Can drugs found in water harm humans?
A mixture of pharmaceuticals at environmentally relevant concentrations is found to inhibit the growth of human embryonic kidney cells.
Although discoveries of Prozac in drinking water and cocaine in Italian rivers get plenty of press, little is actually known about what happens when people are exposed to the mixtures of drugs being found in the environment. But researchers at Italy’s University of Insubria have taken an important step. In the first study to examine the effects of a drug mixture at environmental levels on human cells, posted today to ES&T’s Research ASAP website (DOI: 10.1021/es051715a), they report that a combination of pharmaceutical compounds inhibits the growth of embryonic kidney cells in laboratory tests.
Researchers in Europe began in the early 1990s to identify trace amounts of certain therapeutic drugs in surface waters and groundwater. Since then, survey campaigns in Europe and the U.S. have found about 100 such compounds in surface waters, groundwater, sewage, effluent from wastewater treatment plants, and even tap water—at levels as high as parts per billion. Pharmaceutical compounds enter the environment through several different pathways, including improper disposal and the excretion of nonmetabolized drugs. Often, waters test positive for more than one substance.
Researchers agree that aquatic species face the greatest risk from exposure to low levels of pharmaceuticals, such as synthetic hormones, which can act as endocrine disrupters at environmental levels. However, little is known about the potential human health effects arising from complex drug mixtures.
Corresponding author Franceso Pomati and his colleagues set out to fill this gap. “To make a proper risk assessment,” Pomati explains, “we needed some data about not single drugs, taken one by one, but a mixture that was representative of the real conditions in the environment.”
The researchers designed a cocktail of 13 drugs—including several antibiotics, the popular pain reliever ibuprofen, and a highly toxic cancer medicine—to mimic the mixtures found in several Northern Italian rivers and in wastewater. Individual component concentrations ranged from 10 to 1000 nanograms per liter. “The mixture is complex in terms of [what has] been used [in laboratory tests] before, but it’s nothing; it’s simple in comparison to what’s been found in the environment,” says Pomati.
To his surprise, Pomati observed that this mixture of drugs at environmental levels inhibited the growth of human embryonic kidney cells. After 48 hours of exposure, cell proliferation was reduced by 10–30% compared with controls. However, no inhibition was observed when cells were exposed to only the toxic cancer drug at environmental levels.
The results show that the growth inhibition is not due to the single most cytotoxic compound alone. But that does not conclusively prove that synergistic or additive effects exist between drugs in the mixture, cautions Thomas Heberer of the Institute of Food Chemistry at the Technical University of Berlin. To show that the individual drugs behave additively, Heberer suggests that researchers should analyze the effects of compounds with a common mode of action, such as antibiotics, alone and in various mixtures. Nevertheless, many researchers speculate that such interactions are present, although environmental impact assessments for new pharmaceuticals in the U.S. and Europe are not required to take the possibility of mixture effects into account.
Pomati and his colleagues used proteomic and genomic assays to determine the mechanisms of growth inhibition. They found that the drug mixture stimulated the expression of cell cycle regulation genes and certain proteins (kinases) that signal cell stress. These responses often indicate a slower rate of cell division and thus less cell proliferation.
According to Bent-Halling Sørensen, a professor of chemical toxicology at the Danish University of Pharmaceutical Sciences, the proteomic and genomic assays used by Pomati and his colleagues are becoming increasingly popular in the field of environmental toxicology to study pharmaceuticals. “But you’ll have to remember that you have to translate something going on in an assay to real life,” he cautions, “and that’s a big jump.”
Another challenge lies in determining the bioavailability of the pharmaceutical compounds, says Heberer, and this may depend on solubility and other chemical properties. “So the question is: What really ends up in the cells or close to these cells?”
Pomati concurs that extrapolating from cells to organisms is difficult, but he believes that an understanding of the effects of pharmaceutical mixtures in the environment is needed. “We have to demonstrate scientifically a correlation between what we see in vitro and what we see in vivo. Organisms, they are much more complex than cells, but that doesn’t mean they’re less sensitive.”
