Matthew MacLeod

Processes & Dynamics of Persistent Pollutants

My main research interest is the sources, environmental dynamics, and ultimate sinks of persistent semivolatile organic chemicals (SVOCs). These substances are environmental contaminants of particular concern because they can migrate through the atmosphere, deposit to the surface, and accumulate in the environment and food chains in remote areas such as the Arctic. The twelve persistent organic pollutants (POPs) regulated under the Stockholm Convention are well-known examples of persistent SVOCs. However, chemicals of this type have economically desirable properties, and there are many examples in current production and use. These include brominated flame retardants such as the polybrominated diphenyl ethers (PBDEs), and the cyclic volatile methylsiloxanes that are used in personal care products and are present as residuals in silicone polymers. In addition, mercury has environmental behavior that is very similar to persistent SVOCs due to dynamic speciation between its elemental form, which has a significant vapor pressure, and divalent and methylated forms that can, respectively, deposit from the atmosphere and bioaccumulate in food chains.

Although there is indisputable evidence that long-range transport of persistent SVOCs occurs on a global scale, key uncertainties remain about the mechanisms of transport, and the processes that determine the ultimate fate of these substances. This lack of scientific understanding presents a critical barrier to identifying chemicals with unacceptable environmental behavior before they are put into large-scale production and use, and to developing effective strategies to reduce levels in the environment when contaminants are identified at unacceptable concentrations.

The principal tools used in my research are models of the behavior of chemical contaminants in the multimedia environment, including dynamic exchange between the atmosphere, water, soils and vegetation. These models can be combined with data from field experiments and monitoring programs to provide insights into the processes that determine environmental distribution and levels of pollutants.