研究生英语精读教程第三版上unittwo.doc

Unit twoText:Cancer & Chemicals-Are We Going Too Far?Marla ConeLast year, California governor George Deukmejian called together many of the states best scientific minds to begin implementing Proposition 65, the states Safe Drinking Water and Toxic Enforcement Act. This new law bans industries from discharging chemical suspected of causing cancer (carcinogens) or birth defects into water supplies. Some claim it will also require warning labels on everything that might cause cancer.A day of esoteric science and incomprehensible jargon was predicted. But Bruce Ames, chairman of the department of biochemistry at the University of California at Berkeley, had plans to liven the proceedings.Walking into the room, Ames looked like the quintessential scientist: wire-rimmed bifocals, rumpled suit, tousled hair and a sallow complexion that showed he spent more time in his laboratory than in the California sunshine.As someone intoned about the mechanisms of carcinogenesis, Ames began to interject his own views.The whole world is chock-full of carcinogens, Ames declared.“ A beer, with its 700 parts per billion of formaldehyde and five parts per 100 of alcohol is a thousand times more hazardous than anything in the water. If you have beer on your breath, does that mean you have to warn everyone who comes within ten feet of you? In an era when headlines shout about the latest cancer scare, Ames has a different message: the levels of most man-made carcinogens are generally so low that any danger is trivial compared with the levels of natural carcinogens.Ames is not a quack. At age 59, he is one of the nations most respected authorities on carcinogenesis. His resume is packed with honors, including the Charles. Mott Prize from the General Motors Cancer Research Foundation, one of the most prestigious awards in cancer research, and membership in the National Academy of Sciences.Even his critics say the Ames testhis simple, inexpensive laboratory procedure that helps determine whether a substance might cause canceris a remarkable achievement.But Ames slaughters sacred cows. Hes taking on the environmental movement, which some have called the single most important social movement of the 20th century. In April 1987, for instance, he and two colleagues, Renae Magaw and Lois Swirsky Gold, published a report in Science magazine that ranked various possible cancer risks.Based on animal tests of nearly 1,000 chemicals, the data show that daily consumption of the average peanut-butter sandwich, which contains traces of aflatoxin (a naturally occurring mold carcinogen in peanuts), is 100 times more dangerous than our daily intake of DDT from food, and that a glass of the most polluted well water in the Silicon Valley is 1,000 times less of cancer risk than a glass of wine or beer is.Hes not advising people to stop consuming peanut-butter, beer and wine. What hes saying is that most cancer risks created by man are trivial compared with everyday natural risks, and its not clear how many of these are real risks. Both types distract attention from such enormous risk factors as tobacco.Amess cancer research began about 25 years ago over a bag of potato chips. Ames, then conducting research for the National Institutes of Health in Maryland, was reading the ingredients on the bag. It struck him that no one knew what each chemical did to human genes, and there was no easy way to find out.At that time, scientists testing for carcinogenicity had to set up time consuming and costly lab experiments on rats and mice. Armed with the knowledge that bacteria are sensitive to substances that cause mutation, and that carcinogens were likely to be mutagens, Ames developed a carcinogen test using bacteria. The Ames test was hailed as a major scientific development and is now used worldwide.One day in 1974 Ames, now teaching at Berkeley, suggested that some students test various household products. To his surprise, many common hair dyes tested positive, as did a flame retardant used in childrens pajamas. Almost overnight, Ames became a hero of environmentalists when his findings led to new regulations and bans on certain chemicals. For the next decade public concern over carcinogens continued to rise. Then, Ames says, I started realizing something wasnt right. Too many natural substances also tested positive as carcinogens or mutagens: fruit juices, brown mustard , celery , parsley .In fact, about half of all chemicals tested by Amesboth natural and man-madeturned out to be potentially carcinogenic when given in enormous doses to rats and mice. Ames at first assumed he had erred with his test. He hadnt. His error had been making the common, but naive, assumption that only man-made chemicals could be dangerous. Why assume nature is benign? he now says.The campaign supporting Californias Proposition 65 convinced Ames that he had a duty to explain this to the public. When people said certain birth defects were caused by a part per billion of something in the water, I thought it irresponsible, he says. Its just playing with peoples fears. You can always find a part per billion of something in the water.In testimonybefore a California senate committee, Ames noted that tap water, for instance, contains the carcinogen chloroform at about 83 ppb due to chlorination.But coffee contains two natural carcinogens at about 4,000 ppb each, while human blood averages 3,000 ppb of formaldehyde from normal metabolism. Some people assume Ames is a stooge for the chemical industry, which he is not. He does no consulting for the chemical, drug or food companies, or for law firms. And he accepts no grants from business.Environmentalists reject Amess arguments, saying that we are obligated to keep the total