Heavy Metals

Heavy metals are naturally occurring elements with high densities relative to water, which are toxic at low concentrations.¹ They are part of an ill-defined subset of elements with metallic properties, usually categorized as metals or metalloids.² In trace amounts, many of these elements are necessary to sustain life, but when they accumulate in the body and in ecosystems they can be toxic and pose risks to human and environmental health.³ This toxic accumulation can affect several of the human body’s organ systems. The symptoms and health effects vary, depending on the kind of metal accumulated, its concentration, the form and duration of exposure, and individual factors such as age, gender, genetics, and health status.⁴

Around 80 of the 105 elements in the periodic table are classified as metals or metalloids, but less than half of these have been found to pose health risks for humans. These include antimony, arsenic, bismuth, cadmium, cerium, chromium, cobalt, copper, gallium, gold, iron, lead, manganese, mercury, nickel, platinum, silver, tellurium, thallium, tin, uranium, vanadium, and zinc.⁵ The most toxic of these are arsenic, cadmium, chromium, lead, and mercury.⁶

Unlike other toxic substances, heavy metals are neither created nor destroyed by humans. These substances have become pervasive because they are used in anthropogenic activities such as industrial production, mining and smelting, fossil fuel combustion, agriculture, technology, and in domestic and medical settings. Industrial sources include petroleum combustion, nuclear power stations, microelectronics, metal processing refineries, and wood preservation and paper processing plants.⁷ These activities result in environmental contamination and human exposure, in part because they cause heavy metals to enter the air, water, soil and food, and also because they transform the biochemical form of the elements.⁸

Heavy metals can enter the human body in a number of ways. We can absorb them through our skin, eat or drink contaminated food or water, or inhale dust or air with heavy metal particles.⁹ The accumulation of heavy metals can disrupt functioning of multiple vital organ systems and glands like the heart, brain, kidneys, liver, and nervous system. Heavy metals also compete with and displace essential nutritional minerals.¹⁰ They can cause weakened bones, high blood pressure, and low energy levels. Long-term exposure is linked to increased risk of cancer in adults, and gradually progressing physical, muscular, and neurological degenerative processes similar to multiple sclerosis, Parkinson’s, Alzheimer’s, and muscular dystrophy.¹¹ For pregnant women and fetuses, there are particular risks – miscarriages, stillbirth, and disruption of brain development that can cause learning and behavioral problems. Young children are also vulnerable, as they consume more food in relation to their body weight, have a tendency to put their hands and other objects in their mouths, and absorb metals more easily than adults.¹² In particular, lead poisoning disproportionately affects children. In the United States, children between ages one and three years are the most affected by lead poisoning, although over the last 20 years the number of children with high levels of lead in their blood has dropped by 85 percent.¹³

Because heavy metals do not break down, they accumulate in the environment. Pollution is particularly high in the areas where industrial, metal-based operations like mining, foundries, and smelters are located. However, metals released into the atmosphere can also travel long distances to be deposited in remote regions with little industrial activity. Contamination can also occur through corrosion, soil erosion of metal ions and leaching of heavy metals, sediment re-suspension and metal evaporation into soil and ground water.¹⁴ This has had significant impact on wildlife, from aquatic organisms to vertebrates and plants. For example, the accumulation of heavy metals in the soil can result in reduced concentrations of chlorophyll in plants.¹⁵ Toxic levels of metals have led to decreased growth and reproduction rates in both plants and animals, and some vertebrates have also experienced neurological effects. As anthropogenic activities cause the circulation of heavy metals to increase exponentially, concern for global public health and the environment has also grown.¹⁶

1. National Center for Biotechnology Information: Heavy Metals Toxicity and the Environment
2. National Center For Biotechnology Information: Heavy Metals and Living Systems: An Overview
3. Occupational Safety and Health Administration: Toxic Metals
4. National Center for Biotechnology Information: Heavy Metals Toxicity and the Environment
5. National Center for Biotechnology Information: Toxicity, Mechanism and Health Effects of Some Heavy Metals
6. Pharos: Toxic Heavy Metals
7. National Center for Biotechnology Information: Heavy Metals Toxicity and the Environment
8. Goyer, Robert & Clarkson, Thomas. Toxic Effects of Metals
9. Six Classes: Certain Metals
10. National Center For Biotechnology Information: Heavy Metals and Living Systems: An Overview
11. National Center for Biotechnology Information: Toxicity, Mechanism and Health Effects of Some Heavy Metals
12. Six Classes: Certain Metals
13. National Organization for Rare Disorders: Heavy Metal Poisoning
14. National Center for Biotechnology Information: Heavy Metals Toxicity and the Environment
15. National Center For Biotechnology Information: Heavy Metals and Living Systems: An Overview
16. National Center for Biotechnology Information: Heavy Metals Toxicity and the Environment