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

5. Evaluation of Emissions

5.1 "Lowest Concentration of Interest"
5.2 Indoor-Relevant Time-Values
5.3 Results
5.3.1 Evaluation of Individual Substance Emissions
5.3.2 Evaluation of Emissions from Wood, Wood-Based Materials and Products

Evaluations of health- and comfort effects of emissions from wood and wood-based materials and products are based on toxicological principles and literature data. The toxicological principles used are given in detail in chapter 4.

Evaluation Procedure

The procedure of evaluating the emissions from wood and wood-based materials included:

Basis for Calculations

For evaluation of emissions from wood and wood-based materials concentrations are used, which have been converted into indoor air concentrations for individual substances in the emissions by standard room considerations according to clause 3.2.

A list of substances, which in principle could be expected to be emitted from wood and wood-based materials: "All Chemicals List" and a list of substances quantified by the emission chamber measurements carried out: "Project Specific List" appears from Appendix 5.

Evaluation of Individual Substances

All 84 individual substances quantified by emission chamber measurements were evaluated cf. Appendix 7.

An outline in principle for evaluation of emissions appears from chapter 4, Figure 4.1. By evaluation of the individual substances found in the emissions by chamber measurements, the considerations have, when possible, comprised the following:

	Toxicological effects (carcinogenic, immunologic, reprotoxic or neurotoxic effects)
	Irritation (inflammatory and sensory irritation)
	Other health effects
	Odour
	Amount of unknown substances

Also odour threshold values were included in the considerations. Odour thresholds and irritation thresholds were included in the calculation of the indoor-relevant time-value, cf. clause 5.2 and Appendix 4.

Evaluation of substances without any relevant toxicological information were, when possible, based on the assumption that the toxicological properties corresponded to a known and chemically analogue substance. If there were not sufficient data available for analogue considerations, it was impossible to evaluate the substance, and it was thus considered toxicologically unknown.

5.1 "Lowest Concentration of Interest"

The term Lowest Concentration of Interest in the indoor air, LCI, that first was introduced in a European, theoretical R&D co-operation (ECA, Report No. 18, 1997) is described in detail in clause 4.4.

The LCI-value was laid down on basis of the effect, which was shown of the lowest concentration.

For most of the chemical substances in the emissions from the investigated wood and wood-based materials irritation was the effect, which was decisive for the determination of the LCI-values. More serious effects occurred for most of the substances at concentrations magnitudes higher than irritation.

In more cases the LCI-values have been fixed by analogue considerations. In cases, in which data on substances were missing, and in which it was considered that the most essential effect was irritation, the LCI-values were based on "RD 50-values". "RD 50-values" have been determined based on decrease of the respiratory frequency of mice.

The values have been converted into exposure in the indoor air by introduction of a safety factor of 10 in order to protect sensitive social groups and by taking exposure for 24 hours a day and 7 days a week into consideration (Nielsen, G.D., 1997).

Determination of LCI-values were difficult due to lack of toxicological data for most of the emitted substances in the relatively low concentrations, in which the substances were present in the indoor climate.

The S-value is calculated by adding the contribution of the indoor-relevant concentration divided by the LCI-value for all individual substances of the emissions for effects of the same kind:

hereafter called S

In principle each effect should be summarised individually, and the addition consideration can only be carried out for additive effects such as irritation.

The advantage of using LCI-values (in the shape of S-values) is that they allow a quick comparison of wood and wood-based materials and thus resulting in identification of more indoor air friendly products.

The most extensive limitation is that LCI-values very often are ascribed to limited toxicological documentation, and that no uniform background for determination of LCI-values exist. LCI-values should therefore only be considered by comparison of materials with a uniform emission profile and as a first indication of health and/or comfort problems in the indoor air.

A non-uniform background for determination of LCI-values may entail that the evaluation of individual substances will be more or less restrictive. In the present report the evaluation of formaldehyde follows the coming WHO-recommendation and is relatively less restrictively determined than the other individual substances cf. clause 5.3.1.

5.2 Indoor-Relevant Time-Values

The indoor-relevant time-value for a material or a product is the time, it takes the slowest emitting individual substance of the emission with the lowest odour or irritation threshold to reach down on half of this threshold value. All concentrations and thresholds have been converted into indoor-relevant concentrations by using standard room considerations.

Concerning irritation it is assumed that the impact from more substances is larger than the irritative contribution of the individual substance, accordingly, in case of more substance with irritative effect the requirement to the sum of irritative substances in the emission: S C_i/CL_i in which CL is the acceptable concentration in the indoor air calculated as half the irritation threshold. Like the sum calculations regarding LCI the sum of irritative substances is determined by adding the contribution of the indoor-relevant concentration divided by the CL-value for all individual substances with irritative effect in the emission.

The indoor-relevant time-value is usually based on both chemical emission measurement as well as sensory determination of the air quality. (In the present project the time-value alone is based on chemical measurement, and sensory evaluation has only been carried out directory for 3 of the 23 investigated materials, cf. clauses 3.1 and 3.1.2).

The indoor-relevant time-value in days is a direct measure of the time it takes from a product is installed till the emissions of individual substances no longer are expected to cause odour or risk of irritation in eyes, nose or upper respiratory passage.

Application of indoor-relevant time-values gives like LCI-values the possibility of an indoor-related comparison of wood and wood-based materials and to identify the most indoor air friendly products.

The most essential limitations are that threshold values for odour and irritation have only been found for a limited number of substances (the database: VOCBASE; National Inst. of Occupational Health, 1996, comprising values for approx. 800 substances), and that there are essential deviations between the published odour threshold values. Besides, the threshold values will typically be changed when new knowledge is obtained.

Odour does not imply that the emission causes health effects, nor does no-odour imply that the emission does not cause health effects.

Presently, the indoor-relevant time-value concept, which was developed by the Danish Building Research Institute and the National Institute of Occupational Health, is based on comparison of indoor-relevant concentrations with odour and irritation threshold values. It is thus based on the effects irritation and odour, which by experience in all circumstances are the relevant effects to take into consideration by evaluation of the indoor air impacts from materials. The time-value concept could, however, immediately be extended by further effects such as e.g. carcinogenic and immunologic effects, when generally accepted indoor-air related thresholds for these health effects are available.

Indoor-relevant time-values are the basis of the Indoor Climate Labelling of building products and other products when used in buildings (Danish Society of Indoor Climate, Standard Test Method, 1994), (Wolkoff, P. and Nielsen, P.A., 1996).

5.3 Results

Results of the evaluations of emissions are given as individual substance evaluations in clause 5.3.1 and as evaluations of the investigated wood and wood-based materials in clause 5.3.2. Evaluations in detail of the individual substances quantified by emission chamber measurements are stated in Appendix 7.

5.3.1 Evaluation of Individual Substance Emissions

By evaluation of the 84 individual substances quantified by emission chamber measurements it was only very few of the substances in the emissions from the investigated wood and wood-based materials, which taken the relatively low indoor-relevant concentrations into consideration, were found to have carcinogenic, reprotoxic, immunologic or neurotoxic effects cf. the following text and Appendix 7.

The two effects of formaldehyde: irritation and cancer can have a decisive importance in relation to the total evaluation of the emissions. Evaluation of formaldehyde was in this project based on recommendations from the World Health Organization , WHO’s, re-evaluation in 1996, in which it was concluded that the lowest concentration, which have been linked to nose and throat irritation in humans by short term exposure, is 0.1 mg/m³, even though some individual persons would perceive presence of formaldehyde at lower concentrations.

As the "Air quality guideline"-value is more than one magnitude lower than the threshold value, which is expected to cause cytotoxic damages in the nose mucous membrane, this value (0.1 mg/m³) represents an exposure level, at which the risk of cancer in the respiratory passage in humans is negligible.(Mølhave, L., April 1997) and (Larsen, J.C., April 1997).

The international cancer research institute, IARC, has evaluated the carcinogenic effect of formaldehyde and classified it in group 2A due to safe evidence for animals and limited for humans. Cytotoxicity is believed to play an essential role in the carcinogenic effect.

It is therefore probable that the concentration at lifelong exposure should be beneath 0.1 mg/m³ as a yearly average to take the carcinogenic effect adequately into account. Furthermore, it can be expected that especially sensitive persons will react with mucous membrane irritation at concentrations below 0.1 mg/m³.

5.3.2 Evaluation of Emissions from Wood, Wood-Based Materials and Products

The investigated materials have been evaluated by determination of S-value based on LCI-values and by indoor-relevant time-values based on odour and irritation threshold values. Evaluations of the investigated solid wood species and coated wood-based materials appear from surveys in Table 5.1. and Table 5.2. The stated evaluations comprise determination of S-value as well as indoor-relevant time-value based on odour and irritation threshold values by a material load of 1 m² surface per m³ room air.

A total evaluation of all 23 investigated wood and wood-based materials for a broader interval of material load appears from Appendix 8. The material loads vary from 0.4 m²/m³ corresponding to e.g. flooring or table and 6 chairs to 2.2 m²/m³ corresponding to e.g. ceiling, flooring, and all 4 walls. It should be noted that the stated wide interval for material surface in relation to room volume for a number of the investigated wood and wood-based materials differs from commonly used loads of these materials.

S-Value in Relation to Time-Values

In case of materials not causing emissions with carcinogenic substances, allergens, neurotoxic or reprotoxic substances, the used procedure and the evaluations and the results of the evaluations were similar both according to the S-value and to the indoor-relevant time-value based on the sum 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 became therefore in most cases decisive for the indoor-relevant time-value.

By comparison between the different products and their emissions it should be noted that the LCI-value can be determined more or less restrictively. The LCI-value of formaldehyde is in this material e.g. determined less restrictively than the other LCI-values.

From Tables 5.1 and 5.2 it appears that S-values at the 27/28 days measurement vary from 0.08 for solid ash and beech to 43.7 for solid pine of mainly heartwood at a material load of 1 m² surface area per m³ room volume. The indoor-relevant time-value based on odour varies at a material load of 1 m² surface area per m³ room air from <3 days for UV-curing lacquer on beech veneered particleboard to >28 days for the other surface treated wood-based materials, pine and most of the wood-based panels.

A survey of indoor-relevant time-values for all the investigated wood and wood-based materials including information of the decisive individual substance and effect appears from Table 5.3.

Time-values are stated for the two usual material loads for wood and wood-based materials: Material forming part as a door surface or table top (2 m²) corresponding to a load of 0.12 m²/m³ and material forming part as flooring or table and 6 chairs (7 m²) corresponding to a load of 0.4 m²/m³. Lower S-value and time-value state relatively lower emission of substances with given effect.

Proposal for Classification

Tables 5.1 and 5.2 contain additionally a proposal for classification of wood and wood-based materials in 3 classes: Low-emitting, medium-emitting and high-emitting, classifying ash, beech, oak and spruce as low/medium-emitting and pine as high-emitting. Among the investigated coatings the UV-curing lacquer on beech veneered particleboard was considered as low-emitting, the acid-curing lacquer on beech veneered particleboard as high-emitting, while the other tested lacquers on beech veneered particleboard and the investigated oils on solid beech were considered medium-emitting.

Model for Evaluation

As it appears from the survey examples the proposed model for evaluation based on S-value and indoor-relevant time-values differentiate the emissions of the investigated materials. The project results show that the proposed evaluation model can be used as a joint basis for evaluations of the relative health and comfort impact of wood-based materials and products.

The concept for evaluation based on indoor-relevant time-value can be used independently without using LCI or S-values, if emissions containing carcinogenic substances, allergens, neurotoxic or reprotoxic substances is out of the question. This is seen in the light that comfort at present is not included in the evaluation based on S-value. Furthermore, odour and irritation thresholds are available for evaluation of indoor-relevant time-value for approx. 800 chemical substances in a databank.

It should, however, be noted that substances exist which are carcinogenic, immunologic, neurotoxic or reprotoxic at concentration levels below the irritative effect.

Table 5.1
Classification of investigated surface treated wood-based materials - based on S-value after 27/28 days and an indoor-relevant time-value at a material load of 1 m²/m³.

¤ On basis of the indoor-relevant time-value solely the acid-curing lacquer is at level with lacquers in the category medium-emitting

Table 5.2
Classification of investigated solid wood based on S-value after 27/28 days and indoor-relevant time-value at a material load of 1 m²/m³.

Table 5.3
Indoor-relevant time-value for wood and wood-based materials at a material load of 0.12 m²/m³ and 0.4 m²/m³ respectively

# The concentration is constant during the 28 days

It should, furthermore, be noted that the absolute S-values, LCI-values and odour and irritation thresholds can always be questioned as well as the values could change when new knowledge is available. In consequence of this no exact limits for classification can be given on basis of the present relatively limited experimental basis nor can it be closer laid down where and when modification or substitution could be required.

Reduction of Hazardous Effects

Modification/substitution of materials and products should in principle be carried out, when the emission contains toxicologically unknown substances.

Materials and products should as far as possible not contain chemical substances with carcinogenic, reprotoxic nor immunologic properties. Should this be the case these substances should be exchanged by substances or materials, which are less hazardous or at least modify the material, so that the content is minimised as much as possible.

Selection of Material

In cases where the indoor air is given a high priority, it should be recommended to choose lower-emitting materials and products in order this way to reduce the emissions from materials and products and to obtain a larger probability of reducing effects and possible health effects in consequence of the emission from these materials and products.

Choosing lower emitting materials and products can be carried out by choosing materials and products with a low S-value and a low indoor-relevant time-value.