Megan Brook Kogut

1995 BS Chemistry with Honors
University of Washington Seattle

2000 MS Civil and Environmental Engineering, MIT

In our lab, we determine copper speciation to help predict Cu toxicity in aquatic systems. Uncomplexed, or "free" copper (Cu2+ complexed by water molecules), is toxic to fish and to aquatic insects. But only a small fraction of copper is free in rivers and oceans. Most of the copper (sometimes up to 99.99%) is complexed by "ligands" which hold the copper tightly. Therefore, only a small fraction of total measureable copper in any water sample is directly toxic.

Researchers have shown that plenty of molecules often found in water are able to complex copper tightly, including proteins produced by microorganisms, dissolved organic matter from mud, and sulfide. For example, our lab recently produced results that show humic substances (the colored material leached from plant leaves and mud) strongly bind copper. However, no one is sure of the identity of ligands most important to binding copper in any given natural water sample because the ligands are nearly impossible to separate from all the other matter in water samples. Therefore, it's difficult to prove which ligand sources are most important.

Because we'd like to predict ligand sources and sinks so that we can predict free copper concentrations and therefore copper toxicity, our lab is exploring our current hypothesis that rivers, carrying humic substances, sulfide, proteins, and other ligands, contribute a lot of ligands to estuaries and coastal areas. Because cities are often located near bays and estuaries, many estuaries are polluted with various metals, making them worthy study sites. Rivers could contribute ligands to the estuary to decrease free copper concentrations. However, seawater has chemistry much different than that of river water, and we propose that a change in the chemistry of the riverine ligands will change their copper complexing ability as they travel across the salinity gradient. This change in copper complexing ability is only one part of the "fate" of these riverine ligands.

Our field site is the final three miles of the Saco River, ME, before it empties into the Atlantic Ocean. The ocean tides, rather extreme in the northern state of Maine, push several miles up the river at their high point. The river is therefore salty much of the time. Trees and rocks along the shore and frequent bends in the river make it very scenic. It also has a lot of mud flats (drawn in the USGS map as dotted brown areas next to the river.) We will determine in detail how the copper complexing ability of all the Saco River ligands change as those ligands enter the salty mouth of the river. The Saco River is an ideal site to obtain new information about riverine ligands and to attempt predictions of copper toxicity in other more polluted estuaries.