Formaldehyde Exposure in Office Environments and the Use of Plants to Reduce Levels of Formaldehyde.

Peter Dingle and Shuwee Hu

Formaldehyde is a ubiquitous chemical found in elevated levels in indoor environments. Formaldehyde levels were measured in a number of office environments ranging from 10 ppb up to 2110 ppb. Levels of formaldehyde in conventional offices ranged from 10 ppb to 78 ppb, with the highest concentration in a new office building with new furnishings. Elevated levels exceeding the occupational safety limit were reported in portable office buildings. Preliminary experiments conducted to evaluate the effectiveness of common house plants to reduce formaldehyde levels in portable office buildings found a density of around 2.4 plants/m2 was required before a noticeable reduction in formaldehyde concentrations occurred.

1          INTRODUCTION

Formaldehyde is a toxic substance with adverse health effects detectable at low concentrations.  Formaldehyde causes irritation of the eyes, skin and respiratory tract, wheezing, nausea, coughing, diarrhoea, vomiting, dizziness and lethargy at levels as low as 50 parts per billion (ppb) (0.05 ppm) 1.  Formaldehyde has also been associated with aggravation of asthma, emphysema, hayfever and allergy problems at low levels 2. Formaldehyde is currently considered a potential carcinogen to humans 2.

Formaldehyde is a ubiquitous gas found in elevated concentrations in indoor environments. Concentrations of formaldehyde are typically an order of magnitude greater inside buildings compared to outdoor air 3. Formaldehyde concentrations are particularly high in portable buildings due to the presence of more formaldehyde emitting materials and the relatively smaller interior volumes of air 4. Major sources of formaldehyde indoors are pressed wood products, such as particle board and plywood 16, and urea formaldehyde foam insulation 5. Other sources include carpets, curtains, floor linings, paper products, cosmetics and soaps, tobacco smoke and gas combustion 3,5.

Methods to reduce indoor formaldehyde include source removal or use of non-polluting materials, emission reduction through physical or chemical treatments and dilution through ventilation and air purification. While most solutions involve dilution through ventilation, increased interest in the scientific literature 6,7 as well as in the popular media has been given to the use of plants to purify air in buildings . Most studies however, have been conducted in the laboratory 6,7 and are difficult to extrapolate to real life situations 8.

2          METHOD

Data on formaldehyde concentrations in indoor air were obtained from office environments. Monitoring was conducted in 18 conventional office buildings and 20 portable buildings used as offices in Perth, Western Australia. Monitoring was conducted using passive monitors for formaldehyde. Three or more monitors were placed in each of the conventional office buildings for 3 to 4 days. The office buildings were selected after the occupants of each of the buildings complained of indoor air quality problems and therefore may not be totally representative of the office buildings in Perth. Two monitors were used in each of the portable buildings and monitoring was conducted over 2 days. The portable buildings studied were all on Murdoch University campus.

Experiments to test the effectiveness of plants to reduce formaldehyde levels under real life conditions were conducted in 5 adjacent portable office buildings with dimensions 2.8 x 2.9 x 2.40 m (height). The volume of each room is 19.63 m3 with a floor base of 8.18 m2.

Past experiments with plants as air purifiers have often been concerned with the use of a single plant species. In a real life situation homes have a diversity of species. Plant species included a selection of plants typically found indoors which were placed in groups of five plants. Each group was identical by having plants of the same size and of the same five species. Plant species in each group are listed in table 1. The study protocol included monitoring formaldehyde concentrations in the buildings under increasing numbers of plants by adding five plants to the experimental buildings every 2 days to a maximum of 20 plants after 9 days. The protocol is shown in table 2. Two buildings were used as controls where no plants were placed inside.

Table 1 Plant species

Common name

Scientific name

Spider plant

Chlorophytum comosum

fig tree

ficus  sp.

 

Asperdistra elatior

 

Dieffenbachia amoena

Arum ivy

Epipremum aureum

 

Table 2           Number of plants added each 2 days

Days

Number of plants in building 1, 2&3

Day 1

0

Day 3

5

Day 5

10

Day 7

15

Day 9

20

 

2.1       Analytical procedures

Formaldehyde monitors developed for this study use are based on the work by Levin et al  9,10 and have been extensively used in other studies 11. Uptake rate was calculated at 60 mL per minute and was not influenced by sampling time or relative humidity which is supported by Levin et al.  10. Sensitivity of the monitors were 1 ppb in a 24-hour sample and 3 ppb in an 8-hour sample 10.

Filters were treated with 2,4-dinitrophenylhydrazine. Formaldehyde 2,4-dinitrophenylhydrazone was analysed by high performance liquid chromatography with a mobile phase of 70% Methanol in water. Hydrazone was detected with a variable detector at 365nm. Retention time at a flow rate of 1 ml per minute was 2.9 minutes. Additional details of the technique are reported in other studies 11.

3          RESULTS

Average levels of formaldehyde in office buildings ranged from background levels of 10 ppb to 2110 ppb. Concentrations in the 18 conventional office buildings ranged from 10 ppb in an established office building to 78 ppb in a new four storey office building. Formaldehyde concentrations in 20 portable buildings ranged from 420 ppb to 2110 ppb (Table 3). The highest levels of formaldehyde found were in newly constructed portable buildings. All these levels exceeded the recommended indoor guideline of 100 ppb and frequently exceeded the occupational standard of 1000 ppb.

Table 3 Formaldehyde concentrations in conventional office and portable office buildings

Building

Mean

(ppb)

Range (ppb)

Number

of buildings

Conventional

offices

22

10-78

18

Portable Office

Building

1138

420-2110

20

 

The results of the study of the affect of plants on formaldehyde concentrations are shown in figure 1. These results show no change in formaldehyde concentrations with the addition of 5 or 10 plants in the rooms and only an 11% reduction in formaldehyde concentrations with 20 plants in the room.

Table 4 Concentration of formaldehyde compared to number of plants

Number of plants

mean concentration of formaldehyde(ppb)

0

856

5

866

10

871

15

834

20

761

 

Figure 1          Affect of plant numbers on formaldehyde concentrations.

4          DISCUSSION

 The current exposure guideline for formaldehyde non industrial indoor air environments is 100 ppb in Australia 12(Table ). Exposure standards in the United States 13 and Canada 14 are 100 ppb with a target level of 50 ppb. The WHO set a standard of 82 ppb 15. Levels of formaldehyde in office buildings ranged from background levels of 10 ppb to 2110 ppb (Table 3). Levels in conventional office buildings ranged from below 10 ppb to 78 ppb with a mean level of 22 ppb.

Table 5           Formaldehyde standards

 

Australia

United States

WHO

Indoor

guideline

(ppb)

100

50-100

82

Occupational

guideline( ppb)

1000

750

 

 Major sources of formaldehyde indoors are pressed wood products such as particle board and plywood 16. The importance of these sources are determined by source strength, source loading, and the presence of source combinations.  Source strength affects indoor levels because the more potent source will release higher levels of formaldehyde. The Australian Wood Panels Association in Australia support a voluntary E2 emission standard. In addition, 60% of all particle board in Australia has decorative overlay which reduces emissions to an E1 standard. This percentage is likely to be higher in office buildings.

Levels of formaldehyde in portable office buildings ranged from 420 ppb to 2110 ppb. These buildings frequently exceeded the Australian occupational standard of 1000 ppb and all buildings exceeded the recommended level of 300 ppb established by the American Conference of Government Industrial Hygienists in the United States 17.

Studies in the United States have reported levels of formaldehyde in mobile homes ranging from less than 10 ppb to as high as 2840 ppb 18, with the majority of mobile homes under 400 ppb 19. Formaldehyde concentration levels are particularly high in portable buildings due to higher load factor, that is, they tend to use more formaldehyde emitting materials and they have relatively smaller interior volumes 4. No controls currently exist on the emission of formaldehyde from plywood used on the interior of portable buildings in Australia. In addition, portable buildings have much lower air exchange rates than conventional homes, which leads to an accumulation of formaldehyde concentrations 4.  In 1984, the US department of housing and Urban Development, imposed limits on the formaldehyde emissions from some types of particle board and interior plywood at 300 ppb and 200 ppb test chamber concentrations respectively, to attain indoor air concentrations of no more than 40 ppb in manufactured housing 13.

5.1       Plants

Botanical air purification presents a novel approach to the control of indoor air pollutants. Studies conducted in the laboratory have shown contradictory results and have lead researchers to suggest that purification occurred through the root soil interphase of the plants and are not a result of absorption or photosynthesis at the leaf surface. Further research has suggested that reduction of formaldehyde occurs as a result of the structure and water content of the soil 7.

The effectiveness of plants as air purifiers has come under considerable critique as a result of the design of the experiments. The original studies which showed plants as purifiers were based on a single release of formaldehyde in sealed chambers. The major contributors to indoor formaldehyde concentrations are from composite woods which continue to release formaldehyde over many years. The small scale of these experiments also made it difficult to extrapolate to real life situations.

Figure 1 shows there was no decrease in formaldehyde concentrations with 5 or 10 plants present compared to no plants present and compared to the control. There was a very small reduction in formaldehyde concentrations with 15 plants, although this decrease is not considered significant at this level. A more substantial decrease of around 100 ppb was found with 20 plants in the buildings. These results suggest that achieving an 11% reduction in formaldehyde levels in a real life situation would require the equivalent of one plant to each cubic meter (m3) or 2.4 plants to every meter square (m2). In a 340 m3 home this would mean more than 340 plants. While no field tests have been reported some researchers have calculated that 680 plants would be required in a 340 m3 home to achieve a significant reduction in formaldehyde levels 8.

The most marked reduction in formaldehyde concentrations occurred when 20 plants were present, with no significant reductions occurring when 5, 10, or 15 plants were present. This raises the question of why formaldehyde concentrations were reduced with the addition of only 5 plants from 15 to 20, while no corresponding changes were seen when 5 plants were added at each of the earlier stages of the experiment. This may be explained by a threshold effect at which a certain reduction rate of formaldehyde must be achieved before an actual reduction of formaldehyde concentrations in the air occurs.

Emissions of formaldehyde depend on environmental factors, including the equilibrium concentrations in the air. In stable environmental conditions, formaldehyde will continue to be emitted from the source to reach the equilibrium concentration. If removal of formaldehyde is greater than the release, concentrations will be reduced. If removal is less than the release, concentrations will increase to an equilibrium level where formaldehyde release will equal formaldehyde removal. It is therefore possible that a small number of plants will remove formaldehyde from the air. However, the removal is not likely to be important if strong source emitters are present as the formaldehyde release rate is increased to compensate for the reduction. A reduction in formaldehyde concentration will therefore only occur when sufficient plants are present to reduce formaldehyde below the equilibrium level

6          Conclusion

Formaldehyde concentrations in conventional office buildings do not appear to be a concern, although elevated levels were reported in a new office building with new furnishings. These levels may be a cause for concern with sensitised or susceptible individuals. Portable office buildings represent a significant health risk to occupants as a result of the elevated levels of formaldehyde, often exceeding the occupational standard. Preliminary experiments with plants as air purifiers, suggest that plants in indoor environments may act to remove small amounts of formaldehyde from the air. However, they do not appear to be an efficient means of removal and require large numbers to achieve any detectable reduction in formaldehyde concentrations.

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