THE ROLE OF INDOOR PLANTS IN CHANGING THE QUALITY OF THE AIR ENVIRONMENT IN THE PREMISES OF PRESCHOOL EDUCATIONAL INSTITUTIONS

Full Text

A key aspect of the well-being and prosperity of the State is the strengthening of the health of preschool and school-age children. Currently, the study of the health status of the child population and factors remains an important task that requires special attention and control. In this context, the conditions of education and upbringing in preschool institutions are of particular importance [1].
The period of preschool education has a significant impact on the formation of mental and physical health of students, which depends on the observance of educational conditions and hygienic standards. Adverse environmental factors reduce the child's immunity, which can lead to negative consequences for both mental and physical health. Therefore, monitoring and improving the parameters of the air environment, including primarily physical and chemical factors, is one of the key tasks for creating favorable conditions for spending time in preschool institutions. Special attention should be paid to the quality of the air that children breathe in preschool institutions.: CO2 level, 380-400 ppm- ideal air for health and well-being; 400-600- recommended for schools; 600-1000 - complaints about air quality; more than 1000- weakness, headache, concentration drops by a third, the number of errors in work increases. The concentration of carbon dioxide in the air of group rooms can increase several times by the end of the day. According to doctors, children with high concentrations of carbon dioxide often experience heavy breathing, shortness of breath, dry cough and rhinitis. An increase in the concentration of carbon dioxide in the room leads to asthma attacks in asthmatic children. Due to the increased concentration of carbon dioxide in the room, the number of sick days is increasing. Respiratory infections and asthma are the main diseases in preschool institutions.
Air consists of a mixture of various gases, including nitrogen, oxygen, argon, carbon dioxide, water vapor, and other components. Oxygen, which makes up 20.9% of the air, is the most important element for humans. Violations of physiological processes in the body can occur if the oxygen level decreases to 16-17%. At oxygen concentrations in the range of 11-13%, severe oxygen deficiency is observed, and at 7-8%, death is possible. Oxygen deficiency can occur in enclosed spaces, where oxygen is replaced by carbon dioxide as a result of respiratory activity (oxygen starvation). Carbon dioxide (0.04%) is a colorless, odorless gas and 1.5 times heavier than air, which allows it to accumulate in the lower layers of enclosed spaces. The main source of carbon dioxide is people who are indoors, as they emit it when breathing [2].
The issue of the need to normalize the concentration of carbon dioxide in educational institutions arises primarily due to the inefficiency or inability to ensure adequate ventilation of the premises until all parameters of the microclimate are normalized and stabilized to acceptable levels. For example, the lack of time for high-quality ventilation of the playroom during a daytime walk, when ventilation is prohibited in the presence of children, exacerbates the situation. In addition, the urgency of monitoring the concentration of CO2 in indoor air has increased due to the massive replacement of wooden windows with plastic windows, which makes the room more airtight. This, combined with an imperfect air exchange system, creates conditions for an increase in CO2 levels [3]. 
There are still no legally binding standards on indoor air quality in Germany and other European Union countries. Instead, there are many estimated values, which are called indicative or target values. In Germany, a CO2 value of 0.15% (≈1,500 ppm) is used as a hygienic guideline according to the standard (DIN 1946, Part 2) [3, 4].
The estimated values for indoor CO2 concentrations have been published by the Indoor Air Hygiene Commission (IRK) of the Federal Ministry of the Environment and the State Health Authority. A number of neighboring countries have published standards and recommendations on ventilation in buildings, including schools, which include provisions on limiting the concentration of CO2 in indoor air.
In Finland, the maximum allowable CO2 concentration in a used room under normal weather conditions is 1200 ppm. Norwegian and Swedish standards set a maximum CO2 concentration of 1000 ppm for residential buildings, schools and offices. In Denmark, according to the regulations of the occupational safety and health authority, the carbon dioxide content in kindergartens, schools and offices should not exceed 1000 ppm. Air exchange is considered insufficient if the concentration of Co₂ exceeds the value of 2000 ppm several times a day for a short time. For workplaces subject to the provisions of the Hazardous Substances Directive, according to TRGS 900, a limit value of 5,000 ppm CO2 is set. The more carbon dioxide there is in the air, the more difficult it is to concentrate and cope with the learning load. Knowing this, the US authorities recommend that schools maintain CO2 levels no higher than 600 ppm. In Russia, the mark is slightly higher: the optimal level for children's institutions is 800 ppm or less [3, 5].
One of the experiments at school showed that more than half of the school time the amount of carbon dioxide in the air exceeds 1,500 ppm, and sometimes approaches 2,500 ppm. In such conditions, it is impossible to concentrate, and the ability to perceive information is critically reduced. Other possible symptoms of CO2 overabundance are hyperventilation, sweating, eye inflammation, nasal congestion, and difficulty breathing [3]. 
One of the key means of prevention is the cost-effective installation of indoor plants that contribute to a steady reduction in CO2 levels, preventing its negative impact on health, as well as monitoring and installation of CO2 concentration measuring devices. It is important to note that the design of ventilation systems is based on the normalization of air exchange. In the Russian Federation, the minimum normalized air exchange is 30 m3 / h (in European countries — 72 m3 / h) and does not depend on the area and volume of the room, but is determined only by the "rate of respiration" and the volume of ventilation. In a state of calm wakefulness, the CO2 level can reach 1000 ppm, and during physical exertion it can exceed the permissible limits. Thus, the air exchange rate of 30 m3/h, established in Russia as a standard, does not provide comfortable indoor conditions [3, 6].

The issue of improving the air environment in the enclosed spaces of educational institutions is due to the increase in cases of asthma and respiratory diseases among children who spend a significant part of their lives in school premises, as well as the results of studies confirming the relationship between air quality parameters in the premises of educational and preschool institutions and the presence of diseases, as evidenced by a number of published works by foreign authors. The relationship between the quantitative content of carbon dioxide in the air of educational institutions and the potential consequences for the health of children and adolescents has been revealed by research results [7-15].
Previously, the association of frequent respiratory diseases was often associated only with the quantitative content of carbon dioxide in the indoor air, which later led to the development of a regulatory framework for the school environment, which determines the maximum level of CO2 concentration and minimum air flow rates. For example, according to the results of the Simoni M study [16], it was found that schoolchildren exposed to carbon dioxide (CO2) levels > 1000 ppm had a significantly higher risk of dry cough (OR 2.99, 95% CI 1.65–5.44) and rhinitis (OR 2.07, 95% CI 1.14–3.73). There is also evidence that directly proves that one of the factors in the development of rhinitis in schoolchildren is the presence of sources of formaldehyde [17]. 
Other studies have focused on the assessment of IAQ (indoor air quality) in the school environment.
When studying the air parameters in schools and kindergartens in Europe, geographical differences were observed between the north and south of Europe in terms of the impact of stress on health in indoor educational institutions. For example, pollution levels in Greek educational institutions show an average of 5.33micrograms/m3 (3.1–7.8 micrograms/m3) of benzene and 16.55micrograms/m3 (13.8–20.2micrograms/m3) of formaldehyde. The same chemical compounds show average values in Dutch educational institutions of 1.42micrograms/m3 (0.8-3.0micrograms/m3) of benzene and 13.93 micrograms/m3 (6.1-22.4micrograms/m3) of formaldehyde. It was found that the level of volatile organic compounds in the room and bioaerosol levels in schools and kindergartens are higher than in other places of work. The internal concentrations of atmospheric aldehydes (formaldehyde, acetaldehyde, propionic aldehyde, and benzaldehyde) have higher values than atmospheric concentrations. It is assumed that internal sources are more important factors influencing the level of indoor pollution than external sources, such as the penetration of car exhaust fumes. Higher concentrations of coarse-grained particles are observed at higher indoor air temperatures and CO2 concentrations, while concentrations of fine particle fractions positively correlate with the relative humidity in the room. In noisy places where educational organizations are located, windows are usually closed, especially during classes, which increases the likelihood of classrooms overheating in hot weather and poor air quality due to lack of adequate ventilation.
In recent years, "green architecture" has been created in schools in many countries in order to harmonize human-environmental relations. The creation of "green schools" is an extremely promising process aimed not only at creating additional ecological urban spaces, but also at preserving human health. The architectural environment and design of such schools have a positive impact on the health of students, improve mental and physical comfort, and promote the development of creative and intellectual potential. It has been proven that green space, even in urban areas, has a positive effect on the psycho-emotional state of adolescents, reducing stress even with minimal exposure time, with a subsequent reduction in the risk of developing depressive symptoms in adolescence.
In recent decades, much attention has been paid to the use of indoor plants as air purifiers and a large number of scientific publications have been devoted to them. Tests of the effectiveness of indoor plants as an air purifier, conducted for the first time by NASA, have shown that plants have the ability to reduce indoor pollutants [18]. In addition, there is a growing amount of research on indoor plants by testing the ability of specific plant species to purify indoor air. Several studies have been conducted related to the use of indoor plants and their effect on the morbidity of children. A study conducted by Orwell et al. It showed a significant decrease in the benzene content in the air of the room where the plants were used. The same result was reported by Hong et al. [19] who revealed the ability of ficus plants to purify indoor air by reducing levels of pollutants (VOCs) such as benzene, ethylbenzene, xylene, styrene, formaldehyde, acetaldehyde and toluene. In the study, the levels of pollutants were assessed before and after the plants were used. As a result, the VOC level in the room has decreased significantly.
As a method of atmospheric air purification, phytoremediation (or biofiltration) has attracted much attention abroad in recent decades, probably due to its accessibility and applicability, as well as environmental, economic and social benefits and its ability to achieve zero emissions [20]. It has been proven that a comfortable standard of living, productivity, and mental functioning can be significantly improved, and the perception of pain can also be reduced when plants are present in a room or workplace [20]. During phytoremediation, plants with their related microorganisms are able to extract pollutants from atmospheric air, and then decompose or detoxify it using various mechanisms. It has been proven that this is an environmentally friendly and sustainable process based on plant activity, which effectively reduces air pollution both indoors and outdoors.
In China, the rate of formaldehyde absorption by leaves has also been investigated, as well as the ability of leaf extracts to break down formaldehyde. The results showed that formaldehyde can be transported from the air through leaves and roots to rhizospheric water. When exposed to 0.56 mg/m3 of formaldehyde, the formaldehyde removal rate ranged from 18.64 to 38.47 mcg/h. According to the mass balance in the air-plant-water system, the main mechanism of formaldehyde loss was its destruction in plant tissues caused by both enzymatic and redox reactions. The higher oxidation potentials of Wedelia chinensis and Desmodium motorium leaf extracts corresponded well to the higher cleavage abilities of added formaldehyde than in other plants. The redox mechanism suggests that the removal of formaldehyde can be increased by increasing the level of reactive oxygen species (ROS) caused by stress in plants due to environmental parameters [21].
Based on the results of the literature review, it was confirmed that indoor plants have phytoncidal activity; plants affect the attention and well-being of people indoors, contribute to reducing carbon dioxide in indoor air by releasing oxygen during photosynthesis; prevent a decrease in regulated relative humidity during the active use of heating devices in winter. Due to the beneficial effect on the air and the presence of beneficial properties of plant phytoncidal substances, it is possible to talk about the need to place indoor plants in pre-school institutions in sufficient quantities. Plants provide regulated parameters of the microclimate and the quality characteristics of indoor air, including by reducing the ventilation time of the premises.

THE AIM is to substantiate the health-saving technologies of ecological phytodesign that affect the parameters of the microclimate and the level of carbon dioxide in the air environment in preschool institutions.
MATERIALS AND METHODS
After analyzing the collection of the botanical garden, the most suitable ones for use in preschool institutions were identified. The first criterion for excluding plants from the list was the presence of their toxic properties. The second criterion was the presence of thorns or thorns on the stems and leaves. In addition, the allergenicity of plants was taken into account. As a result, 10 types of indoor plants were identified that meet these criteria.: Chlorophytum comosum, Aspidistra elatior, Begonia ricinifolia, Hibiscus rosa - sinensis, Kalanchoe blossfeldiana, Coleus blumei, Murraya exotica, Nephrolepis exaltata, Sansevieria trifasciata, Cyperus alternifolius.The leaf plate area and its biological parameters (height and width) were determined for these plants [7-15]. 
A certain range of indoor plants was installed in the game rooms, as well as the EClerk-Eco Microclimate and Carbon Dioxide Meter equipment, which allows you to measure microclimate parameters and carbon dioxide concentration online. All values were recorded every minute, with transmission to the electronic database. The values obtained were averaged.
Statistical processing of results The statistical processing methods used in the course of data analysis were selected taking into account the distribution characteristics and were based on the principles of descriptive statistics. At the initial stage of statistical analysis, quantitative data were evaluated for the normality of the distribution using the Kolmogorov-Smirnov criterion (K-S test). The Student's t-test was used to compare the indicators, and variance analysis was used to analyze the averages of several independent samples. The critical significance level of the null statistical hypothesis (p) was set at 0.05. The Kruskal–Wallis test (H-test) was used to verify the equality of the average values of several samples.
results
The effect of indoor plants on the indoor environment has been actively investigated since 1989 to the present. The idea of using plants to remove organic compounds (VOCs) from indoor air was proposed [22]. 
This study presents data on the effect of the area of the leaf apparatus on the concentration of carbon dioxide in the "observation" group and in the "control" group during the stay of children in preschool institutions (Table 1).
Table 1. Data on the carbon dioxide content depending on the area of the leaf apparatus 
Table 1. Carbon dioxide content data depending on the area of the leaf apparatus
It was found that the carbon dioxide content in the indoor air of the "observation" group was significantly lower than in the "control" group, by 1.3 (Kruskal-Wallis test, p <0.05) and 1.2 (Kruskal-Wallis test, p <0.05) times, respectively, when plants with a leaf area of 1.7 and 2.5 m2 per room area of 48 m2 (Table 1).
During the game sessions, the air quality in the group cells deteriorates significantly, as evidenced by the level of CO2 content in the group cells, measured at different time periods (08:00; 11:00; 14:00 and 17:00 hours), fig.1.

An increase in carbon dioxide levels was observed in both observation groups during the entire period of the children's stay in the group cells. However, the average concentrations of CO2 (ppm) in the indoor air in the "observation" group were lower, and at 11:00 and 17:00 the differences were statistically significant (Kruskal-Wallis test, p <0.05).
The CO2 levels in the "observation" group with installed indoor plants were 1.3 times lower (P <0.001) than in the "control" group, which is consistent with the results of relevant studies [23, 24] and suggests the need for monitoring air quality by CO2 content. 
The analysis of variance, which takes into account the time point of measurement and the presence of a plant in the game room as independent variables, adjusted for temperature and relative humidity in the game room, demonstrated a significant effect of the interaction of these factors on the concentration of carbon dioxide (according to the Fisher criterion, P <0.01). The dynamics of a decrease in carbon dioxide concentration in a game room with installed plants is expressed by linear regression y = 131.02x + 535.5; R2 = 0.9697. In the group where there are no plants, y = 153.19x + 698.97; R2 = 0.8288.
Thus, the placement of the presented list of indoor plants with pronounced phytoncidal, transpiratory and gas-absorbing properties in the playroom of a children's institution contributed to a stable decrease in the concentration of carbon dioxide in the playrooms of preschool institutions.
discussion
At the beginning of this century, numerous research results were presented on the possibility of removing volatile substances from indoor air using potted plants. The data obtained is the first comprehensive demonstration of the potted plant system's ability to act as an integrated biofilter in removing these contaminants. For example, a botanical filter with E. aureum was used to remove 12.3±0.24 mg/m3 of formaldehyde. The result showed that this biofilter had a formaldehyde removal efficiency of 32-33% even at 90% high humidity. Torpey F. et al. In their study, they showed a 57% efficiency of removing methyl ethyl ketone using a mixed-type vertical botanical biofilter [25]. 
Our research, conducted directly in the playrooms of preschool institutions, allowed us to identify the optimal area of the leaf apparatus of indoor plants required to reduce carbon dioxide concentrations in the playrooms of preschool institutions to an area of 48 m2 from 1.7 to 2.5 m2.
It has been found that the concentration of CO2 in the air decreases by about 35%; indoor plants can reduce the concentration of CO2 in the room and quantify the amount of carbon absorbed by indoor plants; CO2 is non-toxic, but can have a narcotic effect at higher concentrations of CO2 [26]. Chinese researchers have found that Chlorophytum has an absorption efficiency, with CO2 concentrations ranging from 635 to 650 ppm.  For example, in a room with an area of 30 m2, a houseplant with a leaf area of 3.1 m2 reduced CO2 concentration by 25.7–34.3% compared to a room without plants. The results showed that the larger the leaf area, the higher the CO2 removal efficiency, and that indoor air quality improvement with indoor plants will continue to increase [26].
Studies conducted by domestic researchers in 2021 showed that by the end of the school day in the premises of a sports university, the level of carbon dioxide in the cold season exceeded the permissible standards in 100% of cases. The authors attribute this to the insufficient efficiency of ventilation systems [11-15]. To solve this problem, it is necessary to develop and design air conditioning systems in buildings that will provide comfortable and safe conditions for students in classrooms [27]. 
The work of Russian architects, as well as the research of hygienic scientists, emphasize the importance of creating criteria for assessing the quality of the indoor air environment. Monitoring and control of indoor CO2 levels will help reduce the risks of its negative effects on health [28].
According to literature sources, it is known that the proposed range of plants Chlorophytum comosum, Aspidistra elatior, Begonia ricinifolia, Hibiscus rosa - sinensis, Kalanchoe blossfeldiana, Coleus blumei, Murraya exotica, Nephrolepis exaltata, Sansevieria trifasciata, Cyperus alternifolius has phytoncidal, transpiratory and gas-absorbing properties, does not cause allergic reactions and it is safe for children's health. In addition, these plants require minimal maintenance.
In the course of our research, it was found that the phytoncidal, gas-absorbing and transpiratory properties of plants, both in natural conditions, have a positive effect on optimizing the psycho-emotional state of people. They help to reduce the level of carbon dioxide in the indoor air and help prevent a decrease in the established standards of relative humidity during the active use of heaters in winter. This can be considered as one of the preventive measures.
conclusion
An analysis of the research results published in both Russian and foreign sources shows that the problem of CO2 content attracts considerable attention due to the rapid increase in its concentration in indoor air. Numerous literary sources focus on the study of the influence of various levels of CO2 in the premises on the functional state and health. The results of these studies indicate that even minor deviations from the recommended permissible concentrations (especially in rooms for the education and upbringing of children and adolescents) can cause adverse changes in individual body systems. This, in turn, negatively affects the general well-being of students, manifests itself in decreased working capacity and mental activity, increased fatigue and decreased resistance to infectious and non-communicable diseases, which leads to an increase in cases of upper respiratory tract diseases.

Given the positive effect on the atmosphere and the presence of phytoncidal, transpiratory and gas-absorbing characteristics in indoor plants, it should be emphasized that sufficient plants should be placed in preschool educational institutions to provide an area of 2.5 m2 per square meter of leaf apparatus. Plants contribute to maintaining the established parameters of the microclimate and air composition in enclosed spaces, even with limited ventilation time. The placement of plants with pronounced phytoncidal, gas-absorbing and transpiratory properties in the rooms where the playrooms are located will help reduce the risks and prevent diseases in children. 
Information about financing and conflicts of interest.
The study had no sponsorship. 
The authors declare the absence of obvious and potential conflicts of interest related to the publication of this article.

About the authors

Наталья Чуенко

Federal Budgetary Institution of Science "Novosibirsk Scientific Research Institute of Hygiene" of Rospotrebnadzor

Email: natali26.01.1983@yandex.ru
ORCID iD: 0000-0002-1961-3486
SPIN-code: 9709-3447
Scopus Author ID: 57991470300

Research associate, graduate student

Russian Federation, Parkhomenko str.7

Irina I Novikova

Federal Budgetary Institution “Novosibirsk Research Institute of Hygiene” of Rospotrebnadzor,

Email: novikova_ii@niig.su
ORCID iD: 0000-0003-1105-471X
SPIN-code: 3773-2898
Scopus Author ID: 700 515 3366

Doctor of Medical Sciences, Professor

Russian Federation, 630108 Novosibirsk, 7 Parkhomenko street

Maria A. Lobkis

the Federal Budgetary Institution “Novosibirsk Research Institute of Hygiene” of Rospotrebnadzor,

Email: lobkis_ma@niig.su
ORCID iD: 0000-0002-8483-5229
SPIN-code: 4387-9425

Research Associate

Russian Federation, 630108 Novosibirsk, 7 Parkhomenko street

Sergey P. Romanenko,

Federal Budgetary Institution “Novosibirsk Research Institute of Hygiene” of Rospotrebnadzor,

Author for correspondence.
Email: chuenko_nf@niig.su
ORCID iD: 0000-0003-1375-0647
SPIN-code: 2107-5929

Сandidate of Medical Sciences, Deputy Director for Research 

Russian Federation, 630108 Novosibirsk, 7 Parkhomenko street

Oleg Andreevich Savchenko

Federal Budgetary Institution of Science "Novosibirsk Scientific Research Institute of Hygiene" of Rospotrebnadzor

Email: chuenko_nf@niig.su
ORCID iD: 0000-0002-7110-7871
SPIN-code: 1029-6169
Scopus Author ID: 57220086064

Candidate of Biological Sciences, Professor, Senior Researcher at the Department of Toxicology

Russian Federation, Parkhomenko str.7

Vladimir A. Shirinskii

Federal State Budgetary Educational Institution of Higher Medical Education of the Ministry of Health of Russia

Email: vash1007@mail.ru
ORCID iD: 0009-0007-1929-2620
SPIN-code: 3487-6456

Sciences, Professor 

Russian Federation, 12 Lenin St., Omsk, 644099, Omsk region

Zhanna V. Gudinova

Federal State Budgetary Educational Institution of Higher Medical Education of the Ministry of Health of Russia

Email: gud@list.ru
ORCID iD: 0000-0001-6869-6057
SPIN-code: 6178-8633

Doctor of Medical Sciences, Professor

Russian Federation, 12 Lenin St., Omsk, 644099, Omsk region

References

Supplementary files