Students learn to calculate these ratios and analyze a sample chemical spill to determine if cleanup action is necessary.
Some toxic substances are dangerous even in very small amounts.
For instance, you could find 500 ppm of a pesticide in a lake. Expressing the amount of contamination in ppm or ppb is measuring the concentration of the substance. This way, a scientist can take a relatively small sample of water, from the lake in our example, and measure the concentration of one or more contaminants in that sample, then assume that the concentration is the same in the whole lake without testing the entire lake. For more information on the science of detecting and measuring contamination, see the Suggested Reading list found at the end of the Haz-Ed materials. Instruct the students to guess if necessary to answer these three questions.