First, there are the toxins. Synthetic indigo dyes, which are derived from coal tar and toxic chemicals, are used in 90% of jeans made in China , according to a report in The Guardian. As part of a documentary called RiverBlue, campaigners from Greenpeace tested the outflows near denim factories in Xintang, China, and found five neurotoxic and carcinogenic heavy metals — cadmium, chromium, mercury, lead, and copper — in 17 out of 21 water and sediment samples. Other campaigners found manganese, which can be associated with brain damage, in the rivers. According to a University of Vermont report on Levi’s , the cheapest type of denim dye is sulfur-based, which is extremely damaging to the health of people exposed to it, and to the environment — it tends to remain in wastewater even after treatment. Textile workers have been shown to have high rates of bladder and nose cancer, likely because of benzidine , a chemical compound in synthetic dyes. And more chemicals like sodium hydroxide, hydrosulfate, and formaldehyde are used in the denim manufacturing process.