But CU-Boulder professor David Norris is also concerned about humans' impact on fish -- specifically the way chemicals we either dump out or excrete may be feminizing male fish, or creating ones with characteristics of both genders. In other words, hermaphrodite fish.
These conclusions were strengthened by recent studies of Boulder Creek before and after the 2008 installation of a new, upgraded wastewater treatment plant. Norris, assisted by a team that includes the University of Colorado Denver's Alan Vajda, CU-Boulder's Ashley Bolden and John Woodling, Larry Barber of the U.S. Geological Survey's Water Resource Division in Boulder and St. Cloud University's Heiko Schoenfuss, noted that before the plant went online, a concerning percentage of adult male fathead minnows began to take on feminine characteristics.
The likely reason? Tests of Boulder Creek water showed the presence of ethinylestradiol, a chemical used in many contraceptives, and estrogen-related substances such as bisphenyl A, phthalates used in plastic, and nonylphenols associated with detergents.
None of that's a surprise to Norris.
"Where we have very large domestic populations, we're either excreting or dumping a lot of chemicals down the drain, and a number of them are estrogenic in nature. They get into wastewater treatment plants, which aren't constructed in a way to deal with chemicals in the very low concentrations of these chemicals.
"Inadvertently, the old plant did remove the vast majority of the chemicals from the effluent discharge," he goes on. "And in what was left, we're talking about parts per billion or parts per trillion -- levels that fifteen years ago we didn't even have the techniques to measure. But biological systems can measure them in those concentrations. And we found that downstream, compared to a population upstream, there were more females than males, and more inter-sex fish.
"In the reproductive organs of the fish, they were making both eggs and sperm, which wasn't normal for the species of fish we were looking at. And there was also a contraceptive effect, where there were fewer eggs and fewer sperm being produced."
The potential effect on fish populations from such changes could be devastating. Norris cites a study several years ago that focused on a lake system in Canada populated by the fathead minnow. "In one lake," he explains, "they treated it with the pharmaceutical that's in most birth control, in a concentration of six parts per trillion -- similar to what we often see in wastewater effluent, although Boulder's wasn't quite that high. They treated it for three years in that concentration, and within two years, they'd virtually wiped the fish out of this lake, because the females couldn't make eggs, and the males were so busy making female protein that they weren't making any sperm."
Sounds dire -- but in Boulder, Norris says, the situation improved dramatically "after the wastewater treatment plant went from a trickling filter process to a more efficient system, called activated sludge. This was something mandated by the EPA, because they weren't meeting standards for some of the other chemical requirements for effluents. So it wasn't related to what we were studying. But it had a side benefit."
The team is still analyzing some of the data from tests conducted after the new plant was up and running. But this time around, Norris points out, "we had no demasculinizatoin of fish over a 28 day period, and we only saw a slight feminization -- and we didn't see that until somewhere between day fourteen and day 28. So a modest upgrade of the plant reduced a lot of these chemicals."
This doesn't mean the problem is solved. The gender changes in fish were improved, not eliminated -- and the question about what the long-term effect of these assorted chemicals may have on people who are drinking them remains. In the meantime, though, the situation is better in Boulder Creek.
"This definitely means healthier fish," Norris says.
And less gender bending.
