Estuaries are the meeting grounds between watersheds and the ocean. In an estuary, waters and sediments from the land, bearing whatever contaminants are characteristic to that region, meet with the waters and sediments of the ocean. In addition, estuaries are frequently major sites of human influence with their own significant sources of pollution. Biologically, estuaries are a unique environment, with a physical conditions and biota much different than either the rivers or the ocean they connect. And estuaries vary considerably between each other, depending on the nature of the drainage, the size of the basin and the resulting mixing patterns.

The salinity gradient in estuaries, caused by the progressive mixture of salt and fresh waters has strong implications for the chemistry of trace elements. Many elements are lost from solution and trapped in the sediments of the estuary, presenting a continuing hazard to bottom dwelling organisms. Within the sediments, different elements behave in different ways. Some are sequestered in anoxic sediments, while others may be mobilized and released.

The Trace Element Lab has been studying the movements and effects of a number of trace elements in estuaries since the 1980s. Much of the work has concerned the input of trace metals into the Patuxent River estuary, their distribution in the waters, sediments and organisms, and their potential effects on the biota.