Since Tucson Water started releasing heavily treated sewage effluent into the Santa Cruz River just south of downtown last month, some people have been wading and splashing in it.

This reclaimed water, as it’s called, comes from a Pima County sewage treatment plant, so is it safe to wade in or drink?

The city’s water utility, backed by Arizona’s environmental agency, says “yes” to the first question and “no” to the second.

The reclaimed water from Pima County’s Aqua Nueva sewage plant is rated Class A by the Arizona Department of Environmental Quality. It says Class A reclaimed water is suitable for partial but not full body contact.

Tucson Water says that means walking or wading in the river is OK, but not swimming or other activity that could cause people to accidentally take it in through the mouth, ears, eyes or nose.

Those views match what one of two University of Arizona water quality specialists said in interviews. Risks are minimal, based on very low levels of contaminants found in that water, said David Quanrud, a research scientist for UA’s School of Natural Resources and the Environment.

But the second researcher, David Walker, said he would not go into the river to conduct research without wearing protective clothing.

He acknowledged he doesn’t know if reclaimed water is hazardous to the touch. But to be certain, authorities should research the river water’s biological effects on wildlife in a way that could point to possible effects on humans, said Walker, an assistant research scientist for UA’s School of Renewable Natural Resources.

There’s no disagreement that effluent from Pima County’s Aqua Nueva and Tres Rios sewage treatment plants is far cleaner than a decade ago. County sewer ratepayers have since plunked $606 million into upgrading these plants to meet federal standards.

The plant’s ammonia concentrations in 2017 were less than one-tenth what they were in 2013, a year before the upgrades went online.

The main disagreement about the current quality stems from the presence of numerous compounds in effluent whose health risks have only recently begun to be evaluated. Known as emerging contaminants, these compounds typically exist in reclaimed water in the low parts per trillion range.

They aren’t regulated by the U.S. Environmental Protection Agency, and face no limits on their levels in drinking water.

While they disagree on the safety of physical contact with the compounds, scientists Walker and Quanrud agree that they pose another potential risk — of seeping under the river into the aquifer.

Tucson Water has said that one reason it’s releasing reclaimed water into the river is so it can be more easily pumped out for the utility when and if it needs that water.

At the same time, the utility says it has no plans to use that water for drinking in the foreseeable future.

“Recovery and safe delivery” of that reclaimed water could require treatment of it, just as Tucson Water has treated compounds in drinking water elsewhere, such as 1,4-dioxane and perfluorinated compounds, said James MacAdam, the utility’s superintendent for public information and conservation.

Today, the aquifer along the lower Santa Cruz through Tucson is already impaired from such historical impacts as landfills, sewage disposal, urban stormwater runoff, and other industrial practices, MacAdam said. So Tucson Water doesn’t operate any drinking wells along a large swath of the river.

Safe for irrigation

Reclaimed water has safely irrigated turf at schools, parks and golf courses, and been discharged elsewhere along the Santa Cruz for decades, MacAdam said.

No known health-related problems are linked to the use of reclaimed water, in Arizona or nationally, he said.

The Class A-rated water also can be used to irrigate food crops, most landscaping, orchards and vineyards, ADEQ says. It can be used in recreational impoundments such as reservoirs and for toilet and urinal flushing and snowmaking, ADEQ says.

But one reason not to drink that water, Tucson Water notes, is that it’s not treated to drinking water standards.

Also, once the water reaches the riverbed, it becomes river water, exposed to everything found in the channel, such as waste from wild and domestic animals and urban stormwater runoff.

“River water is not considered suitable for drinking just about everywhere, for a whole host of reasons,” MacAdam said.

People who walk into the channel also should take precautions to insure they don’t get caught in floods, since dangerous floods can happen in the river even when it’s not raining nearby, he said.

A local community activist who is skeptical that the river water is safe to touch said the utility is being inconsistent.

That’s because along some sections of the Santa Cruz River Park above the river, it has posted signs warning people, “Do not drink or play in reclaimed water,” said Tracy Williams. In those areas, trees and other plants are irrigated with reclaimed water through sprinklers.

In response, the utility’s MacAdam said these signs are posted because Tucson Water is concerned that children playing near sprinklers could ingest or get the water in their ears, eyes or nose. That’s similar to “full-body contact” activities like swimming, he said.

Pharmaceutical traces

As for emerging contaminants, close to 30 of them exist in measurable concentrations in Aqua Nueva’s effluent, a 2017 report from the county wastewater agency shows. It’s the only such report readily available.

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They include three varieties of perfluorinated compounds, including some that have tainted groundwater in Tucson and Marana. The vast majority were pharmaceuticals that treat everything from epilepsy, to high blood pressure, to nervous tension, to heart problems.

There were two flame retardant compounds, two artificial sweeteners and three iodine-based compounds.

Overall, the World Health Organization has found that even drinking trace quantities of pharmaceuticals is unlikely to affect human health, a 2016 ADEQ report on emerging contaminants said.

But the same report noted that the U.S. government’s National Institute for Environmental Health Sciences has said it’s important to consider the potential for endocrine disruption from drinking even low concentrations of some pharmaceuticals.

None of the emerging contaminants has been “thoroughly investigated for all potential health impacts at the low concentrations that are being detected in Arizona waters,” the ADEQ report said. The ADEQ report said nothing about skin contact with water containing these contaminants.

Of emerging contaminants found in the Aqua Nueva effluent, the PFAS compounds have received the most attention both locally and nationally because of their frequent contamination of drinking water. But the risk from human body contact with them is almost universally considered minimal.

Even the Environmental Working Group, a national group that has fought for very strict limits on those compounds in drinking water, says that skin contact with PFAS in the low parts-per-trillion range isn’t likely to be a major source of exposure.

Current research indicates people are mainly exposed to PFAS chemicals by ingesting contaminated food and water, said David Andrews, a senior scientist for the group who has studied them for more than a decade.

As for the other emerging contaminants, UA researcher Walker’s concern dates to a study in the middle 2000s. He and numerous other researchers found endangered bonytail chub underwent dramatic sex hormonal changes after spending three months in tanks containing effluent from the old Roger Road plant.

Walker says that he believes to determine impacts of today’s much cleaner effluent, researchers need to do another study comparing fish put in tanks with and without it. He proposes testing zebra fish in which some varieties of human genetic material have been placed.

Fellow researcher Quanrud agreed the research Walker proposes is desirable. But he cites his own research to back up his view that the risk is minimal from wading into water with these compounds at low levels.

He has found that for a handful of these compounds, concentrations in the county wastewater even back in 2002 were low enough that people would have to drink effluent for thousands of years to get the equivalent of a single medicinal dose.

Also, over the last few years, Quanrud has conducted a still-unpublished risk assessment for 106 emerging contaminants found in the Upper Santa Cruz near the Tumacacori National Historic Park, downstream of where the Nogales International sewage plant was also cleaned up, in 2009. He found that 17 were at high enough levels to pose ecological risk to plants or wildlife. But that was because the assessment was based on impacts to the most sensitive species, all selected from a national database, that don't even live in the Santa Cruz valley.

But while these and similar compounds could put stresses on wildlife in both the Upper and Lower Santa Cruz, that hasn't been enough to prevent the major recoveries of wildlife along both stretches of river since sewage plants were cleaned up, he said.

Contact reporter Tony Davis at tdavis@tucson.com or 806-7746. On Twitter@tonydavis987

Tony graduated from Northwestern University and started at the Star in 1997. He has mostly covered environmental stories since 2005, focusing on water supplies, climate change, the Rosemont Mine and the endangered jaguar.