Investigation of nitrate status in agricultural products of Iran and criticism of published studies – a review study

Document Type : Review

Authors

1 Ph.D. student, Department of Soil Science and Engineering, Faculty of Agricultural Engineering and Technology, University of Tehran, Iran.

2 Soil and Water Research Institute, Agricultural Research, Education, and Extension Organization, Karaj, Iran

3 Ph.D Graduate, Department of Soil Science and Engineering, Faculty of Agricultural Engineering and Technology, University of Tehran, Iran

4 Agricultural Research, Education and Extension Organization (AREEO), Soil and Water Research Institute (SWRI), Karaj, Iran.

5 Ph.D. Graduate, Department of Soil Science and Engineering, Faculty of Agricultural Engineering and Technology, University of Tehran, Iran.

Abstract

In the process of conducting this research, 110 studies on monitoring nitrate content in agricultural products produced in Iran were gathered. These studies were published until March 20, 2023. The collected studies underwent evaluation for methodology, quality control, and quality assurance of results and were then assessed based on standard research criteria. The evaluation of the study's methodology revealed that only 27.3% of the studies adhered to standard methods for sampling, storage, and sample transfer. In 15.5% of the studies, the method of preparation and extraction followed standard procedures. Additionally, in 30% of the studies, the nitrate measurement method was conducted according to established standard procedures. The evaluation of quality control in the studies showed that only 20.9% reported some indicators of quality control and assurance. The assessment of nitrate concentration in agricultural products revealed the weighted mean concentrations of nitrate (mg kg-1 fresh weight) as follows: potato 98.7, cucumber 120.9, tomato 40.7, onion 39.6, watermelon 19.9, melon 62.9, carrot 151.1, eggplant 235.2, peppers 329, other root and tuber vegetables 542.4, lettuce 907.7, spinach 995.4, celery 1093.4, fresh edible legumes 37.7, parsley 596.5, cabbages 414.7, other leafy vegetables 635.6, apple 32.4, and orange 37.2. The findings of the present research reveal that the mean nitrate concentrations in Iran’s agricultural products fall below the maximum permissible levels outlined by both the Iranian national standard and international standards. As a result, it can be generally concluded that there is no significant cause for concern regarding residual nitrate concentration in Iran’s agricultural products.

Keywords

Main Subjects

Investigation of nitrate status in agricultural products of Iran and criticism of published studies - a review study

 

EXTENDED ABSTRACT

Aims

The impact of residual nitrate in agricultural products on human health is a concerning issue that intermittently captures the attention of the media and public opinion. Elevated nitrate concentrations exceeding the permissible levels in food products may heighten the risk of gastrointestinal cancer and methemoglobinemia in infants. On a macroeconomic scale and for the nation's economy, the presence of excessive nitrate in agricultural products can result in non-acceptance by other countries, occasionally leading to the return of these products. Given the significance of this matter and recognizing that nearly 80% of the nitrate in the human diet originates from the consumption of agricultural products, particularly vegetables, accurate and precise measurement of nitrate concentration in these products becomes paramount.

Methodology

In this study, we aimed to present a comprehensive overview of the nitrate concentration in agricultural products across Iran at a national scale. This was achieved through a quantitative and qualitative analysis of published studies in the field. To conduct this research, we gathered 110 studies, including papers, theses, and final reports of research projects, focusing on monitoring nitrate content in agricultural products grown in Iran, and covering publications until March 20, 2023. Initially, these studies underwent evaluation concerning methodology, quality control, and quality assurance, following which they were assessed based on standard research criteria. The evaluation specifically focused on the methodology and quality of the studies used to determine the nitrate status of Iranian agricultural products. Only studies meeting the minimum quality criteria were included in the final analysis of this research.

Results

The evaluation of the study's methodology revealed that, in only 27.3% of the studies, the method of sampling, storage, and sample transfer; in 15.5% of the studies, the method of preparation and extraction; and in 30% of the studies, the method of nitrate measurement (including 14.5% zinc rod, 3.6% cadmium column, 8.2% high-performance liquid chromatography, and 3.6% ion chromatography) adhered to standard methods. The assessment of quality control in the studies demonstrated that only 20.9% reported some criteria of quality control and assurance. These criteria included calculating recovery percentage (15.5%), using certified reference materials or CRM (1.8%), and determining the limit of detection (16.4%) and the limit of quantification (18.2%). Based on the evaluation of methodology and quality control, nitrate concentrations published in 74.5% of the studies, which accounted for 15,203 samples (65.4% of all samples analyzed in the studies), met the minimum quality required for inclusion in the final analysis of this research. These data were utilized in the assessment of nitrate status in agricultural products in Iran. However, 34.6% of the studies (including the analysis results of 8057 samples) did not meet the minimally acceptable quality and were consequently excluded. The evaluation of nitrate concentration in agricultural products unveiled the weighted mean concentrations of nitrate (mg kg-1 fresh weight) as follows: potato 98.7, cucumber 120.9, tomato 40.7, onion 39.6, watermelon 19.9, melon 62.9, carrot 151.1, eggplant 235.2, peppers 329, other root and tuber vegetables 542.4, lettuce 907.7, spinach 995.4, celery 1093.4, fresh edible legumes 37.7, parsley 596.5, cabbages 414.7, other leafy vegetables 635.6, apple 32.4, and orange 37.2.

Conclusions

Current research reveals that mean nitrate concentrations in Iran’s agricultural products are lower than the maximum permissible levels recommended by both the Iranian national standard and international standards. Consequently, it can be generally concluded that there is no serious concern about residual nitrate concentration in Iran’s agricultural products. Nitrate levels in agricultural products are crucial for food security, community health, and the associated social and economic effects. Therefore, studies in this area must strictly adhere to the steps and guidelines for measuring, controlling, and ensuring the quality of analyses, following both national and international standards. They should be ready to present this adherence if required.

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Iranian Journal of Soil and Water Research
Volume 54, Issue 11
January 2024
Pages 1779-1820

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