The Great Lakes play a vital role in the lives of Canadians and Americans, but sadly are undergoing great stress from environmental factors and two harmful pollutants: phosphoric acid, which causes eutrophication in lakes, and polychlorinated biphenyls (commonly known as PCBs), highly toxic chemicals found in sediment used as insulators and coolants for electronics. Phosphoric acid can be removed using aluminum sulphate (known as alum), which traps the phosphorus in an easy-to-collect precipitate. Alum is one of the best ways to lower the high levels of phosphoric acid in the Great Lakes as it is nontoxic and effective, although expensive, at an average cost of $148 200/km. Another method is to encourage nearby farmers not to use fertilizers
