Acetic acid

Direct observations: clinical cases, poisoning incidents and other

Administrative data

Endpoint:

direct observations: clinical cases, poisoning incidents and other

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Unpublished, Institute report of non-GLP, non-guideline human population study, some limitations in design and reporting but otherwise acceptable for interpretation.

Data source

Reference

Reference 1

Reference Type:

other: Institute report

Title:

Final report on the Collaborative Demarcation and differentiation, irritative 'and' nuisance 'effects of hazardous substances (FF228)

Author:

HVBG

Year:

2007

Bibliographic source:

Leibniz Research Centre for Working Environment and Human Factors (IfADo). (In preparation for publication)

Reference 2

Reference Type:

other: Institute report

Title:

Statistical analysis addendum to: Final report on the Collaborative Demarcation and differentiation, irritative 'and' nuisance 'effects of hazardous substances (FF228)

Author:

Kleinbeck

Year:

2009

Bibliographic source:

Leibniz Research Centre for Working Environment and Human Factors (IfADo). (In preparation for publication)

Materials and methods

Study type:

study with volunteers

Endpoint addressed:

respiratory irritation

Test guideline

Qualifier:

no guideline required

Principles of method if other than guideline:

This study was conducted in 3 phases.
Phase 1. Objective assessment of both olfactory and irritation thresholds in volunteers.
If there was only a small difference in the threshold values for olfactory and irritation, or if the irritation threshold and OEL values were similar, a more detailed examination was undertaken in the second phase.
Phase 2. Identification, in volunteers, of dose-response relationships between exposure level and subjective perceptions of odour annoyance and irritation.
Critical substances indicating potential for health risks below workplace exposure standards were examined in a third phase.
Phase 3. Examination of odour annoyance and sensory irritation in volunteers exposured to conditions relevant to the workplace.
The 3rd phase of the study, using work-shift simulations and human volunteers to examine odour annoyance and irritative effects of acetic acid, is the main has primarily used for this summary.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Acetic acid

EC Number:

200-580-7

EC Name:

Acetic acid

Cas Number:

64-19-7

Molecular formula:

C2H4O2

IUPAC Name:

acetic acid

Details on test material:

No information provided

Method

Type of population:

general

Subjects:

- Number of subjects exposed: 24
- Sex: 13 men and 11 women
- Age: 18-35
- Race:
- Demographic information:
- Known diseases: Volunteers with chronic respiratory diseases, suspicion of other diseases (such as hypertension) or neurological disorders were excluded from the trial.
- Other: Non-smokers

Ethical approval:

confirmed and informed consent free of coercion received

Reason of exposure:

intentional

Exposure assessment:

measured

Details on exposure:

0.6ppm; 4-hour average (odour control concentration).
5 ppm; 4-hour average, peak was 10 ppm (15 min peak with 1 h interval between successive peaks) (intermediate concentration).
10 ppm; 4-hour average at constan concentration (MAK / TRGS 900).
Note: TRGS: Technische Regeln für Gefahrstoffe (Technical rules for hazardous substances; German regulation).

Examinations:

Introduction.
The postulated effect model used describes the chain reaction in the peripheral chemosensory structures at different levels in the central nervous system (CNS) caused by local irritation in the work environment. The model differentiates CNS-level sensory from cognitive effects. Sensory effects are a specific sensory experience with physiological changes primarily observed, cognitive effects show up mostly as complex behavioural changes. The examinations used to characterise these effects were A, rating of chemosensory-mediated irritaion and acute effects, B, physiological measurements of sensory irriration and C, behavioral measures.

A. Rating chemosensory-mediated irritation and acute symptoms
Two approaches were taken based on 1, the Labelled Magnitude Scale (LMS) and 2, the Swedish Performance Evaluation System (SPES) sympton questionaire.
1. Strength of sensation/perception (LMS scale).
(The Labeled Magnitude Scale (LMS) was developed by Green et al. (1996), van Thriel et al (2005). This scale was designed to rate the intensity of chemosensory stimuli, and the LMS mimics the ratio-like properties of magnitude estimation scaling used to estimate the intensity of the three olfactory sensations (‘odor intensity’, ‘annoyance’, ‘nauseous’) and the eight trigeminal mediated sensations (‘sneeze’, ‘prickling’, ‘tickling’, ‘burning’, ‘sharp’, ‘pungent’, ‘nasal irritation’, ‘eye irritation’). This scaling procedure was applied by means of Pocket PCTM (HP Jornada 540, 240 320 pixel) showing the scale label at the top of the screen (e.g. ‘annoyance’), a slider on the right side, and the six categories (ranging from: ‘barely detectable’ to ‘strongest imaginable’) close to the slider.)
2. Olfactory Symptoms (SPES Symptoms Questionnaire), with no physiology measurements.
During the last 5 years the original version of SPES subtest ‘Acute Symptoms’ has been expanded, and symptoms aimed at acute chemosensory health effects have been added (Seeber et al., 2002; van Thriel et al., 2007). Participants are presented with 29 acute symptoms, one at a time, on a computer screen and asked to rate their severity on a six-point scale ranging from zero (‘‘not at all’’) to five (‘‘very, very much’’). Ratings of similar items are combined into subscales. These subscales are: ‘unspecific/pre-narcotic symptoms’, ‘olfactory symptoms’, ‘taste symptoms’, ‘respiratory symptoms’, ‘general irritations’, ‘nasal irritation’ and ‘eye irritation’).
Timing of chemosensory and irritation tests.
Collected before/after exposure and nine times during exposure. The timepoints were chosen to match the maximum and minimum concentrations of acetic acid during the variable concentration regimen. The pre-exposure timepoints was -55 min). Timepoints during exposure were 0, 30, 60, 85, 125, 150, 175, 205, 235 mins. The post-exposure timepoint was 270 mins.


B. Physiology measurements of sensory irritation.
Blinking frequency (Electromyographic Analysis of the contractions of the M. orbicularis oculi).
(The frequency of blinking, which was measured by electromyographic (EMG) analysis of the contraction of the M. orbicularis oculi indicates irritation of the eyes. This physiological variable was measured continuously during the 4 - hour exposure period. In order to avoid other visual stress, the analysis of this variable was only done for selected time periods in which the volunteers used a vigilance task, the Mackworth Clock. This test lasted 25 minutes and was processed twice per session, once-at the beginning of the exposure (after 30 min) and again at the end of 4 hours (205 minutes). This effects of exposure peaks could be recorded during the changing-concentrations conditions. All procedures as recommended in (Doty et al, 2004).
Respiratory frequency. (Analysis of respiration movements by Respiratory Inductive Plethysmography, RIP)
Changes in the nasal cavity nasal airway (local irritants can cause swelling of the mucous membranes of the nasal cavities resulting in increased nasal airway resistance) . (RESISTANCE by anterior-rhinomanometry. NEUROGENIC INFLAMMATION by ELISA Substance P. ACTIVATION OF EPITHELIAL CELLSs by ELISA 15-HETE).

C. Behavioral measures
1. Selective attention (Inhibition of dominant reactions).
(The Eriksen flanker task modified by Kopp et al., 1996 was used for the response-inhibition (RI) task. An arrowhead was presented as target stimulus, bordered by two flanker stimuli above and below the target stimulus (also described in Willemssen et al., 2004). The subject had to push the button on the right side in front of him when the target stimulus pointed to the right side of the monitor. If it pointed to the other side, the corresponding button had to be pushed. If there was a dot at the target stimulus location, no reaction was required (no-go signal). Following the paradigm of
this task, the number of errors should increase when the flanker stimuli are incompatible to the target stimuli (flanker arrowheads point in one direction, target arrowhead in another direction). In the compatible trials, fewer errors are expected. The participants were urged to react as fast as possible. If they reacted too slow or erroneously a warning signal sounded. This task lasted approximately 12 min.)
2. Divided attention/double task (Resources for concentrating).
(A neurobehavioral subtest from the German attention test battery TAP (Zimmermann and Fimm, 1994) was used to examine divided attention (DA). During this task, visual and auditory stimuli were presented in parallel. Participants were instructed to press a response button whenever four crosses formed a quadrant in a field of varying visual patterns and whenever a tone with equal pitch was presented in a line of alternating tone pitches (low vs. high). Participants were asked to complete both tasks (visual and auditory) at the same time. The duration of this test was approximately 8 min.
3. Change in reactions (reaction flexibility).
(The set-shifting (SS) task assesses selective attention during a shifting attention task. Aim of the task is to alternate between two classes of targets. Two objects, one with a rounded form and another with an angular form, were shown on the left and the right side of a fixation cross. During the first trial the participants had to pay attention to the rounded shape. If the rounded shape for example was displayed on the left side of the screen, they had to press the left response button. In the next trial the participants had to shift attention to the angular shape. If the angular shape was now shown on the left side of the screen, they had to press the left side button again. In the subsequent trials they had to switch attention from one trial to the next (i.e., self-initiated shifting). Errors in the sequence of shifting were indicated by flashing of the
target, so the participants had the change to find back into the correct sequence. This task lasted approximately 5 min.)
Timing of Cognitive Tests
Three tests (RI followed by DA and then SS) were each completed three times (in the same order) at 18, 102 and 192 minutes after the start of exposure .

 

Results and discussion

Results of examinations:

For the Swedish Performance Evaluation System (SPES) olfactory symptoms subscale, pairwise comparisons showed that the 5 ppm (p<0.001) and 10 ppm (p<0.001) exposure conditions differed significantly from the non-irritating odorous control condition (0.6 ppm), but did not differ significantly from each other.
Overall, the results of physiological variables are consistent with the chemosensory data of trigeminal sensations and symptoms of irritation to the upper respiratory tract and eyes.
The neurobehavioral tests (DA, SST, RI) were not affected by the different exposure conditions.

Outcome of incidence:

It can be concluded that the primary effects of acetic acid at exposures up to 10 ppm (TWA) are weak and mostly connected with olfactory effects. Sensory effects on the level of physiological reactions were not observed in reaction behavior and there was no evidence of distracting effects resulting from acetic acid exposure of 10 ppm

Any other information on results incl. tables

Part A. Rating chemosensory-mediated irritation and acute symptoms

SPS and LMS

In general, the SPES and LMS ratings revealed that olfactory pathways mediate acute effects of acetic acid vapors in human volunteers. Only these symptoms (SPES) and intensity rating (LMS) reached levels labeled with intensity descriptor like' somewhat' or 'moderate'. Moreover, the ratings declined over time, mimicking the physiological response pattern of olfactory receptor neurons, namely adaptation. The LMS intensity ratings, thought to reflect trigeminal sensations/ perceptions, were lower and correspond to the labelweakeven during the two higher exposure conditions. Thus, the differences between the conditions were significant but the magnitude of the effect was small. Moreover, the LMS ratings were highly correlated (e.g. above 0.7 for odor intensity and nasal irritation) and therefore, the difference between the exposures might be driven by the olfactory perception of acetic acid.

Part B. Physiology measurements of sensory irritation.

The results of rhinomanometry showed a general increase in nasal airway resistance, but acetic acid concentration had no significant influence on the magnitude of this change.

The average EBF was not affected by the acute exposures to AA (F_(2,22)=0.3, p=0.74). The average EBF were 20.5 min^-1(±9.2) during the 0.6 ppm condition, 20.6 min^-1(±10.2) during the fluctuating condition (0.3-10 ppm), and 19.9 min^-1(±8.9) during the 10 ppm condition. Regardless of the exposure conditions, the EBF significantly increased (F_1,23)=8.4, p<0.01) from the beginning (19.3 min^-1) to the end (21.2 min^-1) of the sessions. The differences among the time courses of EBF of the three exposure scenarios was significant (F_(2,22)=5.87, p<0.01) and figure 4 shows that the increase was most pronounced during the fluctuating condition (0.3-10 ppm). Nevertheless, the confidence intervals indicated that the time-dependent variation was rather weak and within the “normal variation” (EBF during the 0.6 ppm condition) of the investigated sample.

Results of the biochemical analysis showed considerable inter-individual variability. For all exposure conditions, slightly but non-significantly elevated concentrations of substance P occurred after exposure. The biochemical data thus provided no evidence of pathophysiological processes, which could be interpreted in terms of neurogenic inflammation.

Overall, the results of physiological variables are consistent with the chemosensory data of trigeminal sensations and symptoms of irritation to the upper respiratory tract and eyes.

Part C. Behavioral measures

Cognitive effects in reaction behavior were not observed in the test for inhibition of dominant reaction tendencies nor in the dual task (divided attention) test. The results for the reaction change test showed an increase in the reaction time differences over the 4-hour exposure period. This effect was not related to exposure conditions. This effect cannot be interpreted as a distracting effect, as the lowest reaction time difference was found during the changing exposure condition (5ppm, mean with 10ppm peaks). This condition should have the greatest potency for causing cognitive effects.

Average blinking frequencyand change in respiratory resistance (Δ flow)fromthe three acetic acid exposure protocols.

	Blinking frequency[min^-1]	Δ Flow [ml / s]
Odor control	20.5	-17
AGW (variable)	20.6	-65
AGW (constant)	19.9	-36

Additional information on results

During all exposure conditions olfactory symptoms declined over time. There were no statistical differences for the other SPES acute symptoms subscales (unspecific/pre-narcotic, taste, respiratory, general irritation, nasal irritation and eye irritation) and none were rated greater than ‘barely’ during any exposure scenario.

Intensity ratings (Labelled Magnitude Scale (LMS)) averaged over the 4-hour exposure period (3 assessments) differed significantly between the 3 exposure conditions for 8 of the 11 olfactory and trigeminal sensations/ perceptions. Odor intensity (olfactory mediated) and annoyance (olfactory and trigeminal mediated) demonstrated the largest exposure related effects, and pairwise comparisons showed that the 5 ppm and 10 ppm exposure conditions differed significantly from the non-irritating odorous control condition (0.6 ppm) for each of these sensations/perceptions, and also for nauseous (olfactory mediated) and nasal irritation and pungent (trigeminal mediated). There were significant main effects for 3 other trigeminal mediated sensations/perceptions, burning, eye irritation and sharp, with a significant pairwise difference between the 10 ppm and 0.6 ppm exposure conditions for burning, The 5ppm and 10 ppm exposure conditions did not differ significantly from each other in pairwise comparisons for any of the olfactory and trigeminal sensations/ perceptions, including odor intensity and annoyance. In general, the intensity ratings decreased across the 4-hour exposure sessions, and only the LMS ratings of eye irritation increased slightly during the 10 ppm exposure scenario.

SPES and LMS ratings indicated, in general, that olfactory pathways mediate acute effects of acetic acid vapours in human volunteers. Only olfactory symptoms (SPES) and intensity rating (LMS) of odor intensity and annoyance reached levels labelled with intensity descriptor such as 'somewhat' or 'moderate'. The ratings declined over time (adaptation). LMS intensity ratings, thought to reflect trigeminal sensations/ perceptions, were lower and correspond to the label 'weak' even during the two higher exposure conditions. Thus although some differences between the exposure conditions were statistically significant, the magnitude of the effect was small. Moreover, the LMS ratings were highly correlated (e.g. above 0.7 for odor intensity and nasal irritation) and therefore, the difference between the exposures may simply be driven by the olfactory perception of acetic acid.

The average eye blinking frequency (EBF) was not affected by the acute exposures to acetic acid (F(2,22)=0.3, p=0.74).

The results of the rhinomanometry (AAR) revealed that, regardless of the exposure scenario, the nasal flow was reduced after the sessions (F(1,15)=5.71, p=0.03). Deceases during the two higher acetic acid conditions were somewhat stronger, but this difference was mainly caused by higher pre-exposure measures and was not statistically significant (F(2,14)=0.84, p=0.45). Results of the biochemical analysis showed considerable inter-individual variability. The biochemical data provided no evidence of pathophysiological processes, which could be interpreted in terms of neurogenic inflammation.

Applicant's summary and conclusion

Conclusions:

10ppm is considered a NOAEL for this study.