It is prized for being vibrant and long-lasting, and was an important cash crop until humans started making synthetic indigo in the early 1900s.

　　靛蓝染料的价值在于它的鲜艳色泽和持久性，它是一种重要的经济作物，到了20世纪早期人类开始生产人造靛蓝染料。

　　Indigo crystals cling easily to the cotton fibres used in jeans and are resistant to laundry detergents, yet flake off slightly with wear-and-tear to yield the sought-after worn-in look.

　　靛蓝水晶容易附着在用于制作牛仔裤的棉纤维上，而且经得住洗衣液的洗涤，但却会随着磨损而脱落，从而产生人们追求的磨损效果。

　　Some four billion denim garments are produced every year, the vast majority indigo-tinted, said the study authors, and warned of "a serious sustainability problem".

　　研究报告的作者们说，每年生产的牛仔服装大约有40亿件，绝大多数都是靛蓝色的。他们还警告说“这是一个严重的持续性问题”。

　　The first danger: producing indigo dye requires the use of toxic chemicals such as formaldehyde and hydrogen cyanide.

　　第一个危险: 生产靛蓝染料需要使用甲醛和氰化氢等有毒的化学物质。

　　Furthermore, synthesised indigo is insoluble in water, meaning chemicals are needed to make it suitable for dyeing.

　　另外，合成靛蓝不溶于水，这就意味着需要化学物质使其适合染色。

　　Not currently feasible

　　目前不可行

　　One such chemical is sodium dithionite, which decomposes into sulfate and sulfite which can corrode equipment and pipes in dye mills and wastewater treatment plants.

　　这样的一种化学物质是连二亚硫酸钠, 可以分解成硫酸盐和亚硫酸盐，会腐蚀染料厂和污水处理厂的设备和管道。

　　"Many dye mills avoid the additional cost of wastewater treatment by dumping the spent dye materials into rivers, where they have negative ecological impacts," said the research team.