Medicine waste and ice age asteroids

This week, Catriona tells us about research into pharmacological waste or medicines in our waterways, including Prozac (fluoxetine) and oestrogen, and the effect they can have on other species; and Chris examines the Younger Dryas Impact Hypothesis, an asteroid or comet strike some believe to have caused additional cooling at the end of the last ice age, and the status of attempts to prove it by finding a crater.