Sept. 15, 2011 -- In less than 24 hours, apple juice has gone from a subject few had opinions about to a source of controversy because of Dr. Mehmet Oz's comments about arsenic in the juice on "The Dr. Oz Show" Wednesday.

"I want everyone out there who's already purchased apple juice to keep drinking it," Oz said tonight on "World News with Diane Sawyer," where he discussed the issue with ABC News health and medical editor Dr. Richard Besser.

"I don't have any concerns about it in the short run," Oz said. "And the levels that we have detected in the samples that we have looked at are not high enough to make me concerned about short-term issues. My bigger concern is over the next decade or next generation, especially as children grow. Is it possible that because of the changes in where we're getting our food, specifically getting our apples from overseas, we may be exposing our kids to needlessly high levels of arsenic?"

Besser said he had fewer concerns.

"You know, in listening to what Mehmet said there, I think he raises really important issues," said Besser. "I think we have to be concerned about our food supply coming from other countries. And we need to monitor it. But when I look at the evidence of what was in those samples of apple and how the study was done, it doesn't raise concerns to me ... about apple juice right now. ... The disagreement I had was in pointing to apple juice, which plays to the heartstrings of a lot of parents, and saying that this is the demon food. And that was my read on it, and that's why I was upset."

Arsenic can be found in lots of places, Besser said, and the important thing is to continue to test and monitor food so people are consuming acceptable levels of it.

"It's in the air we breathe, it's in the soil we walk on, it's in the water we drink," Besser said. "The issue, and it's an issue that Mehmet raises, is how much and over what period of time" people consume arsenic.

In a spirited showdown hours earlier on "Good Morning America," Besser confronted Oz on what he called "extremely irresponsible" statements.

"Mehmet, I'm very upset about this. I think that this was extremely irresponsible," Besser said. "It reminds me of yelling fire in a movie theater."

"I'm not fear-mongering," Oz fired back. "We did our homework on this risk."

Oz later added on "World News with Diane Sawyer" that the purpose of the show was not to alarm parents, but rather to begin a dialogue on the topic.

"I don't want parents panicking over this," he said. "What I want to have is a conversation so we can bring clarity to this and make it safer."

Oz certainly sparked a debate. Juice manufacturers, government regulators and scientists all weighed in, calling the results of what the show described as an "extensive national investigation" misleading and needlessly frightening to consumers.

In a statement Friday, the U.S. Food and Drug Administration said, "There is no evidence of any public health risk from drinking these juices."

"The FDA reached out about five days ago and said they disagreed with our findings. They called them irresponsible, which I respect," said Oz. "Their job is to go out there and to try to make the world safer for us, and if they think that we're doing a disservice, they should call that to our attention."

According to the "Dr. Oz Show's" website, a laboratory tested "three dozen samples from five different brands of apple juice across three American cities" and compared the levels of arsenic to the limits of arsenic for drinking water set by the Environmental Protection Agency. It found 10 samples of juice with arsenic levels higher than the limits for water.

The show's experiment tested samples of apple juice made by Minute Maid, Apple and Eve, Mott's, Gerber and Juicy Juice.

The show's test results did not a surprise Don Zink, the senior science advisor for the FDA Center for Food Safety and Applied Nutrition. He said the FDA has known for many years that certain foods contain very small amounts of arsenic.

"Arsenic in apple juice is nothing new to us," Zink said. "We have 20 years of data from testing apple juice for arsenic, and all the data say there's simply not a health concern."

Scientists say arsenic is a naturally occurring substance, and is so abundant in the Earth's soil that it often ends up in many of the foods we eat. However, experts make a distinction between this abundant organic arsenic, which is harmless, and inorganic arsenic, which can be found in some pesticides and other chemicals.

"It is the inorganic form of arsenic in the environment that is toxic, and measuring total arsenic is not informative," said Aaron Barchowsky, a professor of environmental health at the University of Pittsburgh who has studied the toxicity of arsenic in drinking water for 15 years.

Oz disagreed that the difference between organic arsenic and inorganic arsenic has been substantiated.

"We don't know enough about organic arsenic to say whether it is safe or not. The FDA has forced companies to pull organic arsenic off the market for fear there might be problems arising from it," he said.

A producer for the "Dr. Oz Show" said its apple juice tests measured total arsenic levels and did not distinguish between organic and inorganic arsenic.

The FDA conducted its own tests of the apple juice investigated by the "Dr. Oz Show." In some of the very same lots of juice tested for the show, the FDA reported finding very low levels of inorganic arsenic -- 6 parts per billion at most, even lower than the 10 parts per billion recommended by the EPA as a safe level for drinking water.

The FDA also recommends 10 parts per billion as a safe level of arsenic for bottled water, but sets 23 parts per billion as the maximum for other foods. The standards are different mainly because of differences in testing methods for water and food products like fruit juices, as well as differences in the kinds of arsenic found in each.

The "Dr. Oz Show" warned consumers to be particularly wary of juice concentrates that are imported to the U.S. from countries including China, where environmental protections against arsenic-containing pesticides and chemicals are lax or nonexistent.

Zink said the FDA tests apple juice products at the U.S. borders, and these products must meet the legal requirements regarding arsenic levels before they can be sold to consumers.

The EPA has banned pesticides containing inorganic arsenic in the U.S. since the 1970's.

The "Dr. Oz Show's" apple juice alert may be fruitless in the eyes of some scientists. But for others, it raises important questions about how much people should know about the food they eat.

Dr. Art Caplan, a bioethicist at the University of Pennsylvania, said consumers have the right to know what is in their food. But he said not all information about food is relevant to a person's health.

"There's all kinds of stuff that's out there," Caplan said. "The job of the media, including Dr. Oz, is not just to tell people what's in their food, but to tell them what they should or should not be concerned about."

Dr. Henry Miller, the founding director of the FDA's Office of Biotechnology, noted that just because a substance like arsenic is present in foods doesn't mean that it is toxic.

"Unless there is evidence that a substance is present at sufficient exposures and levels to cause harm, warnings about its presence in food is irresponsible alarmism," Miller said.

And even Oz said that he as a parent "would not take apple juice out of my kids' containers now" during his GMA appearance.

"When we asked the FDA for information on how to determine safe levels of arsenic in apple juice, they made us file a freedom of information request," Oz said. "We just want to have the conversation, and we've been trying to make this conversation happen."

ABC News' Dan Childs and Ben Forer contributed to this report.