**5. Effect of heavy metals on human**

These do not degrade and accumulate in live beings, resulting in a variety of illnesses and disorders of the neurological, immunological, reproductive, and gastrointestinal systems. Because these heavy metal ions (HMI) are non-biodegradable, they can last for decades or even centuries once released into the environment. Lead (Pb), mercury (Hg), cadmium (Cd), chromium (Cr), and arsenic (As) are among the most poisonous heavy metals [71]. Melanin may protect tissue by filtering or detoxicating heavy metals from the surrounding neuronal retina and photoreceptor cells. The choroid plexus of the brain, like the retinal pigment epithelium, sequesters lead and acts as a protective barrier against harmful materials entering the brain [72]. During pregnancy, potentially dangerous contaminants circulating in a pregnant woman's blood might reach the fetus, posing a risk to the child's health. Because of their ubiquitous exposure, cadmium (Cd), lead (Pb), manganese (Mn), and mercury (Hg) have gotten a lot of attention [73]. Exposure to heavy metals and other

contaminants has resulted in a variety of problems in humans and wildlife, including carcinogenic, mutagenic, and teratogenic effects. Structure anomalies, nutritional imbalance, metabolic disruption, and low have all been observed in plants cultivated in contaminated areas [74]. Furthermore, exposure to these hazardous metals has been linked to several serious disorders, including Alzheimer's disease [75]. Due to the difficulty of completely avoiding heavy metal exposure, chemoprevention is a prominent technique for shielding humans and animals from the risk of major health problems caused by toxic metal exposure. The usefulness of many antioxidants, including vitamins taurine, in reducing heavy metal-induced oxidative DNA damage was investigated [75]. Liquid pollutants can hurt human health as well as the environment. Landfill leachate and mine drainage, among other sources of these toxins, cause serious health and environmental hazards [76]. Lead (Pb), cadmium (Cd), mercury (Hg), and arsenic are the most prevalent heavy metals that can cause health concerns when taken in contaminated foods (As). For thousands of years, heavy metals have been employed in a variety of situations throughout human culture. Even though the severe health consequences of heavy metals have long been known, heavy metal exposure persists and, in certain countries, is even rising. Unfortunately, food and food containers are one of the most prevalent causes of heavy metal contamination in the general population [77].

Cadmium-rich foods can significantly increase the amount of cadmium in people's bodies. Liver, mushrooms, prawns, mussels, cocoa powder, and dried seaweed are just a few examples. The circulatory system is a significant route of exposure, and blood vessels are thought to be the main organs of cadmium poisoning. Chronic inhalation exposure to cadmium particles is linked to pulmonary function abnormalities and chest radiographs that are suggestive of emphysema [78]. Cigarette smokers have greater blood and urine cadmium levels, while former smokers have intermediate levels and nonsmokers have lower levels [79]. High quantities of chromium(VI) in the air might irritate the lining of the nose and cause ulcers. Irritation and ulcers in the stomach and small intestine, anemia, and sperm impairment are the most common health concerns found in animals after consuming chromium(VI) compounds [80]. Lead is the most systemic toxin, affecting the kidneys, liver, central nervous system, hematopoietic system, endocrine system, and reproductive system among other organs [81]. Mercury has an extremely low excretion rate once absorbed. The kidneys, neurological tissue, and the liver store a large part of what is absorbed. Mercury is harmful in all forms, with gastrointestinal toxicity, neurotoxicity, and nephrotoxicity among the side effects [82]. Several additional critical elements, like copper, are required for biological function; nevertheless, excessive amounts of these metals cause cellular and tissue damage, resulting in a range of negative impacts and human diseases. There is a relatively limited range of concentrations between helpful and hazardous effects for several elements, such as chromium and copper [82].
