At first glance, the precautionary principle sounds an awful lot like something your mom might say: If something seems dangerous, don't do it. Back off. Be careful. Look before you leap. Better safe than sorry.

The precautionary principle would appear to be compellingly commonsensical. If your arm hurts when you pinch it, stop pinching it. If you're dumping chemicals into a river and fish are dying, stop dumping.

But what if you can't actually prove -- with any scientific certainty -- that the chemicals are indeed culpable? What if those chemicals are the unavoidable byproducts of producing something undeniably beneficial, such as food or medicine?

Precautionary principle proponents don't blink. If an activity threatens harm to the environment or human health, they say, it should be stopped or changed, even if causative proof of that harm isn't fully established.

"We understand the difficulty of tracking cause and effect. We understand the limitations of science," said Carolyn Raffensperger, executive director of Science and Environmental Health Network, a think tank based in Ames, Iowa, and major proponent of the principle.

"The problem is that many environmental consequences, intended or not, are immediate. Change is happening faster than ever, and we can't always wait for the scientific proof. We think that if you can prevent a problem by taking precautionary action, you should do so, even if the evidence isn't all there."

To which critics of the precautionary principle howl in dismay. Such thinking, they assert, ignores the complexities of real world life and defies more than 300 years of scientific reasoning. The principle, critics contend, plays upon unfounded emotions and fears, not empirical fact.

"The principle is anti-science because it says you should make decisions based not on what you know, but what you don't know," said Elizabeth Whelan, president of the American Council on Science and Health (ACSH), a consumer advocacy group headquartered in New York City. "It says, 'We don't understand everything out there, so let's err on the side of caution.' On the face of it, that sounds fine. But if you followed that philosophy in life, nothing would get done."

The case for

Look around, said Raffensperger. Hazards to your health and the environment abound. Sometimes the threat and its source are obvious and the remedy clear: Cars produce smog. Smog causes respiratory problems. Exhaust emissions from cars need to be reduced, if not eliminated.

But often the causal chain is more complicated, harder to follow. There may be conflicting interests. It may not be possible, using existing scientific standards, to make a conclusive connection, and thus compel action.

The precautionary principle was originally devised as a legal concept by the environmental movement of the 1970s. Over time, it has increasingly been incorporated into law, particularly in Europe and in various international treaties, from the Maastricht Treaty establishing the European Union to the United Nations' Rio Declaration on Environment and Development in 1992. For nations like Sweden and Denmark, the principle is an integral part of their national policy on the environmental and public health.

The precautionary principle is considerably less influential in the United States. It is currently not expressly mentioned in federal law or policy, though at the state and local level, a number of government entities are beginning to consider it. For example, officials within the California Environmental Protection Agency are currently debating whether to overtly incorporate the precautionary principle into regulations likely to affect future legislation and policy.

"It's a big, contentious issue," said Diane Takvorian, executive director of the San Diego-based Environmental Health Coalition, who is involved in the process.

The argument, of course, boils down to what constitutes proof and an undeniable call for action.

"Tobacco is an obvious example," said Raffensperger. "We knew in the 1940s that tobacco was deadly. We knew about the deleterious effects of tar and nicotine. We had all of this information and yet nobody could prove in a court of law that tobacco caused lung cancer because science hadn't yet found the biological mechanism, the precise explanation of how smoking caused disease.

"As a result, the tobacco industry was able to deny linkage for years by insisting there wasn't conclusive proof, that more studies were needed. And all the while, people smoked and died."

The precautionary principle, Raffensperger said, provides a remedy. It urges action -- or inaction -- when logic suggests either is the prudent course.

For example, groups representing veterans of the first Persian Gulf war contend that tens of thousands of U.S. troops were exposed, often unknowingly and without adequate protection, to chemical warfare agents, radioactive materials and various toxins during service in Kuwait and Iraq in 1990 and 1991.

Many of these soldiers have since reported an assortment of maladies, broadly dubbed "the Gulf War syndrome." Veterans groups have demanded aggressive, comprehensive action, both in expanded health care and in reducing any continuing threat to servicemen in the region. The reaction from U.S. military and political leaders has been mixed. Despite numerous studies, independent and government researchers say they have not found conclusive evidence that military service in the Gulf is linked to the various illnesses.

The ongoing debate maddens principle proponents.

"I think we're in a unique time," said Raffensperger. "Events like the anthrax scare and SARS are showing us that we need to learn how to better connect the dots. Why are animal and plant species dying off? Why are rates of learning disabilities, asthma and some kinds of cancer rising? We can't necessarily wait for science in all its splendor to prove connections after the fact."

Yet, Raffensperger and others insist the precautionary principle promotes science by encouraging the search for alternatives to real or perceived harmful practices and products.

"To people who say we're anti-science, I say baloney. Germany has used the principle to force technological innovation in its most polluting industries. Why not use science to help us evaluate lots of alternatives? Why remain stuck in a 'don't ask, don't tell about harm' approach until it's too late?

"We are not afraid of the unknown, but we do want to reduce the unknown by getting people to broaden their thinking beyond the very narrow constraints of scientific cause-and-effect. We're not trying to push the clock back on science. We're trying to help it catch up."

Takvorian, a long-time advocate of the precautionary principle, offers this case in point:

For more than a decade, she said, local environmentalists had complained that a chrome-plating operation in Barrio Logan was releasing dangerous amounts of toxic chemicals into the surrounding residential neighborhood. As a result, they said, children in the area experienced abnormally high levels of asthma and other ailments.

"Common sense tells you that if you spew a known carcinogen onto homes right next door, bad things will happen," said Takvorian.

Takvorian and others repeatedly asked for local or state officials to conduct scientific tests of the facility, but nothing happened for years. Finally, the San Diego County Air Pollution Control District arranged a monitoring program to measure airborne levels of Chromium 6, a known carcinogen. Officials found dangerous amounts, said Takvorian, but the levels exceeded all established risk models, leaving the researchers unable to draw scientifically valid conclusions. It took another monitoring effort last year by the state before the facility was finally shut down.

"Everyone had a gut feeling this was not a good place," said Takvorian. "We tried hard to get the science to back that feeling up, but in the absence of hard data, you have to make a judgment.

"The state spent close to a million dollars, and it took more than a decade to resolve this problem. If somebody had simply taken some precautionary measures earlier -- relocating the company or buying pollution control equipment -- we could (have) avoided all of this and the community would have been healthier earlier."

The case against

Perhaps, but Henry Miller remains no fan of the precautionary principle -- at least not in its broadest terms.

A research fellow at the Hoover Institution, a conservative think tank at Stanford University, Miller believes the precautionary principle abuses science and, as often as not, causes more problems than it solves.

"What I see is a failure to make legitimate comparisons," said Miller. Consider, he said, "the pseudo-crisis over monarch butterflies."

In 1999, a Cornell University study suggested that pollen from Bt -- or genetically modified -- corn might be killing or stunting the growth of migrating butterflies that fed upon it.

"The precautionary principle says if these products kill beneficial insects, then maybe we ought not to use them," said Miller. "In reality, with monarchs, the research was full of half- truths. The initial finding was based on laboratory experiments with monarch larvae fed huge amounts of pollen from Bt corn, which makes the corn more resistant to pests.

"It turned out that the findings did not translate to the field. In areas with vast acreages of Bt corn, there were actually more monarch butterflies. My point is that advocates of the precautionary principle are not making real-world comparisons. They're thinking in terms of some sort of utopian never-never land. They're not comparing the use of Bt corn to using corn that requires spraying with chemical pesticides that kill everything in sight, then wash into waterways."

Whelan at the ACSH agreed.

"I have real problems with consistency and where you draw the line," she said. "Proponents of the principle seem to only focus on things like the levels of synthetic chemicals in food. But all food is made up of chemicals. A potato contains 150 naturally occurring chemicals. Do we stop growing potatoes because they contain trace amounts of naturally occurring arsenic?"

Whelan argues that the precautionary principle wrongly errs on "the side of getting rid of things. It always assumes a worst-case scenario. If there's any perceived risk, it says throw it out. But what about the risks of doing that? What if getting rid of a drug or program or food actually results in different, bigger problems."

She cites as examples current objections to genetically modified foods and stem cell research, both of which promise dramatic social benefits, according to advocates.

Miller, a former regulator with the Food and Drug Administration, complains that precautionary principle advocates want "science to prove a negative, which isn't possible. We should not mistake such advocacy as a good faith effort to protect the environment or public health. It is merely political ideology looking for a new weapon."

Principled debate

And so it goes. Both sides claim reason, logic and science on their side. Principle proponents say their critics are corrupted by excessive commercial interests and preservation of the status quo. Principle opponents counter that the other side is hiding other agendas and ideologies behind the guise of public health and the environment. Both sides predict ultimate victory.

Proponents cite the principle's popularity and increasing utility, especially outside the United States.

Opponents take heart that application of the principle in the United States has indeed been spottier and slower. "I don't see the precautionary principle as being anything more than a fringe idea here," said Whelan.

Only time will tell. The San Francisco Environmental Commission has drafted the principle into a revision of the municipal environmental code, but commission president Randall Hayes is cautious about whether the action will prove wise.

"It sounds great to say, 'Play it safe.' Who's going to be against that? But we'll have to see if the idea actually proves to be a helpful tool. We'll try it out and see if we can learn some lessons."

Mom, one suspects, couldn't have said it better.

Copyright 2003 Union-Tribune Publishing Company. Used by Permission