Fish kills from acid rain

The combustion of fossil fuels releases sulfur and nitrogen oxides. These oxides react with water vapour in the atmosphere to produce acid rain. Some lakes in northern Canada are dead because acid rain has killed the plants, algae, and fish that used to live in them. Forests in Quebec and other parts of Canada have also suffered from acid rain. 

In addition, acid rain has dtered the ecosystems of many lakes in Canada and the United States. Fish kills have been reported, and entire species of fish have vanished from certain lakes. In fact, the ecosystems of entire lakes have been destroyed by acid rain, rendering the lakes lifeless. 

Aluminum is the third most abundant element on Earth (after oxygen and silicon), but it is tightly locked into insoluble minerals such as kaolinite (Al2(0H)4Si205) and bauxite (AlOOH). Acid rain from human activities is a recent change in the history of Earth, and it is introducing soluble forms of aluminum (and lead and mercury) into the environment." Below pH 5, aluminum is mobilized from minerals and its concentration in lake water rises rapidly. At a concentration of 130 fxg/L, aluminum kills fish. In humans, high concentrations... 

Acid rain causes direct and indirect damage to the environment. In lakes it can directly kill a variety of organisms, such as young fish and insect larvae. Acidic water releases aluminium ions from rocks and soil which are washed into lakes. Aluminium ions are toxic and interfere with the gills of fish, preventing them from extracting dissolved oxygen from the water. 

Fish are also killed when aluminium, leached from the soil by acid rain, enters lakes and rivers. The function of fish gills is affected by aluminium, leaving the fish unable to extract oxygen from the water. 

The overall result is that ammonia is oxidised to nitric acid. Chemical engineers must make sure that no nitrogen monoxide or nitrogen dioxide can escape from the plant, since these gases cause acid rain. Besides, if any nitric acid goes down the drain, it will end up in the river, killing fish and other river life. 

As discussed in Chapter 1, fish have been lost from several hundred acidified lakes and streams in the Adirondacks, Ontario and Nova Scotia, as well as in Scandinavia. The death of fish illustrates a particularly insidious aspect of acid rain the effects of acidity can be synergistic. For example, acidity can kill fish by interfering with the fish s salt balance by causing reproductive abnormalities by leaching aluminum into the lake at levels toxic to fish gills, so that the fish literally suffocate and by kUling the organisms on which fish feed. The combined effect of these stresses can wipe out a fish population. 

The rain formed from the condensation of this acidic water is an environmental hazard destroying trees and killing the fish in some lakes. (The pH of the water varies depending upon the level of pollution in the area. The pKa values are about -2 for H2S04 and 1.92 for HS04-.)... 

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