bees examined had ingested one or more of the genes we looked for. The source was not strongly linked to industrial activity, but rather the area of water bodies available for the bees to drink from. This may be because these genes can enter the environment through human wastewater and runoff and then be absorbed by foraging bees.
Bees likely ingest antimicrobial resistance genes from water bodies exposed to runoff from people’s properties or wastewater.
Bees that contained contaminants are actually ingesting them. Our analyses showed contaminants build up within the bee over time and were not present on their exterior. Metal concentrations in matched samples of washed and unwashed bees and they were no different, indicating contaminants were inside the bee. Further, metal concentrations were higher in older, dead bees at the end of their lives than in the younger ones.
Using high-resolution imaging, we found only organic non-metal particles on the outside of bees. This may be because bees have very good self-cleaning habits. These behaviours also keep hives free from parasites and fungi brought in by foraging bees.
Scanning electron microscope images of Nouméa bees. The particles that were identified were not metallic. Research has shown exposure to contaminants, including metals and neonicotinoid insecticides, can impair honey bee development, foraging ability and survival.
Both honey producers and consumers want to know if their honey is safe for consumption. While we previously identified some commercial honeys are adulterated with sugar syrups, this new work focused on potentially toxic trace metals in the honey. The good news is we found trace metals in honey that do not pose a concern were at very low levels. In Nouméa, the main smelter element, nickel, was more than 30 times lower in honey than in bees.
There were similar outcomes in the mining town of Broken Hill, Australia, where lead levels in honey were ten times lower than in the bees themselves.
Bees aren’t the only biomonitors. The earth is facing a multitude of interlacing environmental challenges, including biodiversity loss, climate change, population growth and pervasive chemical pollution. More comprehensive monitoring, including surveillance using bees, will allow us to respond more quickly and effectively to environmental health challenges.