MERCURY IN THE WATER COLUMN OF LAKE MICHIGAN

Robert P. Mason*, Chesapeake Biological Laboratory,University of Maryland, Solomons,MD, 20688, USA, Kristen A. Sullivan, Pfizer, Groton, CT 06340, USA.

Mercury accumulation in fish is an important health concern. The Lake Michigan Mass Balance Mercury Study was designed to assess the concentrations and sources of mercury to Lake Michigan, and the factors controlling the bioaccumlation of mercury into fish. Total mercury concentrations, as well as particulate mercury, were measured in open waters of the lake on several cruises in 1994-1995 as part of this study. Concentrations of total Hg averaged 1.6 pM and were fairly consistent across sites and on a seasonal basis. The particulate fraction was 20-50% of the total. In addition, methylmercury concentrations were measured on occassion with dissolved concentrations ranging from 0.025 to 0.21 pM. Dissolved gaseous mercury was also measured during one cruise and the factors of formation investigated. This paper will describe the results of this study and discuss the factors controlling Hg concentration in Lake Michigan surface and deep waters.