1. Unit C: Topic 4 Notes
How Much is Too Much?

2. PPM – Parts Per Million
PPM is a way of telling us the concentration of a solute is in a solution. The formula is:
PPM = grams of solute/grams of solution * 106
There are 30mg of Salt in a 250 g solution of coca cola. To find the ppm of the salt:
0.03/250 * 106 = 120 parts of salt per million of cola.

3. Heavy Metals
Include: copper, mercury, lead, zinc, cadmium, and nickel.
Even a little amount of any heavy metal can lead to health problems in almost any living thing; This is why they are closely monitored.

4. Lethal Dose 50 – LD50
The amount of a chemical that can kill 50% of test subjects.
Is given in mass of substance per kilogram of human tissue.
75 mg per kg is the LD50 amount for caffeine. That means for an average 70 kg man, 5.25 g of caffeine would have a 50/50 chance of killing him.
The higher the amount, the more toxic/lethal the material to living things.

5. LD50 – Why the Controversy?
Because the only way to find out the LD50 amounts for chemicals is to test them – on animal test subjects. This is problematic for two reasons:
1. Ethical – Groups such as PETA feel that to poison and kill animals is cruel.
2. Accuracy – A lab rat is not built like a human. Therefore results have to be taken with a few grains of salt.

6. Thalidomide and Tetracycline
Both chemicals were found out to produce birth defects. These are cases of fatal or toxic doses being discovered accidentally. Thalidomide was a sleeping pill and tetracycline an acne medication. No one knew that pregnant women shouldn’t take them.