Effects of season and daily changes in nitrate (N03-) contaminant levels of lettuce
2007
Ahmad, Z. | Mohammadreza, M.
Vegetables contain higher concentrations of nitrate than those of other foods, and provide the major contribution to dietry intake of nitrates. Nitrates (NO3-) are present naturally, or may be present as a result of applying nitrogen (N) fertilizers on crops, or from its use as a preservative. There have been health concerns about the presence of NO3- in food as it can be metabolized to potentially carcinogenic N-nitroso compounds. The main sources of NO3- and NO2- in diets are vegetables and meats. According to the U.S. Department of Agriculture, the average adult ingests about 25 mg of NO3- - N per day in foods. Varamin is the most important county for agriculture in Tehran province. Many scientists have studied factors affecting NO3- concentrations in plants. However, none have determined nitrate concentrations in harvested plants. In this study, some of the fields in the Varamin area that have used the same type of N fertilization were chosen at random. Concentrations of NO3- in lettuce were determined by sampling during different seasons and times of the day (3 replications in each fields). The NO3- contaminant levels of lettuce compared with general standards (FAO, EC, WHO standards) using the t-test. For this study, plants were sampled near the harvest, and NO3- concentrations in the plants leaves were measured at 4:00-8:00am and also at 14:00-16:00pm on the same day in the spring and the fall. The standards (EC andamp; WHO) permitted maximum NO3- concentration is 3,000 - 3,500 mg kg-1. We found that NO3- concentrations in lettuce in the morning were much lower than those in lettuce harvested the afternoon. Results showed that the NO3- concentrations in lettuce leaves ranged from 4,287 mg kg-1 to 13,304 mg kg-1. We found significant differences (P less than 0.01) between measurements, and all of our samples would be considered to have some degree of NO3- pollution, in comparison with the EC standards.
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