Why you probably don't need to splurge on organic produce, according to a toxicologist

That question has probably pained every grocery shopper with a budget large enough to consider it.

Every year, an organization called the Environmental Working Group (EWG) tries to help answer this question by highlighting which foods have the most and least "pesticide loads" — the chemicals organic produce is supposed to be grown without. EWG's " target="_blank"Dirty Dozen" list ranks the 12 fruits and vegetables with the highest levels — it includes strawberries, peaches, spinach, and tomatoes.

There's a small problem with the ranking, however, according to Dr. Carl Winter, a professor of toxicology at the University of California, Davis.

The list doesn't use a standard test designed to tell whether something is dangerous for human health. EWG measures the amount of pesticide residues on each piece of produce, but doesn't take into account the tenet that the dose makes the poison.

In other words, the amounts of pesticides found on the Dirty Dozen list are too small to merit concern in the first place.

The "Dirty Dozen" doesn't look at any of the three, Winter says.

Winter recently peeled apart the components of the "Dirty Dozen" ranking in a study he co-authored, which was published in the Journal of Toxicology. In the paper, he finds the following issues with the system used to classify produce as "dirty":

So why does the EWG continue to come out with its "Dirty Dozen" list every year, even though it doesn't really tell you how dangerous specific foods are?

According to Monica Amarelo, EWG's director of communications, "the Shopper’s Guide is not and has never claimed to be a risk assessment. It’s a straightforward ranking of which fruits and vegetables tested by the USDA had the most pesticides."

And some researchers say this has some value, at least for people with young children or toddlers. Indeed, some evidence — such as a 2012 study published in the journal Pediatrics — suggests pesticide exposure may affect little ones more acutely than it does adults.

“Even low levels of pesticide exposure can be harmful to infants, babies and young children, so when possible, parents and caregivers should take steps to lower children's exposures to pesticides while still feeding them diets rich in healthy fruits and vegetables," Dr. Philip Landrigan, a pediatrician at the Mt. Sinai School of Medicine in New York, tells USA Today.

Winter disagrees.

"This latest iteration of the 'Dirty Dozen' follows the same flawed methodology as all of its predecessors and therefore is of dubious value to consumers," Winter says. "My biggest concern is that attention given to the 'Dirty Dozen' will discourage consumers from eating enough fruits and vegetables (either conventional or organic) which will do them much more harm than good."