اندازه‌گیری و مقایسه مقادیر نیترات، نیتریت و عناصر سنگین در برنج برداشت اول و برداشت مجدد

فلزات سمی محیط ‌زیست را آلوده کرده و از طریق زنجیره‌های غذایی اثرات نامطلوبی بر سلامتی انسان باقی می گذارند. امروزه مواد غذایی دارای مقادیر بیشتری نیترات و نیتریت هستند. در این تحقیق از سه مزرعه انتخابی در دو زمان کشت اول و دوم 18 نمونه برنج تهیه شده و میزان نیتریت، نیترات و فلزات سنگین سرب، کادمیوم، آرسنیک و جیوه مورد ارزیابی قرار گرفت. نتایج نشان داد غلظت سرب در تمامی تیمارهای کشت اول بیش از حد مجاز بوده است و در کشت دوم تیمار مزرعه شماره یک و دو بیش از حد مجاز می باشند. میزان سرب درکشت اول در زمین شماره یک، ppb400 بوده و اگرچه در کشت دوم به میزان ppb300 رسیده، ولی همچنان بالاتر از حد مجاز می باشد. غلظت این عنصر در کشت اول زمین شماره دو از ppb470 به ppb421 در کشت دوم رسید و در زمین شماره سه، از ppb162 به ppb57 در کشت دوم رسید. غلظت کادمیم در تمامی تیمارها در حد مجاز می باشد و در کشت دوم، در مزارع شماره یک و سه کاهش و در مزرعه شماره دو افزایش معنی دار یافته است. میزان کادمیم در زمین شماره یک، از ppb30 به ppb17، در زمین شماره دو، از ppb15 به ppb20 و در زمین شماره 3، از ppb45 به ppb37 رسیده است. مقدار آرسنیک در کشت اول مزرعه شماره یک ppb 158 و بیشتر از حد مجاز می باشد و در کشت دوم زمین شماره یک، به ppb115 کاهش یافته است. در زمین شماره دو، مقدار آرسنیک کمتر از حد مجاز بوده و ppb88 گزارش شده است و در کشت دوم این مقدار به ppb58 رسیده است و در زمین شماره سه، مقدار آرسنیک، از ppb82 به ppb72 کاهش یافته است. در خصوص جیوه در مزرعه شماره یک در کشت اول مقدار جیوه ppb21 بوده، که در کشت دوم به ppb40 افزایش یافته است. در مزرعه شماره دو، مقدار جیوه از ppb33 به ppb36 در کشت دوم افزایش یافته و در مزرعه شماره سه کاهش معنی‌داری داشته است، به صورتی‌که میزان جیوه از ppb25 به ppb12 کاهش یافت. غلظت نیتریت و نیترات نیز در تمامی تیمارها ناچیز بوده است. با توجه به نتایج به دست آمده تمامی برنج های کشت شده در کشت اول و کشت دوم دارای مقداری آرسنیک، کادمیوم و سرب هستند. میزان اندازه گیری شده در برخی نمونه ها بیشتر از حد تعیین شده در استاندارد ملی ایران است و مصرف آنها می تواند برای مصرف کنندگان خطرناک باشد.

measurement and comparison of nitrate, nitrite and toxic elements in first harvest and re-harvest rice

introduction rice as a staple food, especially in asian countries, can be a major source of heavy metals. heavy metals also enter the soils where crops grow naturally and / or through human activities. metals are absorbed and accumulated in the edible parts of the plant and enter the food chain. toxic metals, which are present in nature due to industrialization, have polluted the environment, including soil, air, water and food, and have adverse effects on human health through food chains. the codex organization has set maximum levels for these elements in various cereals to protect trade and health. nitrate and nitrite are naturally present in soil, water and food. but today, foods have higher levels of nitrate and nitrite. excessive use of nitrogen fertilizers to achieve higher yields and improper disposal of human and animal wastes may lead to nitrate accumulation in agricultural products. very few studies have been performed on the measurement of heavy metal and nitrogen indices in replanted rice. the aim of this study was to measure the amounts of heavy metals (lead, cadmium and arsenic) and the amounts of nitrate and nitrite in first harvest rice and re-harvest rice and compare it with the standard values of the world health organization. methods and materials in this study, a total of 18 rice samples were prepared from three selected farms in the first and second cultivation times and the amount of nitrite, nitrate and heavy metals lead, cadmium, arsenic and mercury were evaluated.  results and discussion the results showed that in all farms in the second crop the concentration of lead decreased significantly (p<0.05). the concentration of lead in all treatments of the first crop has been more than allowed and in the second cultivation, the treatment of field number one and two, is more than allowed (p<0.05). the concentration of cadmium in all treatments is within the allowable range and in the second crop compared to the first crop of fields number one and three has a significant decrease and in field number two has increased significantly (p <0.05). the highest amount of cadmium is related to field treatments number three. the highest amount of arsenic was observed in the first crop of farm number one and it is more than the allowable limit and in other treatments the amount of arsenic was less than the allowable level and in all three farms the concentration of arsenic in the second crop was significantly reduced compared to the first crop. regarding mercury, in fields number one and two, with the change of cultivation, the amount of mercury increased significantly and in field number three, there was a significant decrease (p <0.05). mercury concentration is less than the allowable limit only in the second culture sample of farm number three. nitrite and nitrate concentrations were also low in all treatments and were considered zero. experiments showed the amount of nitrite and nitrate in all samples to be negligible and undetectable. due to the fact that the detection limit of the method (loq) used to measure nitrate and nitrite is 100 ppb, the amount of nitrate and nitrite in all samples can be less than 100 ppb. the permissible level of nitrate in food products and rice grains is set at 50 mg/kg according to national standard 16596. the results of the samples showed that all 18 samples had lower amounts of nitrate than the allowable limit. therefore, rice samples prepared from the first and second crops, their nitrate content is less than the allowable limit and have a complete degree of health.  conclusion according to the results obtained, all rice cultivated in the first and second crops have some arsenic, cadmium and lead, but the amount measured in some samples is less and in others, more than specified in the national standard of iran.  their consumption may be dangerous for consumers. these results also indicate that due to the stability of the field and plant type, there is a positive and significant relationship between the amount of heavy metals studied in rice and the time of cultivation, and this requires further studies on heavy metal contamination in the region. take place. therefore, with the conducted studies, it can be concluded that there are concerns in the consumption of rice cultivated in the city of mazandaran province, in terms of the possibility of endangering the health of consumers.