In a sampling from farmers' markets and bulk vendors in the Kansas City metro area, researchers found that four out of 10 spices registered at least one of three contaminants, including heavy metals (like lead or iron), mycotoxins (toxins left behind after food gets damp and molds), and bacteria (including salmonella).
The spices that most frequently tested positive for salmonella were black pepper, thyme, oregano, and turmeric — pretty run-of-the-mill cooking fare. How do these common herbs and spices manage to be major carriers of bacteria? Unfortunately, the causes of contamination are the same things that make farmers' markets unique: Unlike in a grocery store, a market's bulk herbs are usually displayed out in the open, allowing you (and everyone else) a chance to get a whiff of that freshly harvested goodness before you buy. Charming? Yes. Healthy? Not quite. That open-air approach makes spices vulnerable to the elements — and to the touching, sniffing, and coughing of shoppers. Farms themselves may also be to blame; heavy metals can find their way into produce if a farm's irrigation system uses industrial wastewater or rusty harvesting equipment.
Luckily, there are ways to avoid the risks of contaminated spices; you’re safe as long as you plan on using them in a dish cooked at 160 degrees or higher. But, if you're just looking for some black pepper to grind and use raw, the prepackaged kind from the grocery store is your safest bet for staying bacteria- and metals-free. Because, heavy metal belongs on your iPod — not in your food.