What are Heavy Metals in Water?

Heavy metals are compounds that naturally occur in the environment as well as from industrial applications. Heavy metals include compounds such as lead, arsenic, copper, mercury, chromium, nickel, thallium, zinc, and many more. These types of metals can be toxic to living organisms in large concentrations or continued exposure over time.

Heavy metals occur in two forms—dissolved or particulate form.

Typically, a certified lab analysis using inductively coupled plasma – mass spectrometer (ICP-MS) is the most accurate testing for understanding the metals in your water. This testing will identify the different metals in your water.

Water samples typically will test for two types of metals: dissolved metals and total recoverable metals.

When testing the water sample for dissolved metals, the sample shall pass through a 0.45 micron filter, and then acidified to a pH of less than 2.

When testing the water sample for total recoverable metals, the sample is not filtered and is preserved with an acid digestion process to maintain the chemical compounds stability.

There are many sources of heavy metals in water. Heavy metals commonly occur from the following sites:

Heavy metals can be toxic with long-term exposure and high concentrations with impacts being on wildlife and human health and our overall environment.

Health: Overtime the accumulation of heavy metals can build up in the body or tissue resulting in damaged organs. This process is called bioaccumulation; this process is when organisms gradually accumulate a substance in their body at a faster rate than their body can metabolize.

Environment: Heavy metals enter the environment naturally and by human activities. Over time the environment is impacted by heavy metals bioaccumulating in organisms which are magnified by the food chain and causes disruption and health impacts on ecosystems, wildlife, and humans.

There are approximately 30-40 heavy metals. Heavy metals are commonly defined as having a density greater than 5 g/cm3, and are metallic elements that cause environmental and health toxicity. A few common and more frequently monitored heavy metals include:

Water chemistry is an important factor for determining the state and toxicity of the heavy metal. The dissolved oxygen content (DOC), hardness of the water, pH of the water, and temperature are important factors in determining if the heavy metal is dissolved or in particulate form.

At lower pH values the environment is more acidic and heavy metals are often soluble and therefore are commonly referred to as dissolved heavy metals. At higher pH values, the heavy metals will precipitate out and be suspended in the water as a particulate heavy metal.

Higher temperatures generally increase the mobility and solubility of metals. Whereas lower temperatures will generally decrease mobility and keep metals in sediment or bound to a particulate.

High DOC will increase the concentration of insoluble metals therefore promoting metals to precipitate in water. Whereas lower DOC will release metals therefore promoting metals to be dissolved in water.

When dissolved metals exist in the water they will exist as ions. These dissolved heavy metals are positively charge ions, also known as cations. With the cations in the water this will make the solution more conductive. Conductivity of the water is a common parameter that is measured when evaluating a water sample. The concentration of dissolved metals is directly related to the conductivity of the water.

Dissolved heavy metals commonly use filtration (such as organoclay filtration), reverse osmosis, ion exchange, or chemical treatment to oxidize the dissolved metal. These types of processes will remove the dissolved metal when they are in ionic form.

Particulate or insoluble heavy metals can be removed with chemical precipitation and physical filtration to remove them from water. Types of treatment for this include coagulation/flocculation to aggregate the particulates then use filtration such as final removal.

Hydrosil’s HS-MT is designed to remove dissolved heavy metals from contaminated water. The HS-MT is a 50/50 blend of modified earth and HS-200 (organoclay). The product has a high capacity for dissolved metals including but not limited to chromium, copper, nickel, lead, thallium, and zinc.