Pathogen pollution, mainly virus, bacteria, parasites and other pollution. Its harm is mainly manifested in the spread of diseases: bacteria can cause dysentery, typhoid fever, cholera and so on; Viruses can cause viral hepatitis A, polio and so on. Parasites can cause schistosomiasis and leptospirosis. Typhoid fever, cholera, gastroenteritis, dysentery and infectious hepatitis are the five major diseases of human beings, all caused by unclean water.
Drinking water contaminated by arsenic, mercury, chromium, lead, cadmium, nickel, aldehydes, ketones, phenols, nitro compounds, polychlorinated biphenyls (PCB) and benzopyrazine for a long time, or eating contaminated aquatic products through the food chain will cause acute and chronic poisoning or cause cancer in the body, which is very harmful. For example, water and food contaminated by cadmium can cause kidney and bone diseases after people eat it; Ingestion of 20 mg of cadmium sulfate can cause death. Mercury can cause central nervous system diseases, and methylmercury can cause a disease called Minamata disease. Phenol can cause dizziness, memory loss, rash, itching, anemia and so on.
Lead poisoning can lead to anemia and nerve damage. Chromium can irritate and corrode skin and mucous membrane, which can cause allergic dermatitis. Hexavalent chromium is very toxic, which will lead to skin ulcers and cancer. Drinking arsenic-containing water can cause acute or chronic poisoning. Arsenic inhibits or deactivates many enzymes, leading to metabolic disorders, skin keratinization and skin cancer.
Organophosphorus pesticides can cause neurotoxicity, while organochlorine pesticides can accumulate in fat and have hormone-like effects, which are harmful to endocrine, immune and reproductive functions of human beings and animals.
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.
Urban tap water is treated natural water. The water purification process adopted by general water supply companies is "coagulation-clarification-filtration-chlorination disinfection" mode. Although chlorine gas (liquid chlorine, sodium hypochlorite, bleaching powder, etc.) was added. There are many advantages for disinfection, including low price and simplicity. Scientists have found many problems: First, the residual chlorine in water will affect the taste and smell of water and reduce the water quality; Second, the residual chlorine in the water is insufficient, and the disinfection effect cannot be guaranteed; More importantly, it is found that chlorinated organic matter will be produced when the content of organic matter in source water is slightly higher. Most chlorinated organic compounds have carcinogenic, teratogenic and mutagenic effects. Trihalomethane (THM) is a typical example. Therefore, developed countries such as Europe and America began to transition to chlorine-free disinfection in the 1970s.
In addition, water pollution not only affects the survival of aquatic organisms, but also leads to the chronic accumulation of toxic substances in aquatic organisms, which makes people eat these aquatic products and produces chronic toxic effects; Moreover, polluted water can also pollute the soil by irrigating farmland, so that crops are also polluted, leading to the accumulation of vegetables and food poisons, which indirectly affects human health.