Canelectricitycausecancer?Inas-考网

Canelectricity cause cancer?In a society that literally runs on electric power,the very idea seems preposterous.But for more than a decade,a growing band ofscientists and journalists has pointed to studies that seem to link exposure toelectromagnetic fields with increased risk of leukemia and other malignancies.The implications are unsettling,to say the least,since everyone comes intocontact with such fields,which are generated by everything electrical,frompower lines and antennas to personal computers and micro-wave ovens.Becauseevidence on the subject is inconclusive and often contradictory,it has beenhard to decide whether concern about the health effects of electricity islegitimate——or the worst kind of paranoia.

Now thealarmists have gained some qualified support from the U.S.EnvironmentalProtection Agency.In the executive summary of a new scientific review,released in draft form late last week,the EPA has put forward what amounts tothe most serious government warning to date.The agency tentatively concludesthat scientific evidence“suggests a casual link”between extremely low-frequencyelectromagnetic fields--those having very long wave-lengths--and leukemia,lymphoma and brain cancer,while the report falls short of classifying ELFfields as probable carcinogens,it does identify the common 60-hertz magneticfield as“a possible,but not proven,cause of cancer in humans”.

The report is no reason topanic--or even to lost sleep.If there is a cancer risk,it is a small one.Theevidence is still so controversial that the draft stirred a great deal ofdebate within the Administration,and the EPA released it over strongobjections from the Pentagon and the White House.But now no one can deny thatthe issue must be taken seriously and that much more research is needed.

At theheart of the debate is a simple and well-understood physical phenomenon:Whenan electric current passes through a wire,it generates an electromagneticfield that exerts forces on surrounding objects.For many years,scientistsdismissed any suggestion that such forces might be harmful,primarily becausethey are so extraordinarily weak.The ELF magnetic field generated by a videoterminal measures only a few milligauss,or about one-hundredth the strength ofthe earth's

ownmagnetic field,the electric fields surrounding a power line can be as high as10 kilovolts per meter,but the corresponding field induced in human cells willbe only about 1 millivolt per meter.This is far less than the electric fieldsthat the cells themselves generate.

Howcould such minuscule forces pose a health danger?The consensus used to be thatthey could not,and for decades,scientists concentrated on more powerful kindsof radiation,like X-rays,that pack sufficient wallop to knock electrons outof the molecules that make up the human body.Such“ionizing”radiations havebeen clearly linked to increased cancer risks and there are regulations tocontrol emissions.

Butepidemiological studies,which find statistical associations between sets ofdata,do not prove cause and effect.Though there is a body of laboratory workshowing that exposure to ELF fields can have biological effects on animaltissues,a mechanism by which those effects could lead to cancerous growths hasnever been found.

ThePentagon is far from persuaded.In a blistering 33-page critique of the EPAreport,Air Force scientists charge its authors with having“biased the entiredocument”toward proving a link.“Our reviewers are convinced that there is no suggestion that(electromagnetic fields)present in the environment induce or promote cancer,”the Air Force concludes.“It is astonishing that the EPA would lendits imprimatur on this report.”Then Pentagon's concern is understandable.There is hardly a unit of the modern military that does not depend on the heavyuse of some kind of electronic equipment,from huge ground-based radar towersto the defense systems built into every warship and plane.

Whatdo you think ordinary citizens may do after reading the different arguments?查看材料