How to Conduct Reference Toxicity Tests With Lettuce Seeds

According to recent studies by the Environmental Defense and the U.S. Environmental Protection Agency, "The vast majority of chemicals in widespread commercial use lack basic toxicity data in the public record." So, knowing how to conduct your own reference toxicity tests is a useful skill. The following is an example experiment explaining how to use lettuce seeds to determine the reference toxicity of table salt. You can alter this experiment to test the toxicity of other chemical compounds, as well.

Things You'll Need

• Bleach
• Water
• Extra absorbent, nontoxic paper towels or coffee filters
• 5, 9 cm petri dishes
• Labels
• Table salt
• 5 Beakers
• Measuring spoons
• Sealed plastic bag
• Ruler
• Recordkeeping book

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Instructions

• 1

  Make a bleach solution containing 10 percent bleach and 90 percent water. Soak the lettuce seeds in this mixture for 20 minutes. Remove the seeds, and rinse them in water five times. It's best to use distilled or deionized water, but tap water works as well.

• 2

  Cut paper towels or coffee filters into five 7.5 cm circles.

• 3

  Place one 7.5 cm circle into a petri dish, and label five dishes with the following concentration levels: 0.2, 0.1, 0.075, 0.05 and 0.025.

• 4

  Make a testing solution by mixing 11.69 grams of table salt (that's roughly 3 tbsp.) with 1 liter of water. Label five beakers with: 0.2, 0.1, 0.075, 0.05 and 0.025 (concentration levels).

• 5

  Fill each beaker with the testing solution as follows. 0.2 gets 100 ml of solution, 0.1 gets 50 ml, 0.075 gets 37.5 ml, 0.05 gets 25 ml and 0.025 gets 12.5 ml. (Tip: 1 tbsp. equals 15 ml.)

• 6

  Put 2 ml of the appropriate testing solution into the corresponding petri dish.

• 7

  Space out five lettuce seeds evenly in each of the petri dishes filled with the testing solution. Make sure none of the seeds touch each other.

• 8

  Put all of the dishes in a sealed plastic bag, and then put the bag in a dark place where the temperature stays the same (room temperature). Leave them there for five days.

• 9

  After five days, look at the petri dishes, and count the number of germinated seeds. For all the seeds that have germinated, measure the root length of each using a ruler (and round to the nearest mm). Measure just the root, not the sprout and the root. Record your findings.

• 10

  Look at your results. If no sprouting occurred, the test organisms (lettuce seeds) were killed, which means that the level of chemical concentration (testing solution) was heavily toxic. If some sprouting occurred, that level of concentration is moderately toxic. Basically, the more sprouting you see (measured by root length) means less toxicity.