Evaluation of Nitrate Status in Some Highly Consumed Vegetables of Kermanshah City in Winter

Nitrogen is essential for plant growth. Excessive use of nitrogen fertilizers causes nitrate uptake and accumulation in edible parts of plants. This study was conducted to evaluate the nitrate concentration in some vegetables collected from the Kermanshah vegetable market in winter 2020.

vegetable samples include leafy, fruit-bearing, and tuberous vegetables were collected from the main vegetable market in Kermanshah city four times. Leafy samples were cress, lettuce, spinach, and celery. Fruit-bearing samples included cucumber and tomato. Tuberous samples included red and yellow onions and potatoes. The sampling times were January, early and mid-February, and March. Our previous study showed that vegetables in the main vegetable market of Kermanshah have been provided by different cities of Iran. Therefore, if there was one vegetable type has been supplied from different locations or different cultivation methods (i.e. traditionally vs. in greenhouse conditions), individual samples were collected. The nitrate concentration of vegetable samples was determined by the colorimetric method (Cataldo et al., 1975) after their preparation and extraction (Jones, 2001). The results were analyzed via SPSS v.26 by one-way ANOVA after testing the normal distribution. The means were compared by Duncan’s test (P<0.05). However, to determine the health status of vegetables, their concentrations were compared with the nitrate limit defined by the World Health Organization (WHO) (WHO, 1978) and the Institute of Standards and Industrial Research of Iran (ISIRI) (ISIIR, 2013). The differences in nitrate concentration of crops were also compared according to the time of sampling, the place (i.e. city that crops were grown), and the cultivation methods.

The results showed that nitrate concentration in lettuce, celery, cucumber, tomato, yellow onion, and potato was significantly lower than the ISIRI nitrate limit (P<0.001). Also, the nitrate concentration in cress samples in last February and March, spinach samples in mid-and las-February, and red onion samples in January and mid-February were lower than the permissible nitrate limit. However, nitrate concentration in cress and red onion (in January and mid-February) and spinach (in January and March) was higher than the WHO and ISIRI nitrate limit. ANOVA results revealed significant differences in vegetable nitrate concentration between months (P<0.001). The results also indicated that the variances of nitrate concentration in cress, cucumber, and tomato samples were highly influenced by place (P<.01). Moreover, nitrate concentration in the above-mentioned samples traditionally cultivated was found to be not significantly different from those grown in the greenhouse.

The results of this study showed that the time of sampling and the place where vegetables are grown affects the variation of nitrate concentration. However, the cultivation method showed no significant impact. However, the number of samples in this study was less than the amount to conclude this result certainly. Therefore, it is recommended that the nitrate concentration of the vegetables be measured at different sampling times as well as for vegetables grown in different places with more samples to assess the status of nitrate more confidently. This would help to have a reasonable allowable nitrate concentration limit for vegetables in comparison with the WHO standard.