Arsenic, Cadmium, Lead and Mercury are the most commonly known heavy metals that can cause adverse health problems. These metals are heavily used by the manufacturing industry, and they can act as pollutants to contaminate our air, water, and food sources.
Arsenic is a natural metal found in soil; it can contaminate ground water as well as crops that grow on contaminated soil. It is also used for the production of pesticide. The most common exposure to arsenic for the general exposure is through contaminated food, though the arsenic level found in food is very low (Health Canada, 2008). Contaminated drinking water poses a greater risk to human health, and it is known that long term exposure to arsenic via drinking water is associated with increased risk of lung, kidney, bladder, and skin cancer.
Cadmium is used in the manufacturing alloys, plastics, pigments and fertilizer and re-chargeable batteries. Improper disposal of cadmium-containing products can contaminate soil, which can pollute crops and vegetables. The most common route of exposure for cadmium is contaminated food, and ingestion in high level can result in kidney damage.
Lead is used extensively in the modern manufacturing industry, and it can be found in air, water, dust, and soil. Lead was a major air contaminants when lead petroleum was introduced in 1920s. Airborne lead released from industrial emissions can land on crops or soils, thus contaminating the food supply Fortunately, following the banning of leaded petroleum in the 1990s, the level of lead in the air has dropped below detectable level. Lead was used in the manufacturing paint, which has been banned in the 1970s. Therefore, houses that were painted prior to 1970s are at risk of lead contamination, and it should be carefully remediated. Lead was also used in the production of plumbing and water pipes, which can contaminate water supplies. Short term exposure to high level of lead can cause vomiting, diarrhea, convulsion, coma or even death, while long term exposure at low level can damage nervous system and impair mental function. Young children and pregnant women are especially susceptible to lead poisoning. It is notorious for causing physical and mental developmental disorder among infants and children.
Mercury level in the natural environment has been dramatically increased due to human activities. It is a toxic metal that cannot be broken down. Some bacteria and fungi can convert mercury into methyl mercury, which is a highly toxic organic compound that can be absorbed and accumulate in living organisms' body easily. Consumption of marine lives is the major route of exposure for methyl-mercury, and large predatory fishes, such as shark, swordfish, certain species of tuna, and marlin tend to have a highest methyl mercury level. Amalgam fillings for dental care can also be another source of mercury exposure. Mercury poisoning can induce cognitive symptoms such as tremor, depression, anxiety, sleep disturbance and even change of personalities. It is also an allergen that can cause skin irritation and eczema upon contact. Methyl-mercury, the organic form of the metal, can cause more severe nervous system damage that can impair one's motor coordination, vision, and hearing.