Particulate matter (PM) is a mixture of solid particles and liquid droplets suspended in the air. These particles vary widely in size and composition, ranging from less than 0.1µm to several microns in diameter. Sources of particulate matter include natural phenomena like dust storms and wildfires, as well as human activities such as industrial processes, transportation, burning fossil fuels and the degradation of plastic items. Particulate matter is classified based on its aerodynamic diameter, and its toxicity depends on particle size and chemical composition. Coarse particles (PM10) are less than 10 microns (µm) in diameter, approximately the size of pollen grains, and are comprised of dust and mineral particles. Fine particles (PM2.5) are less than 2.5 µm in diameter and are generated by combustion, some industrial processes and natural chemical reactions in the atmosphere.
Particulate matter is a pervasive air pollutant which has been shown to have negative effects on human health, causing cardiovascular and respiratory diseases, and cellular damage. Despite this, there has been little research into its effects on insect physiology. The limited research that has been carried out has shown that honeybees can accumulate airborne particulate matter on their head, wings and legs (Negri et al., 2015), and researchers have detected pollution from traffic and incineration on sampled bees (Capitani et al., 2021). Researchers in India found that increased particulate matter deposition was significantly correlated with changes in Giant Asian honeybee (Apis dorsata) survival, flower visitation, heart rate, hemocyte levels, and gene expression associated with lipid metabolism, stress, and immunity (Thimmegowda et al., 2020).
Microplastics are small plastic particles (<5mm) which are emerging pollutants of global concern. Microplastics have been detected throughout the environment, and in recent years there has been increasing interest in the effects of microplastics on honeybees. Researchers in Denmark found thirteen synthetic polymer microplastics on honeybees sampled from Copenhagen and nearby semi-urban and rural areas (Edo et al., 2021). Laboratory studies where honeybees have been fed syrups containing microplastics revealed detectable plastic particles in the gut and crop of honeybees (Buteler et al., 2022), and in larvae, honey, and wax within the hive (Alma et al., 2023). Oral exposure to polystyrene particles has been shown to reduce honeybee body weight (Al Naggaret al., 2023; Wang et al., 2022), and reduce good gut bacteria, stimulate immune inhibitory genes, depress genes related to detoxification and energy balance, and increase susceptibility to pathogenic bacteria (Wang et al., 2022).
While foraging honeybees accumulate particulate matter on their hair-covered, electrostatically charged bodies and collect nectar, pollen, water and ingredients for propolis which are then stored within the hive. The pollutants on and inside honeybee bodies, and in the hive matrices such as honey, wax and pollen, can be identified and quantified to provide information about the pollutants present in the local environment. In order to investigate the presence of particulate matter and microplastics in apiaries, we used a citizen science approach, engaging beekeepers in sample collection and knowledge sharing. The Midlands was chosen as the study area to minimise the variation in environmental variables such as climate and altitude which may impact particulate deposition. Some examples of the microplastics that we have found on sampled honeybees are shown in Figure 1.
Al Naggar, Y., Sayes, C.M., Collom, C., Ayorinde, T., Qi, S., El-Seedi, H.R., Paxton, R.J. and Wang, K., 2023. Chronic Exposure to Polystyrene Microplastic Fragments Has No Effect on Honey Bee Survival, but Reduces Feeding Rate and Body Weight. Toxics, 11, 100.
Alma, A.M., de Groot, G.S. and Buteler, M., 2023. Microplastics incorporated by honeybees from food are transferred to honey, wax and larvae. Environmental Pollution, 320,121078.
Buteler, M., Alma, A.M., Stadler, T., Gingold, A.C., Manattini, M.C., and Lozada, M., 2022. Acute toxicity of microplastic fibers to honeybees and effects on foraging behaviour. Science of The Total Environment, 822.
Capitani G., Papa, G., Pellecchia, M., and Negri, I. 2021. Disentangling multiple PM emission sources in the Po Valley (Italy) using honeybees. Heliyon, 7 (2), e06194.
Edo, C., Fernández-Alba, A.R., Vejsnæs, F., van der Steen, J.J.M., Fernández-Piñas, F., and Rosal, R., 2021. Honeybees as active samplers for microplastics. Science of The Total Environment, 767.
Negri, I., Mavris, C., Di Prisco, G., Caprio, E., and Pellecchia, M., 2015. Honey Bees (Apis mellifera, L.) as Active Samplers of Airborne Particulate Matter. PLoS ONE, 10(7): e0132491.
Thimmegowda, G.G., Mullen, S., Sottilare, K., Sharma, A., Mohanta, S.S., Brockmann, A., Dhandapany, P.S. and Olsson, S.B., 2020. A field-based quantitative analysis of sublethal effects of air pollution on pollinators. Proceedings of the National Academy of Sciences, 117(34), 20653-20661.
Wang, K., Zhu, K., Rao, L., Liang, Z., Wang, Y., Wu, X., Zheng, H., and Liao, H., 2022. Nano- and micro-polystyrene plastics disturb gut microbiota and intestinal immune system in honeybee. Science of The Total Environment. 842, 156819.