Results from as yet unpublished studies are beginning to shed light on the extent and possible effects of trace amounts of antibiotics, synthetic hormones and other pharmaceuticals and chemicals that are leaching from effluent flowing in the Santa Cruz River into ground water in and around Marana.
Although minute amounts of the chemicals have been found in shallow monitoring wells operated by Tucson Water near south Marana, representatives from Tucson and Marana's water utilities say the deeper wells used for drinking water remain uncontaminated.
Preliminary findings from one of the new studies indicate the highest concentration of the compounds are near the two sewage treatment plants south of Marana. Another study underway looks at estrogen levels in the surface flow and ground water.
The presence of the compounds were revealed in a landmark study by the U.S. Geological Survey published last year that sampled streams fed by waste water for pharmaceuticals at 138 locations nationwide.
The drugs are excreted by humans and remains in sewage that is treated and released as effluent. Caffeine, nicotine and chemicals from mosquito repellent and detergents that are common in sewage also are being found in small amounts.
The pharmaceuticals and other chemicals are being identified with new techniques able to detect amounts of the compounds in parts-per-billion, whereas in the past the chemicals were discovered only if they were within a ratio of parts-per-million.
Researchers are unsure what, if any, effect the trace amount of chemicals will have on humans or the environment.
In Marana, the federal study detailed last year found pharmaceuticals in the Santa Cruz near Cortaro Road that included the antibiotics erythromycin, trimethroprim, tylosin, tetracycline, and ciprofloxacin. In all, the study detected trace amounts of 21 chemicals in the flow.
Gail Cordy, a supervisory hydrologist with the U.S.G.S.'s National Water Quality Assessment Program in Tucson, said a recent follow-up study found the amount of chemicals detected in the surface flow of the effluent declined the farther it moved from the wastewater treatment plants.
The study was conducted by the U.S.G.S. in November and sampled the effluent flow five times at four locations in the span of about 34 hours, Cordy said. The sites sampled were at the outfall of the effluent at Pima County's two wastewater treatment plants at Roger and Ina roads, and the Santa Cruz at Cortaro Road and further north upstream at Trico Road.
Cordy stressed the results were preliminary and have yet to be analyzed, and it may be as long as a year before the findings are published.
"Not unexpectedly, we found more compounds at the treatment plants then at Trico Road. You have about a 15-to-20-mile span between the treatment plants and Trico Road, and we're finding that some of these compounds are probably degrading," Cordy said.
The lessening of the concentrations is due in part to evaporation, degradation and breaking up of the compounds in sunlight, or adhering to the banks of the river, she said.
In addition to distance, time and periods of concentrations also are playing a role in the amount of compounds detected.
"The flow coming out of the treatment plant is kind of on a human schedule, so we get peaks and valleys. For example, everybody gets up in the morning and goes to the bathroom, and that creates a higher flow from the plants. The higher flow actually dilutes the concentration of the compounds," Cordy said.
One of the concerns about potential health effects - if the chemicals reach the ground water used by humans - is the presence of hormones from pharmaceuticals used in birth control or hormonal treatments that could effect the human endocrine system.
Researchers with the University of Arizona have spent the last year analyzing ground water taken from the monitoring wells near the Santa Cruz and Cortaro Road.
Most of the UA researchers working on the project are engineers, said Robert Arnold, a professor with the UA's college of chemical and environmental engineering.
"We're look for estrogenic activity and we think there's a good reason for that," Arnold said. "Previous studies have shown abnormal sexual development in fish above and below waste water out-falls, particularly in England. We think that's a critical area."
Arnold said the UA research found "strong estrogenic activity" in the surface flows in the Santa Cruz and in ground water samples, but is still analyzing the data to determine the significance. One indication so far is the estrogen levels seem to decrease dramatically as the flow moves north and away from the waste water treatment plants.
"As the water flows downstream, the 20-to-25-mile length of the stream, we're finding that the estrogenic activity decreases as much as 75 percent," Arnold said.
In some areas, the estrogen signature also is being found in ground water that has passed through an estimated 100 feet of sediment.
"But the odd thing is, we've looked at the Sweetwater recharge project where the water is concentrated and also goes through the about 100 feet of sentiment, and we found almost all of that estrogenic activity is gone. But the same does not seem to hold true at several other points in the river," Arnold said.
One source of the estrogen detected derives from an oral contraceptive that is "armored" to remain in a woman's body longer. Arnold said the "armoring" seems to allow the estrogen to persist in the waste water and not degrade as well as some other chemicals analyzed.
The findings may be published by the end of the year, Arnold said.
The danger to human health is unknown, but Arnold said the extremely low concentrations of the various compounds make him doubt any danger exists.
"One good way to look at it is the caffeine that has been detected in some of the waste water flows. One estimate is that if you were to drink two liters of that water everyday for 68 years, you would get the equivalent caffeine from drinking a cup of coffee," Arnold said.
While scientists and engineers all agree that the chemical levels in the water are extremely low, other researchers raise concern about the "synergic" effects of so many compounds mixed together.
At a joint meeting of Marana's Water Utility Advisory Committee and the Manager's Water Committee May 13 in which Cordy briefed officials on her study's findings, she was asked about the effects of so many chemicals taken as a whole.
"That's the questions that has no answer and probably will not have any answers. There are quite a few researchers who are doing studies right now. You can take compounds and subject a minnow to them at different concentrations and you can figure out if there are health effects or reproductive effects. You can't do that to humans," Cordy said.
She also referenced a recent study in which a researcher subjected macro invertebrates, or water bugs, to differing concentration of individual compounds with no effect.
"But then the researcher put two together. She put two of the compounds that are found in waste streams together and tried it, and it killed them. Of course whether we can extrapolate from those little bugs to ourselves is a different story. The point is we just don't know," Cordy said.
Brad DeSpain, director of Marana's water utility who attended Cordy's briefing, said he doesn't believe there's cause for alarm.
"There's just so much unknown about this that we're just trying to get a handle on things right now to see if we're all right or if we have to go off and find a way to treat it," DeSpain said. "I'm kind of concerned, but not really. (The effluent) has been in there for 30 years now and we don't know of any fatalities or harmful effects that have come from it. But naturally, you're always concerned about the quality of your water," DeSpain said.