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TOXIC WATER: Water contaminated with chemicals from dyeing blue jeans spills into a river in Lesotho, a small nation in Africa.
STANDARDS
NGSS: Core Idea: PS1.B
CCSS: Literacy in Science: 3
TEKS: 6.2A, 6.5D, 7.2A, 8.2A, 8.5E, C.2E, C.4A
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Greener Jeans
Can researchers find a way to make jeans blue without using toxic chemicals?
ESSENTIAL QUESTION: How might clothing production affect the environment?
Blue jeans are some of the most popular clothing items of all time. But manufacturing them comes with a hidden cost: Many of the chemicals used to produce jeans’ characteristic blue color are toxic and can end up polluting the environment. Now scientists are working on a greener way to make jeans blue with help from an unusual source—bacteria.
Blue jeans are some of the most popular clothing items of all time. But making them has a hidden cost. Many of the chemicals that give jeans their well-known blue color are toxic. They can pollute the environment. Now scientists are working on a greener way to make jeans blue. They’re getting help from an unusual source—bacteria.
TOXIC DYE
Blue jeans were originally colored with natural indigo, a blue dye derived from several tropical plants, including Indigofera tinctura. Eventually, chemists developed a synthetic, or artificial, version of indigo to keep up with the high demand for the dye. “Synthetic indigo is very useful for industry, but it’s made in an unsustainable way,” says Tammy Hsu, a biochemist at the University of California, Berkeley.
At first, blue jeans were colored with natural indigo. This blue dye comes from several tropical plants, including Indigofera tinctura. Later, chemists made a synthetic, or artificial, version of indigo. This helped to keep up with the high demand for the dye. “Synthetic indigo is very useful for industry, but it’s made in an unsustainable way,” says Tammy Hsu. She’s a biochemist at the University of California, Berkeley.
Researchers added traits of indigo-producing plants to bacteria and used it to dye jeans blue.
Synthetic indigo is not soluble—able to dissolve—in water. To make synthetic indigo soluble so it can attach to fabric, jean manufacturers must mix it with harsh chemicals (see Making Jeans Blue). Unfortunately, jean factories overseas sometimes release water tainted by these chemicals into lakes and streams during the dyeing process. The pollution puts people and wildlife at risk.
Synthetic indigo isn’t soluble, meaning it doesn’t dissolve in water. Jean manufacturers must mix it with harsh chemicals. This makes the dye soluble so it can attach to fabric (see Making Jeans Blue). Water that contains these chemicals is used during the dyeing process. Sadly, jean factories in other countries sometimes release this water into lakes and streams. The pollution puts people and wildlife in danger.
Getting your jeans that perfect blue color is far from an eco-friendly process. Check out the color chemistry behind your favorite pair of pants.
Chemists produce synthetic indigo in a lab using petroleum products.
The synthetic indigo is mixed with a base (opposite of an acid) and harsh chemicals like sodium dithionite.
The chemicals react with the indigo to make it water soluble, allowing the indigo to stick to the yarn. After dyeing, the yarn has a yellowish color.
The indigo oxidizes—combines with oxygen (O2)—in the air, causing another chemical reaction that turns the yarn blue.
The blue yarn is woven into denim that’s cut and sewn into blue jeans.
BACTERIAL BLUE
COURTESY OF TAMMY HSU
SCIENCE IN ACTION: Biochemist Tammy Hsu looks at a beaker of indigo dye.
Recently, Hsu and her colleagues found a way to bioengineer a less toxic substitute for synthetic indigo. They tweaked the DNA, or hereditary material, of E. coli bacteria to produce a chemical found in I. tinctura plants. This chemical can dye cloth blue when mixed with an enzyme—a substance that helps speed up chemical reactions.
It’s too soon to tell whether this indigo alternative could someday replace the synthetic version. “The next step is to see if we can make a pair of jeans using our method,” says Hsu. Until then, your blue jeans will still be blue—just not entirely green.
Not long ago, Hsu and her co-workers found a way to bioengineer a less toxic dye. It could take the place of synthetic indigo. They changed the DNA, or hereditary material, of E. coli bacteria to make a chemical found in I. tinctura plants. This chemical can dye cloth blue when mixed with an enzyme. That’s a substance that helps speed up chemical reactions.
It’s too soon to tell if this new dye could someday replace synthetic indigo. “The next step is to see if we can make a pair of jeans using our method,” says Hsu. Until then, your blue jeans will still be blue. They’re just not completely green.
CORE QUESTION: Using what you learned in the article, explain in your own words what bioengineering is.
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