21. Think about what you like to wear on the weekend. You probably like to put on a pair of blue jeans. At any moment, about half of the world's people are wearing jeans. But according to a new study, our love for jeans may be bad for Earth. Denim(牛仔布) may be putting some sea animals in danger.
Every time we wash our jeans, very small bits of denim will flow out of our washing machines, down into the rivers, lakes and oceans.
You might wonder:Isn't denim made of cotton, a natural material?How can it become a danger to nature?Well, when people make jeans, denim is treated with many kinds of man-made chemicals (化学物质). Some improve its durability. A pair of jeans may be worm for many years. Others give jeans their blue color. It makes jeans fashionable.
Scientists studied the Great Lakes in America and the Arctic Ocean in northern Canada. They found denim waste in all of the samples(样本). In the study, the scientists also washed jeans to see how many bits of denim each pair would drop each time to wash. The answer was terrible:About 50, 000. Not all of them make their way into the environment. Some good plants hold back 83 to 99 percent of them. This may sound pretty good. However, one percent of 50, 000 bits are still 500 per wash. Now think about the number of jeans around the world and the times each of them gets washed.
Does this mean we shouldn't wear jeans?Probably not. "We need to buy fewer jeans and only wash them when we truly need to do it, says Sam Athey, one of the scientists. "You don't need to wash your jeans after wearing them only several times."