Metals exist all around us.

They occur naturally in the environment and can be found in a variety of food sources.

Many metals pose no threat to health but certain heavy metalsie.

Joel Kahn, M.D.

(Take thehigh levels of lead in the water in Flint, Michigan, for example.)

Here are four sources of heavy metals to look out for and avoid consuming in high doses.

There are health benefits to eating seafood, but some fish contain high levels of the heavy metal mercury.

Joel Kahn, M.D.

Frequent fish eaters had 11 times more mercury than a group who rarely ate fish.

Whether you’re pregnant or not, you’ll want to avoid eating mercury-laden fish.

Lead in bone broth.

Bone brothis a popular ingredient thought to lower inflammation, nourish skin, and promote gastrointestinal health.

Not much research has looked into heavy metals in bone broth.

The broth was found to have markedly high lead concentrations compared to water cooked in the same cookware.

I am unaware of any commercially available bone broth or collagen powder that test for lead levels.

Cadmium and heavy metals in e-cigarettes.

Cadmium is a toxic heavy metal that has beenlinked to increased risk of certain cancers.

Cigarette smoking, in particular, is known toexpose people to high levels of cadmium.

Some stateslike Californiaare looking to label these products as potentially carcinogenic, similar to the labeling required in Canada.

Exposure to inorganic arsenic has been linked toheart disease, kidney disease, brain disease, and diabetes.

Barley, multigrain, and oats are preferred nutrition sources.

Adults buying rice can refer to thisConsumer Reports resourceto find grains that are less likely to contain heavy metals.

The bottom line.

While not all metals are dangerous, some can harm human health.

The big four to look out for are mercury, lead, arsenic, and cadmium.

Dr. Joel Kahnis the founder of theKahn Center for Cardiac Longevity.

He is owner ofGreenSpace Cafein Ferndale, Michigan.