A recent study by the United States Geological Survey indicates that our nation's streams contain low concentrations of human and veterinary pharmaceuticals, hormones, and other organic wastewater-related chemicals.
"The concentrations we find are very low," said Herbert Buxton, coordinator of the USGS toxic substances hydrology program. "The vast majority of them are a part per billion or lower, but, even with those very low concentrations, there are reasons to be concerned."
Some water quality standards are measured at part per billion concentrations. Thirty-three of the 95 detected compounds areknown, or suspected to be, hormonally active—capable of interfering with human and ecologic health. Other detected compounds are in the early stages of being studied for their potential health effects.
Of the 95 chemicals surveyed, only 14 are covered by drinking-water standards and these rarely exceeded the criteria. The most frequently detected compounds were coprostanol (fecal steroid), cholesterol (plant and animal steroid), N-N-diethyltoluamide (insect repellant), caffeine (stimulant), triclosan (antimicrobial disinfectant), tri (2-chloroethyl) phosphate, (fire retardant), and 4-nonylphenol (detergent metabolite). The full report can be found in the journal Environmental Science & Technology, Vol. 36, No. 6, www.pubs.acs.org.
"We are not surprised that we found these types of compounds," said Dana Kolpin, a USGS research hydrologist involved with the project. "But it was a little bit unexpected to find the wide variety of mixtures that we did. On average, we found seven or more compounds in a single stream. Thirty-eight was the maximum."
Perhaps the most worrisome chemicals found were the various antimicrobials, although researchers cannot tell whether they come from human or animal sources, or a combination of both.
"The question still remains as to whether even the very low concentrations [of antimicrobials] that we find in the environment might in some way, through long-term exposure, help encourage development of antibiotic resistance," Buxton said.
The scientists plan to pursue a number of avenues as they continue their research, including measuring antimicrobial degradation products—results of some studies indicate these products may be as toxic as their parent. They will analyze sediment to get a more accurate picture of environmental exposure, and they will study how factors such as soil characteristics, air temperatures, and rainfall patterns mingle and affect water transport. Comparing and contrasting areas that have, for example, more poultry than swine, is another goal.
Currently, USGS researchers are attempting to identify whether different sources, urban environments or agricultural areas, have the most influence. "We are looking for combinations of compounds that may help us indicate signatures of different sources," Buxton said. For example, if caffeine and antimicrobials are found in the same area, it might be more likely that they are from a human source rather than an animal source.
As the researchers begin the next phases of the project, they encourage input from the veterinary community. "Maybe there are ways that veterinarians can help us," Buxton said, "[such as] make suggestions as to how you find chemical use-type information and what other chemicals we should identify as priorities [to test for]."