The particularly worrisome types of contaminants found in coffee are known as mycotoxins and ochratoxins, and neither one of them are good news. These toxins come from mold in your coffee, and nearly all low-quality varieties are afflicted with them. According to Bulletproof Coffee's Dave Asprey, this is particularly a problem in bargain coffees and blended types. In both instances, a higher percentage of moldy beans can be used, and in the case of blended coffee, cheap beans sourced from various locales make the introduction of toxins a near certainty.
Kelly Reynolds, a germ specialist from the University of Arizona, agreed with the NSF study, pointing out that human bodies can deal with the presence of contaminants in measured doses.
"Coffee makers are certainly a moist environment where mold and bacteria are known to grow in high numbers; our bodies can deal with them, but at some point they'll grow to levels high enough to cause sickness."
Other researchers have pointed out that coffee makers are particularly susceptible to these issues, since mold and mildew can grow on hard plastic surfaces (like the interior of a reservoir). They point to an increasingly bitter taste in your coffee as evidence that it may be contaminated.
That is not to say, however, that they are without their negative effects: mycotoxins have been linked to cancer, kidney disease, cardiomyopathy, and even brain damage. Ochratoxin A, meanwhile, is known to cause cancer and damage the immune system, negatively impacting the kidneys as well.
Mycotoxins are nothing new, and coffee makers are well aware of the issue. While it always pays to investigate the substances you take in and proceed with your own due diligence, the positive effects of coffee are likely to outweigh the negative impacts of mold and toxins in the short run. In the long term, however, experience shows us that it never hurts to limit exposure to contaminants. Luckily for those of us interested in a sustainable lifestyle, there is no shortage of options (like Bulletproof Coffee or various herbal replacements) that can make limiting mold in your coffee a painless procedure.