Louisiana’s state health officer on Tuesday defended his decision last week to warn Donaldsonville residents not to drink their tap water because of possibly high chlorine dioxide levels.

Dr. Jimmy Guidry said he was being cautious with public health at a moment of troubling uncertainty.

Guidry, when asked, also said Tuesday the U.S. Environmental Protection Agency is part of a state Department of Health and Hospitals probe into why the private water utility, Peoples Water Service Co., didn’t report high levels of the chemical disinfectant even though the company had been finding them at its treatment plant since September.

Tulane University toxicologist LuAnn White, who Guidry said is DHH’s informal expert on such matters, said Thursday the elevated levels of chlorine dioxide found at the plant probably didn’t pose a risk even to young children and fetuses due to safety margins built into federal drinking water standards. Much higher levels likely would have been needed to bring about feared nervous system effects on fetuses, for example, she said.

But Guidry said he consulted with White — Louisiana’s health agency does not have a toxicologist on staff — when the problems in the Peoples Water system were first uncovered after a routine, three-year inspection March 21 and she spelled out the possible risks.

“So it’s a judgment call at the time. We don’t know everything we need to know. We already know there are some exceedances. We don’t know what levels were out in the system. We don’t have other data at this point, and so from what you’re telling me, that it could affect health, I think the safest thing is to go ahead and tell people not to drink the water until I get more answers,” Guidry said, recounting his discussions then with White.

Guidry said White didn’t disagree with his decision to call for the initial ban to keep young children and pregnant women from drinking the water.

White, who reiterated her view of the slight risks Tuesday, agreed with Guidry’s decision. She said the federal standard, which is enforceable by law, is designed for state health officials to make the kind of moves Guidry made to ensure residents stop drinking tainted water.

“He was absolutely right because there were a lot of unknowns,” said White, senior associate dean of the Tulane School of Public Health and Tropical Medicine.

At the same time, she said, those drinking water limits don’t mean health effects are certain to happen as soon as they are exceeded.

“These are regulatory standards that are meant to protect people. They are not predictive of what will happen. We can’t predict down to that small of an amount,” White said.

Donaldsonville Mayor Leroy Sullivan said Tuesday that residents have gone back to using the water after DHH lifted its ban Saturday.

Sullivan, who declared a state of emergency last week as city and parish officials distributed bottled water to residents, said that while he accepts White’s view on the risk potential, unless other information calls it into question, he also thinks Guidry made the right call.

“I think it is better to be overly cautious than to try to minimize it and saying it’s not a big deal,” Sullivan said.

After calling for young children and pregnant woman not to drink the water March 22, Guidry expanded the ban to all residents March 23 due to a drop in disinfection levels. Guidry had ordered Peoples Water to stop using chlorine dioxide and switch to another method.

EPA Region 6 spokesman Joe Hubbard said he had nothing to add regarding Guidry’s comments Tuesday about EPA’s involvement in the Peoples Water investigation.

The EPA has previously said only that their scientists were talking with DHH officials about the water problems in Donaldsonville but that DHH had the lead.

DHH officials have said they downloaded data from Peoples Water’s testing equipment showing the company found water at its Donaldsonville treatment plant had chlorine dioxide levels as much as 6.5 times greater than the drinking water standard.

The high levels were found for nine days between September and March.

At the same time, DHH officials said, the company, in monthly reports to the agency, said the same water was within standards on those days, in conflict with company’s own internal results.

Company officials, who declined to comment Tuesday, have said the meter may have been in error and that tainted water never reached residents. But they have also acknowledged there were reporting problems over their chlorine dioxide findings.

Under the law, though, even with those exceedances, erroneous or not, the company should have told DHH, conducted sampling to see if the high chlorine dioxide water reached the distribution system and notified the public within 24 hours, DHH officials have said.

Even at this point, Guidry said, state officials still don’t know, and may never know, if water containing high levels of chlorine dioxide or its harmful byproduct, chlorite, ever reached the distribution system because the company has not produced required backup testing.

“There’s just no evidence. I mean what you have is exceedances somewhere in the plant and you don’t know what amount got into the system ’cause I have no measurement in the system to tell me what people were exposed to,” he said.

Guidry said the chlorite byproduct will dissipate, so contemporaneous testing is needed to show if high levels at the plant reached homes and businesses.

State officials also can’t say for sure that Peoples Water didn’t have high chlorine dioxide levels at its plant before September.

Guidry said that in September, Peoples Water began using a new EPA-approved chlorine dioxide meter that stores data as a extra check on reported test findings.

DHH downloaded all the data from September to the present but does not have that kind of backup information before September.

“I think the issue here is technology captures the data and you have to explain what the data means, and before that, we depended totally on self-reporting,” Guidry said.

He said the meter, which many other companies use, has particular testing and reporting requirements and had a learning curve that could have led to some “user issues.”

He said he may have been able to accept a couple instances of out-of-character results if they were reported and explained.

“But six months of no reporting is hard to explain,” Guidry said.

Mayor Sullivan said people in Donaldsonville want to know what happened and why Peoples Water found one thing and told DHH something else.

“We are waiting patiently to get the answers to all of those questions,” he said.

Follow David J. Mitchell on Twitter, @NewsieDave.