TRANSLOCATION OF HEAVY METALS (Pb, Zn, Cu) IN THE SEROZEM-ALFALFA SYSTEM AND THEIR EFFECT ON THE ACTIVITY OF THE CATALASE ENZYME

ТРАНСЛОКАЦИЯ ТЯЖЕЛЫХ МЕТАЛЛОВ (Pb, Zn, Cu) В СИСТЕМЕ СЕРОЗЕМ-ЛЮЦЕРНА И ИХ ВЛИЯНИЕ НА АКТИВНОСТЬ ФЕРМЕНТА КАТАЛАЗЫ

Научная статья

Юлдашбек Д.Х.^1, *, Алайдаров М.А.², Колушпаева A.T.³

¹ ORCID: 0000-0001-9342-7502;

^{1, 2} Международный казахско-турецкий университет имени Ходжи Ахмеда Ясави, Туркестан, Казахстан;

³ Алматы Менеджмент Университет, Алматы, Казахстан

* Корреспондирующий автор (davlat-1995.95[at]mail.ru)

Аннотация

Активность почвенных ферментов зависит от биомассы микроорганизмов, а их жизнедеятельность от экологического состояния почвенной системы. В данной работе рассмотрена связь между ферментативной активностью каталазы и уровнем загрязнения тяжелыми металлами сероземной почвы Туркестанской области. Результаты экспериментальных исследований показали, что ферментативная активность изменяется с ростом содержания тяжелых металлов (Pb, Zn, Cu).

Внесение вермикомпоста (биогумуса) в почву привело к повышению каталазной активности изучаемой почвенно-растительной системы. Наблюдаемое объясняется стимулированием физиологической активности и образованием большей массы микроорганизмов в результате улучшения агрохимических свойств серозема. Результаты экспериментальных исследований также свидетельствуют о значительном влиянии вермикомпоста на транслокационную способность тяжелого металла (Pb, Zn, Cu). Значительная часть тяжелых металлов, образуя комплексные соединения с гуминовыми кислотами, содержащимися в вермикомпосте, превращаются в малоподвижную форму. Благодаря этому резко снижается скорость процесса миграции ТМ как в почвенной системе, так и системе почва-растение. Снижение транслокации ТМ из почвы в растения создает возможность получения экологически чистых сельскохозяйственных продуктов.

Ключевые слова: свинец, медь, цинк, тяжелые металлы, активность каталазы, серозем, вермикомпост, люцерна.

TRANSLOCATION OF HEAVY METALS (Pb, Zn, Cu) IN THE SEROZEM-ALFALFA SYSTEM AND THEIR EFFECT ON THE ACTIVITY OF THE CATALASE ENZYME

Research article

Yuldashbek D.H.^1, *, Alaydarov M.A.², Kolushpaeva A.T.³

¹ ORCID: 0000-0001-9342-7502;

^{1, 2} International Kazakh-Turkish University named after Khoja Ahmed Yasawi, Turkestan, Kazakhstan;

³ Almaty Management University, Almaty, Kazakhstan

* Corresponding author (davlat-1995.95[at]mail.ru)

Abstract

The activity of soil enzymes depends on the biomass of microorganisms, and their vital activity depends on the ecological state of the soil system. In this paper, the relationship between the enzymatic activity of catalase and the level of heavy metal contamination of the gray-earth soil of the Turkestan region is considered. The results of experimental studies have shown that the enzymatic activity changes with an increase in the content of heavy metals (Pb, Zn, Cu).

The introduction of vermicompost (vermicompost) into the soil led to an increase in the catalase activity of the studied soil-plant system. The observed phenomenon is explained by the stimulation of physiological activity and the formation of a larger mass of microorganisms as a result of improving the agrochemical properties of serozem. The results of experimental studies also indicate a significant effect of vermicompost on the translocation ability of heavy metal (Pb, Zn, Cu). A significant part of heavy metals, forming complex compounds with humic acids contained in the vermicompost, turn into a sedentary form. Due to this, the rate of HM migration process in both the soil system and the soil-plant system is sharply reduced. Reducing the translocation of HM from soil to plants creates the possibility of obtaining environmentally friendly agricultural products.

Keywords: lead, copper, zinc, heavy metals, catalase activity, serozem, vermicompost, alfalfa.

Introduction

Heavy metals are one of the sources of toxic substances that pollute the biosphere layer of the Earth. Heavy metals, both individually and in combination with other toxic substances, for example, with petroleum products, dioxins, pesticides, pose an extreme danger to the viability of biota, including the human body. In this regard, every year, as a result of the increase in the anthropogenic load on the environment, both the number of diseases and the number of new previously unknown diseases are growing exponentially. For example, we can note the frequent manifestation of a genetic mutation, an increase in the number of cancer patients, people prone to cardiovascular diseases, allergic reactions. This is explained by a decrease in immunity, especially in the younger generation.

The main reason for the appearance of such high concentrations of toxic substances in environmental objects is the lack of ecological culture among the population, an undeveloped network of industrial and household waste management, and other factors.

The main object depositing heavy metals (HM) and other ecotoxicants is the soil system. In the soil, their accumulation is carried out from adjacent environments, namely from atmospheric air, from water bodies, plants. Many pollutants in the soil persist for a long time in their original or transformed form. Natural self-cleaning of the soil system is a very long and slow process for many harmful substances. For example, this applies to HM compounds, namely, for zinc, decontamination takes from 71 to 510 years, for Pb-740-5900 years, for Cu – 300-1500 years [1].

The greatest danger among heavy metals is Pb, Zn, Cd, Hg, Cu. Getting into the human and animal bodies in significant quantities, they cause deep denaturation of proteins. In this case, HM interact with the functional groups-SH, - COOH of amino acids, which leads to the suppression of active centers, that is, the activity of enzymes decreases. The manifestation of the effects of harmful substances is possible in subsequent generations. These include gonadotropic, embryotoxic, carcinogenic, mutagenic effects [2].

Uncontrolled intake of HM into the human body can lead to irreversible changes in internal organs, leading to incurable diseases of the gastrointestinal tract, liver, kidneys, paralysis and deaths. In this regard, it is necessary to minimize the level of intake and content of heavy metals in the soil, in plant products and in the water system. In the conditions of global environmental pollution with a wide range of ecotoxicants, along with others, the problem of deterioration of the biological properties of soils is acute. With any changes in these soil properties, biological resources, namely the microbiota and the vegetation growing on them, are the first to react to them.

As the results of numerous studies have shown [3], [4], [5], one of the most reliable information for assessing the ecological state of soils is the change in the composition of the microbial community and the associated enzyme activity. For example, the works [6] show the influence of technogenic contamination of soils with heavy metals on the qualitative and quantitative composition of the microbiota. It is concluded that of all the indicators of biological activity, enzymatic activity is the most stable indicator. This allowed many researchers to recommend enzymatic activity to assess the ecological state of the soil system [7]. Thanks to enzymes, various types of biochemical reactions are carried out in the soil system, for example, there is a transformation of both substances entering the soil from the outside and existing in it, and a change in energy indicators.

Enzymes are complex protein molecules that have a high catalytic activity that accelerates vital chemical reactions in the cells of organisms. They are products of the vital activity of microorganisms, plant root systems and mesofauna. As catalysts, each of the enzymes forms unstable intermediates with its participants during the course of a certain process. These intermediates, after the formation of the final product, disintegrate and the enzyme again takes its original state.

More than 900 types of enzymes are known, and each of them accelerates only one reaction or a group of similar reactions [8]. Enzymes differ from each other in their functional activity on soil processes. According to their functional activity, they are divided into 6 classes (hydrolases, oxidoreductases, lyases, transferases, isomerases, ligases or synthetases). Among them, hydrolases (urease, protease, invertase, phosphatase) and oxidoreductases (catalase, peroxidase, dehydrogenase, polyphenol oxidase) are the most important for understanding the essence of soil processes.

Catalase is an enzyme of an antioxidant complex that protects the body from the destructive action of free radicals. Catalase is a heme-containing enzyme of the class of oxyreductases that catalyzes the decomposition of hydrogen peroxide to form oxygen and water 2H₂O₂ = O2 + 2 H₂O, it is widely distributed in animal and plant tissues. One catalase molecule decomposes up to 6 million hydrogen peroxide molecules per second. In the case of a decrease in the concentration of hydrogen peroxide, catalase begins to show catalytic activity in the other direction, i.e. it accelerates the oxidation reaction of alcohols, formaldehydes and nitrates with hydrogen peroxide. Enzymes are involved in the synthesis and decomposition of humus and fresh organic matter (including the bodies of microorganisms themselves), in redox reactions.

The activity of enzymes largely determines the level of soil fertility. The results of experimental experiments of numerous studies indicate that the conditions favorable for the manifestation of the activity of soil enzymes largely coincide with the optimal conditions for the growth of agricultural crops [9], [10].

Of all the enzymes, catalase has the most stability and, having accumulated in the soil, it persists for a long time. In this regard, the activity of the catalase enzyme can be an indicator of both the functional activity of the soil microflora and the ability to influence stress factors. Currently, the information available in the literature on the enzymatic activity of soils under various anthropogenic influences is still insufficient and requires further study. This makes it very relevant in practical and theoretical terms to study the enzymatic activity of soils under conditions of intense anthropogenic impact and the possibility of using it to diagnose the ecological state of soils.

The chemical, mineralogical composition and physical condition of soils are the main determinants of enzymatic activity. The activity of soil enzymes is correlated with the values of the reaction of the medium (pH), with the presence of moisture and other ecotoxicants in the gaseous, solid and liquid states. For example, many heavy metals inhibit the activity of enzymes, form complex organic compounds that can penetrate through cell membranes [11].

Of particular scientific interest is the study of the activity of various enzymes during the artificial introduction of fertilizers, meliorants of organic and inorganic nature into the soil. The results of our experimental studies devoted to the study of the effects of vermicompost on the enzymatic activity and agrochemical properties of gray-earth soils are presented below.

The aim of the work is to study the effect of heavy metals (Pb, Zn, Cu) on the growth and development of alfalfa and the activity of the catalase enzyme when applying vermicompost to gray-earth soil.

Objects and methods of research

For the study of the dependence of the translocation of heavy metals on the type of plant and on the presence of vermicompost in the soil – plant system, we selected the alfalfa plant (Medicago) as the object of study. This plant is a cosmopolitan plant species, growing in all climatic zones and on all types of soils. It is widely used as a forage crop. This type of plant has a developed root system, thus, along with enriching the soil with nitrogen, it improves its structure.

Experimental studies were carried out with gray-earth soils taken from clean, unpolluted HM sites. For laboratory (model) experiments, gray – earth soil uncontaminated with HM with a content of humus substances of 1.0-1.4 % (0-30 cm) was used. Vermicompost was introduced into the soil to stimulate the growth and development of alfalfa. Model experiments were carried out using wooden boxes without a bottom with a height of 50 cm and an area of 30x50 cm. Heavy metals are introduced in the form of easily soluble acetates in doses:

1) control (without introduction);

2) 1.0 MPC;

3) 10.0 MPC.

The calculation of metal concentrations was carried out based on the values of the MPC. The research work was carried out for 8 months. The enzymatic activity of catalase was determined in soil samples. All tests were carried out in a three-fold repetition. To determine the enzymatic activity of catalase, a gasometric method was used. The catalase activity was determined by the method of A. Sh. Galstyan, described by F.H. Khaziev [12].

Results and discussion

As a result of field microdel studies, differences in the biological activity of the soil under alfalfa compared to fallow soil were established. The difference increases with the growth of alfalfa, reaching the greatest values during the earing phase and beyond. The time of this phase falls on the hottest days of the year, which can be explained by a change in the rate of the peroxide decomposition reaction and a shift in the reaction equilibrium towards the formation of oxygen (2H₂O₂ → 2H₂O + O₂).

An increase in the level of contamination of the soil environment with heavy metals had a direct impact on the change in the activity of the catalase enzyme in alfalfa. The decrease in catalase activity depended on the nature of heavy metals. Alfalfa grown on unpolluted soil had a higher catalase content than in soils artificially polluted with heavy metals. Heavy metals contained in the soil system inhibit the activity of the catalase enzyme and the decomposition reaction of hydrogen peroxide slows down. Under negative influences, the formation of reactive oxygen species in plant cells increases, which can eventually lead to oxidative stress. Therefore, catalase activity can serve as an indicator of environmental pollution.

The results of experimental studies obtained when studying the effect of heavy metals (Pb, Zn, Cu) on the catalase activity of treated and untreated soils with vermicompost (VC) are presented in Table 1 and Figures 1-2.

 

Table 1 – Effect of heavy metals (Pb, Zn, Cu) on catalase activity

Heavy metals and their concentrations, MPC		Catalase activity (volume of oxygen released, in terms of 1 g of soil)
		Soil		Soil+Vermicompost
		ml / min	%	ml / min	%
Pb	0	2,4	-	2,7	-
	1,0	1,7	29,2	2,0	25,9
	10,0	0,9	62,5	1,3	51,8
Zn	0	2,4	-	2,7	-
	1,0	2,0	16,7	2,2	14,8
	10,0	1,2	50,0	1,8	33,3
Cu	0	2,4	-	2,7	-
	1,0	1,4	41,7	1,7	37,0
	10,0	0,7	70,8	1,0	62,9

 

The determination of catalase activity in soil samples treated and untreated with vermicompost showed a decrease in the activity of the enzyme during HM contamination. The greatest decrease in catalase activity was found for Cu, the smallest-for Zn. The catalase activity with the introduction of 10 MPC Cu decreases by 70.8% compared to the control, with 10 MPC Pb – by 62.5%, with 10 MPC Zn – by 50.0% (see Figure 1-2).

 

Fig. 1 – Influence of different concentrations of heavy metals (Pb, Zn, Cu) on catalase activity

Fig. 2 – Change in catalase activity when applying vermicompost to soil contaminated with heavy metals (Pb, Zn, Cu)

 

According to the results of model experiments, it was found that an increase in the concentrations of HM introduced into the soil leads to a decrease in catalase activity. The observed phenomenon can be explained by inhibition of enzyme production, that is, a decrease in the number of soil microorganisms in the presence of heavy metals.

Catalase activity at HM (Pb, Zn and Cu) contents from 1.0-10.0 MPC increases when vermicompost is introduced into the soil system. An increase in the activity of enzymes when applying fertilizers to the soil is associated with the transition of a certain part of HM to a stationary state as a result of their interaction with anions, for example, with sulfate, sulfide and others, with the formation of insoluble compounds, as well as with an increase in the content of organic substances. The obtained data suggest that the enzymatic activity of the soil is a reflection of the interaction of heavy metals and microorganisms.

Conclusion

From the studied indicators of catalase activity of contaminated soils with HM, a large response was found. In this regard, the activity of catalase in conditions of various anthropogenic impacts (fertilization, heavy metal pollution) can be used as an indicator indicator when conducting environmental monitoring of soils.

Thus, the different sensitivity of the soil enzyme catalase in the gray-earth soils of the Turkestan region in relation to different doses of heavy metals was established. The studied heavy metals (Pb, Zn and Cu) in elevated concentrations inhibit the activity of catalase. The sensitivity of catalase is different in relation to different doses of HM.

The enzymatic activity of catalase increased when an organic fertilizer-vermicompost was introduced into the soil system, which, accordingly, led to an increase in the rate of the decomposition reaction of hydrogen peroxide.

Конфликт интересов Не указан.

Conflict of Interest None declared.

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