Detergents are relatively mild substances. At the opposite end of the spectrum are highly toxic chemicals such as polychlorinated biphenyls (PCBs) . They were once widely used to manufacture electronic circuit boards , but their harmful effects have now been recognized and their use is highly restricted in many countries. Nevertheless, an estimated half million tons of PCBs were discharged into the environment during the 20th century.  In a classic example of transboundary pollution, traces of PCBs have even been found in birds and fish in the Arctic. They were carried there through the oceans, thousands of miles from where they originally entered the environment. Although PCBs are widely banned, their effects will be felt for many decades because they last a long time in the environment without breaking down.
Flooding during monsoons worsens India's water pollution problem, as it washes and moves solid waste and contaminated soils into its rivers and wetlands. The annual average precipitation in India is about 4000 billion cubic metres.  From this, with the state of Indian infrastructure in 2005, the available water resource through the rivers is about 1869 billion cubic meters. Accounting to uneven distribution of rain over the country each year, water resources available for utilization, including ground water, is claimed to be about 1122 billion cubic meters. Much of this water is unsafe, because pollution degrades water quality. Water pollution severely limits the amount of water available to Indian consumer, its industry and its agriculture.