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Toxicological information

Exposure related observations in humans: other data

Administrative data

exposure-related observations in humans: other data
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
supporting study
Study period:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles.

Data source

Reference Type:
Human reactions to indoor air pollutants: n-Decane
Kjaergaard, S., Melhave, L., Find Pedersen, O.
Bibliographic source:
Environment International 15: 473 -482

Materials and methods

Endpoint addressed:
eye irritation
Test guideline
no guideline available
Principles of method if other than guideline:
The sensation of irritation in nose, eyes, and throat were examined in response to n-decane exposure.
GLP compliance:
not specified

Test material



Ethical approval:
confirmed, but no further information available
Details on study design:
The study was performed in an 83 m3 stainless steel climate chamber with four subjects per day exposed six hours to either 0, 10, 35, or 100 uL/L pure n-decane. In the present study, humidity and air changes per hour (ach) were 5 ach and 45% RH. Exposure was established by pure n-decane, flash-evaporated at 300°C in a nitrogen atmosphere and subsequently mixed into the chamber ventilation system. The exposure concentrations were continuously controlled by a flame ionization detector (FID) sampled from four points in the chamber. Exposure was measured in toluene equivalents. Charcoal tube sampling equipment was used to measure the daily average exposure. They were later desorbed and analyzed by gas chromatography. The measured concentrations only slightly exceeded intended values. Using a new method, individual exposure was measured by the alveolar concentration of n-decane. To avoid bias arising both from the investigator and from the participating subjects, a double blind design was used in the study. Odorous substances to mask the odors from the air pollutant under investigation were not used. There were four exposure days in each of four weeks. An exposure day included pre-exposure measurements, exposure measurements, and post-exposure measurements. Subjects were divided into 16 groups which were exposed according to a balanced latin square design to eliminate interactions of the season and of the day in the week. The four exposure groups did not differ significantly with regard to age, sex, number of smokers, and level of school education. No differences in temperature, humidity, and noise exposure levels in the climate chamber were seen among the exposure groups.

63 participants completed the study. The group of participants had the same age and sex distribution as the general population.

Measurements of Human Reactions:
Before exposure three tests were performed to measure subject sensitivity. These were Stingers test, the odor threshold test, and the eye irritation threshold test. The subjective reactions to the exposure were measured by questionnaires and a linear potentiometer. Physiological reactions to the exposure were measured in the external eye by the tear film stability test, a photographic test of changes in eye redness, and by a cytological evaluation of tear secretion.Test procedures were as follows.
1. Using Stinger’s test, skin reactivity was measured. A cotton wrapped stick was used to smear on the cheek in a single stroke a 6.5% lactic acid in 0.9% sodium chloride solution. As a control, a 0.9% sodium chloride solution was smeared on the opposite cheek. Subjects reported strength and duration of the sensation on either cheek within the following 10 minute period. The test was used as an indicator of skin sensitivity and was done during the pre-examination.
2. Odor threshold to n-butanol was measured by a triangle olfactometer and was done during the pre-examination. Subjects identified one out of three possible tubes which was contaminated with n-butanol vapor. Six increasing concentrations were used. The lowest correctly identified concentration was used as an indication of threshold concentration and was done during pre-examination.
3. Eye irritation threshold to carbon dioxide was the third indicator of sensitivity. This is a test developed for this study and was done during the pre-examination. Wearing a mask covering the eyes, the subjects were seated. Increasing doses (10 mL/L, 20 mL/L, 40 mL/L, 80 mL/L, 160 mL/L) were administered into the mask for 10 minutes (2 minutes for each dose), and the subjects were asked to tell if and when they felt any itching, dryness, etc. The CO2 concentration and time of the reaction were recorded.
4. Subjective complaints were registered in two versions of 60 mm linear visual analogue rating scales. The first method was based on a standardized questionnaire containing 25 questions concerning odor intensity, indoor climate, irritation, and neurological symptoms, which were answered before and three times during exposure. Three of the air quality questions referring to air quality, odor intensity, and wish to ventilate were added into an olfactory index, and analyzed like the rest of the questions. Differences between pre-exposure and exposure ratings were used as variables. According to the second method, the subjects used a linear potentiometer to quantify the sensation of irritation in mucous membranes in eyes, nose, and throat. The subjects were told to change the setting of the potentiometer whenever they felt any change in irritation, and every 30 minutes they were reminded to check the setting.
5. The eyes secrete tears, mucus, and lipids to protect the epithelium, especially the corneal epithelium. These secretions are redistributed over the cornea by each eye blink. Low stability of the tear film is associated with dry eye syndromes and the sensation of irritation and may be of importance for protection against irritants. Using a slit lamp microscope, Lear film stability was measured before and three times during exposure. Subjects were seated with their heads in fixed positions after installation of 10 ul 1% Na-flourescein, a vital staining dye, in the conjunctival sac. Stability was measured as the time from an eye-blink to the break up of the pre-corneal tear film, as observed in the microscope with cobalt blue light. The mean of three measurements was recorded.
6. Changes in eye redness were registered photographically and measured by visual comparison of the pre-exposure photograph to the post-exposure photograph. Comparisons of redness in an area limited laterally by the eyelids and medially by the cornea were performed in a double blind randomized design. The pre-exposure photographs were evaluated for the number of blood vessels in an arbitrary unit area by counting blood vessels crossing the outline of a square and an inserted cross.
7. Cytotogical examination of small samples of conjunctival secretions (mucus and tears) taken under the lower lid was done by microscopy. A small specially designed pipette was used for sampling tear fluid. Samples were fixated on glass slides with formaldehyde, stained by formol-fuchsin eosin, and the total number of polymorphonuclear leucocytes, lymphocytes, columnar, cuboidal, and squamous epithelial cells were counted by a single trained technician. Samples were taken before and after exposure. Increased numbers of polymorphonuclear leucocytes and of epithelial cells are well-known indicators of irritation of mucous membranes of the eye.
8. Statistical analysis was performed by a mainframe version SPSS. Analysis of variance and t-tests were performed initially to identify major reactions during exposure. Regression analysis was performed afterwards to outline dose-dependency. In most cases the square root of exposure was used as the independent variable. When the data could not be approximated to a normal distribution, i-square, log- linear analysis, or Kruskal-Wallis one-way analysis of variance were used. A p-value less than or equal to 0.05 was considered significant, and a p-value less than or equal to 0.10 was considered indicative for further investigation and is therefore reported.
Exposure assessment:

Results and discussion

We wanted to evaluate whether the subjective feeling of inconvenience was correlated with characteristics of the subjects as well as the exposure levels. Therefore, the relationship between the measured subjective effects of n-decane exposure and the three objective tests characterizing subject sensitivity-Stingers test, odor threshold, and eye irritation threshold-were examined in a multiple regression analysis with a stepwise inclusion/exclusion of the variables. In all analyses the exposure was included either as the square-root of n-decane concentration or as the alveolar concentration of n-decane. Only effects with a significant relationship to n-decane exposure were tried as dependent variables. These included air quality, odor intensity, olfactory index, potentiometer test, and the break up time.

Among all predictors in the analysis, only the eye irritation threshold was correlated with both olfaction and irritation. Stingers test was associated with odor intensity and the olfactory index, while low odor thresholds were not associated with any of the effect indicators.

Answers to the questionnaire showed a significantly reduced indoor air quality due to the exposure (p <0.001 in the analysis of variance) in all exposed groups, measured immediately after the concentration had reached the desired level. The reduction of air quality was dose-dependent (p <0.01). Similar results were encountered by the question related to odor intensity (p <0.01) and for the olfactory index. No dose-dependent differences were, however, found at the end of the exposure day for any of the questions about air quality, as the effects apparently decreased during the exposure period in the group exposed to 35 or 100 uL/L. This may indicate adaptation. The other questions in the questionaire showed no relationship to low level exposures.

The continuous measurements of mucous membrane irritation (potentiometer test) were significantly related to the exposure, but due to the inhomogeneity of variances neither the analysis of variance nor the regression analysis are conclusive. A nonparametric test, however, showed significantly increased scores for exposed groups compared with nonexposed groups (p<0.05).

The changes in cellular contents of tear fluids were significant for the cuboidal epithelial cells in a Kruskal-Wallis one-way analysis of variance, but only the group exposed to 35 uL/L reacted with significantly increased numbers of cells. In non-exposed subjects, the number of polymorphonuclear leucocytes decreased during the day. This decrease was less for the subjects exposed to 10 uL/L. In those exposed to 35 uL/L an increase was seen. This was even more pronounced in those exposed to 100 uL/L. The changes in polymorphonuclear leucocytes were significant in a log-Linear analysis of trend. For lymphocytes, columnar epithelium, and squamous epithelium no significant changes were seen.

Initial eye redness was more pronounced among smokers than among non-smokers. Eyes became less red during the day. This was not associated with exposure to n-decane, and tobacco smokers had more decreasing eye redness than non-smokers. Pre-exposure redness was similar in all four exposure groups, and negatively correlated to changes in eye-redness, as an indication of a regression towards the mean. Tear film stability decreased throughout the day in all exposed groups but more so with increasing exposure (p <0.035). Statistical analyses are presented for the six hour measurement only, i.e. just before the end of exposure. No changes were seen during the day among the subjects exposed to clean air. Since differences were strongly negatively correlated with the baseline values measured in the morning, these values were included in the analysis as a covariate, but the relation to exposure was still significant (p <0.001) and dose-dependent.

Applicant's summary and conclusion

Executive summary:

A dose-response study of human reactions to the indoor air pollutant n-decane was performed in a climate chamber. Sixty-three healthy subjects, randomly selected from the normal population, were exposed to n-decane concentrations of either 0, 10, 35, or 100 uL/L in a controlled, double blind study using a Latin square exposure design. The most significant findings were dose-dependent changes in irritation of mucous membranes, increased sensation of odor intensity, and reduced air quality. Adaptation was seen at the highest exposure levels, but not at the levels relevant for a non-industrial environment. The physiological measurements showed decreased tear film stability at all exposure concentrations. The number of conjunctival polymorphonuelear leucocytes increased in a dose-related manner. Predictors of the sensitivity to exposure, i.e. mucous membrane irritation threshold and skin irritation (Stingers test), were correlated to subjective ratings of odor intensity and irritation of mucous membranes.