In which vegetables is more nitrate accumulated?

Dr. Abbas Yadollahi, biotechnology and tree improvement expert and faculty member at the teacher training university, "food industry", will tell us how we should consume each of mostly used fruit and vegetables to take the most advantage of eating them.
 

Which group of vegetables is more polluted?

Accumulation of nitrate fertilizers and chemicals is more in leafy vegetables such as lettuce and then, in the glandular or root vegetables. The final rating is assigned to the fruit vegetables.

QUESTION: So shouldn’t we eat leafy vegetables?

Yes, we should. But we should eat them in respect of health and sanitation principles. For example, don’t eat old leafy vegetables, pearl the cucumber before eating, (although cucumber skill is rich in potassium, but with regard to our nowadays agriculture and absorption of pollutants by cucumber skin, pearling is recommended) or avoid eating the outer leaves of lettuce and white rigid middle of the lettuce. 
Question: what is the talk about the pollution of fresh pistachio nuts?
Fresh pistachios are among useful edibles, but if 2 or 3 days remain at home, afla-toxin poisoning in them is excreted. Thus, fresh and beneficial nuts will be turned to be polluted and dangerous ones.
Question: What is the way to prevent the secretion of toxins?

Once you buy the new pistachios and bring them home, freeze them. Every time bring as much as you need out of the freezer and consume.

Source: Health website (health Weekly information data base)