Three stories have hit the news lately concerning three corporations that have done — or may have done — serious environmental harm. They are coping with the situation in very different ways. Taken together, the stories suggest an odd combination of hope and cynicism. There are signs of honesty, good will, real learning. But the damage is great, and the learning is slow.

Story No. 1 is the latest development in a decades-long saga involving General Electric. In the 1940s, two GE capacitor plants in Hudson Falls and Fort Edward, N.Y., started using the new chemicals called PCBs and spilling them lavishly into the Hudson River. Thirty years later the nation adopted a Clean Water Act, and PCBs were found to be bad news. They last almost forever in the environment, they concentrate in animal and human tissue, they are linked with cancer and reproductive failure.

By the time PCBs had been fully indicted, millions of pounds of them had sunk into the mud of the Hudson for 200 miles downstream from the GE plants. There followed a 25-year battle about how the river should be cleaned up and who should pay for it. GE fought in the way we have unfortunately come to expect from corporations. Denial, obfuscation, leaning upon politicians, threatening to pull 55,000 jobs out of the state if the company were held liable.

Now the EPA has ordered PCB-laced mud to be dredged out of the Hudson at a cost to GE of a billion or so dollars. GE is objecting, saying the river has safely covered over the contaminated sediment. The company has a point. Disturbing the mud could churn up more damage than leaving it. Once dredged it would still have to be put somewhere. But the EPA has a point too. A storm or flood could stir up old sediment, and meanwhile it slowly percolates down to the sea.

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The problem for GE is that, though it may or may not be credible now, its past behavior has destroyed its credibility in this matter. Negative legacies can last a long time.

So here’s a better story. On May 11, William C. Ford, chair of the Ford Motor Company (and great-grandson of founder Henry Ford), told his stockholders that sports utility vehicles are gross polluters and dangerous on the road. Ford, of course, makes the biggest road hog of all, the Excursion, which weighs twice as much as a Grand Cherokee and gets 10 miles to the gallon. SUVs, said Ford, are three times more likely than regular cars to kill occupants of other cars in a crash. And their own occupants are not safe either. Death rates in SUVs are as high as in cars, because SUVs tend to roll over and to crumple.

Breathtaking confession. Maybe the era of corporate denial is passing. Indeed, Ford warned that if car companies don’t fix the problems of SUVs, their reputations might someday fall to the level of tobacco companies.

He talked of fixing the trucks, however, making them safer and more fuel-efficient, not ceasing to make them. Honesty, yes; sacrifice of profit for public safety, not yet. But in the third story, a company goes one step further, phasing out a problem product by its own decision.

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The company is 3M, which prides itself on its environmental record. The questionable product is an organic fluorine compound of many uses. Most of us use it to repel stains and call it Scotchgard. Three years ago, the company was doing a routine blood test of its workers, part of its ongoing concern for workers’ health. For comparison with people who do not work in a chemical factory, it also tested blood from a commercial blood bank.

It found tiny amounts of Scotchgard in the general public’s blood. Utterly surprised, the company looked further and found its trademark organofluorines in people and wildlife all over the globe. The only place it wasn’t found was in the stored blood of Korean War soldiers — samples taken before Scotchgard was invented.

Another immortal human-made chemical. But does it do harm? There was no evidence of any, until 3M fed huge doses to rats and monkeys. The monkeys had convulsions. The rats’ offspring all died.

The company informed the EPA promptly of these findings. Then, after months of soul-searching, it announced that it will stop making Scotchgard by the end of this year. That means a loss of $500 million in annual sales — about 3 percent of total revenues — and a threat to jobs in three factories. It was a decision that EPA may have forced at some point. The company might have been able to fight it off, but its voluntary phaseout saved everyone years of struggle and expense.

William Ford has received praise for his honesty, and 3M even more praise for its phaseout. Katherine E. Reed, 3M’s director of environmental technology, set a standard for all companies by saying, “We believe that our responsibility for materials continues into disposal. It’s a concept we call life-cycle management.”

It’s wonderful to hear even one company say that. We would hope to hear more. Meanwhile, PCBs sit in the Hudson, SUVs assault our lungs, our climate, and our safety, and molecules of stain repellent circulate through our veins. Negative legacies can last a long time.