Food Adulteration

Pretty common practice, especially without regulations and inspections to keep the hominids more or less in line (where "the market" is, the world wonders), and even then…

Passive

Toxins can accumulate as plants pull said toxins from the environment. This may not technically be adulteration, as adulteration has a whiff of an agent to it, though humans can screw up here with poor choices as where to put the fields, or maybe the fields were already there when a big, beautiful chemical plant moved in next door. Good luck getting those Teflon charges to stick?

Indirect

The intent was not to poison people, but somehow it happens. Maybe dirt is used to filter the beer, but the dirt has high levels of arsenic, arsenic unrelated to human antics with chemical factories, superfund sites, or whatever. Whoops? Or what if during the kilning stage of malting one burns some clean, beautiful coal and that coal somehow manages to deposit arsenic onto the malt and thence to the drink? Whoops!

Additionally, one pub was fined for selling contaminated beer after they were notified of the presence of arsenic by the manufacturer.

Active

"The Bad Sleep Well". Akira Kurosawa. 1960.