The first study to investigate pharmaceutical mixtures in aquatic ecosystems finds that a mixture of three commonly used drugs has adverse effects on plankton, plants, and fish. Although the study concentrations for individual drugs are up to 100,000 times higher than those found in the environment to date, they are 10 to 200 times lower than typical dosages taken by humans, say the authors. The results were presented at the Society of Toxicology and Chemistry European Meeting in Vienna, Austria, on May 16.
“This study shows that we should be concerned about effects of pharmaceutical mixtures to aquatic species, especially in effluent-dominated streams,” says aquatic biologist Thomas LaPoint, at the University of North Texas in Denton. Concerning the relevance of the concentrations investigated, he says, “Remember that we still know very little about drug levels in the environment.” In addition, large numbers of drugs are being found in many streams. The recent United States Geological Survey (USGS) study found as many as 38 targeted compounds in a single water sample.
European studies and a recent USGS report have determined that many waterways contain low concentrations (maximum about 10 µg/L, most median concentrations <1µg/L) of dozens of over-the-counter pain relievers, prescription drugs, hormones, and antibiotics (Environ Sci. Technol. 2002, 36, 140A–145A). Scientists believe that bioactive compounds at these low concentrations are highly unlikely to affect human health, but there is concern that aquatic life could be adversely affected by constant exposure. Without toxicological data on the effects of these mixtures, however, scientists cannot evaluate the risk.
Treatment concentrations compared to U.S. Geological Survey measured values. All measurements are in micrograms per liter.
USGS Low Medium High Ibuprofen 1.0 6 60 600 Fluoxetine 0.012 10 100 1000 Ciprofloxacin 0.03 10 100 1000 Source: U.S. Geological Survey
Keith Solomon and a team of scientists from the Universities of Guelph and Toronto exposed microcosms—small confined aquatic ecosystems that contain bacteria, plankton, plants, and fish—to mixtures of three common pharmaceuticals: the painkiller ibuprofen, the antidepressant fluoxetine, and the antibiotic ciprofloxicin at three different concentration levels (see table). The team chose the drugs because they are widely used and have different modes of action, says Solomon. The Guelph team sampled and treated the water in the study’s eight 11,500-liter microcosms about once every two days to maintain approximately constant drug levels throughout the 35-day study. Three lagoons were controls; one received the low treatment, one the medium treatment, and three the high treatment. Biological and other chemical measurements were made at least once a week.
When dosed with the medium- and high-concentration mixtures, the overall abundance of zooplankton and phytoplankton increased but the number of different species decreased. Growth of a common pond plant (duckweed or Lemna gibba) stopped and sunfish (Lepomis gibbosus) died.
“We were surprised by these results. Our high-dose mixture is clearly toxic. Compared to the USGS survey, our concentrations are high, but our concentrations are 10 to 200 times lower than the therapeutic doses we take as humans” says team member Sean Richards.
The plankton response is important, Richards adds, because it shows that some plankton are adversely affected by the dosing, while others aren’t. “We’re seeing a change in the plankton community because the sensitive species are dying and the unaffected species are filling in the gaps. This raises lots of questions to try and tease out the mechanisms,” he says.
Laboratory results presented by Guelph scientist David Johnson at the Vienna meeting suggest that ciprofloxicin is curtailing the duckweed growth. He finds that various antibiotics affect the weed with different potencies and that these antibiotics have an additive effect. The scientists suspect that ciprofloxicin, which disrupts the workings of bacterial DNA, may be having the same effect on the plant’s chloroplast DNA. The chloroplast DNA is thought to function in an analogous way to bacterial DNA, says Johnson.
“This kind of ecotoxicological work on mixtures is very important,” says EPA scientist Christian Daughton. “But at these concentrations, I’d be surprised if they didn’t see effects,” he says, noting that fluoxetine stimulates spawning in both female and male clams at low microgram-per-liter levels.
The Guelph scientists have archived biological samples from the microcosms so that they can look for biomarkers that could be indicative of low-level exposure in the environment. They are also conducting further microcosm studies involving more drugs at lower concentrations.
Just about all household chemicals on the market, from pharmaceuticals and hormones to detergents and disinfectants, have, in one form or another, found their way into aquatic environments. Most of the data on these substances have come from Europe, and until recently, little has been known about the prevalence of such compounds in U.S. waters. Researchers at the U.S. Geological Survey (USGS), however, have been working to change that.
In the March 15 issue of ES&T (pp. 1202–1211), Dana Kolpin and colleagues at the USGS report some of the first monitoring data for pharmaceuticals, hormones, and other emerging organic contaminants in streams throughout the United States. The study is the first in a series of USGS reports on the topic and looks at 95 contaminants from industrial, human, and agricultural wastewater sources, in 139 U.S. streams during 1999–2000. Data from the stream study are available on the Web in a companion USGS Open-File Report.
In a feature article in the April 1 issue of ES&T [pp. 140A–145A (400 kb PDF)], Britt E. Erickson examines how little is known about these emerging organic contaminants, in terms of their toxicity and behavior in the environment, and how U.S. and European risk-assessment attitudes differ. She considers what it takes to become a targeted wastewater pollutant, pointing out that if history is any indication, it has a lot to do with the availability of analytical methods and reference standards.
Because of the great flurry of interest in the USGS stream monitoring study, ES&T has decided to make Erickson’s feature available before its April 1, 2002, publication date, so that its release coincides with the publication of the Kolpin et al. paper.
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