Put a bird on it

This week I am going to try and relate each post to birds. For today’s chemistry themed post I am going to talk about transport of brominated flame retardants and birds as biovectors for transport.

Persistent organic pollutants (POPs) can enter the environment in several ways. Many brominated flame retardants (BFRs) are considered to be POPs, and the processes by which they reach the environment include volatilization and leaching from products during manufacturing or usage, by breakdown of foam products, by disposal of products, through leaching from landfills, combustion and recycling of waste products, or adsorption onto dusts.

POPs released in one part of the world can, through a repeated (and often seasonal) process of release, deposit, release, and deposit, be transported to regions far away from their original source. This is one reason why POPs can be found in the Arctic, thousands of kilometres from any major source of POPs.

Once in the environment, BFRs are capable of travelling long distances from the site of release, largely through atmospheric transport. Removal of BFRs from the atmosphere largely depends on partitioning between the gas and the particle phase, since the deposition process of gases is different from particles. A flame retardant depositing and accumulating on the surface of a particle can re-volatilize into the atmosphere, the rate of which depends on the characteristics of the compound, surface characteristics, and temperature. Due to enhanced condensation at lower temperatures, semi-volatile BFRs will migrate towards the colder regions of the earth. This type of long range atmospheric transport (LRAT) is commonly known as the “grasshopper effect“.

In addition to LRAT by physical systems, such as winds and ocean-currents, it has also been suggested that biologically-mediated (biovector) transport of hydrophobic, semi-volatile compounds may be a contributing factor to the accumulation of these compounds in remote areas far from emission sources.

A colony of seabirds, congregated en masse, offloading their contaminant burden.

Biovector transport can occur over large ranges in distances, from meters to thousands of kilometers. In this case, migratory birds may accumulate a large body-burden of contaminants (e.g. BFRs), then migrate to locations where they congregate in large numbers. Once they have arrived en masse these migratory birds offload all or some of their contaminant burden through feces, molting, or mortality. This results in a local increase in concentrations of contaminants far from their sources, creating a hot-spot. Because of the nature of the offloading, the contaminant burden from the seabirds is bioavailable and can enter directly into the food web, which may pose a risk for top level predators.

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