英语访谈节目:危险化学品六价铬污染美国饮水系统

JEFFREY BROWN:And now to part two of our investigative look at the safety of America's drinking water.

Science correspondent Miles O'Brien reports on the toxic chemical made famous in the movie "Erin Brockovich," its potentially harmful effect on human cells, and the agency charged with regulating it.

His report is the result of a partnership with the Center for Public Integrity.

AMIE HOLMES, University of Southern Maine: There is some lead chromate in here and some zinc chromate.

MILES O’BRIEN:At the Wise Laboratory at the University of Southern Maine, they are very wise indeed about a widely used heavy metal that gives millions of Americans shiny bumpers, vivid paint, and, possibly, cancer. It is hexavalent chromium, or chromium 6.

AMIE HOLMES:As you can see, there's a lot of different colors to chromium.

MILES O’BRIEN:Yes.

And there are many shades of gray to the story, right?

AMIE HOLMES:Yes.

MILES O’BRIEN:Chromium 6 was also used as a coolant here at a natural gas pumping station owned by Pacific Gas & Electric in Hinkley, Calif. The utility dumped 26 tons of the chemical into unlined holding ponds in the 1950s and '60s. It leeched into the groundwater, poisoning the wells.

The health fallout and the David and Goliath legal battle against PG&E became the basis for the 2000 movie "Erin Brockovich" starring Julia Roberts.

JULIA ROBERTS, Actress: People are dying, Scott. You have got document after document here. Right under your nose, it says why, and you haven't said one word about it. I want to know how the hell you sleep at night.

MILES O’BRIEN:Hinkley is not alone.

Public utility testing records reveal more than 70 million Americans are now drinking tap water tainted by chromium 6.

AMIE HOLMES:This is what happens when the cells are exposed to chromium.

MILES O’BRIEN:Wise researcher Amie Holmes showed me what scientists can say for certain about the link between chromium 6 and cancer. These are slides of human lung cells in the midst of replicating, a process called mitosis.

In normal cells, there are two centrosomes, the yellowish-white dots. They search and capture 46 chromosomes each, then pull apart, making an identical daughter cell.

AMIE HOLMES:You want to make sure that each cell has the same amount of DNA in each.

MILES O’BRIEN:Take a look at these lung cells exposed to chromium 6. Notice the yellowish-white centrosomes? Instead of two, there are four.

AMIE HOLMES:What's going to happen, and when this cell divides, instead of dividing into two, it could potentially pull the DNA into four or it's going to unevenly separate the DNA.

MILES O’BRIEN:With four centrosomes, it's not going to end well.

AMIE HOLMES:It's not going to end well.

MILES O’BRIEN:Scientists call this centrosome amplification. They suspect chromium 6 changes the chemistry of the proteins in our cells, and that creates the extra centrosomes.

The resulting defective cells that survive are what we call cancer.

JOHN WISE, University of Southern Maine: Yes, it causes cancer. That's the biggest health concern.

MILES O’BRIEN:We know that for sure?

JOHN WISE:Right. Yes.

MILES O’BRIEN:There's no doubt about that?

JOHN WISE:There's no doubt about it. It's considered a human carcinogen by all the major regulatory agencies in the world.

MILES O’BRIEN:So, what's in here?

JOHN WISE:Cells.

MILES O’BRIEN:Lab director John Wise can say that with certainty chromium 6 is carcinogenic when inhaled, occupational exposure in factories. But when the chemical is ingested in the stomach, it is a murkier picture.

Sandy Wise offered me a demonstration. Water that is heavily contaminated with chromium 6, like this, turns bright yellow. Now watch what happens when she adds vitamin C, which is acidic, not unlike the human stomach.

SANDY WISE, University of Southern Maine: So, you can see it's starting to change color.

MILES O’BRIEN:The water turns green as the chromium 6 is transformed into trivalent chromium, or chromium 3.

Our cells don't absorb chromium 3 as they do chromium 6. So the human stomach offers a natural antidote to chromium 6 in water. But what are the limits of this alchemy?

John Wise says we can't say for certain.

JOHN WISE:There's just holes in the data, so there's a lot that we don't know.

MILES O’BRIEN:What more science needs to be done?

JOHN WISE:I don't think we have enough studies to tell us whether—clearly whether it's a drinking water carcinogen or not.