(1) After water pollution harms human health, pollutants enter the human body through drinking water or food chain, causing acute or chronic poisoning. Arsenic, chromium, ammonium, benzopyrene, etc. It can also induce cancer. Water polluted by parasites, viruses or other pathogenic bacteria will cause many infectious diseases and parasitic diseases. Water polluted by heavy metals is harmful to human health. Water and food polluted by cadmium will cause kidney and bone diseases after people eat it. Ingestion of 20 mg of cadmium sulfate will lead to death. Lead poisoning can lead to anemia and insanity. Hexavalent chromium is very toxic, which can cause skin ulcers and cause cancer. Drinking arsenic-containing water can cause acute or chronic poisoning. Arsenic inhibits or inactivates many enzymes, leading to metabolic disorders, skin keratinization and skin cancer. Organophosphorus pesticides can cause neurotoxicity, while organochlorine pesticides can accumulate in fat, which is harmful to endocrine, immune and reproductive functions of human beings and animals. Most polycyclic aromatic hydrocarbons are carcinogenic. Cyanide is also a highly toxic substance. After entering the blood, it combines with the pigment oxidase of cells, which interrupts breathing and causes respiratory failure, suffocation and death. We know that 80% of the diseases in the world are related to water. Typhoid fever, cholera, gastroenteritis, dysentery and infectious liver disease are the five major diseases of human beings, all of which are caused by unclean water.
(2) Water pollution is harmful to industrial and agricultural production, and industrial water must be treated with more expenses, resulting in a waste of resources and energy. The food industry has stricter requirements for water. If the water quality is unqualified, it will stop production. This is also a factor of low efficiency and poor quality of industrial enterprises. The use of sewage in agriculture will reduce crop yield and quality, even harm people and animals, pollute large areas of farmland and reduce soil quality. The consequences of marine pollution are also very serious, such as oil pollution, which causes the death of seabirds and marine life.
(3) Harm of water eutrophication Under normal circumstances, oxygen has certain solubility in water. Dissolved oxygen is not only the survival condition of aquatic organisms, but also participates in various redox reactions in water, promoting the transformation and degradation of pollutants, which is an important reason why natural water bodies have self-purification ability. The discharge of domestic sewage containing a large amount of nitrogen, phosphorus and potassium leads to the degradation of a large number of organic substances and the release of nutrients in the water, which promotes the excessive growth of algae and plants in the water, makes the water body poorly ventilated, reduces dissolved oxygen and even appears anaerobic layer. A large number of aquatic plants die, the water surface turns black, and the water stinks to form a "dead lake", "dead river" and "dead sea", which in turn becomes a swamp. This phenomenon is called water eutrophication. Eutrophicated water has an unpleasant smell, dark color and many bacteria. This kind of water is of poor quality and can't be used directly, which prevents the fish from dying.