Toxicity of metals

Toxicity of metals

Toxicity is the ability of a chemical molecule or compound of a poison to reach biologically sensitive sites to cause damage to the body. Metal material damage to the body in the short term, such as rejection, swelling, pain and other clinical manifestations; long-term damage to the immune function and destroy the physiological function of human organs, such as carcinogenic, teratogenic, disabling and so on.

All metals are toxic to the human body, but most of the metal elements contained in the metal elements are necessary for the human body, the key is the toxic dose of metal elements contained in the human body. Insoluble metals as well as metal compound forms often exhibit negligible toxicity; heavy metals are often considered to be synonymous with toxic metals; and radioactive metal elements are radiotoxic and chemically toxic.

The six types of harmful elements recognized as the greatest threat to human health are lead Pb, cadmium Cd, mercury Hg, hexavalent chromium Cr6, PBDE PBDE and PBB. The latter two are toxic organic compounds, and the rest are metal elements. The European Union has formulated environmental protection restrictions and material-related regulations (RoHS, PPW and ELV) several years ago. It can be seen that lead Pb, cadmium Cd, mercury Hg, hexavalent chromium Cr6, and the element content needs to be strictly controlled. In order to facilitate the recycling of electrical and electronic equipment and ensure the enforceability of equipment recycling, the European Union proposed the WEEE Waste Electrical and Electronic Equipment Directive.

Metal lead is prone to chemical reactions in the air, soil and water, and its surface will form a layer of protective and insoluble inorganic lead compounds. These lead compounds are classified as harmful substances, and their toxic effects are different. Lead is often found in rubber production, dyes, printing, ceramics, lead glass, solder, cables and lead pipes, production wastewater and waste. In addition, tetraethyl lead in automobile exhaust is a highly toxic substance. In humans, lead affects the central nervous system and kidneys. When the lead concentration in the blood exceeds 10 μg/dL, the body will produce sensitive biochemical reactions. If the blood lead concentration reaches 60-70 μg/dL for a long time, it will cause clinical lead poisoning in the human body.

The toxicity of metal cadmium is very low, but its compounds are very toxic. Cadmium poisoning in the human body is mainly caused by the ingestion of cadmium-contaminated water, food and air through the digestive tract. Cadmium in the human body has the role of accumulation, the incubation period can be as long as 10-30 years. It is reported that when the cadmium in the water exceeds 0.2mg/L, the cadmium in the long-term drinking water and food intake of residents is not qualitative, which can cause "bone pain disease". Experimental studies have shown that cadmium entering humans and animals mainly accumulates in the liver, kidney, pancreas, thyroid and bones, causing pathological changes in kidney organs, which can cause anemia, hypertension, neuropathy, soft bone, nephritis and secretion. Disorders and other diseases, and affect the normal activities of people. Since 1960, when the impact of cadmium on human health and the environment was discovered, it has been widely concerned and discussed. When the human body is exposed to high concentrations of cadmium smoke smoke suspended particles in the dust for a long time due to the impact of the work environment, it will seriously affect the kidney and respiratory system, and even kidney failure.

Mercury is present in power supply equipment and light source equipment, and is classified as a dangerous substance, which is a toxic substance and has a bioaccumulation effect. The effect on the human body is mainly affecting the central nervous and renal systems. Poisoning can lead to significant memory loss, inattention, general fatigue and so on. It has the potential threat of transformation into organic mercury under certain environmental conditions, resulting in an increase in its toxic properties. Mercury has a significant potential for bioaccumulation and biomagnification. This conclusion has been confirmed by the environmental toxicity effects of various organisms.
Chromium is one of the more abundant metals in the earth's crust and is a very hard gray-white metal. Chromium is used in stainless steel, electroplating, paint pigments, anti-corrosion treatment, anti-rust treatment, alloys, etc. Common decorative chrome plating, including equipment fasteners, automotive fasteners, hand tools, etc. Hexavalent chromium is swallowed poison and inhaled poison, skin contact may lead to allergy, more likely to cause genetic defects resulting in fetal mental retardation, inhalation may cause carcinogenic disease induced gene mutation, there is a lasting risk to the environment. The oral lethal dose of hexavalent chromium compound is about 1.5g, and if the content of hexavalent chromium in water exceeds 0.1mg/L, it will be poisoned. The toxic effect of chromium on human body is similar to that of arsenic, and its toxicity varies with medium, content, temperature and affected person. However, metallic chromium, trivalent or tetravalent chromium does not have these toxicities. At present, the trivalent chromium formula is expensive and still contains chromium, so the substitution is only temporary, and the future development should be completely chromium-free, such as alloy or composite plating.

In addition to lead Pb, cadmium Cd, mercury Hg, hexavalent chromium Cr6 metal elements, toxic class metal trivalent arsenic As3 and excessive aluminum Al are harmful to the human body, and even poisoning death. The World Health Organization stipulates that the daily intake of aluminum should be controlled below 0.004g. Aluminum is slowly accumulated in the human body, and the toxicity caused by it is slow and difficult to detect. Once the toxic reaction of metabolic disorder occurs, the consequences are very serious. Therefore, cooking utensils made of aluminum should be avoided.