The Six Chemical Classes Series: Certain Metals

From the alluring glint of gold to the quiet dangers of lead, heavy metals including mercury, arsenic and cadmium naturally occur in the Earth's crust. They have also made their way into our homes. Lead and cadmium can be found in electrical solder and circuit boards, for example, while compact fluorescent lamps contain mercury. Thus, it's important to be aware that the extraction of these metals and the use and disposal of products containing them have led to adverse health effects and environmental contamination.

Health Concerns

Heavy metals, including lead, mercury, cadmium, arsenic and thallium, continue to raise significant health concerns for humans. Prolonged exposure can result in a range of health problems. Lead exposure, particularly detrimental to children, is associated with cognitive and behavioral impairments, while mercury poses risks to the nervous system, especially in developing fetuses and young children. Cadmium can lead to kidney damage and bone health issues, while chronic arsenic exposure is linked to cancer. Thallium exposure may result in a host of neurological symptoms and gastrointestinal and organ problems.

Environmental Concerns

Despite heavy metals being naturally occurring, there are environmental concerns rising from human activities that disturb the delicate balance in which these elements exist. Lead is dispersed through industrial emissions, infiltrating air and soil. Mercury, often associated with clandestine pollutant releases, finds its way into water bodies, creating a web of consequences for aquatic ecosystems. Cadmium, a residue of industrial processes and waste disposal, leaves its mark on soil integrity. Arsenic, a by-product of mining activities, seeps into groundwater, posing threats to ecological systems and human populations. The disposal of products containing heavy metals is also problematic should the products reach the sewer system as they can kill the bacteria which is introduced at the treatment plant.

Routes of Exposure

Ingestion, inhalation and some medical treatments are common routes of heavy metal exposure. Mercury, often from coal-burning plants and contaminated fish, can also come from certain face creams, dental fillings and fluorescent lights. The major source of arsenic exposure is food. Rice, mushrooms, apples and grapes can absorb arsenic from contaminated water and soil. Arsenic is also found in pressure-treated wood and some drinking water sources. Cadmium is found in cigarette smoke, house dust, certain foods (like shellfish and leafy vegetables), some glassware, rechargeable batteries and household items such as paints. Lead exposure is mainly due to old paint, plumbing fixtures and consumer products like toys and vinyl.

Reducing the Impact

Mercury exposure:

Avoid fish that are high in mercury – see this chart by the FDA. Be mindful of other mercury sources like dental fillings and use filtration systems for well water. Purchase LED light bulbs instead of compact fluorescent light bulbs. Properly clean up broken thermometers, CFL bulbs and other items containing mercury – EPA guidance here. Ensure proper disposal of mercury-containing products.

Arsenic exposure:

When cooking, use cold tap water for drinking and cooking, as hot water can contain higher concentrations of arsenic. Rinse rice thoroughly before cooking. Be cautious with pressure-treated wood manufactured before 2004 as it may contain arsenic-based preservatives – consider sealing or replacing it. Finally, avoid using pesticides and herbicides in the garden that may contain arsenic.

Cadmium exposure:

Quitting smoking or creating a smoke-free environment can substantially decrease exposure. Choose cookware made from stainless steel or cast iron and avoid using older ceramic or enamel-coated items. Regularly dusting of living spaces can help minimize exposure. Avoid inexpensive metal jewelry or rechargeable batteries labeled NiCd or NiCad.

Lead exposure:

Test for lead in drinking water, especially if living in an older home with plumbing that may contain lead pipes or solder and consider installing water filters certified for lead removal. Regularly clean floors and other surfaces to reduce dust. If renovating, hire certified professionals to address lead-based paint and ensure proper cleaning afterward. Wash hands frequently, especially before eating. Opt for lead-free or low-lead dishes, cookware and toys.

Disposal:

Proper disposal of items containing heavy metals, such as batteries and paints, is crucial to prevent environmental contamination. Batteries should be taken to specific recycling locations, and often paints must be disposed of at designated hazardous waste facilities. Check with your local authority about waste disposal and recycling guidelines, as they can vary depending on where you live.

Regulatory Initiatives

In the USA, policies to mitigate the impacts of heavy metals on human health are primarily implemented through federal agencies such as the Environmental Protection Agency (EPA). The Clean Air Act and Clean Water Act set standards to control emissions and discharges of heavy metals, while the Toxic Substances Control Act and Resource Conservation and Recovery Act regulate the manufacturing, distribution and disposal of hazardous substances, including some heavy metals. To further reduce exposure, continued phase-outs, abatement programs, emission regulations, adoption of cleaner technologies and proper disposal practices are essential.

Photography: Patrish Jackson /Adobe