When we hear the term ‘heavy metals’, our brain naturally interprets them to be metallic elements with higher atomic weights. It is true as we classify metals as heavy metals if their specific gravity is 5 or more. Nonetheless, heavy metals are metals or metalloids of environmental concern. Living organisms require only trace amounts of heavy metals, thus their excessive levels are considered as toxic as they are detrimental for human health and also for other organisms. Heavy metals mainly include lead, mercury, cadmium and arsenic. Other metals such as cobalt, copper, manganese, vanadium, strontium, and zinc are also classified in this category.
Heavy metal toxicity is the accumulation of heavy metals in soft tissues of the body. It is an issue of global importance. Not only humans, but all life forms are affected by it. The source of these heavy metals can be soil, food sources and water bodies. They contaminate drinking water and food chain resulting in health concerns.
Pakistan is primarily an agricultural country. The soil despite being fertile is not good enough to cater for the needs on entire population, considering the fact that population is on an all time growth. With increased population more and more land is cleared to utilize it for growing crops or converting it to new establishments. In order to improve the quality of crops, farmers use fertilizers. These fertilizers are washed off to water bodies contaminating the water supplies.
Apart from this, the increase in industrialization offered another problem; that of disposal of waste or industrial discharge. When industrial waste is discharged into the environment, it contaminates soil and water bodies. In Pakistan, main contributors to the surface and ground water pollution are the byproducts of various industries such as textile, metal, dying chemicals, fertilizers, pesticides, cement, petrochemical, energy and power, leather, sugar processing, construction, steel, engineering, food processing, mining, and others. Industrial zone of Islamabad is accumulated with higher concentration of lead, copper and Zinc. Industrial zones of Lahore, Sheikhopura and Kala Shah Kaku are also at high risk of contamination.
Number of vehicles has also increased in the last few years. Excessive traffic is another contributing factor for the elevated levels of heavy metals in the environment. The most common heavy metals released from vehicles are cadmium, copper, lead, nickel and zinc. As heavy metals are non biodegradable, their deposition over time can lead to metal contamination of soil. When this contaminated soil is washed off due to rain, metals enter water bodies thus contaminating them. Soil analysis has shown that soil in Rawalpindi district is contaminated with cadmium and chromium.
In Pakistan, areas like Islamabad, Rawalpindi, Faisalabad, Lahore, Sheikhpora, Kala Shah Kaku, Multan, Peshawar, Mardan, Sawabi, Nowshera, Charasda, Khyber agency, Kohat, and Karak are among the leading contaminated areas due to industrial contamination, fertilizer, automobile, mining and natural constituents of the soil.
Environmental contamination and human exposure have increased dramatically during the last one hundred years. Heavy metals accumulate in bodies and cause toxicity. Due to over population and to limited access to clean drinking water, a fairly large number of people consume contaminated water. Food items placed on roadside also contain deposits of pollutants including heavy metals from vehicle emissions and construction work. They also serve as a source of intake of toxic metals. Marine life living in such water bodies are also at risk. Many fish and other life forms die of poisoning due to industrial discharge in water bodies. Heavy metals also accumulate in fish etc. which if consumed can result in serious toxicity in humans.
As stated earlier, heavy metals accumulate in fatty tissues and internal organs in human bodies. They can affect central nervous system and may act as helper agents for different diseases. Young children are more vulnerable to heavy metal toxicity because this is the time during which maximum brain growth and differentiation takes place.
Mercury can cause widespread toxicity and symptoms in several organ systems including nervous system which results in, personality changes, tremors, memory deficits and loss of coordination; cardiovascular system which causes increased risk of arterial obstruction, hypertension, stroke, atherosclerosis, heart attacks, and increased inflammation; GI tract resulting in, nausea, diarrhea and ulceration; and kidneys leading to renal failure Mercury may also accumulate in the thyroid and increase the risk of autoimmune disorders and may cause contact dermatitis. Nickel compounds are carcinogenic to humans. Mixtures of Nickel metal and compounds are known to cause cancers of the lung, nasal cavity and paranasal sinuses. Arsenic is also carcinogenic. Arsenic exposure causes a higher risk for developing a number of cancers, especially skin cancer and cancers of the liver, lung, bladder, and possibly the kidney and colon. Cadmium and its compounds cause lung cancer. It is also found to be associated with cancers of the kidney and of the prostate. Cadmium intoxication can also leads to pulmonary damages, kidney damage, skeletal damage, and itai-itai disease. Itai-itai disease was officially recognized as the first disease induced by environmental pollution in Japan in 1968. Lead exposure in children and adults can cause a wide spectrum of health problems, ranging from small effects on metabolism and intelligence to kidney failure, coma and even death in extreme cases. Adverse affects of zinc toxicity includes acute gastrointestinal effects and headaches. It also weakens immune function. Arsenic, cadmium, mercury and nickel are also known neurotoxins.
Qaisar Jamal, Palwasha Durani et al, 2013, Heavy Metals Accumulation and Their Toxic Effects: Review, Journal of Bio-Molecular Sciences (JBMS)
Yasir Faiz et al, 2009, Road dust pollution of Cd, Cu, Ni, Pb and Zn along Islamabad Expressway, Pakistan, Microchemical Journal 92