Heavy Metal Contamination In Water And Risks To Human Health

By: Prof. Nand Lal, Dean, Faculty of Life Sciences & Former Pro-VC, C.S.J.M.Kanpur University & Priti Sachan     

The presence of lead in the drinking water can cause damage to the kidney, nervous system, and learning difficulties.

KANPUR: Water resources in the world have been profoundly influenced over the last years by human activities, whereby the world is currently facing critical water supply and drinking water quality problems. Increased urbanization and industrialization are to blame for an increased level of trace metals, especially heavy metals in water bodies.

In addition to drinking water, humans can be exposed to heavy metals through inhalation of air pollutants, exposure to contaminated soils or industrial waste, or consumption of contaminated food.

Exposure to some metals, such as mercury and lead, may also cause development of autoimmunity, in which a person’s immune system attacks its own cells. This can lead to joint diseases such as rheumatoid arthritis, and diseases of the kidneys, circulatory system, and nervous system. Heavy metals of major human health concern are:

Mercury (Hg): Mercury enters through the leaching of soil because of acid rain, coal consuming, industrial, household and mining waste. Mercury in drinking water can cause damage to the nervous system and kidneys. Toxicity of mercury is dependent on whether it takes the form of elemental mercury, inorganic mercury or organic mercury compounds (particularly alkyl mercury compounds such as methyl mercury and ethyl methyl salts).

In terms of methyl mercury, dietary ingestion is the major source of human exposure, especially for seafood and fish and it acts as a potent neurotoxin adversely impacting the developing human brain. It passes readily through the placental barrier and the blood-brain barrier making any exposure during pregnancy of great concern.

Inhalation of elementary mercury vapour leads to tremors, emotional liability, insomnia, memory loss, neuromuscular changes, and headaches as well as kidney and thyroid impairments. The acute exposure to elemental Hg vapours can cause “pink disease” or acrodynia.

High exposures lead to death via critical effects are neurotoxin and renal. Minamata disease (name given after methyl mercury in seafood in Minamata and Niigata in Japan in the 1950- 1960’s) caused the death of thousands of people.

Even minor increases in methyl mercury exposures can cause harmful effects on the cardiovascular system, blisters in the upper gastrointestinal tract, vomiting, abdominal pain, constipation and gastritis. It is absorbed in the gastrointestinal track, immediately entering the blood stream. It readily passes the placental barrier affecting the developing nervous system of the foetus. Continuous exposure to elemental Hg can lead to its accumulation in the thyroid.

Lead (Pb): Lead in the drinking water usually comes from the corrosion of old pipes. The presence of lead in the drinking water can cause damage to the kidney, nervous system, and learning difficulties.

Lead is harmful in youngs and results in learning disabilities resulting in a decreased intelligence (decreased IQ), attention deficit disorder, behaviour issues, nervous system damage, speech and language impairment, decreased muscle growth, decreased bone growth and kidney damage.

Lead exposure is a concern for adults as well where more lead is needed to cause injury but the harm it can do to an adult is much serious. High levels of lead can cause increased chance of illness during pregnancy, high blood pressure, digestive issues, nerve disorders, memory and concentration problems, and muscle and joint pain.

Cadmium (Cd): It is the by-product of the mining and smelting of lead and zinc Cadmium enters the water supply from mining, and plastic industries, as well as sewage. Cadmium is a normal constituent of tobacco, as Nicotine is able to concentrate cadmium independent of soil-Cd content. Itai-itai disease is caused by large amounts of cadmium in the villages.

Cadmium is a cumulative toxicant and carcinogen that affects kidneys, generates various toxic effects in the body, disturbs bone metabolism and deforms reproductive tract as well as endocrine system. Exposure to cadmium enhances calcium excretion causing skeletal demineralization, probably leading to increases in bone fragility and risk of fractures.

Occupational human exposure to cadmium is correlated with lung cancer, and during pregnancy, it leads to reduced birth weights and premature births.

Arsenic (As): Arsenic is the most widely known for heavy metal poisoning in adults. It is discharged into nature by the refining procedure of copper, zinc, and lead, and also by the manufacturing of chemicals and glasses. Arsenic contamination in drinking water can cause damage to skin, liver, and eyes and may also cause cancer.

In humans toxicity occurs due to ingestion of arsenic containing powders or solutions accidentally, suicide, homicide, or consumption of contaminated food or drinking water. Arsenic exposure has been associated with hypertension and serious impacts on the cardiovascular system, and even hepatic damage at high doses.

There is correlation between arsenic exposure and diabetes mellitus (type II). Besides these, arsenic also leads to various dermal effects like hyperkeratosis, hyper pigmentation and hypo pigmentation, per orbital swelling, the occurrence of spontaneous abortion and damage of the nervous system.

The World is currently facing critical water supply and drinking water quality problems. A global effort to offer affordable and healthy drinking water needs to be launched along with updating and creating various laws and regulations to protect and improve the utilization of drinking water resources throughout the world, especially in the low income countries.

Politic, industrial and public education programs are required on awareness of health risks associated with HM-polluted drinking water. Also, the development of robust, cheap and sustainable technologies to improve the drinking water quality is necessary, especially for rural or low income households.

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