Diving Into Water Contaminants: Heavy Metals


Heavy metal contaminants continue to plague some of the world’s drinking water sources, cropping up in both tap and bottled water. 

Despite the lengths some municipal water treatment plants go to free water from contaminants, contamination can still happen in the last leg of the tap water journey – through the pipes of your home. What’s more, wastewater treatment plants can indirectly contribute to contaminated water, because of their own wastewater by-products that remain.

Given the many types of human activity contributing to contamination, it’s worth understanding how exactly heavy metals leach into our water systems, and more importantly, what this means for our health.

What are heavy metals and how common are they?

Heavy metals are metallic chemical elements that are natural components of the Earth’s crust. They cannot be destroyed or degraded overtime and can get toxic or poisonous, depending on the concentrations present. 

Examples of heavy metals include mercury, arsenic, chromium, copper, cadmium and lead. They can enter the body from drinking water contamination (for example, in lead pipes), as well as intake from food (for example, rice), or even from breathing air with high concentrations of heavy metals. 

These metals leach into water systems precisely because they are used across a myriad of industries, namely, agricultural, industrial, domestic, medical and technological – making their distribution into the environment and its effect on human health widespread. In fact, ten of the twelve EECCA countries identify heavy metals as a major problem in their rivers, the most common of which is nitrate contamination as a result of agricultural activities.

Where do heavy metals come from?

The short answer is: us. Major sources of toxic metals arise from human activities, predominantly from domestic and industrial wastewater and their associated solid waste discharge. 

There are some less identifiable, non-point sources of heavy metal pollutants like the ones that show up in stormwater runoff within urban areas, leaching in from roof shingles or motor vehicles, for example. These sources are often difficult to identify because they are dispersed in nature: pollutants are discharged into the environment from large land areas such as crop fields, streets and lawns, into other large land areas. 

Other sources are more identifiable in how they discharge pollutants into waterways, such as municipal wastewater-treatment plants or manufacturing industries. As it happens, municipal wastewater-treatment plants – plants that clean sewage and water to be returned to the environment – are often not completely effective in preventing contamination. 70-90% of cadmium, chromium, copper, lead and zinc are removed as solid wastes in most cases, but the other 10-30% of these heavy metals remain dissolved in the water that is released back into the river, thereby contributing to this vicious cycle. 

Mining and agricultural cultivation and fertilization are other sources of heavy metal water contaminants. In fact, metal contamination in soils from agriculture often leads to a contaminated water supply: acidic rain breaks down those soils, thus releasing the substances in these soils into streams, lakes, rivers, and groundwater. Similarly, mining also introduces substantial amounts of metals into rivers, due to the leaching of mine tailings and drainage from mined areas.

How exactly do they get into our water?

How heavy metals directly enter a water supply is particularly emphasised within the industrial activity of coal plants or fossil fuel power stations.

These power stations rely on ash ponds (also known as coal ash basins) to work as a landfill for the disposal of ash, a coal combustion by-product. Coal ash is essentially a powder that remains after coal is burned. It is estimated that  110 million tons of coal ash is generated each year

The idea is to prevent the release of this powder – which contains substances such as lead, arsenic, nickel and mercury – into the atmosphere. This is done by mixing the remains with water to be stored in huge basins nearby. However, this liquid often leaches into waterways through these basins, posing a significant threat to wildlife as well as human health. As it happens, 95% of the ash basins in the States have leaked into rivers and groundwater supplies, according to the federal Environmental Protection Agency. This is largely due to the basins being unlined. 

What’s more, around 11 million Americans live within three miles of a coal plant that discharges pollutants into a public waterway.  And despite regulations intended to limit this leaching, these rules are subject to rollbacks and the relaxing of these requirements.

In Europe, whilst progress has been made in reducing levels of some pollutants in recent years, pollution of water is still a significant problem, tending to be concentrated in localised hotspots downstream of cities, industrialised or agricultural areas and mining regions.

The health risks 

All heavy metals can have adverse health effects, with drinking water being one of the most common ways to ingest them. 

If we take the example of burned coal, as mentioned, you can find heavy metals such as arsenic, lead and mercury. The ingestion of all three can lead to nervous system damage and cardiovascular problems, and more.

According to the World Health Organization, arsenic is a confirmed carcinogen. It is also shown to be harmful to developing fetuses and young children, causing significant developmental harm such as a reduced IQ. Inhalation and absorption through skin can also cause lung cancer and skin cancer, respectively. 

Exposure to lead, a heavy metal that has plagued the water supply of Flint due to the city’s old pipes, is especially liable to result in brain swelling and kidney damage. It is also acknowledged that there is no safe level of lead exposure, particularly for children, who will be more likely to suffer from learning difficulties and a shorter attention span. 

Chromium 6, a substance used in the manufacturing of stainless steel, textiles and leather tanning, can also cause cancer and serious health problems. 

Are better water-treatment plants the solution for cleaner drinking water?

To purify water completely before it reaches your city’s pipe systems, there are still a few grey areas.

While the Environmental Protection Agency has put limits on approximately 90 water contaminants, this still poses the idea that there is a permissible amount of contaminants that can be ingested. These limits also only apply to regulated areas, leaving unregulated water systems and its related contaminants unknown. The systems that do have limits and rules – invoked by the Clean Water Act – are still subject to changes in legislation, making water protection in each individual water system hard to predict for the future.

Directly treating the water that gets leached into our water systems, like ash water, has its own set of complications. The unique water chemistry of ash pond water requires the integration of multiple treatment solutions to make it truly free of pollutants.

What’s more, treatment of water doesn’t stop it from getting contaminated later on: whilst water can be purified and stripped of contaminants during treatment, its drinkability very much depends on your own pipe system. And the potential negative repercussions of a faulty pipe system can be a long process to recuperate from, as Flint’s lead-infested pipes have proven all too well.

Regulations of contaminants in bottled water can also be a grey area. Without the need for annual test reports of contaminants present, the contents of bottled water can be uncertain, with some brands having already been reported to contain high levels of arsenic.

Contaminant-free water therefore comes down to tougher regulations for both tap and bottled water, as well as better measures to protect water supplies from getting infected by coal, mining or wastewater by-products in the first place. For now, contaminant-free depends on your own pipe system, and the quality and purifying ability of your water filter.

In our research at Mitte, we see the trend for taking control of drinking water and health gaining huge traction. And we believe decentralized solutions for drinking water will be the ones that we predominantly rely on in the future.

By Lauren — Jun 23, 2020
The information contained in this article is provided for educational and informational purposes only, and should not be construed as health or nutritional advice.

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