In 19th century London, the River Thames was heavily polluted. The contaminants included untreated sewage, which caused cholera and typhoid outbreaks that claimed thousands of lives, and coal tar. The overpowering smell of the sewage during the “Great Stink of 1858” led to the construction of a sewer system that is still in use. As for the coal tar, a discovery that it could be distilled into the building blocks of synthetic dyes caused businesses to stop dumping it into the river and instead repurpose it into valuable dye compounds.