The term “heavy metals” refers to elements with an atomic number larger than 20 and an atomic density greater than 5 g cm3, as well as having the characteristics of a metal. Heavy metals (HMs) can be generically divided into necessary and non-essential. Living things need essential HMs to carry out their basic functions, including growth, metabolism, and the formation of various organs. Plants need a variety of critical heavy metals, including Cu, Fe, Mn, Co, Zn, and Ni, as they produce cofactors crucial for the structural and functional integrity of enzymes and other proteins. Micronutrients are essential components frequently needed in tiny concentrations between 10-15 ppm. Plants don’t need non-essential heavy metals like Cd, Pb, Hg, Cr, or Al, not even in tiny amounts, for their metabolic activities.
In this article, we are further going to discuss the Impact of Heavy Metals on the Environment and Human Health.
How do heavy metals get into and affect the environment?
The pollution of soils may result from both natural and anthropogenic sources of heavy metals, such as soil erosion, volcanic eruptions, forest fires, mining operations, industrial activities, fertilizer applications, and urban wastes. In ores, heavy metals naturally exist in various chemical forms, such as sulfides or oxides. Multiple processes, including the production of chemicals, oil refinement, metal processing, plating, tanneries, and plastics, cause industrial pollution. The main elements influencing the mobility of heavy metals in soil and landscape are wind, water, and gravity. The metal distribution between the solid and solution phases is influenced by the chemical forms of the metals in each step and by chemical elements like pH, metal concentration, and soil makeup. The loss of soil fauna populations due to heavy metal poisoning of the soil may influence soil fertility.
In the atmosphere, heavy metals are primarily found as particulates. A mixture of solid and liquid particles scattered in the air is called particulate matter. It comprises primary particles released into the atmosphere directly and secondary particulates produced due to the chemical oxidation of gaseous pollutants. Natural activities (volcanic eruption, soil erosion, sand storms, dust re-suspension) and anthropogenic sources (mainly industrial, agricultural, and vehicle emissions) contribute to the atmospheric concentration of metals. A significant class of inorganic particles in the atmosphere is metal oxides. They emerge from the burning of fuels that include metals. In general, winter has higher atmospheric heavy metal concentrations than summer. This is most likely caused by the summer’s high temperatures, robust diffusion capabilities, and rainy weather. In contrast, summer tends to have higher atmospheric deposition rates of heavy metals than winter.
The “Minamata illness” and “itai-itai” or “ouch-ouch disease” outbreaks in Japan in the 1940s and 1950s brought the environmental dangers brought on by aquatic heavy metal contamination to the attention of the world. Ouch-ouch sickness was brought on by eating rice contaminated with deadly levels of cadmium. In contrast, Minamata disease was brought on by eating fish and shellfish tainted with poisonous methylmercury.
Both natural and man-made processes lead to the entry of heavy metals into the aquatic environment. The entrance can occur directly through discharges into freshwater and marine habitats or indirectly through wet and dry deposition. Potential sources of heavy metal pollution in the aquatic environment include anthropogenically produced wastes, geochemical structures, and mining effluents. Heavy metals are dispersed across four interacting compartments after they are introduced to the marine environment (water, suspended matter, sediment, and biota). Metals can be found in the aquatic environment as dissolved or particulate matter. The fundamental mechanisms controlling the distribution of heavy metals in aqueous ecosystems are sedimentation, adsorption/desorption, dilution, and dispersion. The concentration of heavy metals in living organisms may rise due to their uptake by both flora and fauna. Slow evacuation could lead to a bioaccumulation phenomenon that could contaminate the aquatic food chain.
What are the impacts of Heavy metals on Human health?
One of the earliest heavy metals, lead (Pb), was once employed as pesticides, ceramic glazes, and hair dyes. Ingesting tainted food and water and accidental consumption of dust and soil are the main ways that lead exposure occurs. Older homes’ lead-based paint is another important exposure route. When lead enters the body, it is transported throughout the blood and soft tissues before building up in the skeletal system. Lead’s capacity to interact with proteins and decrease enzyme activity by competing with necessary metallic cations for binding sites is one of the main causes of lead poisoning. Chronic toxicity can result in neurological disorders, cognitive impairments, premature birth, brain injury, kidney dysfunction, reproductive pathologies, liver damage, paralysis, and even death. Acute toxicity can cause fatigue, irritability, sleeplessness, headache, loss of appetite, dullness, hypertension, and vertigo.
The most significant route for cadmium exposure in humans is dietary intake. Another route of exposure to the metal that contains significant levels of it is tobacco smoke. Smoking considerably adds to the overall body burden since the lungs absorb cadmium far faster than the digestive system. High blood pressure, fetal development restriction, pregnancy loss, iron shortage, gastrointestinal problems, bone fracture, nephrotoxicity, renal dysfunction, neurological issues, lung damage, and lung cancer are some of the harmful effects of cadmium toxicity.
Seafood intake and dental amalgam are the principal causes of mercury exposure in humans. Another important route of exposure is the inhalation of mercury vapor. Elemental mercury and methylmercury are readily absorbed in the tissues due to their high lipophilicity. The major clinical features of mercury acute and chronic exposures are insomnia, weight loss, vomiting, diarrhea, cough, dyspnea, fever, tremors, gingivitis, erythrism, delusions, hallucinations, acrodynia disease, congenital malformation, renal tubular dysfunction, neurologic disorders, paralysis, and death.
Humans have been exposed to various toxins due to environmental contamination, including pesticides, heavy metals, and polycyclic aromatic hydrocarbons. Unlike most organic contaminants, natural mechanisms do not eliminate heavy metals from ecosystems. In biotic and abiotic environments, they frequently build up to dangerous amounts. Heavy metals can enter the environment as a result of both natural occurrences like volcanic eruptions, soil erosion, and forest fires, as well as a man-made activity like mining, fertilizers, and home and industrial effluents.
Several heavy metals are thought to be necessary for human health. They are significant components of several major enzymes and are essential in numerous biochemical processes. An insufficient supply of certain elements brings on several deficiency syndromes. Some micronutrients can, however, become poisonous in the body at a certain level. Some substances are harmful to health and toxic even at low concentrations. This is the situation with lead, cadmium, and mercury, three of the ten chemicals the public is most concerned about because of their high water solubility, toxicity, and carcinogenic potential. Chronic and acute exposure to these elements harms human health and may result in fatal, incurable conditions.