Research pick: Don’t eat the yellow snow - "Characteristics of polycyclic aromatic hydrocarbons in fresh snow in the Changping district, Beijing"

Don’t eat the yellow snow, it’s good parental advice to every child playing in their local winter wonderland, but there’s a good reason not to eat any snow – it could be contaminated with high levels of polyaromatic hydrocarbons (PAHs). Writing in the International Journal of Environment and Pollution a team from China has analysed snow in the Changping District for 16 priority PAHs. Their worrying analysis reveals that the total PAH content of their samples were all at the high-risk level in terms of environmental health.

Polycyclic aromatic hydrocarbon are organic compounds (compounds of carbon other than carbon dioxide and carbonates) that are composed of multiple aromatic rings. The term “aromatic” in this context refers to the way in which the carbon atoms are held together in those rings, although etymologically it does refer to the strong odour of the simpler aromatic compounds, such as benzene.

The simplest PAH is naphthalene, which resembles two benzene rings joined, anthracene and phenanthrene contain three such rings, there are many more with more rings in various arrangements. Many of these molecules are volatile, inflammable, toxic and carcinogenic. They are commonly formed through partial combustion of fuels such as coal and biomass and are present in fossil fuels.

The team’s analysis revealed that the most common PAHs in the snow samples contained 4 or 5 rings. PAHs with 3 or 6 rings were next highest concentration, followed by naphthalene and its derivatives. The team suggests that it is rather worrying that the PAHs are present at risky concentrations in snow. Snow persists and is often ploughed to the side of roads. When it thaws the PAH content will be carried into the drainage system and beyond.

“It is interesting and should be noted that fresh snow, which is a naturally occurring substance as one important way of water circulation, was proven to be able to absorb and dissolve PAHs especially for high molecular weight molecules and multiring molecules, and can be monitored to trace pollution sources from the air in a short duration in cities,” the team writes.

Wan, Y-Y., Fei, J-J., Zhang, Y., Shi, S-X., Dong, L. and Zhang, Z-H. (2021) ‘Characteristics of polycyclic aromatic hydrocarbons in fresh snow in the Changping district, Beijing’, Int. J. Environment and Pollution, Vol. 69, Nos. 3/4, pp.277–304.