a useful tool
In a perfect world, everyone would have access to all of the organically-grown produce that they wished to eat. However, budgetary restrictions might prevent this in many households, including my own. The Dirty Dozen produce list, compiled by the Environmental Working Group, is a useful tool for balancing the goals of eating a lot of produce, limiting our exposure to pesticides, and keeping the grocery bill within the budget.
This list is a ranking of the fruits and vegetables with the highest residual pesticide load. There is a companion list, The Clean Fifteen, and a full list that includes other popular produce that falls in the middle of the pesticide spectrum. According to EWG, eating produce listed on the D12 list will cause you to be exposed to ten or more pesticides a day; eating the produce on the C15 list would limit your exposure to two or fewer pesticides a day.
Does this mean that you shouldn't eat celery, the top veggie listed on the D12? No, but knowing that it is the most likely to be contaminated, you might choose to buy organic celery instead of conventionally grown. The list can help you determine on which foods it makes sense to spend the extra money to buy organically grown produce. For example, I choose to save a little money on avocados (on the C15), but spend a little extra on organic apples (on the D12) It's handy to consult this list not only when buying fresh produce, but also when choosing frozen fruit and veggies, and items such as apple sauce or juice.
In general, I avoid buying conventional produce that's on the D12, but ultimately, I base my buying decisions on the foods that I need and want to eat. For example, I buy kale and collard greens on a regular basis. A large bunch of conventionally-grown greens can be had for less than a buck at many markets, while organic kale is usually available only at Whole Foods for $4. So, I tend to buy the conventionally-grown greens, because I think that it's important to eat a lot of dark, leafy greens. Another approach would be to buy low-pesticide-load broccoli most of the time, and buy the organic leafy greens as an occasional splurge.
I hope that you appreciate the information that this list provides, and that you find a way to make it work for you. I think it's important to remember that the vegan diet eliminates exposure to many toxins, because we aren't consuming all of the chemicals that are stored in the fat of animals, which are usually fed a diet of highly-sprayed grains (in addition to other unsavory junk). Since more organic choices are available when a certain produce is in season, shopping according to the D12 also promotes buying seasonal and local produce.