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What elements are harmful to living organisms and how do they get into our environment?

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Welcome to CoreFacts, where we're always short on time and big on science. I'm Jessica Robertson. Today's question involves harmful elements.

What elements are harmful to living organisms and how do they get into our environment?

Trace essential elements such as fluorine, copper, selenium and others can be hazardous to living organisms if present at high levels. Nonessential heavy metals such as arsenic, lead, mercury, cadmium and chromium are usually toxic to organisms at much lower levels than trace essential elements.

Both natural and human processes can control the movement of elements at the Earth's surface, and the combination of natural processes with human activities can increase a substance's harmful or toxic level. Elements can be quite mobile in water, and the majority of our environmental problems are ultimately associated with the contamination of surface and ground water. When water comes into contact with rocks and soils, some of the minerals and organic substances dissolve and enter the natural waters.

Toxic substances may also have both natural and human sources. Natural sources of toxic substance include rocks, volcanoes, sediments, and soils. Human activities that add toxic substances to the environment include manufacturing, refining, chemical processing, fertilizer application, irrigation, and waste disposal.

There are several characteristics of substances that must be considered when determining whether there is a problem. These include concentration size, the amount of the substance released, the rate of release, its availability to organisms, and its residence time in a particular ecosystem.

And now you know. Join us again every weekday for a new CoreFact. For other CoreFacts, or for CoreCast, our in-depth science podcast, go to If you'd like to have a question featured on our show, give us an email at or a phone call at 703-648-5600. Remember, long distance fees do apply.

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