Many man-made materials and human activities are now threatening the health of the planet and its inhabitants. The problem with the use of many chemicals is that their impact may not become evident immediately or to people in the geographical vicinity where they are released. Some effects of chemicals are so subtle and intertwined with natural phenomena that it is difficult to point an accusing finger at a specific chemical or process. The environmental impact of chemicals can be classified into certain categories, some of them of local, other of global scale. Water pollution Water, essential for the life of man and many organisms, may become polluted as a result of numerous human activities.
Polluted water can have detrimental effects on animals, plant life and humans themselves.
A major consequence of the discharge of untreated industrial and urban sewage into the waterways is the depletion of the oxygen content of the water. Oxygen is essential for water organisms, including fish, and most plant species. Ground water pumped by hand pumps or from wells is used in most parts of the world for drinking purposes. There have been incidents of ground water pollution by waste from industrial and urban discharges, resulting in grave public health problems. Some common types of chemical wastes produced by industrial activities and their impact on the freshwater ecosystems and humans are given in Table 3.1.