Attorney General Lori Swanson had no doubt that 3M endangered Minnesotans by dumping waste from perfluoroalkyl and polyfluoroalkyl substances.
Swanson sued 3M for $5 billion.
She settled the case for $850 million in February 2018. The company never admitted guilt.
One reason it did not have to was the lack of a national toxicity standard for the chemicals involved.
The absence of mandatory, enforceable limits on the substances, known as PFAS, complicates and sometimes cripples attempts by governments and individuals to hold producers accountable for what has become a national pollution problem, legal and scientific specialists say.
"Until the federal government says it is hazardous, there is no need to admit guilt," said Alexandra Klass, an environmental law professor at the University of Minnesota.
PFAS help make products heat-, stain-, water- and grease-resistant. Decades of use have spread the chemicals throughout the environment and alarmed public health groups and regulators. They worry about animal tests and epidemiology that link PFAS to cancer, liver problems and developmental issues in rodents, as well as weakened immune and vaccine responses in humans.
Despite two decades of study by the EPA, no mandatory limits exist for any type of PFAS. There are only advisory drinking-water limits on two major types. Companies do not have to follow these recommendations and cannot be held legally accountable if they breach them.