Academic journal article The Science Teacher

Safer Use of Toxic Chemicals

Academic journal article The Science Teacher

Safer Use of Toxic Chemicals

Article excerpt

As most high school science teachers know, poisons exist in high school science labs. Poisons, or toxic chemicals, have even made the National Institutes of Health's list of laboratory hazard classes (see "On the web"). Science teachers should determine the toxicity of the chemical they plan to use and take steps to protect themselves and their students accordingly. Better yet, teachers should avoid activities that require moderately or highly toxic chemicals whenever possible.

How to determine toxicity

First, a teacher must determine whether the chemical is toxic. Refer to section 11 of the Occupational Safety and Health Administration's (OSHA) Hazard Communication Safety Data Sheets (SDS), which shows routes of exposure, symptoms, effects, and measures of toxicity. Also view the GHS toxicity pictogram in section 2 of the SDS. Another quick resource for looking up toxicity for common lab chemicals is Rehab the Lab (see "On the web").

Next, determine whether the chemical has acute toxicity--adverse effects that arise after a test animal is exposed to a substance (OSHA). To estimate the acute toxicity of chemicals on humans, toxicologists use LD50 values, the lethal dose (LD) in milligrams of chemical per kilogram of body weight. LD50 statements include how the substance was administered to the test animal (e.g., via injection, orally, or via absorption). The "50" refers to the mortality rate of 50%. For example, "Sodium Chloride LD50 oral-rat: 3,000 mg/kg" means a single oral dose of 3,000 mg/kg killed 50% of the test sample of rats.

The lower the LD50 value, the more toxic the substance. Chemicals with LD50 values less than 300 mg/kg are considered highly toxic and should not be used. Chemicals with LD50 values between 300 and 1,000 mg/kg are considered moderately toxic.

Chemicals with LD50 values between 1,000 and 5,000 mg/kg are considered slightly toxic. Because LD50 values are dependent on body weight, a given chemical may not harm an adult but could harm an adolescent.

Protecting teachers and students

Finally, if the teacher decides to use the toxic chemical, he or she must determine how to protect everyone in the class. When dealing with any hazardous chemical, including toxic substances:

* make sure engineering controls are fully operational, especially lab vents and the fume hood;

* use appropriate personal protective equipment, including sanitized indirectly vented chemical-splash goggles, gloves, and aprons;

* use any volatile chemical under a fume hood;

* do not permit food or beverages in the lab;

* use caution not to cross-contaminate articles such as books and book bags by, for example, placing them on lab benches where toxic substances are being used;

* always immediately clean up any spills;

* always wash hands with soap and water at the end of the lab activity; and

* when possible, substitute a less toxic chemical or consider a different activity. …

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