To buy organic or not to buy? That is a good question. Organic foods are one of the fastest-growing categories in the food industry today with almost two-thirds of Americans buying some type of organic food or beverage in the past year — up from about half in 2004.

But of course, because they are more labor-intensive to produce, they can cost more than double the price of regular foods. When it comes to fruits and vegetables, however, the price may be worth it for long term health.

The US Department of Agriculture found that even after washing, some fruits and vegetables consistently carry higher levels of pesticide residue than others. According to the Environmental Protection Agency, some pesticides can cause health problems such as birth defects, nerve damage, and cancer depending upon the chemical’s toxicity and how much of it is consumed.

A recent study out this month in the Journal of Pediatrics found that organophosphate pesticides, commonly found on berries, celery and other produce, could raise the risk for attention-deficit/hyperactivity disorder (ADHD) in children. According to the study author, organophosphates are some of the most widely used pesticides in agriculture and high doses may inhibit a nervous system enzyme linked to the development of ADHD. Dr. Philip Landrigan of Mount Sinai Hospital said that the link is "consistent with other studies that have looked at organophosphate pesticides and have found that exposure of children…in early life can cause brain injury."

The Environmental Working Group (EWG) in 2009 compiled a list of 47 fruits and vegetables that had the greatest levels of pesticides at the point of purchase. Twelve of those have come to be known as the "Dirty Dozen", and the group estimates that if a consumer makes the switch to organic, they can reduce their pesticide exposure by up to 80%.

Here are the "Dirty Dozen" Must-Buy Organic Foods ranked with those containing the most pesticides at the top.

• Peaches
• Apples
• Sweet Bell Peppers
• Celery
• Nectarines
• Strawberries
• Cherries
• Kale
• Lettuce
• Grapes
• Carrots
• Pears

You can further limit your exposure to pesticides by washing all produce, organic or not, thoroughly before eating. Special soaps or washes are not needed, just wash in cold, clean water and scrub with a brush, if appropriate. Wash just before preparation or eating to maintain freshness. Also, trim the tops and very outer portions of celery, lettuce, cabbages, and other leafy vegetables that contain the bulk of pesticide residues.

Because buying organic produce is more expensive, take advantage of local farmer's markets or comparison shop in local grocery stores to find the best price. Also, buy fruits and vegetables in season. Not only are the foods usually cheaper, but they also are more likely to contain fewer pesticides.

If you liked this post, you may also like "Even Organic Foods Have Calories."

This post was included in the All Things Eco Blog Carnival, Vol. 102.