Introduction: Vegetables are the main food of the world's population, especially in developing countries. Currently, many vegetables, especially leafy vegetables, have a high percentage of nitrate due to the overuse of nitrogen fertilizers to accelerate vegetative growth. Many researches have been done on nitrate accumulation in crops worldwide, because of the harmful effects of excess nitrate in edible plants for humans and live stocks. Due to the necessity of such studies in country as well as the control of nitrate concentration in leafy vegetable and cucurbits, this study was done to investigate and monitor the nitrate concentration in some leafy vegetables and cucurbits (cucumber, tomato, potato, eggplant, pepper, onion, scallion and leafy vegetables) produced in some greenhouse and farms of Isfahan province.
Materials and Methods: In this study 142 different leafy vegetables (coriander, basil, chives, parsley, garden cress, dill, tarragon, mint, fenugreek) and cucurbits (fruit vegetables) including (cucumber, tomato, eggplant, pepper, onion, scallion and potato in coarse and fine sizes) collected from greenhouses and agricultural fields of Isfahan, Dorcheh, Falavarjan, Tiran, Dastgerd, Dehaghan and their surroundings. Nitrate content of plant samples was measured by spectrophotometer based on colorimetric method after reduction and production of aminoazo color complex. Then the nitrate concentration in the samples was compared with the maximum allowable nitrate concentration in agricultural products provided by the National Standard Organization of Iran.
Results and discussion: The results showed that the mean concentration of nitrate in cucumber samples was 1.48 times more than the Iranian National Standardization Organization (90 mg kg-1 of fresh weight); whereas the mean concentration of nitrate in potato, tomato and pepper samples was lower than the standard limits provided by National Iranian Standards Organization (170., 150 and 200 mg kg-1 of fresh weight respectively). The mean concentration of nitrate in fine sizes of potato, tomato and pepper was more than nitrate concentration in coarse sizes. Between the studied cucurbits, the highest and lowest average nitrate concentration were observed in cucumber and tomato respectively. Also the average nitrate concentration in cucumber skin was 16.7 times more than the mean nitrate concentration of its fruit. In general, the mean concentration of nitrate in leafy vegetables was more than the Iranian National Standardization Organization (1000 mg kg-1 of fresh weight). Between the studied leafy vegetables, the average concentration of nitrate in mint (457 mg kg-1 of fresh weight), fenugreek (262 mg kg-1 of fresh weight) and tarragon (695 mg kg-1 of fresh weight) was just lower than the Iranian National Standardization Organization. The others leafy vegetables probably have nitrate limitation for consumption.
Conclusion: According to the results, it seems that fruit size is not a suitable criterion for plant nitrate content and the management aspects of farms play a major role in plant nitrate content. On the other hand, the changes of nitrate content in the farms are very high, so it cannot be clearly stated that the consumption of vegetables is restricted in terms of nitrate content. However, it seems that the consumption of vegetables produced in the studied areas may be restricted for consumers’ health in some cases.