The Environmental Working Group puts mushrooms on the Clean Fifteen at #14 among fruits and vegetables with the lowest pesticide residues, but this doesn’t mean mushrooms don’t have pesticide residues.

The U.S. government’s Pesticide Data Program found residues of the anti-mold pesticide thiabendazole in 54.5 percent of conventionally grown mushrooms.

The EPA classifies thiabendazole as likely to be carcinogenic when doses are high enough to disrupt thyroid hormones.  According to the EPA’s assessment, thiabendazole also harms the immune and nervous systems. The European Food Safety Authority determined that thiabendazole is associated with adverse effects on the thyroid hormone function.

Thiabendazole is one of the most commonly detected pesticides on produce. In addition to mushrooms, it’s found on most citrus fruits.

A single serving of a food with high pesticide residues presents a greater impact than a serving of a low-pesticide food, but as Beyond Pesticides points out, it is the cumulative impact of consuming both high and low residue foods that determines our total pesticide exposure.

The interactions of various pesticides, when you’re exposed to so many, is also important.

When thiabendazole is present with chlorpyrifos, imazalil, and malathion, exposure to this mixture of pesticides is associated with a higher risk of postmenopausal breast cancer.

Exposure to a mix of thiabendazole, azoxystrobin, chlorpyrifos, imazalil, malathion, and profenofos, increases the risk of type-two diabetes.

This information comes from French studies that identified specific patterns of dietary pesticide exposures using questionnaires from more than 33,000 women to estimate daily pesticide intake based on the foods consumed and reported pesticide residues for each item.

The researchers found that while the dietary pattern representing higher exposure to imazalil, chlorpyrifos, thiabendazole and malathion was associated with a 73 percent increase in breast cancer risk, a diet high in organic foods and low in synthetic pesticides was associated with a 43 percent reduction in breast cancer risk.

If we’re concerned about the health effects on farm workers and rural communities in addition to consumers, we shouldn’t just be looking at pesticide residues per pound of produce, we should also be looking at pesticide usage per acre of farmland.

If you look at pesticide residues per pound of produce, as the Environmental Working Group does, mushrooms make the Clean Fifteen, but if you look at pesticides per acre of farmland, as the Pesticide Action Network has done, mushrooms would be #2 on the Dirty Dozen, second only to potatoes.

When the Pesticide Action Network looked at the total amount of pesticides applied to the Dirty Dozen and Clean Fifteen by acre, they found that the cleanest crop is actually spinach, with only 0.4 lbs of pesticides per acre, even though by weight, the measure the Environmental Working Group uses, it is the dirtiest. By acre, the crops with most intensive pesticide use are sweet potatoes and mushrooms, with 110.3 lbs/acre and 106.1 lbs/acre, respectively. By weight, potatoes are among the dirtiest, but mushrooms some of the cleanest.

Overall, the Pesticide Action Network found that the two lists weren’t much different in per-acre pesticide use: 26.2 lbs/acre for the Clean Fifteen and 29.8 lbs/acre for the Dirty Dozen.

By that measure, there is no Clean Fifteen or Dirty Dozen, there are only crops grown with pesticides and crops grown without.

The only answer is to always eat organic!