The past decade has seen a steady accumulation of evidence that the residues of pharmaceutical products can be detected in the environment and even in drinking water. But the implications for human health of these nanogram measurements are still uncertain. While scientists debate the issue, the tectonic plates of regulation—within countries and in Europe as a whole—are undergoing small but discernible signs of movement.

The issue of drug residues was the subject of a meeting organised recently by the Royal Society of Medicine. Ecopharmacovigilance, as the study of medicinal drugs in the environment is now known, emerged as a discipline still characterised as much by speculation as by fact. But that is no criticism of the scientists involved; they face some tough challenges.

For a start, information is piecemeal—a study of fluoxetine in this river, another of antihypertensives in that lake—and often reflects local circumstances from which it’s hard to generalise. Harm to wildlife can sometimes be established: …