It’s another Summer Series episode of greatest hits, in which we hear from immunologist and science communicator Catriona Nguyen-Robertson about her recently completed PhD research and direct personal experience of how the immune system's T cells can also target fats and oils; and Catriona also tells us about studies into pharmacological waste or medicines in our waterways, including Prozac (fluoxetine) and oestrogen, and the effect they can have on other species.