The Association between Indoor Carbon Dioxide Reduction by Plants and Health Effects

Chuang, Kai-Jen; Lee, Chien-Yu; Wang, Sen-Te; Liu, I-Jung; Chuang, Hsiao-Chi; Ho, Kin-Fai

doi:https://doi.org/10.1155/2023/1558047

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Abstract Introduction Methods Results Discussion Data Availability Additional Points Disclosure Conflicts of Interest Acknowledgments References Copyright Related Articles

Research Article | Open Access

Volume 2023 | Article ID 1558047 | https://doi.org/10.1155/2023/1558047

The Association between Indoor Carbon Dioxide Reduction by Plants and Health Effects

Kai-Jen Chuang,^1,2Chien-Yu Lee,¹Sen-Te Wang,^3,4I-Jung Liu,⁵Hsiao-Chi Chuang,^6,7,8and Kin-Fai Ho⁹

Academic Editor: Orish Ebere Orisakwe

Received20 Oct 2022

Revised07 Jan 2023

Accepted18 Mar 2023

Published17 Apr 2023

Abstract

Residents and workers exposure to high carbon dioxide (CO₂) levels in buildings may cause headache, dyspnea, fatigue, or drowsiness. However, the effect of plants on in-building CO₂ reduction and adverse effect relief is largely unknown. We recruited 36 healthy participants from an office room with plants and 32 healthy participants from another office room without plant in the same office building in Taipei. The participants in the office room with plants during 2020 would move to the office room without plant in 2021. The twelve repeated measurements per year of CO₂, fine particles (PM_2.5), total volatile organic compounds (TVOCs), blood pressure (BP), serum CO₂ (TCO₂), and four rating questions of headache, dyspnea, fatigue, and drowsiness were obtained for each participant. The statistical results showed that levels of drowsiness and systolic BP were significantly lower among participants in the office room with plants compared to those in the office room without plants by -test and paired -test. The associations between increased indoor CO₂ and increased serum CO₂ were observed in the office room with plants (1.32%) and without plant (4.52%) by mixed-effects models. Also, the associations between indoor CO₂ and drowsiness were observed in office rooms (with plants: 14.57%; without plant: 3.82%). The conclusion of the present study is that plants in office environment can reduce CO₂ levels and may lower CO₂-related health effects.

1. Introduction

Carbon dioxide (CO₂) level can be used as an indicator of indoor air quality in buildings. The concentrations of CO₂ are significantly correlated with factors that affect indoor air quality, such as ventilation rate, temperature, and humidity. Moreover, the results of locations where CO₂ is monitored reflect the actual conditions residents and workers are exposed to [1]. High CO₂ levels in buildings are often the result of poor ventilation. Most buildings, especially office buildings, are enclosed indoor spaces. Besides, high-rise office buildings often rely on central air conditioning systems for ventilation. However, office buildings using glass facades can easily develop poor ventilation over time, allowing CO₂ to build up and exposing residents and workers to adverse health effects, such as headache, dyspnea, fatigue, and drowsiness [1, 2].

Previous studies have demonstrated high relative risks of sick building syndrome symptoms and respiratory illnesses for a low ventilation rate compared to a high ventilation rate. Increases in ventilation rate could significantly reduce adverse health effects and improve indoor air quality [3]. Therefore, effective ventilation in buildings is one component of a comprehensive method to create and maintain a comfortable and healthy indoor air environment. However, increases in ventilation may increase building energy consumption [4, 5]. High energy consumptions would result in high greenhouse gas emissions and then make the world less sustainable [6].

Plant needs CO₂ to grow and propagate in the world [7]. Previous studies have reported the abilities of an indoor plant on CO₂ reduction [8–10]. Also, plant is one of the effective methods to sustain indoor air quality using nonmechanical and at the same time reduce energy consumption. However, the biological mechanism linking indoor CO₂ levels to perceived health effects and adverse health effects is still unclear.

Therefore, the present study was designed to investigate the association between indoor CO₂, serum CO₂, blood pressure (BP), and perceived health effects among healthy participants in an office room with indoor plants and an office room without plants. The study results might reveal whether indoor CO₂, serum CO₂, blood pressure (BP), and perceived health effects would respond to indoor CO₂ variation by plants.

2. Methods

2.1. Study Subjects and Study Design

The present study recruited 68 healthy subjects aged 32 to 43 years living in the Taipei metropolitan area, which includes Taipei, New Taipei City, and Keelung. These participants work in a document and legal word processing company in an office building in Taipei. Thirty-six of these participants work in an office room with plants while the others work in an office without plants. This company was one of the 41 companies in Taipei metropolitan area invited by the principal investigator and agreed to join our study after the present study design had been explained. These participants were healthy nonsmokers without cardiopulmonary diseases according to the company’s health examination records.

The study is a cross-over study design (Figure 1) that included 24 measurements of 8-hour averaged CO₂, fine particles (PM_2.5), total volatile organic compounds (TVOCs), temperature and humidity, and 24 measurements of BP, serum CO₂, and four rating questions about headache, dyspnea, fatigue, and drowsiness (from 0 (never) to 10 (extremely)) at the end of the work (approximately 5 : 00 p.m.) for each participant. The 24 measurements (twelve measurements per year for each participant) were occurred at one-month intervals from January 2020 to December 2021. Each participant’s characteristics, such as gender, body mass index (BMI), and age, were recorded using a questionnaire at first measurement (January 2020). The 36 participants who worked in an office room with plants in 2020 were moved to an office room without a plant in 2021. On the other hand, the 32 participants who worked in an office room without a plant in 2020 were moved to an office room with plants in 2021. The office movement was routinely arranged by the company’s human resource department according to the company’s annual schedule. The principal investigator discussed with the manager of the human resource department and then recruited participants from these two offices. The size of the office room was approximately 1765 square feet, and the height was about 12 feet for the office room. The plants in the office room with plants were 30 Epipremnum aureum. The rate at which outdoor air was supplied to the office room was set to 15 cubic feet per minute per person. The ventilation rate was measured once a month on a working day by the occupational health and safety department according to the company’s annual schedule using AccuBalance® Air Capture Hood 8380 (TSI Inc., Shoreview, MN, USA). The average ventilation rates of the two offices were 14.5 and 14.6 cubic meter per hour, respectively, during the study period.

Our study design was reviewed and approved by a local ethics committee in Taipei, Taiwan. Written informed consent was obtained from each subject before the study.

2.2. Indoor Air Pollution and Weather Monitoring

We used Q-TRAK IAQ (model 8551; TSI, Shoreview, MN, USA) for indoor CO₂ monitoring. A dust monitor (DUST-check portable dust monitor, model 11A; temperature and humidity sensor, model 1.153FH; Grimm Labortechnik Ltd., Ainring, Germany) was used for indoor PM_2.5, temperature, and relative humidity monitoring. A MiniRAE 3000 (model PGM-7320; RAE Systems, Inc., San Jose, CA, USA) was used for TVOC monitoring. All air pollutants, temperature, and humidity were monitored every minute. These monitors were calibrated by manufacturers before sampling. All data were matched with the sampling time of BP monitoring and then computed to 8-hour means if 75% of the data were present.

2.3. Serum CO₂

The serum CO₂ was measured by total concentration carbon dioxide (TCO₂ mmol/L). The trained nurses collected blood (0.5 mL) that was collected from the brachial vein into a disposable 1.5 mL tube with anticoagulant heparin lithium. Blood samples were stored on ice in coolers before use, and TCO₂ were measured immediately after blood sample collection. TCO₂ of blood samples were evaluated using the Abbott i-STAT portable clinical analyzer and CG8+ cartridges (Abbott Laboratories, Nepean, Canada).

2.4. BP Monitoring

A portable cardiac monitor (DynaPulse, model 5000A; Pulse Metric, San Diego, CA) was used to measure systolic BP (SBP) and diastolic BP (DBP) at the end of the work. We used a mercury blood pressure monitor and stethoscope to calibrate our portable cardiac monitor before all measurements (24 measurements for each participant).

2.5. Statistical Analysis

-tests were used for the between-group comparisons between the participants in office room with plants and participants in office room without a plant. Paired -tests were used for within-group comparisons within the participants in office room with plants and the same participants in office room without a plant. The association of indoor CO₂ with serum CO₂, BP, or drowsiness was examined by mixed-effects model. The exposure variables were 8-hour means of CO₂, PM_2.5, and total VOCs, and the outcome variables were SBP, DBP, serum CO₂, and drowsiness. The participant’s sex, age, BMI, temperature, humidity, and air pollution were treated as fixed effects, and the participant was fitted as a random intercept term in our mixed-effects model. The plant (with plants versus without a plant) was only adjusted in all data (all study participants) mixed-effects models. The effects of pollution on health variables were expressed as percent changes multiplied by the interquartile range (IQR) changes, i.e., , where and are the estimated regression coefficient and the mean of BP and serum CO₂, respectively. All statistical analyses were performed with the R Statistical Software, V.4.2.1 [11].

3. Results

The mean age of 68 nonsmoking participants was 33.2 years (), the mean BMI was 23.6 kg/m² (), and the male/female ratio was 1 : 1.42 (28 versus 40). The mean serum CO₂, SBP, and DBP were 22.9 mmol/L (), 117.3 mmHg (), and 75.6 mmHg (), respectively. There were no significant differences in age, BMI, and between the two groups (36 participants work in an office room with plants versus 32 participants work in an office room without a plant in 2020). None of them had cardiopulmonary diseases or took related medicine.

Table 1 summarizes the blood pressure, serum CO₂, 8-hour mean indoor CO₂, air pollution and weather, and the between-group comparisons between the office room with plants and office room without a plant. The participants in the office room without a plant were exposed to relatively higher CO₂, and PM_2.5 levels had higher serum CO₂, SBP, and drowsiness scores compared with those in the office room with plants (-test, value <0.05). There were no significant differences in gender, age, BMI, temperature, and relative humidity between participants in the office room without and with plants. For the within-group comparisons between the office room with plants and office room without a plant (Table 2), the participants in the office room without plants had relatively higher levels of CO₂ and PM_2.5 exposure as well as higher serum CO₂, SBP, and drowsiness scores compared to their values when they were in the office room with plants (paired -test, value <0.05).

In order to investigate the impact of plants on CO₂ concentrations in office rooms, we summarized the 8-hour mean level of CO₂ in the two office rooms on Sundays (no participant in the two office rooms) during the study period. The result of between-group comparison showed that the office room with plants had significantly lower CO₂ concentration () than the office room without plants () ( value <0.01). Also, the result of within-group comparison showed that the office room with plants had significantly lower CO₂ concentration () than the office room without plants () ( value <0.01).

Table 3 reports percentage changes in serum CO₂ and BP and drowsiness for an IQR change of air pollution levels among 68 participants in different modes. We found that indoor CO₂ was significantly associated with increased serum CO₂ in all data, with plants and without plant modes (1.61%; 4.52%; 1.32%). Also, the significant association between indoor CO₂ and drowsiness was observed in all data, with plants and without plant modes (7.62%; 14.57%; 3.82%). However, PM_2.5 and TVOCs were not associated with increased serum CO₂. For BP, the association of increased SBP with CO₂, PM_2.5, and TVOCs was observed in without plant modes. Moreover, the relationship between increased SBP and PM_2.5 exposure was found in all data modes.

We further explored the association between serum CO₂ and drowsiness. The results showed that elevated serum CO₂ was significantly associated with an increased drowsiness score among participants in the room with plants (6.78%) and all data (2.52%). There was no significant association between serum CO₂ level and drowsiness score among participants in the room without a plant.

4. Discussion

The present study observed the association between 8-hour mean CO₂ exposure and increased level of BP and serum CO₂ among a panel of healthy participants in an office building. The participants in the office room with plants had lower CO₂ and PM_2.5 exposures compare to those in the office room without a plant. Also, levels of SBP and serum CO₂ were relatively low among the participants in the office room with plants. These findings suggest that indoor plants might play an important role in indoor CO₂ reduction and health improvement for workers in an office building. Theoretically, in-building CO₂ is mainly from human breathing during normal respiration process. CO₂ would become an indoor air quality issue when the indoor level is increased above threshold limit [12], which have been set in the building that is below 1000 ppm [13]. Once CO₂ concentration is over 1000 ppm, adverse effects of CO₂ on cardiopulmonary system including drowsiness, increased heart rate, and elevated BP may occur among residents and/or workers in that indoor environment. Indoor plant is a possible solution to modify the association between high-level CO₂ exposure and adverse health effects. Previous studies have demonstrated the abilities of an indoor plant on indoor air quality enhancement for health benefits by air pollution reduction including PM_2.5, TVOCs, and CO₂ [8–10, 14]. The present study findings on indoor air quality improvement are consistent with previous findings and provide further support to our previous study’s conclusions [15].

The present study observed the association of elevated SBP with increased PM_2.5 and TVOCs among participants during 8-hour working in the office room without a plant. Such findings not only support the statement of the American Heart Association expert panel on biological mechanisms of air pollution effects on the cardiovascular system involving autonomic dysfunction [16] but also confirm previous findings on the association between SBP, PM_2.5, and TVOCs in an epidemiological study [17] and a randomized, double-blind cross-over trial [18]. Furthermore, the present study did not observe the relationship between air pollution and BP among participants in the office room with plants. Such finding is consistent with our previous observations demonstrating effects of houseplant on PM_2.5 reduction and decreased SBP among elderly participants [15]. According to previous studies, Pegas et al. [19] explored the effect of plants on indoor air quality in a primary school by a 9-week intensive monitoring campaign of air pollution in a classroom without and with plants. They found a decrease of approximately 30% in PM₁₀ concentrations during periods of occupancy with the presence of 6 potted plants. El-Tanbouly et al. [20] studied the role of indoor plants in air purification and human health by reviewing related publications. They concluded that the use of indoor plants is a new possible ecofriendly tool for indoor air purification and for reducing the spread of bioaerosol in confined places. Hence, the present findings provided evidence to support previous findings and suggested that indoor plant can be a part of a comprehensive strategy to improve indoor air quality and its health effects.

Although the actual biological mechanism linking indoor CO₂ to fatigue, drowsiness, or tiredness is not fully understood, the observed association of drowsiness with indoor CO₂ or serum CO₂ in the present study was in accordance with previous findings. Vehviläinen et al. [21] found that blood CO₂ level was significantly higher after the 4-hour meeting in the nonventilated office room (CO₂ max 4917 ppm) than after the 4-hour meeting in the ventilated office room (CO₂ max 1452 ppm). The subjective sleepiness assessed by the KSS questionnaire increased in the nonventilated room. No significant change in the KSS Scale was observed in the ventilated room. Satish et al. [22] conducted a controlled exposure study using a chamber outfitted like an office with CO₂ concentrations of 600, 1,000, and 2,500 ppm. The result showed that CO₂ level at 1000 ppm was associated with a reduction in the decision-making performance. The reduction of decision-making performance was reported to be influenced by fatigue [23] and drowsiness [24]. These findings may suggest that the relationship between CO₂ exposure and drowsiness is biologically plausible.

There were limitations in our study that should be noted. First, the present study design could not entirely exclude contributions of unmeasured indoor air pollution, such as bioaerosols from indoor sources. Therefore, exposure misclassification and/or measurement error could be possible and bias the observed relationships in the present study [25]. Second, the subjective bias of headache, dyspnea, fatigue, or drowsiness measurement could not be completely excluded. The study subjects were not blinded to the office room with or without a plant. However, the consistency of between-group, within-group, and mixed-effects model results regarding indoor CO₂ exposure and drowsiness makes it impossible that the present findings arose entirely from subjective bias. Finally, the present findings could not be extrapolated to various building patterns with longer working hours or different ventilation conditions.

Although these study limitations should be considered carefully when we interpret our study results, the present findings generally suggest that indoor CO₂ is associated with increased serum CO₂, SBP, and drowsiness. The reduction of indoor CO₂ by plants is a sustainable strategy to improve indoor air quality and lower SBP and drowsiness levels among a panel of healthy participants in an office environment.

Data Availability

The indoor monitoring data and questionnaire data used to support the findings of this study have not been made available due to the nondisclosure agreement signed with the company.

Additional Points

Practical Implications. Plants in the office environment can reduce CO₂ and particle levels and may lower CO₂-related health effects including less drowsiness and decreased systolic blood pressure.

Disclosure

The funder had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

This study was supported by grant (MOST 107-2314-B-038-076-MY2) from the Ministry of Science and Technology of Taiwan.

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Copyright © 2023 Kai-Jen Chuang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Indoor Air

The Association between Indoor Carbon Dioxide Reduction by Plants and Health Effects

Abstract

1. Introduction

2. Methods

2.1. Study Subjects and Study Design

2.2. Indoor Air Pollution and Weather Monitoring

2.3. Serum CO2

2.4. BP Monitoring

2.5. Statistical Analysis

3. Results

4. Discussion

Data Availability

Additional Points

Disclosure

Conflicts of Interest

Acknowledgments

References

Copyright

2.3. Serum CO₂