The Science of Water Pollution in Lake Michigan

The Great Lakes hold 1/5 of the fresh water on Earth. The Great Lakes basin has been used as a resource for industry, agriculture, shipping, and recreation for over 200 years. As a result of eutrophication, overfishing, and the wide spread presence of toxic substances in the early 1960's, the quality of water began to deteriorate. By the 1970's the Great Lakes had become dumping sites for agricultural, industrial, and domestic wastes.

Lake Michigan is the third largest of the Great Lakes, and the fifth largest lake in the world. It is the only of the Great Lakes to be entirely in the United States. It allows only small amounts of water to flow out through the straits between Lakes Michigan and Huron. Because it takes so long to "flush" Lake Michigan (it takes 100 years for a complete change of water), water pollution is a serious concern.

Lake Michigan also has the largest sport fishery on the Great Lakes. Therefore it is especially threatening because pollution has been shown to interfere with reproduction in birds and lake trout. It also has been implicated in the development of neoplastic tumors in bottom-dwelling fish. High concentrations of PCBs have led to some advisories restricting the consumption of certain fish.

People can be exposed to Great Lakes pollutants through inhalation of air, ingestion of water, food or contaminated soil, and dermal contact with water or airborne particulates. 80-90% of human exposure is a result of ingestion through the food chain. 5-10% is from air, and less than 1% is from water. Studies of people living in Great Lakes states demonstrate increased tissue levels of toxic substances that may be associated with or result in reproductive, develop- mental, behavioral, neurological, endocrinological, and immunological effects. People are at greater risk along Lake Michigan because more people are drawn to it because it has the largest lakeshore sand dunes in the world along with many beaches, coastal state parks and national lakeshores.

Lake Michigan supports a wealth of plant and animal life (biological diversity) found no- where else in the world. Agricultural and industrial products such as iron ore, coal, limestone, metals, petroleum, coke, and chemicals are derived from the basin’s resources. It provides industrial process and cooling water, and water for agricultural irrigation.

The Great Lake are so polluted because of the long retention times (for Lake Michigan 100 years), and the internal recycling of contaminants. Pollutants are absorbed into particles and settle on the bottom of the lake. There is a reserve of PCBs in the sediments that will continue to redisperse them at significant rates for decades.

There have been 362 different contaminants identified in the Great Lakes. 1/3 have been proven to have a toxic effect on aquatic life, wildlife, and human health. The most critical of these pollutants are: polychlorinated biphenyls (PCBs), dichlorodiphenyl trichlorethane (DDT) and metabolytes, and benzo[a]pyrene (member of a class of substances known as PAHS). These substances bioaccumulate in organisms and biomagnify in food webs.

Organochlorine compounds are persistent, ubiquitous, and toxic. Heavy metals are toxic because of their chemical characteristics and demonstrated toxicity. Lipophilic pollutants biomagnify within the aquatic food chain, and spread to humans. PAHS, methylmercury, and alkylated lead bioaccumulate in human tissues. "People have begun to realize that changes to one part of the ecosystem impact the health of the entire system."

Summary of Small Group Presentation:

Our group had the science of water pollution.  Our presentation included both the natural and social science of the problem.  We compared water pollution to an invasion of the United States by Canada.  The pollution were the Canadians, who managed to sneak, unobserved, into the US and built up an army and bases in a certain "Midwestern region".  This region was Lake Michigan.  The three types of Canadian soldiers were the three main types of water pollution-.  PCBS, DDTS, and PAHS.  Each had a caricature drawn of it to help the class visualize the attributes of that particular form of pollution.

The guests of the military general doing the debriefing for the soldiers included a natural scientist and social scientist.  The natural scientist used water pollution (water with food coloring added) to demonstrate the rapidity with which the Canadians could invade.  The scientist also relayed the specific characteristics of the different "soldiers".  The social scientist’s role was to describe the social problems that an "invasion" would have, and to make the class aware of the importance of social change.

Having presented the facts in the form of Canadian military tactics, we asked the class to divide into groups of 3-4 to devise plans of attack/defense and to create heightened social awareness of the invasion.  After the groups presented their ideas about the invasion, we distributed handouts containing  “the facts” on water pollution and we the explained our metaphor of “warfare”.  We explained how water pollution, although it had an obvious natural science aspect to it, was really more of a social problem, and that we doubted that anything could be done about it without first changing public opinion / increasing public awareness.  As a result, any solution must address natural and social science to achieve success.

Critical Pollutants
polychlorinted biphenyls (PCBS)
dichlorodiphenyl trichloroethane (DDT)
a class of substances known as PAHS)
 hexachlorobenzene mirex
 alkylated lead furans
 methylmercury dieldrin
 toxophene dioxins

People are exposed to pollutants by ingestion of foodstuffs or contaminated soil (80-90%), inhalation of air (5-10%), and from ingestion of water (less than 1%)

By: Xochi, Cathy and Emily

Last updated 2/20/1999
Image Copyright (c) 1997 Index Stock