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

4. Principles for Comfort and Health Evaluation of Chemical Substances Emitted from Wood and Wood-Based Materials

4.1 In General
4.2 Evaluation of Health Effects
4.2.1 Threshold Compounds
4.2.2 Non-Threshold Compounds
4.3 Odour
4.4 LCI, Lowest Concentration of Interest

In the following section a general procedure for the evaluation of emissions from wood and wood-based materials is outlined.

Quantitative Analyses

The selection of the substances for quantitative analyses was carried out according to the following criteria:

	Substances identified by screening analysis
	Substances with carcinogenic, reprotoxic, immunologic or neurotoxic effects suspected to be emitted from wood and wood-based materials (See "All Chemicals List")

KRAN-Substances

Substances with carcinogenic, reprotoxic, immunologic or neurotoxic effects follow the "KRAN-lists" from the Danish Working Environment Service and the National Institute of Occupational Health, as K: Carcinogenic effect has been defined according to the list on Threshold Limit Values for chemical substances in the work environment (Danish Working Environment Service, 1994), R: reprotoxic effect has been defined according to the list on Reproductive toxicants in the working environment (Hass. U., Danish Working Environment Service, 1990), A: Immunologic effect has been defined according to the list on Allergens in the working environment (Thomsen, K. G., National Institute of Occupational Health, 1990) and N: neurotoxic effect has been defined according to the list on Neurotoxic substances in the working environment (Danish Working Environment Service, 1990).

Lists

The list of the substances expected to be emitted from wood and wood-based materials and products: "All chemicals list" and a "Project Specific List" of substances quantified by chamber testing in the project are shown in Appendix 5.

Toxicological Evaluation

For all substances quantified in the chamber testing an evaluation of toxicological effects was made according to description in 4.1 - 4.4.

Three Classes

Three classes of toxic effects were considered. The first was adverse effects such as carcinogenic effect, allergy, reproductive toxicity. The second class was other effects such as neurotoxic effects, irritation (inflammatory and sensory irritation) and the third was sensory effects. Substances that may cause cancer and allergy or show reproductive toxicity shall in principle not be accepted and shall generally be replaced by other with less hazardous properties.

For the second group the lowest concentration of interest in the indoor air, LCI, was estimated. Also odour threshold values were included in the assessments and together with sensory irritation thresholds used in calculation of the indoor-relevant time-value described in Appendix 4.

Assessment of substances with little available relevant toxicological information was based on an assumption that their toxicological properties correspond to known and chemically analog substances. If this assessment was impossible, the substance was considered as toxicologically unknown.

The general principles of evaluation of emissions from wood and wood-based materials are shown in Figure 4.1.

Evaluation of individual VOC’s is given in Appendix 7 and in brief in "All Chemicals List" and "Project Specific List" in Appendix 5. The lists given in Appendix 5 summerize information on chemical identity and health and comfort effects.

4.1 In General

During the last years approximately 300 different volatile organic compounds have been identified in the indoor climate (Nielsen, P.A., 1994). Some of these substances can be traced back to substances present in wood and wood-based materials and their emission. Some of the emissions are intensive in the initial period of usage.

There are, however, some emissions (certain organic substances), which do not decline or decline very slowly with time. It is difficult to eliminate such emissions of VOC’s. It is, however, important to know possible health and sensory effects of VOC’s in this period, within which the critical health emission takes place.

Health effects commonly associated with indoor air pollution have non-specific symptomology (Mølhave, L., 1986). Headache, fatigue, reduced attention span, irritability, nasal congestion, difficulties in breathing, nosebleeds, dry skin and nausea are commonly seen in connection with "sick buildings". Exposure to VOC’s in the indoor air may also lead to discomfort caused by sensory effects. Although, sensory effects are not related to critical health effects they may have important influence on human well being in the indoor environment.

Epidemiological studies of the toxic effects of the indoor air pollution are difficult to conduct as there are many different sources of pollution and many toxicants. In the indoor air besides VOC’s other chemical toxicants occur, e.g. carbon monoxide, nitrogen dioxide and radon, and a variety of toxicants of animal and microbial origin.

There is an international consensus on the general principles for the evaluation of the health effects and for determination of threshold limit values within the environmental area such as pollution of air, drinking water and soil (WHO 1984, WHO Air Quality Guidelines for Europe 1987, Ministry of the Environment 1992, WHO 1994 and ASHRAE 1989). These principles have been applied to the evaluation of the health effects of VOC’s emitted from wood and wood-based materials and for determination of Lowest Concentration of Interest, LCI-values, for VOC’s (refer to 4.4).

Critical emission of VOC’s shall be limited as much as possible. There are two ways (besides increased ventilation) of the limitation of critical emissions, namely to:

	Substitute and modify wood or wood-materials by alternatives
	Assess time necessary for decline of critical emissions

When a substitution has been decided, attention shall be paid to the entire life cycle of the alternatives so that alternatives don’t create any new environmental problems, e.g. waste disposal problems.

Critical emissions from a majority of wood and wood-based products decline with time. Careful assessment of this time may be a practical way to ensure safety and comfort in the indoor environment.

Substances with no data available are often emitted in the indoor air. Emission of "toxicological unknown" substances and emission of substances which are difficult to measure shall be limited as much as possible, e.g. substitution/modification.

4.2 Evaluation of Health Effects

Evaluation of health effects includes dose-response assessment, exposure assessment and characterization of uncertainty. Three approaches, namely threshold compounds, non-threshold compounds and sensory thresholds have been proposed for assessment of the dose-response relationship. It is generally recognized that for the majority of toxicological responses, a threshold do exist. It has been assumed in the present work that for irritation, acute, subchronic and chronic toxicity a threshold value (a concentration at which no hazardous effect may be observed) can be determined. For carcinogenic and sensory substances and allergens another procedure has to be adopted.

4.2.1 Threshold Compounds

Threshold compounds represent substances having other effects than carcinogenic and immunologic effects.

The majority of VOC’s exert their hazardous effects only above a certain minimum concentration in the indoor air. They show a distinct dose-response relationship leading to the concept of a threshold, which means a dose (concentration) below which the probability of toxic action is zero.

Determination of a "safe" threshold limit value for human exposure in the indoor air is often based on evaluation of toxicological documentation from animal studies. In addition to animal data other relevant information can be obtained either from epidemiological studies (occupational environment) or from the clinic. However, epidemiological studies are seldom available for individual VOC’s.

For toxicologically well known substances a threshold limit value may be based on the no-observed-adverse-effect-level (NOAEL) or lowest-observed-adverse-effect-level (LOAEL) chosen from the most relevant toxicological study.

Having established the NOAEL or LOAEL, safety factors are used to obtain a sufficient margin of safety. Traditionally, the total safety factor is composed of one factor of 10 for extrapolation between species (animal to human) and a second factor of 10 to protect the most sensitive member of the population e.g. children. When the weight of evidence, namely quality and relevance of data are not adequate, a third safety factor may be used and the size of this factor varies. The total safety factor is calculated as a product of all safety factors.

Pollution of the indoor air consists, among others, of a complex mixture of many different VOC’s. Considering the complexity of the exposure it is essential to know the possible interactions between different substances. An interaction could result in an increase of effects (synergy) or a decrease of effects (antagonism). Information on possible interaction is rarely available. An interaction most commonly observed when two substances act together. An additive effect occurs when the combined effect of two substances equals the sum of the effects of each substance given alone. Dose additivity is based on the assumption that substances acting together have the same mode of action and elicit the same toxicological effects. When substances elicit a similar effect, e.g. irritancy, the additive model assess the "join action" of toxicological similar substances under the condition that no

interaction takes place. This model does not always represent a biologically plausible approach, as the different substances may or may not have the same mode of toxicological action. Several studies, however, have demonstrated that the dose additive model reasonably predicts the toxicity of a mixture composed of a variety of substances (Casarett & Doull, 1995).

The relevant toxicological documentation is very limited for several VOC’s identified in the emission from indoor sources. The hazard identification based on the structure-activity relationship may be useful assessing the relative toxicity of chemically related substances.

Physical-chemical data like e.g. solubility, pH, chemical structure and reactivity may provide important information for hazard identification.

The concept of Total Volatile Organic Compounds (TVOC) was the first attempt to describe low-level exposure to a mixture of volatile substances in non-industrial environments. This concept assumes that the human health effects may be proportional to the sum of mass-concentrations (mg/m³) of the VOC’s in the air and that the substances are of equal strength and mode of action. No-effect level for TVOC has been suggested to be 0.2 mg/m³ whereas discomfort at a concentration above 3 mg/ m³ is to be expected (Mølhave, L. 1991).

The importance of a low concentration of a toxicological potent substance can be underestimated, while that of a low-toxicity substance can be overestimated, if TVOC is estimated as one compound. Scientific literature is inconclusive with respect to TVOC as an expression of risk for health and comfort effects in buildings, despite a very large amount of research in this field. In 1996 it was concluded that TVOC is still an undocumented hypothesis and there is not a scientific basis for establishment of limit values or guidelines for TVOC for emissions from materials and products used indoors (Andersson, K., Consensus meeting 1996).

For the great majority of VOC’s, however, sensory effects and skin irritation are most probably the critical effects at the very low exposure level in the indoor environment.

Skin irritants and fibres in the air may contribute to the skin symptoms described as a part of the "sick building syndrome" (WHO, Criteria for classification of skin- and airway sensitizing substances, 1996).

Irritation includes both sensory and inflammatory irritation. The perception of comfort in the indoor environment is greatly influenced by both sensory irritation and odour.

Sensory irritation is stimulation of the trigeminal nerve endings in the eye cornea and nasal mucosa. Animal experiments showed that such irritations cause reflectory decreases in the respiratory rate. This irritation is characterized by a latency period before the perception of the effect is reached.

A mouse model is commonly used for assessment of irritating properties of VOC’s (Nielsen, G.D., 1995 and Wolkoff, P., 1997). The concentration that induces 50% decrease in the respiratory rate in mice, the RD₅₀ value, is used to quantify the irritating potency of a substance. It has been proven that the mouse model has a predictive value for human responses to sensory irritation.

In practice an evaluation of 3% of the RD₅₀ concentration is believed to be safe for man in respect to inflammatory irritation and is used as an estimate of a safety level for the occupational environment (Schaper, M., 1993).

In general, the occupational exposure levels are suggested (Nielsen, G.D., 1995) to be used for evaluation of health effects in the indoor air by using an additional safety factor of 40. Furthermore, the lowest acceptable concentration of interest in the indoor air may be calculated by taking exposure 24 hours a day and 7 days a week (8/24 x 5/7 = 1/4) and a safety factor of 10 for the sensitive group into account.

4.2.2 Non-Threshold Compounds

Non-threshold compounds represent substances having particular hazardous effects e.g. carcinogenic effects.

Non-threshold compounds are substances that do not show a distinct dose-response relationship. No observable adverse effects level, NOAEL, can not be obtained directly from the experimental data. Genotoxic carcinogens and sensitizing substances may be considered to be non-threshold compounds.

Genotoxic carcinogens produce DNA damage, and theoretically even one molecule may lead to development of carcinogenicity. Several mathematical models are used to extrapolate from high doses to the region of the dose-response curve for which no experimental data are available. In addition to experimental data determination of a "safe" threshold limit value for genotoxic carcinogens is based on an assumption of a tolerable risk level.

A risk level of about 10^-6 is regarded as tolerable and a risk level of

10^-7 is regarded as acceptable for, among others, the Danish society (Ministry of the Environment, 1992 and Dragsted, L., 1990).

Existing mathematical models for low-dose extrapolation may not be appropriate for non-genotoxic carcinogens.

The International Agency for Research on Cancer (IARC) prepares and publishes critical reviews on the carcinogenicity of a wide range of chemicals to which humans are or may be exposed. The evaluation of the strength of the evidence for carcinogenicity is arising from human and experimental animal data. The total body of evidence leads to categorization of chemicals into one of the following groups: group 1, group 2A, group 2B, group 3 or group 4.

Chemicals that are carcinogenic to humans are categorized to group 1. Group 2A encompasses chemicals that are probably carcinogenic to humans, and group 2B-the chemical is possibly carcinogenic to humans.

Some of the VOC’s are well known skin sensitizers. Most experimental studies are conducted on animals, using much higher doses than those relevant for the indoor air. Dose response studies are extremely sparse and extrapolation from experiments conducted in animals using high doses directly on the skin, to small doses, airborne, in humans, is questionable.

Sensitizing chemicals exposed to the skin by direct contact or indirectly through adherence to particles in the air, may cause allergic contact dermatitis. Several data from experimental studies in animals as well as human clinical data from direct skin contact are available.

Chemicals may in rare cases cause airway hypersensitivity by an immunological mechanism different from that of skin-sensitization. The symptoms evoked are asthma and possible urticarial reactions. Data on airway sensitisation caused by VOC’s are extremely sparse and no eligible animal models are available.

Once sensitization has occurred, allergic reactions may result from exposure to relatively low doses. The manifestations of allergy are numerous and may involve various organs and range in severity from minor skin effects to fatal anaphylactic shock.

The main principles of evaluation of these effects is that substances causing these effects should not be present in normal indoor air.

4.3 Odour

The olfactory organ is situated in the upper part of the nasal cavity and consists of olfactory receptor cells, the density of which varies among species. To stimulate the receptor cells, contact must be made between the inhaled volatile substances and the epithelial surfaces. There is no known relation between toxic and olfactory properties.

Odour is affected by the degree of volatility of a substance and its solubility in the mucous layer of the epithelium. This explains why some very volatile substances are only slightly odorous and have a very high threshold perception value.

The odours may be described as aromatic, etheric, alcoholic, phenolic etc. or as pleasant and unpleasant. Perception of odour encompasses grades from just perceivable smell to unbearable smell.

Smell adaptation occurs due to prolonged exposure and is caused by several mechanisms one of which is a temporary exhaustion of the receptive mechanism in the mucous membranes of the olfactory region.

Odour properties can be characterized by detection and/or recognition thresholds, the lowest concentration of a volatile substance that e.g. 50%, 20% or 10% of panel members can detect or recognize. These values heavily depend on the method, instruments and the panel used for odour threshold value determination.

Within the indoor environment the perceived odour will often result from exposures to a mixture of several odourants. Such mixture interactions between odourants take place in the form of neutralisation or masking. On this background it is not possible to predict the resulting odour of a mixture of VOC’s.

4.4 LCI, Lowest Concentration of Interest

To facilitate the assessment of health effects and comparison of wood and wood-based products we propose use of Lowest Concentration of Interest-values, LCI-values. LCI is the lowest concentration of a particular volatile substance presented in the indoor air that just can be accepted. In principle a higher concentration of a pollutant shall not be accepted as it may have consequences on human health and/or comfort. The LCI concept was introduced in a theoretical European R&D-collaboration (ECA, Report No. 18, 1997). The principle behind the LCI-value is well known from occupational and other environmental regulation, but has not been documented or tested in Indoor Air Quality context. Therefore, LCI-values are used as weighing factors indicating the relative hazard of substances and not as criteria for indoor air quality or as fixed threshold limit values.

LCI is defined as the lowest concentration of a certain substance, which according to our present knowledge - at continued exposure in the indoor air will not cause damaging impact on humans.

The advantage is, however, that use of LCI-values enables a quick comparison of sources as wood and wood-based products and therefore promote a more "healthy" indoor environment.

The limitation of LCI-values is that they very often are derived either from limited toxicological documentation, or from structure-activity relationship, or based on odour threshold values. The LCI-values have to be considered as a first indication of health and/or comfort problems with the indoor air, as there is no uniform background for determination of LCI-values.

The LCI-values can typically be changed, when new knowledge is available. In this report LCI-values are only used as weighting factors.

Exposure

The main exposure route of volatile organic compounds present in the indoor air is inhalation, thus contributing to health effects via airways.

This exposure is defined as the concentration of substances in the breathing zone and is usually expressed as an average concentration over a reference period. VOC’s may also enter the body (and may cause harm) by passing through the intact skin or by ingestion. Furthermore, VOC’s can cause skin effects following dermal exposure. It is difficult to predict which fraction of the inhaled substances may be absorbed. For this reason, health assessments were based on an assumption that the entire quantity of inhaled substances is absorbed via the lungs.

For the great majority of VOC’s available toxicological documentation is based on oral studies. Extrapolation of results from such studies to inhalation scenario is extremely difficult and limited by the extent of data. For this reason, toxicological data obtained from oral exposure were anticipated valid for assessment of exposure by inhalation.

Exposure for pollutants in the indoor air encompasses an indefinite period of time and is very complex. To prevent underestimation of exposure, a worst-case scenario is considered, namely a day and night exposure of especially vulnerable groups of people, e.g. children.

Standard Room

Concentrations of substances in the indoor air can be calculated from the concentrations of the substances measured by chamber testing using a standard room approach. A standard room commonly used for general calculations of indoor air concentrations has a relatively large surface area compared to the room volume (DS/INF 90, 1994). E.g. amount a flooring material to 7 m² and a material covering all surfaces of a room to 38 m² in a room volume of 17.4 m³, corresponding to calculated standard room concentrations for an area-interval of 7 - 38 m². A part of a piece of furniture (e.g. edges of a table) might amount to as little as 0.1 m². When the conditions in the test chamber and in a room are similar, the calculated concentration can be used without correction due to climate parameters.

Dose-Response

An important step towards determination of the LCI-value is characterization of a relationship between dose (concentration) and response (toxic effect). Hazard identification is the process of gathering and assessing all available data, which shall reveal the adverse biological effects as a result of inherent properties of a substance. A variety of toxicological effects, e.g. cancer, birth defects or sensitization may be evident.

The necessary information is provided from the databases TOXLINE, RTECS, ECDIN, NIOSHtic and Medline. In connection with dose-response relationship the word dose has a defined meaning: the concentration of a substance in the air inhaled. Concentration-effect relationship is usually very difficult ascertainable from most older toxicological studies. To prevent underlying of on-effect level several safety factors were applied to the toxicological data.

Structure - Activity Relation

When available toxicological data do not give toxicological endpoints, or when only limited data exists, the use of structure - activity relationship may be considered of value indicating a potential hazard. Quantitative structure - activity relationship, particularly useful for determination of threshold limit values for unknown chemicals is still in progress. Consideration of structure - activity relationships have supported determination of some LCI-values.

Irritation and Odour Thresholds

Some of the effects, to which attention at least must be paid in relation to indoor air, are irritation and odour. Determination of sensory effects heavily depends on subjects and method used. A great diversity is also found between the odour threshold values published.

When no relevant toxicological effects were known, LCI-values were based on odour threshold published in the databank VOCBASE, National Institute of Occupational Health, 1996.

C-Values

In connection with industrial air pollution guidelines by the Danish Environmental Protection Agency has assessed several VOC’s. For these substances the maximum concentration allowed in the air as emission was defined by the authorities and termed as a contribution value, C-value, (Ministry of the Environment, 1992).

These values are determined on the basis of the Agency’s principles for determination of threshold limit values for chemical substances and used for the calculations of the height of chimneys. Although it is stipulated that the C-value does not supply emission values (air quality standards) their establishment follow the common principles for determination threshold limit values and therefore the C-values have been considered and were adopted as LCI-values, where possible.

The Danish Environmental Protection Agency has carried out a toxicological evaluation of the chemical substances in air pollution, in drinking water and in soil pollution. The toxicological principles used by the Danish Environmental Protection Agency were in accordance with the principles used in this investigation in the cases where the Danish Environmental Protection Agency’s evaluation was based on the effects of a substance and not based on odour. In the cases, in which the Danish Environmental Protection Agency had a toxicological evaluation of a chemical substance with a fixed C-value based on the effect of the substance, this was used. If the LCI-values differs from this, it has been commented in the individual substance evaluation in Appendix 7.

Sum

For all determined VOC’s from a particular wood or wood-based material standard room concentrations are calculated at day 3-4, 9-11 and 27-28 based on test chamber concentrations determined by chemical analyses. The standard room concentration were divided by the determined LCI-values and fractions for each substance were obtained. All the fractions were added for effects of the same kind and a sum (S-value) was obtained for each wood and wood-based material according to the formula:

The sum indicates the severity of health and/or sensory effect of the emission from a particular material. The lower sum value the more acceptable the wood and wood-based material. This sum, however, is expected to be below one, for mixture of VOC’s in the working environment and for VOC’s emitted from industrial installations to the external environment.