A pesticide builds up

A pesticide that is not biodegradable reaches a river. Its concentration, in parts per million (ppm), is measured in the water. At each step up the chain it becomes a number of times more concentrated. You will find the concentration at every level and the first level above a safe limit. Then you will find how many times more concentrated it is at the top.

The idea. Concentration at a level = concentration at the level below $\times$ the factor for that step.

Your tasks.

1. Set ppm to the list of concentrations at the five levels, starting with the water.
2. Set first_unsafe to the name of the first level above the safe limit of $1$ ppm.
3. Set times to the concentration at the top divided by the concentration in the water.