Which metals are harmful to humans?

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Of the 109 chemical elements, 83 are metals. Metal is an essential material that is indispensable in human production and daily life. According to current research, various heavy metals possess reproductive toxicity in humans, among which the four most common ones are lead, mercury, manganese, and cadmium. 　　Here, focusing on lead, its effects on male reproduction are explained. Lead was already in use by 4200 BC. Severe lead pollution existed as early as in ancient Rome; especially among the elite classes of the Roman Empire, it was common to add lead white in order to increase the sweetness of grape juice and wine. This led to lead poisoning, as well as a general decline in fertility and birth defects. According to data from an elite neighborhood, among 101 men aged 19, 35 were married; of these, 18 had no children, 10 had only one child, and 7 had 2–3 children. In total, only 27 of them had children ； The survival rate of offspring is very low, and even those that survive often suffer from poor physical and intellectual development. Therefore, it has been suggested that the decline of the Roman Empire may be related to lead poisoning among the Roman elite, which led to reduced fertility and a significant decline in the quality of the population. 　　In recent years, cases of lead poisoning have continued to occur due to the consumption of shochu contaminated with lead and the use of drugs containing lead. For example, in 1994, villagers in a certain county suffered from 95 cases of collective lead poisoning after drinking locally brewed \"sweet potato liquor\". Each household uses a distillation apparatus to produce it; this apparatus is made by adding lead from used battery terminals to tin, which results in a very high lead content. Distilling liquor using such containers will of course result in liquor heavily contaminated with lead. According to analyses, the lead content in this liquor averages 273 milligrams per liter (the health standard for lead content in baijiu is 1 milligram per liter). Among those who drank this type of alcohol, there were 189 men and 9 women. 95 people had elevated urinary lead levels, among whom 53 men exhibited symptoms of lead poisoning. It is also reported that a study was conducted on 24 married male workers exposed to lead; one of these workers’ wives gave birth to a daughter with congenital epilepsy, while another’s wife gave birth to a child with congenital heart disease. This shows that lead has certain effects on future generations. 　　Lead can act directly on the core organs of the male reproductive system. **The normal physiological functions of the testes are primarily to produce sperm and synthesize male hormones. Any impairment in either of these functions can affect a man’s reproductive capacity, resulting in changes in the quality and quantity of sperm – characterized by a decrease in sperm count, an increase in the rate of abnormal sperm, and reduced motility. The author analyzed the **level in 38 workers exposed to lead and found that the average value of **lead was 3.2 micromoles per liter, which is not only significantly higher than the 0.8 micromoles per liter observed in those who were not exposed, but also significantly higher than the average blood lead level of 2.3 micromoles per liter among these lead-exposed workers themselves. This indicates that lead can indeed enter ** through the blood-testis barrier, and there is a certain degree of accumulation. Lead can also indirectly affect male reproductive function by disrupting the regulatory functions of the hypothalamic-pituitary-** axis, thereby impacting the secretion of reproductive hormones, such as causing a significant decrease in testosterone levels. 　　 Mercury also has an impact on male reproductive function. It has been reported that in one accidental occupational incident involving mercury exposure, 9 people were exposed to high concentrations of mercury; 6 of them suffered severe poisoning, and they continued to experience various complications resulting from the poisoning even years after treatment. Sexual dysfunction is the prominent symptom, manifesting as a significant decrease in libido and erectile dysfunction; these symptoms can persist for a long time, with libido not returning in two cases even 8 years after the poisoning. 　　 The effects of manganese on sexual function are mainly manifested as decreased libido, ejaculation disorders, reduced erection duration during intercourse, premature ejaculation, impotence, and other similar issues. Abroad, it has been reported that among 13 patients with chronic manganese poisoning, 8 developed impotence. Manganese also has an impact on the growth and development of offspring