Do your fish look lackluster lately? Have the males given up aggressively patrolling the tank in favor of listening to show tunes? Are the females looking strangely bulked up? Is this about the new brine shrimp you’re feeding them, or is it something in the water?
University of Arizona (U of A) scientist Dr. David Walker is trying to find out. While it is a known fact that endocrine disruptors are present in reclaimed water, whether or not they have a long-term effect—or any effect at all—on wildlife has been a matter of conjecture. Until now.
At Walker’s research facility, tucked off to the side of Tucson’s International Airport, treated wastewater is altering the hormones of native fish.
These fish (bonytail chub, Gila elegans, a species native to the southwestern U.S.) have not technically changed sex but hormones in treated fish have drastically altered. Ecologically speaking, the androgenization of females is a critical effect. “If females are no longer receptive to males, they stop mating. That could mean the end of a species, “ Walker said.
Is the effect limited to Arizona wastewater? Hardly. Federal scientists have recently reported male smallmouth bass in the Potomac River are making sperm—and laying eggs. Is the effect limited to these little brown fish? “All vertebrates are similar, when you get right down to it,” he added, noting he believes there are human implications given the similarities in our endocrine systems.
This was a controlled study examining the effect of differing dosages of treated wastewater on these fish and comparing them to fish in control tanks, filled with tap water treated by carbon filtration and reverse osmosis. All tanks had the same passive filtration systems (sand filters and reverse-flow bioreactors filled with specially graded sand). “That basically consisted of providing surface area for nitrifying bacteria, since accumulating ammonia/ammonium levels would have quickly killed all of the fish in a re-circulating system,” Walker explained.
The fish had passive infrared transducers surgically implanted so that individuals could be monitored over time. Plasma hormone analyses were carried out and fish were randomly selected at the end of each dose cycle for additional analyses. (Fish don’t like giving blood samples any more than people do, according to Walker. It’s one of the main reasons for the netting over the tanks—when they get stressed, they try to leave. They are lightly anaesthetized for blood draws and other measurements, such as weight and length.)
The fish have been exposed to three different ‘doses’ of wastewater, each lasting for a three-month test period: a one-third dilution of wastewater to RO water; a two-third dilution of wastewater to RO water and in full-strength wastewater. The belief here was that the scientists were increasing the dosages but actually, the one-third dose had the highest concentration of known endocrine disrupting compounds. “So, the treatment effect was more pronounced at the beginning rather than the end of the project. What this proves is that the effect is very real and likely plastic if affected fish are ‘cleaned out’ with water containing lower levels (or none at all) of EDCs.” What’s an endocrine disruptor? The U.S. EPA has adopted the definition, ‘an exogenous agent that interferes with the synthesis, secretion, transport, binding, action or elimination of natural hormones in the body which are responsible for the maintenance or homeostasis, reproduction, development and or behavior.’ A European workshop in 2001 identified a candidate list of 553 substances that could be identified as such. In Walker’s research, the changes in the fish appear to be due to compounds typically found in wastewater.
“There’s been both discussion and research about endocrine disrupting compounds,” Walker said, “but the real-world biological effect is poorly understood.”
Most work to date, he continued, focused on the feminization of male fish, but if they still produce sperm, even at low levels, the long-term consequences would likely not be as threatening to the species as masculization of females.
Does this mean we should scrap toilet-to-tap intentions? Not at all—it simply means identifying and removing EDCs at the treatment plant. “Advanced treatment options, including RO and ozone, will help to reduce the number of endocrine disrupting compounds released to the environment, but the biological effect of degradation by-products are also poorly understood at this time,” Walker said.
Walker et al. presented their preliminary findings at the National Ground Water Association conference in March. The fish declined to comment, but appear to be enjoying their accommodations!
About the scientist
Photos by Mark A.W. Smith