I’ve learned a few things working with chemotherapy agents in research, such as the vast majority kill cancer cells by the same mechanisms that cause the cancer in the first place. In the lab we use very small amounts and are very careful about our waste disposal, but I was wondering: what happens when patients are on chemotherapy? Many drugs are excreted nonmetabolized, and with so many people taking drugs for all kinds of things these days, should we be worried about what’s going down the john? —Anonymous, via e-mail
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The issue first popped up in the mid-70s, when EPA chemist Wayne Garrison analyzed sewage and found evidence of caffeine, aspirin, and various other chemicals consumed by humans. This didn’t exactly set off a frenzy of further studies, at least not right away—it being the 70s, there was a full slate of old-school environmental disasters to deal with. In the 80s, though, scientists in Europe (where population is more concentrated around bodies of water) started to pay attention to the drug-residue phenomenon, and by the mid-90s U.S. researchers were taking another look too.
The good news is that we’re talking about some very, very small quantities of drugs here—the levels found so far have typically been measured in parts per billion or even trillion. And after three decades of study, no one’s yet produced any evidence that drug residue puts humans at risk. The less-good news runs a little longer. First, there may be long-term cumulative effects we haven’t identified yet, especially considering how persistent some residues are—clofibric acid, one by-product of a cholesterol drug, can hang around for two-plus decades. Second, the extremely low concentrations of residue in water make it hard to distinguish any such effects from ones caused by the zillion other chemicals we’re constantly exposed to. Then there’s the ongoing boom in prescription drug use: a 2004 report points out that while the U.S. population grew 13 percent between 1993 and 2003, the amount of prescription drugs we bought went up 70 percent over the same period.
Update 9/11/2018: A new headline was added.
