With the rapid development of industry and agriculture, chemical products increase rapidly, and more and more harmful substances enter the water environment through various channels, causing serious pollution to the water body. On the one hand, it harms the aquatic ecosystem and has various harmful effects on aquatic organisms; On the other hand, it directly or indirectly affects human health through drinking water, skin contact and food chain. In the process of industrial wastewater discharge, a considerable amount of heavy metal elements are deposited in natural water, among which mercury, cadmium, chromium and lead are the most toxic.
I. Mercury
The most toxic element in heavy metal pollution. Inorganic mercury salts and organic mercury compounds [such as methylmercury (Ch3)2HG] are harmful to human body. But they have different effects on human body. The fundamental reason for the toxicity of inorganic mercury salts is that mercury ions combine with enzyme proteins, which inhibits the activities of various enzymes and hinders the normal function of cells. Methyl mercury is the most toxic organic mercury compound because it is more soluble in fat than in water. It can be absorbed almost completely after entering the human body, and it is not easy to be excreted. It accumulates in the body and invades the nervous system, destroying the cerebral vessels, showing numbness of limbs, speech disorder, narrowing vision and hearing failure. These are typical features of the famous public hazard "Minamata disease" (Minamata disease is a urinary disease that first occurred in Minamata, Japan). This is because mercury in factories is discharged into rivers and seas, and mercury accumulates in fish, leading to poisoning and even death.
Two. cadmium (Cd)
Cadmium and zinc are metal elements of the same family, and often coexist with zinc, copper and lead. In copper and zinc smelting and cadmium plating plants, a considerable amount of cadmium elements and compounds are discharged into the atmosphere and wastewater, and cadmium in wastewater is discharged to the bottom of river sediments and absorbed biologically.
Cadmium is not an essential trace element for human body. There is almost no cadmium in the newborn baby, and cadmium in the human body enters the human body through the external environment (such as drinking water, food and cigarettes) after birth. The main symptoms of cadmium poisoning are arteriosclerosis, renal atrophy and nephritis. Cadmium can replace part of calcium in bones, causing bone loosening, softening and spasm, and even natural fracture in severe cases. In addition, cadmium has been found to have carcinogenic and teratogenic effects.
Three. chrome
There are trace amounts of chromium in unpolluted lower atmosphere and natural water. For example, the chromium content in rainwater is 2-4 micrograms per liter, and the chromium content in soil is about 0/00-500 milligrams per liter. Among them, hexavalent chromium is more toxic than trivalent chromium, and hexavalent chromium is a common carcinogen, which has toxic effects on human body and crops. It can reduce the oxygen demand in the biochemical process, thus causing suffocation, and chromium salt can stimulate the stomach. Chromium compounds are widely used in industries, such as electroplating, chemical industry, printing and dyeing, etc., and discharge wastewater containing trivalent chromium or hexavalent chromium, which makes local areas polluted by chromium.
Four. lead
The increase of human lead load has certain damage to human neurobehavioral function. Especially in the battery industry, lead is discharged into the water with wastewater, accumulated in the water and absorbed by the human body, which has a chronic poisoning effect. Through the study of children's blood lead load and neurobehavioral function, it is considered that children who have been exposed to lead for a long time have slow reaction and slow vision.
The pollution problem caused by industrial wastewater in China is quite serious. How to make people drink clean drinking water and remove heavy metal elements from water has attracted great attention of environmental protection departments and water treatment industry in China. However, the problems of single removal of some heavy metal elements in water body are high investment cost and high maintenance equipment cost. Therefore, the best solution to solve heavy metal pollution is to strictly monitor industrial sewage, eliminate pollution sources and adopt high-tech, high-quality and efficient water purification facilities to meet the basic needs of the people.