Question: Recently, the safety of PTC paper, used widely for demonstrating the ability to taste vs the inability to taste PTC, has been called into question. Many school boards in the USA subsequently banned its use. What is the perspective of the STAO Safety Committee with regard to the use of PTC paper as a student activity in Senior Biology?
Answer: The chemical in PTC paper is phenylthiocarbamide. It is also known as phenylthiourea. A quick look at an MSD sheet for this substance indicates that it is highly toxic, with an LD50 of 3mg/kg. OSHA has classified it as hazardous. The 2004 USA publication, Investigating Safety: A Guide for High School Teachers by Texley et al., suggested that the PTC content was high enough to be of concern. As a result, many school boards in the United States banned its use.
Dr. Steven Wooding is a research geneticist and is currently an Assistant Professor of Health at the University of California. Wooding et al. (2004) sequenced the coding region of TAS8R38 (detection of PTC) in 165 humans, one common chimp, and one gorilla. When asked to comment on the safety of PTC paper for the University of Utah, he stated that:
PTC is so intensely bitter that tasters can detect it in miniscule quantities. A single test paper from Carolina Biological Supply contains just 0.007 mg of PTC. And the amount that is licked off the paper by a test subject is much less than this. Assuming a linear dose-response curve, we calculate that the 230 mg of NaCl in a vending machine bag of potato chips is about 100 times more toxic than the 0.007 mg of PTC in a taste paper.
STAO has published two documents (SOS and Safer Use of Chemicals) where PTC paper was listed as toxic and not recommended for use. Instead, STAO suggests using sodium benzoate as a safer alternative. If it tastes salty, bitter, or sweet, then you are either homozygous dominant or heterozygous. If you do not taste sodium benzoate, then you are recessive.
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