The phytoremediation of indoor air pollution: a review on the technology development from the potted plant through to functional green wall biofilters

Poor indoor air quality is a health problem of escalating magnitude, as communities become increasingly urbanised and people’s behaviours change, lending to lives spent almost exclusively in indoor environments. The accumulation of, and continued exposure to, indoor air pollution has been shown to result in detrimental health outcomes. Particulate matter penetrating into the building, volatile organic compounds (VOCs) outgassing from synthetic materials and carbon dioxide from human respiration are the main contributors to these indoor air quality concerns. Whilst a range of physiochemical methods have been developed to remove contaminants from indoor air, all methods have high maintenance costs. Despite many years of study and substantial market demand, a well evidenced procedure for indoor air bioremediation for all applications is yet to be developed. This review presents the main aspects of using horticultural biotechnological tools for improving indoor air quality, and explores the history of the technology, from the humble potted plant through to active botanical biofiltration. Regarding the procedure of air purification by potted plants, many researchers and decades of work have confirmed that the plants remove CO₂ through photosynthesis, degrade VOCs through the metabolic action of rhizospheric microbes, and can sequester particulate matter through a range of physical mechanisms. These benefits notwithstanding, there are practical barriers reducing the value of potted plants as standalone air cleaning devices. Recent technological advancements have led to the development of active botanical biofilters, or functional green walls, which are becoming increasingly efficient and have the potential for the functional mitigation of indoor air pollutant concentrations.     

Investigations on the surveys of office environments and the total evaluation method—IAQ-Index

1. 1. A comprehensive study was made to establish evaluation methods for better office environments.

2. 2. In our study, measurements of thermal, acoustic, lighting, airflow and air quality conditions in indoor environments were made as well as questionnaire to the occupants on the evaluations of indoor environments and the feeling of fatigue.

3. 3. We also made an attempt to rate the evaluation value based on concepts and standards to evaluate totally office environments in a view point of “the office environments where people can work healthy and vigorously”. The evaluation values were called IAQ-index.

Review on modeling heat transfer and thermoregulatory responses in human body

Several mathematical models of human thermoregulation have been developed, contributing to a deep understanding of thermal responses in different thermal conditions and applications. In these models, the human body is represented by two interacting systems of thermoregulation: the controlling active system and the controlled passive system. This paper reviews the recent research of human thermoregulation models. The accuracy and scope of the thermal models are improved, for the consideration of individual differences, integration to clothing models, exposure to cold and hot conditions, and the changes of physiological responses for the elders. The experimental validated methods for human subjects and manikin are compared. The coupled method is provided for the manikin, controlled by the thermal model as an active system. Computational Fluid Dynamics (CFD) is also used along with the manikin or/and the thermal model, to evaluate the thermal responses of human body in various applications, such as evaluation of thermal comfort to increase the energy efficiency, prediction of tolerance limits and thermal acceptability exposed to hostile environments, indoor air quality assessment in the car and aerospace industry, and design protective equipment to improve function of the human activities.     

Indoor climate and air quality

 In industrialized countries about 90% of the time is spent indoors. The ambient parameters affecting indoor thermal comfort are air temperature and humidity, air velocity, and radiant heat exchange within an enclosure. In assessing the thermal environment, one needs to consider all ambient parameters, the insulating properties of the occupants’ clothing, and the activity level of the occupants by means of heat balance models of the human body. Apart from thermal parameters, air quality (measured and perceived) is also of importance for well-being and health in indoor environments. Pollutant levels are influenced by both outdoor concentrations and by indoor emissions. Indoor levels can thus be lower (e.g. in the case of ozone and SO₂) or higher (e.g. for CO₂ and formaldehyde) than outdoor levels. Emissions from cooking play an important role, especially in developing countries. The humidity of the ambient air has a wide range of effects on the energy and water balance of the body as well as on elasticity, air quality perception, build-up of electrostatic charge and the formation or mould. However, its effect on the indoor climate is often overestimated. While air-handling systems are commonly used for achieving comfortable indoor climates, their use has also been linked to a variety of problems, some of which have received attention within the context of ”sick building syndrome”. Received: 27 October 1997 / Accepted 26 November 1997     

Fungal pollution of indoor environments and its management

Indoor environments play important roles in human health. The health hazards posed by polluted indoor environments include allergy, infections and toxicity. Life style changes have resulted in a shift from open air environments to air tight, energy efficient, environments, in which people spend a substantial portion of their time. Most indoor air pollution comes from the hazardous non biological agents and biological agents. Fungi are ubiquitous in distribution and are a serious threat to public health in indoor environments. In this communication, we have reviewed the current status on biotic indoor air pollution, role of fungi as biological contaminants and their impact on human health.     

Detection of airborne Stachybotrys chartarum macrocyclic trichothecene mycotoxins in the indoor environment

The existence of airborne mycotoxins in mold-contaminated buildings has long been hypothesized to be a potential occupant health risk. However, little work has been done to demonstrate the presence of these compounds in such environments. The presence of airborne macrocyclic trichothecene mycotoxins in indoor environments with known Stachybotrys chartarum contamination was therefore investigated. In seven buildings, air was collected using a high-volume liquid impaction bioaerosol sampler (SpinCon PAS 450-10) under static or disturbed conditions. An additional building was sampled using an Andersen GPS-1 PUF sampler modified to separate and collect particulates smaller than conidia. Four control buildings (i.e., no detectable S. chartarum growth or history of water damage) and outdoor air were also tested. Samples were analyzed using a macrocyclic trichothecene-specific enzyme-linked immunosorbent assay (ELISA). ELISA specificity was tested using phosphate-buffered saline extracts of the fungal genera Aspergillus, Chaetomium, Cladosporium, Fusarium, Memnoniella, Penicillium, Rhizopus, and Trichoderma, five Stachybotrys strains, and the indoor air allergens Can f 1, Der p 1, and Fel d 1. For test buildings, the results showed that detectable toxin concentrations increased with the sampling time and short periods of air disturbance. Trichothecene values ranged from <10 to >1,300 pg/m3 of sampled air. The control environments demonstrated statistically significantly (P < 0.001) lower levels of airborne trichothecenes. ELISA specificity experiments demonstrated a high specificity for the trichothecene-producing strain of S. chartarum. Our data indicate that airborne macrocyclic trichothecenes can exist in Stachybotrys-contaminated buildings, and this should be taken into consideration in future indoor air quality investigations.     

Biological treatment of indoor air for VOC removal: potential and challenges

There is nowadays no single fully satisfactory method for VOC removal from indoor air due to the difficulties linked to the very low concentration (microg m(-3) range), diversity, and variability at which VOCs are typically found in the indoor environment. Although biological methods have shown a certain potential for this purpose, the specific characteristic of indoor air and the indoor air environment brings numerous challenges. In particular, new methods must be developed to inoculate, express, and maintain a suitable and diverse catabolic ability under conditions of trace substrate concentration which might not sustain microbial growth. In addition, the biological treatment of indoor air must be able to purify large amounts of air in confined environments with minimal nuisances and release of microorganisms. This requires technical innovations, the development of specific testing protocols and a deep understanding of microbial activities and the mechanisms of substrate uptake at trace concentrations.     

Practices contributing to biotic pollution in Air-conditioned indoor environments

Indoor environments play important roles in human health. The health hazards posed by polluted indoor environments include allergy, infections and toxicity. The term ‘sick building syndrome’ (SBS) describes causes of building occupants experiencing adverse health effects that appear to be linked to the time spent in a building. Questionnaire-based data were collected from the people who live or work in air-conditioned (A/C) rooms. Responses of the occupants were analyzed to understand the practices contributing to biotic pollution of indoor air-conditioned environments. Our survey revealed some interesting facts about the users of A/C rooms and their practices that may be contributing to the indoor air quality. The allergy complaints and use of anti-allergy medicines were noted commonly among the occupants of government (Govt.) organizations and computer training centers where cleaning of room and A/C filters were not done periodically. Cleaning practices may reduce the complaints.     

The airborne metagenome in an indoor urban environment

The indoor atmosphere is an ecological unit that impacts on public health. To investigate the composition of organisms in this space, we applied culture-independent approaches to microbes harvested from the air of two densely populated urban buildings, from which we analyzed 80 megabases genomic DNA sequence and 6000 16S rDNA clones. The air microbiota is primarily bacteria, including potential opportunistic pathogens commonly isolated from human-inhabited environments such as hospitals, but none of the data contain matches to virulent pathogens or bioterror agents. Comparison of air samples with each other and nearby environments suggested that the indoor air microbes are not random transients from surrounding outdoor environments, but rather originate from indoor niches. Sequence annotation by gene function revealed specific adaptive capabilities enriched in the air environment, including genes potentially involved in resistance to desiccation and oxidative damage. This baseline index of air microbiota will be valuable for improving designs of surveillance for natural or man-made release of virulent pathogens.     

Thermal comfort in naturally ventilated and air-conditioned buildings in humid subtropical climate zone in China

A thermal comfort field study has been carried out in five cities in the humid subtropical climate zone in China. The survey was performed in naturally ventilated and air-conditioned buildings during the summer season in 2006. There were 229 occupants from 111 buildings who participated in this study and 229 questionnaire responses were collected. Thermal acceptability assessment reveals that the indoor environment in naturally ventilated buildings could not meet the 80% acceptability criteria prescribed by ASHRAE Standard 55, and people tended to feel more comfortable in air-conditioned buildings with the air-conditioned occupants voting with higher acceptability (89%) than the naturally ventilated occupants (58%). The neutral temperatures in naturally ventilated and air-conditioned buildings were 28.3°C and 27.7°C, respectively. The range of accepted temperature in naturally ventilated buildings (25.0∼31.6°C) was wider than that in air-conditioned buildings (25.1∼30.3°C), which suggests that occupants in naturally ventilated buildings seemed to be more tolerant of higher temperatures. Preferred temperatures were 27.9°C and 27.3°C in naturally ventilated and air-conditioned buildings, respectively, both of which were 0.4°C cooler than neutral temperatures. This result suggests that people of hot climates may use words like “slightly cool” to describe their preferred thermal state. The relationship between draught sensation and indoor air velocity at different temperature ranges indicates that indoor air velocity had a significant influence over the occupants’ comfort sensation, and air velocities required by occupants increased with the increasing of operative temperatures. Thus, an effective way of natural ventilation which can create the preferred higher air movement is called for. Finally, the indoor set-point temperature of 26°C or even higher in air-conditioned buildings was confirmed as making people comfortable, which supports the regulation in China that in public and office buildings the set-point temperature of air-conditioning system should not be lower than 26°C.     

Detection of Satratoxin G and H in Indoor Air from a Water-Damaged Building

The occurrence of Stachybotrys chartarum in indoor environments has been linked to adverse health effects as well as few cases of pulmonary haemorrhages in humans. Although the highly toxic secondary metabolites of this fungus, like satratoxin G and H, were frequently claimed with outbreaks of such diseases, these toxins have hardly been identified in the air of naturally contaminated indoor environments. Herein, a case of a LC-MS/MS-confirmed occurrence of airborne S. chartarum-toxins in a water-damaged dwelling is reported. Satratoxin G (0.25 ng/m(3)) and satratoxin H (0.43 ng/m(3)) were detected. This provides further evidence that Stachybotrys-toxins can be transferred from mouldy indoor materials into air, which could be a factor in the aetiology of health symptoms related to the sick building syndrome.     

Recent advances in biological systems for improving indoor air quality

Reviews in Environmental Science and Bio/Technology - Studies on human exposure to indoor air pollution reveal that indoor environments could be at least twice as polluted as outdoor environments....     

Effects of exercise and poor indoor air quality on learning,memory and blood IGF-1 in adolescent mice

It is known that regular aerobic exercise enhances cognitive functions and increases blood insulin-like growth factor 1 (IGF-1) levels. People living in urban areas spend most of their time indoors and indoor air quality can affect health. We investigated the effects of aerobic exercise in poor and good air quality environments on hippocampus and prefrontal cortex (PFC) neurons, anxiety, and spatial learning and memory in adolescent mice. Poor air quality impaired spatial learning and memory; exercise did not affect learning or memory impairment. Exercise in a good air quality environment improved spatial learning and memory. Poor air quality increased apoptosis in the hippocampus and PFC. Both exercised and sedentary groups living in a poor air quality environment had lower serum IGF-1 levels than those living in a good air quality environment. Living in a poor air quality environment has negative effects on the hippocampus, PFC and blood IGF-1 levels in adolescent mice, but exercise did not alter the negative effects of poor air quality.     

Detection and identification of moulds in dutch houses and non-industrial working environments

The mycoflora of indoor non-industrial environments is reported from “case” studies in The Netherlands. Both air sampling by a RCS-Reutcr centrifugal air sampler and surface sampling by swabs and cellotape preparations were carried out in homes, archives and libraries, musea, offices and schools. Common species encountered in these indoor environments are Aspergillus versicolor, Penicillium brevicompactum, P. chrysogenum, Cladosporium spp. and the xerophilic fungi Eurotium spp. and Wallemia sebi. Aspergillus fumigatus, Scopulariopsis spp. and Stachybotrys chartarum were occasionally isolated. It is not always possible to detect the mycoflora growing on surfaces by air sampling. Therefore direct microscopical examination and sampling from surfaces in addition to air sampling is strongly recommended for the detection of viable moulds in indoor environments. Selection of the most suitable media for isolation of fungi is discussed.     

Comparison of environmental tobacco smoke concentrations and mutagenicity for several indoor environments

Environmental tobacco smoke (ETS) is a major source for indoor air pollution. Although ETS-caused indoor air pollution has been well studied in the developed countries, few studies have examined ETS indoor air pollution in China, which currently has the largest population of tobacco smokers. In this study, respirable-particulate (RP) from ETS-contaminated (RP-ETS) indoor air was collected and measured in 5 different indoor environments during the winter in the northwestern Liaoning Province, China. The extractable portion of RP-ETS (ERP-ETS) was obtained by dichloromethane extraction and used in the Salmonella mutagenicity assay in the presence of S9 using strains TA98, TA100, and TA1538. The percentage of RP-ETS attributable to ETS (ETS-RP) and the percentage of ERP-ETS attributable to ETS (ETS-ERP) were estimated by measuring the concentration of solanesol, an ETS marker. Comparative results in 5 different indoor environments were: (1) the concentration of RP-ETS ranged from 197.3 to 1227.6 microg/m(3) and approximately 64.7 to 92. 0% of the RP-ETS originated from ETS; (2) the concentration of ERP-ETS ranged 88.8 to 601.5 microg/m(3) and approximately 83.1 to 95.4% of the ERP-ETS originated from ETS; (3) the mutagenic potency (revertants/m(3)) of ERP-ETS ranged from 60.4 to 595.5 for TA98, from 33.7 to 312.8 for TA100, and from 49.7 to 475.2 for TA1538. The data indicate that the extent of ETS pollution and the potential health hazards of ETS to humans in the five indoor environments are in the following increasing order: rural bedrooms, urban living rooms, office rooms, restaurants, and passenger cars in that area.     

Airborne bacteria and fungal spores in the indoor environment. A case study in Singapore

The concentration of airborne fungal spores and bacteria as related to room temperature, humidity and occupancy levels within a library building in Singapore was determined. Measurement of indoor air quality with respect to microorganisms is of particular importance in tropical environments due to the extensive use of air‐conditioning systems and the potential implications for human health. This study has revealed a number of interesting relationships between the concentrations of fungal spores and bacteria in relation to both environmental and human factors. The levels of fungal spores measured in the indoor environment were approximately fifty times lower than those measured outside, probably because of the lowered humidity caused by air‐conditioning in the indoor environment. The variation in fungal spore concentration in the outdoor environment is likely to be due to the diurnal periodicity of spore release and the response to environmental factors such as light temperature and humidity. The indoor concentration of fungal spores in air was not clearly correlated to concentrations measured in air outside of the library building and remained relatively constant, unaffected by the difference in the numbers of occupants in the library. In contrast, the indoor concentrations of bacteria in air were approximately ten times higher than those measured outdoors, indicating a signficant internal source of bacteria. The elevated levels of indoor bacteria were primarily attributed to the number of library occupants. Increased human shedding of skin cells, ejection of microorganisms and particulates from the respiratory tract, and the transport of bacteria on suspended dust particles from floor surfaces probably accounts for the strong positive correlation between occupancy levels and the concentration of bacteria in internal air.     

Biological responses to indoor air contaminants

Summary The scientific study of indoor air quality has been a topic for research in the last two decades; in the late 70's it became an issue of general public perception. The public perceptions have been such tremendous stimuli because they involve aspects of health and welfare (comfort and economics). Various biomedical studies were performed to evaluate adverse biological effects associated with ambient and occupational pollutants. However, it became obvious that humans were exposed more, on a temporal basis, to their normal indoor environments than they were either in the workplace or outside. Concern with biological contaminants was always an issue, but rarely examined indoors until recently. Biological responses to the indoor environment will be discussed in this paper.     

Bioclimatic evaluation of the human discomfort level for several Antarctic regions

A set of unfavorable climatic factors determines how extreme the environment is for humans in particular regions. The Arctic and Antarctic (polar) regions are generally considered to be the most extreme environments. Assessing the extreme conditions is of importance for developing life support systems and personal protective equipment, implementing proper labor management, and preventing frostbite. Several methods are currently used to assess the climate severity, but none of them addresses the level of discomfort for humans. Two indices, the Wind Chill Index (WCI) and Bioclimatic Index of Severity of Climatic Regime (BISCR), were previously developed to estimate the level of bioclimatic discomfort. With the indices, bioclimatic parameters were evaluated for eight Antarctic stations: Amundsen–Scott, Bellingshausen, Byrd, McMurdo, Mirny, Molodezhnaya, Novolazarevskaya, and Vostok. Monthly and annual data on air temperature, wind speed, relative humidity, altitude, and air pressure were used to calculate the WCI and BISCR. The BISCR, which includes hypoxia as a component of bioclimatic discomfort, was found to better predict the impact of meteorological conditions on the human body in Antarctica and to allow comparisons of outdoor climatic conditions and indoor microclimate for Antarctic stations. The WCI proved to detect no difference between stations from different climatic zones, especially in indoor conditions, thus being unsuitable for comparisons. The findings can be used for labor management at inland Antarctic stations to minimize possible health risks.     

Microbiological indoor air quality in healthy buildings

There is a growing interest in indoor air quality for a better quality environment both at home and at work because many people spend at least 80% of their time indoors. The aim of our study was to evaluate the indoor concentration of airborne bacteria and fungi in a University auditorium, in an office of public buildings and in an apartment in the presence and in absence of building's occupants, building materials and furnishings. The concentrations of airborne bacteria and fungi were determined using a Surface Air System (SAS). In presence of people and furnishings the average air concentrations of bacteria (University auditorium: 925-1225 CFU m(-3); office: 493 CFU m(-3); apartment: 92-182 CFU m(-3)) were higher than in absence (respectively: 190-315 CFU m(-3); 126 CFU m(-3); 66-80 CFU m(-3)). The average air concentrations fungal were higher in presence of people and furnishings (University auditorium: 1256-1769 CFU m(-3); office: 858 CFU m(-3); apartment: 147-297 CFU m(-3)) than in absence (respectively: 301-431 CFU m(-3); 224 CFU m(-3); 102-132 CFU m(-3)). The obtained data can be considered as a step to identify acceptable levels for bioaerosols in common indoor environments.     

Detection of Airborne Stachybotrys chartarum Macrocyclic Trichothecene Mycotoxins in the Indoor Environment

The existence of airborne mycotoxins in mold-contaminated buildings has long been hypothesized to be a potential occupant health risk. However, little work has been done to demonstrate the presence of these compounds in such environments. The presence of airborne macrocyclic trichothecene mycotoxins in indoor environments with known Stachybotrys chartarum contamination was therefore investigated. In seven buildings, air was collected using a high-volume liquid impaction bioaerosol sampler (SpinCon PAS 450-10) under static or disturbed conditions. An additional building was sampled using an Andersen GPS-1 PUF sampler modified to separate and collect particulates smaller than conidia. Four control buildings (i.e., no detectable S. chartarum growth or history of water damage) and outdoor air were also tested. Samples were analyzed using a macrocyclic trichothecene-specific enzyme-linked immunosorbent assay (ELISA). ELISA specificity was tested using phosphate-buffered saline extracts of the fungal genera Aspergillus, Chaetomium, Cladosporium, Fusarium, Memnoniella, Penicillium, Rhizopus, and Trichoderma, five Stachybotrys strains, and the indoor air allergens Can f 1, Der p 1, and Fel d 1. For test buildings, the results showed that detectable toxin concentrations increased with the sampling time and short periods of air disturbance. Trichothecene values ranged from <10 to >1,300 pg/m³ of sampled air. The control environments demonstrated statistically significantly (P < 0.001) lower levels of airborne trichothecenes. ELISA specificity experiments demonstrated a high specificity for the trichothecene-producing strain of S. chartarum. Our data indicate that airborne macrocyclic trichothecenes can exist in Stachybotrys-contaminated buildings, and this should be taken into consideration in future indoor air quality investigations.