For example, automobiles and industries commonly release nitrates and sulphates into the air. These combine with the water in the atmosphere to produce nitric acid and sulphuric acid. Pesticides With the increasing demands for food-production, many farmers rely heavily on pesticides in the attempt to eliminate such perceived pests as weeds, insects, and so on. After all, pesticides applied to the soil of a field may well not stay there, but be washed, for example, into streams, rivers, lakes, and the ocean by rain and other precipitation. Moreover, pesticides, generally being poisons, may be potentially harmful to the farmers and other humans exposed to them.
Many human activities produce heat.
For example, water is used in the generation of electric-power, which results in the heating of that water. In some power-plants, such water is released into ponds to cool, or, even, into rivers and streams. In any case, there commonly is an increase in the temperature of local waters and in the atmosphere overhead. Increase in the rate of evaporation of the water, which may serve to concentrate chemical pollutants. Reduction in the concentration of oxygen in the water, because warmer water can hold less dissolved gas than can cooler water.