Which is more toxic - a chemical with toxic level of 3 ppm or a chemical with a toxic level of 0.03 ppm?Why?
ppm is an acronym for parts per million. A chemical which has a toxic level of 3 ppm means that a mass of just 3 in a mixture with a mass of one million would prove toxic. On the other hand a toxic level of 0.03 ppm, implies just a mass of 0.03 in a mixture with a mass of one million is toxic. This means the second chemical is 3/0.03 = 100 times more toxic than the first.
Toxicity increases with a decrease in the amount of the substance that is sufficient to cause adverse reactions. A chemical that requires just 1% the mass of another chemical to cause adverse reactions is more toxic.