Mercury Dynamics in a Warmwater Stream
Receiving Municipal Wastewater
KENT L. BAINBRIDGE, Graduate Student
FRANK M. D'lTRI, Associate Professor
THOMAS G. BAHR, Associate Professor
Institute of Water Research and Department of Fisheries and Wildlife
Michigan State University
East Lansing, Michigan 48824
INTRODUCTION
The potential hazards of mercury released to the environment became dramatically
clear during the I950's when small amounts of methylmercurials discharged into the waters
of Minamata Bay, Japan, caused an epidemic of poisonings; 121 cases including 46 deaths,
among the people of that area (1,2). It was originally assumed that mercury released into an
aquatic system would become diluted and/ or adsorbed onto the sediments until it no longer
represented an environmental threat. However, investigations subsequent to the Minamata
tragedy have demonstrated that both biological methylation and concentration of mercury
occur in aquatic ecosystems (3, 4, 5).
Most public attention has been focused on industrial mercury pollution. However, the
convenient sanitary sewer network offers a large number of people a ready disposal system
for unwanted chemicals, including many mercury containing consumer products. These
include: the mercury found in water based paints, cosmetics, broken thermometers,
mercury amalgam tooth fillings, discarded pharmaceuticals, household and laundry
disinfectants, as well as the runoff of mercury fungicides from lawns and gardens.
On the average, the mercury concentration in sewage effluent is an order of magnitude
greater than the receiving watercourse (6). These data are substantiated by Klein and
Goldberg (7) who reported that the mercury concentration in sediments near an ocean
outfall of a sewage treatment plant was eight to ten times higher than similar deposits
farther from the outfall. Recent studies have reported mercury concentrations in sewage
treatment plant effluents ranging from 0.1 to 240 ppb (8, 9, 10, 11). Although the
concentration of mercury in sewage treatment plant effluents are higher than the receiving
waters, substantial amounts of mercury are adsorbed and removed by the activated sludge
process in conventional plants. Andersson (12) found that decayed sludge from Swedish
sewage treatment plants contained from 6 to 29 ppm of mercury on a dry weight basis.
Recently, Van Loon (13) reported that sludges from Ontario, Canada sewage treatment
plants contained from 1 to 35 ppm mercury on a dry weight basis. Therefore, sewage
treatment plants appear to play a significant role in reducing the potential release of
mercury into the aquatic environment.
The objectives of this investigation were threefold: 1) to develop a mercury budget for
the East Lansing, Michigan Sewage Treatment Plant; 2) to establish mercury levels in fish,
benthos, water and sediments taken from various points along a segment of the Red Cedar
River which receives the treated effluent; and 3) to determine if mercury fungicides applied
in 1971 to a golf course adjacent to the river contributed to the mercury burden of the river.
FIELD SAMPLING
Four sampling stations were selected on the Red Cedar River, a small warm water
stream which drains into the Grand River in southern Michigan. Sample Stations 2 (SS 2)
and 3 (SS 3), respectively, were located immediately downstream from the golf course and
sewage treatment plant outfall and station number 1 (SS 1) was designated as the upstream
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