Emission of Volatile Organic Compounds from Wood and Wood-Based Materials

Summary and Conclusion

Background

The impact of emissions from wood-based furniture and building products on the indoor environment is gaining more and more attention. In an increasing number of cases the emission to the indoor air has become an essential product selection criterion for both end-users and professional users.

Wood is generally considered as an advantageous material in a wide environmental perspective, even though studies performed only rarely comprise material emissions except for formaldehyde emission.

This project was carried out to extend the limited knowledge on emissions from wood and wood-based materials for interior use and to propose a model for evaluation of emissions from these materials and methods to reduce material emissions. It has not been the intention to evaluate the emission from wood in relation to other material emissions.

Test Programme

This study was based on chemical analysis of emissions from 23 materials representing solid wood and wood-based materials commonly used in furniture, interior furnishings and building products in 1996. The test scheme comprised materials and products in varying degrees of complexity from solid wood to coated veneered panels. The study comprised the solid wood species: ash, beech, spruce and pine; six different wood-based panels: particleboard of pine and spruce with different glues, MDF (medium density fibreboards) and OSB (oriented strand board) of conifer and plywood of birch; beech veneered particleboards with two different glue types for veneer gluing; two floor oils on solid beech on urethane alkyd/linseed oil and natural resin basis respectively; five different lacquered beech veneered particleboards coated with nitrocellulose lacquer, UV-curing lacquer, acid-curing lacquer, water-borne acrylic lacquer and polyurethane lacquer respectively.

The selected 23 wood-based materials and measured emissions are to be considered examples and can neither be considered representative for all wood-based materials for interior use nor be generally representative for emissions from wood and wood-based materials.

The project task, which only comprised emission from wood and wood-based products to the indoor environment, does not lay the foundations of a weighting of the emissions in relation to other material types or weighing the emission in relation to other indoor environment factors.

Emission Testing

Prior to testing and analysis the chemical substances expected to emit from the selected materials were identified, so were the substances included in national or international lists as health hazardous in respect to cancer, allergy, reprotoxicity and neurotoxicity

The selected materials were initially examined by a qualitative screening to identify the above mentioned substances and to determine an analysis programme for the quantitative determinations for each of the wood-based materials.

Of the 144 different chemical substances identified by the screening analyses 42 were aldehydes (saturated or unsaturated) or ketones and 20 hydrocarbons of the terpene types: mono- and sesquiterpenes.

The quantitative determinations were carried out by emission chamber testing under conditions common in building interiors according to a test method for determination of volatile organic compounds especially adjusted to wood-based products.

The analysis programme for the quantitative measurements comprised determination of all individual volatile organic compounds, VOC’s, by gas chromatography with mass spectrometric detection, liquid chromatography and photometry by the acetylacetone method.

Results

By the chamber measurements totally 84 individual substances were quantified. The predominant emissions determined from uncoated wood and wood-based materials were aldehydes, mainly acetaldehyde, propanal, butanal, pentanal and hexanal, as well as the ketone: acetone. The aldehydes varied in content in the different materials. Formaldehyde was the predominant single emittant in the case of urea-formaldehyde-glued panels. In the emission from pine also emissions of terpenes, mainly a -pinene, 3-carene and limonene, were detected in larger concentrations. The emissions from the investigated wood-based panels varied as expected considerably dependent on the applied glue systems.

The emissions from surface treated wood-based materials originate mainly from the oils and lacquers, and were mainly alcohols, unsaturated aldehydes, esters, glycol ethers and -esters. The emission of most aldehydes from the treated materials can be traced back to both coating or oil and wood.

A part study of four variations of pine of varying origin (northern Finland and southern Sweden respectively) and content of heartwood and sapwood showed considerable difference in emission rates of especially 3-carene and a -pinene. It should be noted that the growth conditions and place can be of major importance.

From the results there is no documentation that indoor air problems are caused by wood.

Concentrations of the chemical substances quantified by chamber measurements were converted into concentrations to which persons are exposed in the indoor air by means of standard room considerations.

Very limited indoor air concentrations were seen from solid ash, beech and oak calculated at a material-load of 0.4 m²/m³ corresponding to, for example, a floor or a table and 6 chairs. Solid pine gave considerably larger emissions than the other tested wood species. Solid ash, beech, oak, wood-based panels and beech veneered particleboards are examples of materials seldom used in practice without surface treatment.

A small cottage covered with a -pinene and 3-carene rich untreated pine on the floor, ceiling and all four walls is an example of a scenario resulting in relatively high indoor air concentrations in consequence of emissions from wood. Worst case occur if the cottage is newly built of fresh wood and if it for some reason is made relatively air tight, hence resulting in a low air exchange rate.

Evaluations of the Comfort and Health Effects

The evaluation of comfort and possible health effects of emissions from wood and wood-based materials was based on experiences from the above mentioned experimental work and general principles for toxicological evaluation and literature data.

Evaluation of single substances included all the 84 substances quantified by the emission chamber measurements.

Concentrations converted from test chamber to concentrations, to which humans are exposed in the indoor air, were compared with the toxicological determined "Lowest Concentration of Interest in the indoor air (LCI)" and odour threshold values.

The influence of materials and products on the indoor environment was evaluated by:

A sum of concentrations in the indoor air divided by the "lowest concentration of interest in the indoor air" for additive effects of the same type,

hereafter called S

An indoor-relevant time-value based on odour and irritation thresholds

LCI- and S-Value

LCI is defined as the lowest concentration of a certain substance, which will not - with our present knowledge - cause risk of hazardous effects on humans. For most of the chemical substances the LCI-values in this investigation were based on irritation. More severe effects occurred for most of the chemical substances at concentrations magnitudes higher than odour and irritation.

Determination of LCI-values was difficult due to lack of toxicological data for most of the emitted substances in the relatively low concentrations, in which the substances are present in the indoor air. In several cases the LCI-values were determined by analogue considerations. In cases, in which the data on the substances lacked, and in which it was evaluated that the most essential effect was irritation, the LCI-values were based on "RD50-values", which are determined based on decrease of the respiratory frequency of mice.

Irritation is thus the most frequent toxicological effect for the examined wood and wood-based materials and gave the basis of the S-value calculations.

The indoor-relevant time-value in days is an expression of the period of time necessary for the decline of the emissions into acceptable concentration levels, where neither irritation of eyes, nose and the upper respiratory tract nor odour may be expected.

Model for Evaluation

The proposed model for assessment based on the S-value and the indoor-relevant time-value differentiates the emissions from the investigated materials and can be used as a common basis for relative evaluations of wood, wood-based materials and products. It should, however, be noted that the absolute S-values as well as LCI-values, odour and irritation threshold values can always be questioned, and the values might change, as new knowledge occur.

In the case of materials, which do not cause emissions containing carcinogens, allergens or reproductive toxicants, the procedures and results of the evaluations were basically the same both according to the S-value and to the indoor-relevant time-value based on the addition of the irritative impact.

The time-values based on odour thresholds, resulted, however, in longer time-values than time-values based on irritation thresholds - for all decisive individual substances apart from formaldehyde - and consequently odour became determining for the indoor-relevant time-values in most cases.

If health hazardous effects except from respiratory irritation due to emission could be excluded, the evaluation could solely be based on the concept of indoor-relevant time-value.

When the indoor air is of high priority, it should be advised to select products made of lower-emitting materials, in order to limit the emission to the indoor air. Thus a larger probability of reducing the discomfort and possible health effects caused by emission from these materials and products is achieved.

Selection of relatively lower-emitting materials and products can be made by selection of materials and products with a relatively low S-value and a relatively low indoor-relevant time-value.

A proposed classification based on 28 days measurement in test chamber divides wood and wood-based materials in three classes: low-emitting, medium-emitting and high-emitting materials. Among the tested coatings the UV-curing lacquer on beech veneered particleboards was low-emitting, the acid-curing lacquer on beech veneered particleboards was high-emitting, while the other investigated lacquers on beech veneered particleboards and investigated oils on solid beech were considered medium-emitting. Among the tested solid wood species ash, beech, oak and spruce were low/medium emitting and pine high-emitting. It should be taken into account that it is different types of chemical substances that are emitted depending on wood species and type of surface treatment.

Reduction of Hazardous Effects

Modification/substitution of materials should be considered when the emission contains toxicologically unknown chemical substances. Materials and products should as far as possible not contain chemical substances with carcinogenic, reprotoxic or immunologic effects. Should this be the case these substances should be replaced by substances or materials, which are less hazardous or the material should at least be modified to minimize the content as much as possible.

Modification of materials and products should be considered for the materials and products with relatively large S-values and high indoor-relevant time-values.

Factors of importance for modification/substitution considerations have been systematized and applied on six examples of wood and wood-based materials and products.

The examples, which have been based on a theme for inspiration for modification/substitution considerations, illustrate primary relations of importance for the impact of materials on the indoor environment. Further environment a.o. working environment, and economics should be involved, where these are of decisive importance for the modification/substitution, and if their consequences are known. Description of a product in relation to a given application as well as general and specific comments elaborates the considerations.

The six examples of substitution/modification considerations for wood furniture, interior furnishings and wood-based building products comprise: A wooden floor treated with different types of lacquer and oil; wardrobe of veneered panel coated with different types of transparent lacquer; coffee table of uncoated solid wood and respectively veneered panel coated with different types of transparent lacquer; bookcase of uncoated solid wood and respectively veneered panel coated with different types of transparent lacquer; office table of veneered particleboard coated with different types of transparent lacquer and a cottage of pine. Finally, a proposal is given for a model for relative description of materials of the similar type exemplified for wooden floor treated with different lacquers and oils.