Think about what you like to wear on the weekend . There’s a good chance that you like to put on a pair of blue jeans. At any moment, about half of the world’s population is wearing jeans. But according to a new study, our love for jeans may be bad for Earth. Denim （牛仔布）might be putting some sea animals in danger. Every time we wash our jeans, tiny bits of denim will flow out of our washing machines, down into the world’s 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, in the process of making jeans, denim is treated with many types of man-made chemicals. Some improve its durability （耐用性）and feel; others give jeans their blue color. 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）they had collected . It is feared that the harmful chemicals in denim have spread far and wide. Scientists aren’t yet sure how these chemicals might harm animals. In the study, the scientists also washed jeans to see how many bits of denim each pair would drop per wash. The answer was frightening: About 50,000. Not all of them make their way into the environment. Wastewater treatment 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 . As a result, a large amount of denim waste still gets into the environment. 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 having worn them only a couple of times.