The Clean Water Act focused on water pollution from human sewage outflow, which has now been markedly reduced across the nation. Later we realized that the effective control of water pollution also demands removal of nitrogen and phosphorus, derived from sewage degradation. Many sewage treatment plants now include tanks to remove nitrate by denitrification and to remove dissolved phosphorus by complexing it with other compounds. Still, nitrogen and phosphorus are problematic, causing hypoxic zones to develop in lakes and coastal waters.
Now a new class of water pollutants perplexes those who design and manage sewage treatment operations — the residues of drugs and personal care products. With a visit to a local drugstore, one can appreciate the volume of pharmaceuticals that taken by the American public on a regular basis. Many of these are not fully degraded by our own metabolism, primarily in the liver, so significant quantities are excreted in urine. Others are too frequently flushed down the toilet when we no longer need them or they have passed their expiration date. Other drugs, which we apply to our skin in soaps, antibacterial lotions and insect repellents, are simply washed off.
Sewage treatment plants were never designed to handle these compounds, so they pass through the various treatment procedures and are released to natural waterways. Some residues also pass through septic systems. Analysis of runoff waters in southern California and Baltimore, Maryland reveal drug residues, including estrogens and amphetamines. It is likely that the organisms in many streams across the U.S. are bathed in a weak solution of birth control pills, caffeine, hypertension blockers, and lithium. These join pesticides and flame-retardants in a complex toxic mix, which we understand only poorly.
Even at low concentrations, drug residues have measurable effects on the stream-bottom algae and fishes in aquatic ecosystems. At concentrations less than one part per billion, amphetamines reduce the growth of stream algae. Even lower concentrations of estrogens led to the feminization of male fishes in a lake experiment in Canada, so their reproduction ceased.
It is easy to see how drug-take-back-programs can reduce the disposal of unwanted drugs in sewage waters, but the amounts excreted by patients following their doctor’s prescriptions are more difficult and costly to control. The documented effects of water-borne drug residues on fishes should give us some concern. Some of these same waters are tapped as a source of drinking water for humans living downstream of the initial point of release, and some of the same compounds with effects on fishes can disrupt our own endocrine hormones.
This post originally appeared on William H. Schlesinger’s blog Citizen Scientist, published by Duke’s Nicholas School of the Environment.