The abuse of illicit drugs is growing in the UK with a recent European survey showing that there are higher levels of cocaine and amphetamine abuse in Britain than anywhere else in Europe. Drugs enter the aquatic environment as a result of their excretion by users and the subsequent failure of wastewater treatment plants to remove them from the wastewater stream.
A Swedish study shows that European perch exposed to a single drug (oxazepam) caused the fish to become less sociable, eat more and became more adventurous and such behavioural changes could have unexpected ecological impacts.
The wider risk of drugs on the environment can only be assessed by knowing how stable they are in sewage, how well they can be treated and which drug residues are present in the environment and in what form i.e. as the excreted drug conjugate, the parent drug or its metabolite or transformation product.