What is Se?

  Selenium is an element.

Se is element 34 on the periodic table, in group 16 or VIA, depending on the table you are looking at.

As a rule, elements in the same group have similar chemical behaviors. Selenium is in the same group with sulfur. Sulfur is found in many proteins and provides necessary structural links within the protein.

Of course, elements in the same group have unique properties as well. For instance, Se, which otherwise is an electrical insulator, becomes an electrical conductor when exposed to visible light. Can you think of any uses for this property--

Selenium is a nutrient.

Selenium is a necessary micronutrient. We need 50 to 200 micrograms per day of Se, an amount found in a serving of fresh vegetables. In these quantities Se may have a role in preventing heart disease and cancer.

Selenium is in most soils.

Selenium occurs naturally as a trace element in most soils, rocks, and waters. A few places in the western U.S., Australia, and China don't have enough natural Se. Keshan Disease, an Se deficiency that affects the heart, is named for the province in China where it was first documented. Only rarely, however, do people need to artificially add Se to their diets.

Too much Se is toxic.

Selenium toxicity in animals results from drinking contaminated water or eating plants or animals (particularly insects) in places where contaminated water has entered the food chain. The most common cause of Se poisoning in humans is overdosing on vitamins.

The mechanism of Se poisoning is not well understood, but might result from Se replacing sulfur in protein structures.

To pursue the ideas presented here, click on the activity button:


CLUE #1: Selenium is an element that has similarities with sulfur. It is widely distributed in soils, rocks, and water. In small amounts, it is a nutrient; in large amounts, a toxin. It might achieve its toxic effect through its ability to replace sulfur in proteins. Selenium poisoning in animals results when they drink contaminated water or ingest Se that has worked its way up the food chain.

Wetlands Introduction

Clue #2

Clue #3

Clue #4

Putting the Pieces Together


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