INCREASING THE LEVEL OF CONTAMINATION OF THE HUMAN BODY WITH CADMIUM WHEN SUPPLEMENTING ITS DIET WITH SUNFLOWER SEEDS

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INTRODUCTION

In the human trophic niche, sunflower does not occupy the most significant place, like, for example, cereals, but no less significant.

Scientists note the wide composition of phytochemicals and mineral elements of sunflower, which, in terms of their concentration in seeds and human tolerance, is often superior to nuts [1, 2]. Its consumption helps protect the skin from free radicals [3, 4], reduce the risk of developing cardiovascular diseases, reduce cholesterol levels, control blood pressure and type II diabetes [5, 6, 7]. The introduction of 30 grams of sunflower seeds into the daily diet reduces sugar levels due to the content of chlorogenic acid in them [7]. This amount of unroasted peeled sunflower seeds from the recommended daily requirement for an adult contains more than 40% phosphorus, copper, selenium, vitamins E and B5, 30% manganese, 17–18% vitamins B9 and PP and about 10% potassium and magnesium. [8].

Along with the nutritional value of the product, it is also necessary to take into account food safety indicators for humans, primarily in terms of the content of lead, cadmium, mercury and arsenic, the toxic effect of which is associated with complexation with SH groups of proteins. The accumulation of these elements is associated with bioaccumulation and biomagnification in organs and tissues in cases of elevated concentrations that suppress the physiological and biochemical mechanisms of resistance to their entry [9].

Suppression of lipase activity in sunflower seeds occurs when it is contaminated with cadmium at a level of 0.2 MAC [10]. The content of mercury ions at a level of 0.25 MAC reduces the activity of acid and alkaline lipase by 42.4-45.8%, at a level of 1.0 MAC the enzyme activity is almost completely inhibited. Compared to the effects of cadmium and mercury, the inhibitory ability of lead ions is lower; at a concentration of 1.0 MAC, it decreases by 1.7 times [11].

Under all other identical conditions, cadmium will accumulate in sunflower seeds in slightly larger quantities than in most other grain and oilseed crops. Assuming that the WHO recommended weekly intake of cadmium is met, the cadmium limit is 490 mcg per week when consuming one ounce of seeds for 48 weeks, i.e. 28.35 g, no effect on the body of volunteers was noted [12].

In populations consuming rice as a staple diet, people are more susceptible to cadmium poisoning. An experiment on laboratory rats showed that the introduction of sunflower kernels into the diet, due to the significant content of calcium, iron and zinc, minimizes the absorption of cadmium [13]. The positive effect of a moderate excess of some microelements in reducing the absorption and retention of cadmium has also been proven in studies on Japanese quails [14].

Among heavy metals, cadmium is one of the most common environmental pollutants in large cities. It belongs to the cumulative poisons with a elimination period of 25–30 years [15].

From a food safety point of view, cadmium concentration is an important parameter to be monitored, since food products are the main source of Cd intake into the human body [16]. Experts from WHO and FAO (Food and Agriculture Organization of the United Nations) accepted the tolerable weekly intake for cadmium at the level of 7 mcg per 1 kg of human body weight.

The absorption of cadmium from the gastrointestinal tract is only 5–10%, however, when it enters the bloodstream into the liver and is absorbed by hepatocytes, it stimulates the synthesis of metallothionein. The resulting complex, cadmium metallothionein (Cd-MT), is released from the liver through the bloodstream and reaches the kidneys, where, due to their high reabsorption activity, it induces damage to the proximal tubules [17, 18].

During a subchronic experiment of inoculating rats with cadmium salts, conducted by toxicologists of the Ufa Research Institute of Occupational Medicine and Human Ecology, when the safe dose was ten times higher, a greater accumulation of the metal was observed not in the kidneys, but in the liver [19].

Russian production of sunflower seeds and sunflower oil with a gross harvest of 5.65 million on an area of ​​22.9% of the world's sown areas is a world leader [20]. From time to time, the media raises questions about high concentrations of metals determined in sunflower seeds sold through supermarkets; most often it comes to cadmium, the content of which can exceed the level of 0.2 mg/kg.

 

The main mechanism of cadmium's toxic effect is the replacement of other divalent cations, mainly in proteins. During evolution, plants have formed mechanisms to protect the most important processes from harmful influences, but in the case of sunflower, cadmium overcomes the plant’s detoxification mechanisms along the same transport pathways as microelements and disrupts the transport pathways of nutrients. Depositing the toxicant in the seeds protects the root system from possible adverse effects produced by this element. The possibility of achieving a concentration of 10–20 mcg/g in cotyledons has been experimentally shown, which means that the consumption of only seven seeds is sufficient, at which the permissible limit of daily cadmium intake of 70 mg will be reached. Regarding microelements, a significant imbalance of metals in the seeds was noted, affecting not only the levels of copper, manganese and iron, but also changing their distribution in sunflower seeds. Since cotyledons are the main part used for human food, sunflower plants grown in soil with the same cadmium contamination as in the above study would pose a real risk to human health [21].

In terms of the degree of bioavailability of basic and toxic metals in the edible parts of nuts and sunflower seeds, dialyzability of mercury does not exceed 3.8%, cadmium, like the main share of trace elements, is characterized by moderate percentages, arsenic translocation varies between 28–75%. The degree of bioavailability correlates with the content of carbohydrates and fats. Fat content negatively affects the ability of metals to dialyze; carbohydrates increase the dialyzability coefficients of metals. Protein and dietary fiber do not affect the bioavailability of metals [1, 22].

 

Thus, in parallel with the increase in knowledge about the biological value of sunflower, its seeds occupy an increasingly important place in the trophic niche of humans, at the same time there are publications about sunflower as a plant - a cadmium concentrator, with the deposition of xenobiotic in the seeds, in light of which the aim of the research was an ecological and hygienic assessment of the added contamination of the human body with heavy metals when supplementing the diet with sunflower seeds.

MATERIALS AND METHODS

For the study, sunflower seeds of 10 brands were purchased, and 16 samples of sunflower seeds of the economic ripeness phase were selected from suburban areas of the industrialized city of Ufa, 500 g from each point. The crushed seeds, freed from the husk, weighing about 0.5 g, were placed in Teflon beakers with 8 ml of concentrated nitric acid (65% for analysis by Merck KGaA EMD Millipore Corporation) and subjected to microwave decomposition in accordance with the recommendations of the manufacturer of the Speedwave Xpert microwave system (Berghof, Germany) . Quantitative determination of metal content in the samples was obtained by flame atomization and graphite furnace atomic absorption spectrometry (AA240F, AAS GTA 120, AA240Z, Varian, Australia). The total mercury in the samples was determined by the “cold vapor” atomic absorption method using a PA-915M mercury analyzer. Sample preparation of seeds for mercury was carried out by thermal destruction of the sample and transfer of mercury to the atomic state by pyrolysis in the PIRO-915+ attachment from LUMEX-MARKETING.

The cadmium content in water was determined by atomic absorption spectrometry with electrothermal atomization in a graphite furnace (AAS GTA 120, AA240Z, Varian, Australia).

The analytical work was carried out in the accredited laboratory of the Testing Center of the Ufa Research Institute of Occupational Medicine and Human Ecology.

The calculation of oral intake of cadmium during the week was made with the written consent of 160 people whose data met the following conditions: health status – group I; gender-appropriate fertile age (15–65 years); normal body mass index (Quetelet index) – 20.0–25.9; weight – close to the calculated one according to WHO requirements – 70 kg.

Oral intake of cadmium was calculated based on the average regional values ​​of the toxicant in local food products and drinking water in the respondents’ area of ​​residence, obtained by the Test Center operating on the basis of the Ufa Research Institute of Occupational Medicine and Human Ecology.

When statistically processing the material (calculating average indicators, standard deviation of the coefficient of variation), standard MS Excel software packages were used.

RESULTS AND DISCUSSION

The reconnaissance analysis of sunflower seeds was the result of an answer to the question periodically raised in the media about increased levels of cadmium contamination in sunflower seeds sold through stores. The social activists’ conclusions were supported by specialists from the testing laboratory of the Omsk branch of the Federal State Budgetary Institution “Grain Quality Assessment Center”, who determined the average cadmium content in sunflower seeds as exceeding a concentration of 0.1 mg/kg in 24% of cases [23]. A similar level of safety is adhered to by: the independent center ANO "Soyuzexpertiza" of the Chamber of Commerce and Industry of the Russian Federation, the society for the protection of consumer rights "Public Control", although today there are "Unified sanitary-epidemiological and hygienic requirements for products (goods) subject to sanitary-epidemiological supervision (control) ). Decision of the Customs Union Commission dated May 28, 2010 N 299,” which states that the maximum permissible limit for cadmium is 0.2 mg/kg. The overestimation of the permissible norm for sunflower seeds is justified by the Fat and Oil Union of Russia “... by the objective situation with this type of raw material on the Russian market” [24]. The fundamental document “Technical Regulations of the Customs Union “On Food Safety” 021/2011” does not regulate cadmium and mercury in sunflower seeds at all.

At the first stage of the study, a quantitative analysis of the content of toxic elements in industrially packaged sunflower seeds intended for direct consumption was carried out, for which the entire range of rodent seeds was purchased in a large supermarket (Table 1).

Table 1. The content of toxic elements in sunflower seeds supplied by manufacturers to the retail network

sample	toxicants
	Pb	Cd	As	Hg
	Content, mg/kg
№ 1	0,23±0,08	0,013±0,004	<0,01	<0,0025
№ 8	0,28±0,10	0,027±0,008	<0,01	<0,0025
№ 7	0,25±0,09	0,034±0,010	<0,01	<0,0025
№ 4	0,33±0,12	0,091±0,027	<0,01	<0,0025
№ 5	0,03±0,01	0,184±0,055	<0,01	<0,0025
№ 10	<0,02	0,193±0,058	<0,01	<0,0025
№ 2	<0,02	0,203±0,061	<0,01	<0,0025
№ 3	<0,02	0,250±0,075	<0,01	<0,0025
№ 9	<0,02	0,253±0,076	<0,01	<0,0025
№ 6	<0,02	0,295±0,089	<0,01	<0,0025

In all samples of seed kernels from different producers, arsenic and mercury are determined below the detection level of the method. The quantitative content of lead does not exceed 0.3 MPL. The concentration of cadmium in seeds was up to 0.1 mg/kg in 3 samples, up to 0.2 mg/kg in one, up to 0.3 mg/kg in five. This confirms the fact that even with such a small sample, the high probability of excess doses of cadmium entering the human body through the consumption of seeds is confirmed.

Based on the results of assessing the actual data on cadmium from 92 samples of sunflower seeds from different regions of Russia, the Federal State Budgetary Scientific Institution “All-Russian Scientific Research Institute of Fats” noted a significant scatter in the obtained metal content values, depending on the place of origin of the seeds [24]. In connection with this, we carried out an analysis of sunflower seeds from agricultural fields and private farmsteads adjacent to the millionaire city of the Republic of Bashkortostan.

The result of an atomic absorption study of 16 samples of sunflower seeds grown in the Central Industrial Region of Bashkiria is presented in Table 2.

Table 2. Variational and statistical indicators of the content of toxicants in sunflower

Location of sampling	sample	Pb	Cd	As	Hg
		Content, mg/kg
Field along the highway M-7	From the highway 15 m	1,52±0,53	0,24±0,07	<0,01	<0,0025
	From the highway 25 m	1,09±0,38	0,28±0,09	<0,01	0,017±0,007
	From the highway 50 m	1,11±0,39	0,25±0,08	<0,01	<0,0025
Cottage village highway M-5	Residential area	0,31±0,11	0,40±0,12	<0,01	<0,0025
	New building	0,71±0,25	1,16±0,35	<0,01	<0,0025
Garden association	along the railroad	0,62±0,22	1,38±0,41	<0,01	0,088±0,025
Agricultural district	Seed to seed	0,12±0,04	0,073±0,022	0,035±0,012	0,006±0,002
	Seed for mixed fodder	0,45±0,16	0,095±0,029	<0,001	<0,0025
	Field 1	0,55±0,19	0,049±0,015	<0,001	<0,0025
	Field 2	0,38±0,13	0,093±0,028	<0,01	<0,0025
	Field 3	0,31±0,11	0,091±0,027	<0,01	<0,0025
	Field 4	0,33±0,12	0,14±0,04	<0,001	<0,0025
Experimental farm material	high quality	0,18±0,06	0,016±0,005	0,05±0,02	<0,0025
	ecologically friendly	<0,02	0,016±0,005	0,05±0,02	<0,0025
	forage	0,17±0,06			<0,0025
	substandard	0,21±0,07	0,067±0,020	0,05±0,02	<0,0025

In these samples, the presence of arsenic was noted to be no higher than 0.2 MPL and a case of excess mercury in seeds at the sampling point near the railway.

Lead was found in high concentrations in seeds collected in areas with heavy traffic; above the MPL in samples collected along the route, they also show the maximum value of cadmium excess. Our results are fully explained by the experimental data of the Voronezh State Agrarian University on the analysis of mobile forms of heavy metals in the soils of roadside sunflower agrocenoses. Researchers have found that under sunflower, the level of the mobile form of lead in the roadside zone compared to the background value increases by 2.9–5.3 times, depending on the distance to the road and options with fertilizers and herbicides. The increase in the ability of cadmium to translocate into sunflower, under the same conditions, was estimated by them to be 1.4–3.2 times [25] and the transition of cadmium from soil to sunflower inflorescences does not depend on the soil subtype [26].

Thus, sunflower is definitely a plant that accumulates cadmium to such an extent that, in conditions of polluted anthropogenic environment, the concentration previously considered the maximum permissible is today perceived by agricultural industrialists as almost a background level.

The lack of consensus on the level of safe levels of cadmium in sunflower seeds makes it worthwhile to determine the possible contribution of oral cadmium intake to humans.

For this purpose, a seven-day analysis of nutrition and drinking was carried out for 160 athletes, coaches and physical education teachers, first health group, reproductive age (35±14 years), with a normal body mass index (24.7±3.7) and weight (69.4 ±12.1 kg).

An assessment of 1120 diets of respondents in the selected group allows us to say that with a quantitative consumption of 1611±638 g of food and water (including that included in soups and drinks) 986±237 g of cadmium enters the body of healthy residents of Bashkiria 0.004 mg (with food 0.0033± 0.0012 and water 0.0007±0.0003 mg), which, according to calculations by the Federal Scientific Center for Medical and Preventive Technologies for Public Health Risk Management, does not exceed the reference dose of cadmium of 0.00055 mg/kg/day [27].

Against this background, the significant increase in the intake of cadmium into the human body when consuming sunflower seeds is evident. Just 50 grams of sunflower contain on average 2 times more cadmium (x̅varieties = 0.007 mg; x̅analyzed samples = 0.009 mg) compared to the 0.004 mg of metal received daily from the 1611 g of food consumed by the experiment participants.

The determination of the reference dose for supertoxicants is assessed based on an analysis of the effect on the reproductive system and neurotoxic, hematological, cytotoxic, cytogenetic and immunotoxic effects. As for cadmium, its accumulation occurs in various tissues and organs with a low ability to metabolize and detoxify [28].

Food is the predominant source of cadmium entering the body (up to 90%), the low level of excretion (about 0.001%, mainly in urine) requires serious approaches to its regulation, on the issue of which scientists have significant differences (Table 3).

Table 3. Permissible daily doses of chronic oral intake of cadmium

Source	Permissible daily intake of Cd, mg/day	country
Agency for Toxic Substances and Disease Registry (ATSDR)	0,007	USA (Federal)
Human Health Risk Assessment from Environmental Chemicals	0,035	Russia
California Office of Environmental Health Hazard Assessment		USA (California)
Food and Agriculture Organization, (FAO)	0,07	UN
World Health Organization (WHO)		WHO
EPA's Integrated Risk Information System (IRIS)		USA (Federal)

CONCLUSION

Bibliographic analysis of scientific works allows us to judge the high biological and nutritional value of sunflower, which improves the quality of nutrition for farm animals and humans without the use of synthesized additives. A negative factor in this situation is the increased accumulation of cadmium by the plant in its reproductive part.

In the analytical part of the work, in 40% of cases, the sale of sunflower seeds that did not meet safety requirements for cadmium content was recorded; For Shrovetide sunflower varieties, an increase in contamination with heavy metals in sunflower is expected to occur in areas of fields adjacent to transport infrastructure.

We simulated the situation of increasing the level of cadmium in the diet of respondents by adding a biologically justified amount of sunflower seeds of the studied samples.

Analyzing the data obtained, attention is drawn to the fact that just 50 g of whole sunflower grains can contain more than 0.007 mg/day or more, i.e. оnly sunflower seeds exceed the Agency for Toxic Substances and Disease Registry limit.

Simulation modeling allows us to talk about a low level of risk of oral intake of cadmium (0.012±0.006 mg/day) at the level of 17.2% of the safe level according to WHO and an average of 34.5% of the safe level adopted in the Russian Federation. However, it should be taken into account that the construction of this model is based on the diets of healthy respondents and adequate eating behavior; The calculation of the cadmium content in diet ingredients was made based on regional values, which means that the characteristics of the contribution of heavy metals to the dose load may be higher.

Thus, there is no doubt about the environmental and economic feasibility of introducing whole grain sunflower into the diet of the population. But economic ensuring the country’s food security and independence should not come at the expense of the environmental safety of food resources for humanity.

About the authors

Svetlana R. Afonkina

Ufa Research Institute of Occupational Health and Human Ecology

Author for correspondence.
Email: svetafonk1@mail.ru
ORCID iD: 0000-0003-0445-9057
SPIN-code: 3521-1536

Cand. Sci. (chemical), senior researcher, the Department of Analytical Chemistry

Russian Federation, 450106, Ufa, Russia, st. Stepan Kuvykin, 94

Margarita R. Yakhina

Ufa research Institute of occupational medicine and human ecology

Email: zmr3313@yandex.ru
ORCID iD: 0000-0003-2692-372X
SPIN-code: 5925-2360

MD, Ph.D., senior researcher of the Department of Occupational Health, Ufa research Institute of occupational health and human ecology

Russian Federation, 450106, Ufa, Russia, st. Stepan Kuvykin, 94

Elza N. Usmanova

Ufa Research Institute of Occupational Health and Human Ecology

Email: 4usmanova@gmail.com
ORCID iD: 0000-0002-5455-6472
SPIN-code: 9088-3293

MD, junior researcher of the Chemical analysis Department

Russian Federation, 450106, Ufa, Russia, st. Stepan Kuvykin, 94

Guzel R. Allayarova

Ufa Research Institute of Occupational Health and Human Ecology

Email: guzel-all@mail.ru
ORCID iD: 0000-0003-0838-3598
SPIN-code: 3704-1010

MD, PhD, Senior Researcher of Chemical analysis Department

Russian Federation, 450106, Ufa, Russia, st. Stepan Kuvykin, 94

Margarita I. Astakhova

Federal State Budgetary Educational Institution of Higher Education “Bashkir State Medical University” of the Ministry of Health of the Russian Federation

Email: Astachova_mi@mail.ru
ORCID iD: 0000-0002-8750-3852
SPIN-code: 4405-3181

Cand. Sci. (medical), assoc. prof., Candidate of Medical Sciences, Associate Professor, Associate Professor of the Department of Therapeutic Dentistry

Russian Federation, 450000, Russia, Ufa, st. Lenin, 3

Tatyana K. Larionova

Ufa Institute of Occupational Health and Human Ecology

Email: larionovatk@yandex.ru
ORCID iD: 0000-0001-9754-4685
SPIN-code: 5305-0589

Cand. Sci. (Biol.), Assoc. Prof., leading researcher of the Department of Analytical Chemistry

Russian Federation, 450106, Ufa, Russia, st. Stepan Kuvykin, 94

Rustem A. Daukaev

Ufa Research Institute of Occupational Health and Human Ecology

Email: ufa.lab@yandex.ru
ORCID iD: 0000-0002-0421-4802
SPIN-code: 4086-7132

MD, Ph.D., head of Department of Chemical analysis

Russian Federation, 450106, Ufa, Russia, st. Stepan Kuvykin, 94

Anna S. Fazlieva

Ufa Research Institute of Occupational Health and Human Ecology

Email: nytik-21@yandex.ru
ORCID iD: 0000-0002-0037-6791
SPIN-code: 6215-4556

junior researcher of the Department of Analytical Chemistry

Russian Federation, 450106, Ufa, Russia, st. Stepan Kuvykin, 94

References

Supplementary files