3 Exposure scenarios

Survey and health assessment of chemical substances in essential oils and fragrance oils

Based on the description of use patterns, an exposure scenario has been chosen; diffusion of fragrances in a room by use of aroma lamps, fragrance streamer, and aroma pillows, etc.

At some occasions 2-10 drops are used which, over a short period, is diffused to a room where the user is present. The most used method is use of candle diffuser, but aroma figures and stones, ceramic lamp ring or electrical air fresheners in principle work the same way. There may be a difference in which substances are emitted and which quantities depending on whether the oils are heated, but the scenario to which degree the user will be exposed to the different substances will mainly be the same. By use of fragrance spray the diffusion will take place over a very short period, but it will still be a variant of the same basic scenario.

Description of use pattern

The typical use of a candle diffuser is to fill a bowl with 20 ml of water and add 2-10 drops of oil into the water. In some cases the oil may be seen as a separate phase, but some of the substances will be dissolved in the water. It can either be a fragrance oil, a single essential oil or a mixture of essential oils. The lamp is placed in the room where you are, typically the living room or another room. A candle is lit under the bowl and the water is heated gradually to approx. 50° C and the aroma substances will evaporate and be emitted to the air. The candle typically puts out after a period of ½ to 2 hours and the lamp is cooling off. The remaining water is either poured out or additional water is added.

The typical user uses the lamp occasionally, but some users use the candle diffusers on a daily basis.

Exposure happens when the user inhales the air in the room where the aroma lamp is used.

Exposure model

The used exposure model is described in the following. For each parameter included in the calculations, abbreviations will be used in accordance with the descriptions used for similar scenarios in EU's Technical Guidance Document (TGD 2003). However, some of the parameters that are part of the present model are not covered by examples in TGD 2003.

When calculating the possible exposure by use of aroma lamps the following worst case parameters are used:

Quantity of oil to be used, Q_prod: 10 drops ~ 0.4 g .
Volume of the room, V_room: 17.4 m³ (equals a small room, is used as a standard room for exposure calculations in relation to exposure calculations for emission of substances from building materials).
Time the lamp is used, T_use: 2 hours
Time of exposure at use cycle, T_contact: 4 hours (the person has left the room or a thorough air circulation has been made before then)
Air exchange rate, R_room: 50% per hour
No of use cycles per day, n: = 1
Body weight, BW = 60 kg for women and 70 kg for men (standard i TGD 2003)
Respiration rate, IH_air: 20 m³/day for adults equals 0.83 m³/hour or 0.014 m³/min (standard i TGD 2003)

Exposure of a person in the room will be a function of the actual persons' respiration rate and the concentration of the substance in the room.

The concentration in the room will however vary during a use cycle and it is thus necessary to calculate the exposure by integrating the varied exposure in a use cycle.

Concentration in the room

The concentration in the room depends on the rate of which the substances are emitted to the room, the size of the room and the rate the substances are removed from the room by exchanging with the surroundings.

Changes in the concentration in the room within a time period can be expressed by the formula:

Formula

C_air is the concentration of the substance in the room at the time t

R is quantities of what is added by emission in the time period dt

V_room is the volume of the room

Q is the quantity removed from the room by ventilation in the time period dt

As there is a gradually heating of the water, the emission rate (and thus the quantity added to the room) will gradually increase in the beginning of the period and it will later decrease when the concentration of the actual substance in the candle diffuser falls. To simplify, we calculate that the total quantity of substances emitted to the room is emitted with the same average rate as within a two hours period.

In figure 3.1 the concentration sequence at a total emission of 60 mg of the substance has been shown, equivalent to the emission of d-limonene from 10 drops no. 34 oil used in the climate chamber test no. 3. On the figure is shown the concentration sequence in the room, when the 60 mg are assumed to be emitted during 0.5 and 2 hours, respectively.

We have here chosen a numeric solution of the calculations where all calculations are made stepwise in intervals of 1 minute.

It is assumed that the person stays in the room for 4 hours, so that the average concentration in these 4 hours is calculated. The average concentration in these 4 hours is 1,450 µg/m³ when the oil is emitted for 30 minutes and 1,320 µg/m³, if the emission takes place for 2 hours. The average concentration the person is exposed to is thus not very depending on how quick the oil evaporates, whereas the maximum concentration the person is exposed to is higher when the evaporation takes place within a shorter period.

For the exposure assessment a scenario is used where it is estimated that the oil is emitted equally over a period of 2 hours.

Figure 3.1 Concentration in the air in a 17.4 m³ room with an air circulation rate of 50% per hour. It is assumed that 60 mg in total of the substance is emitted at a constant rate for ½ time (gray curve) and 2 hours (black curve). The 60 mg equals the content of the d-limonene in 10 drops of oil no. 34 used in climate chamber tests.

Total quantity of substance emitted to the room in a user cycle can be calculated as:

Formula

where

M_subst,emiss is the total amount of substance emitted during a user cycle (in mg)

Q_prod is the quantity of oil added to the candle diffuser (in kg)

FC_prod is the concentration of the actual substance in the oil (in mg/kg)

E_stof is the emission factors for the substance, i.e. the part of the substance in the added oil liberated to the air during a user cycle (out of scale)

Q_Prod is determined by weighing the 10 drops of oil added to the lamp,

FC_prod is determined by use quantitative analyses of content, whereas

E_stof is determined by use of climate chamber tests.

Inhalatory intake

A person staying in the room will inhale a part of the substance, depending on the persons' respiration rate and the concentration of the substance in the air in the room.

A part of the inhaled substance will be absorbed via the respiratory tract. The quantity that is inhaled, the inhalatory intake, depends on to which degree the substance appears as a gas or is linked to aerosols of different size.

Calculations show that in cases where the total quantity in 0.5 hour, the person will, during a 4 hour user cycle, inhale 8.1% of the emitted quantity, i.e. mainly the same quantity as when the total quantity is emitted over 2 hours. It is thus of less importance how fast the substances are emitted within a 4 hours user period.