It's not the only study to document such a link. I summarized two of Dr. Duk-Hee Lee's studies here, both of which described an association between persistent organic pollutants (POPS, a collective term that includes dioxins and PCBs) and diabetes.
The risk for exposure to PCBs doesn't have to occur through an accident. We take in small amounts of PCBs regularly through our diet, especially when we eat animal foods. Quoting Dr. Lee:
"Greater than 90% of POPs comes from animal foods."Why are animal foods more likely to harbor PCBs? The Wisconsin Department of Natural Resources explains:1
"PCB molecules attached to sediment particles eventually sink to the river bottom, where they are eaten by tiny organisms. Small fish eat these organisms and retain the PCBs they carry in their body fat, and so on up the food chain to larger fish, birds of prey, and people. This process is called bioaccumulation or biomagnification."PCBs and other POPs are dissolved and stored in an animal's fat tissue. When we consume animal foods, we may be consuming dissolved dioxins along with them.
1 What Are PCBs?, Wisconsin Department of Natural Resources