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Repeated dose toxicity: inhalation

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Administrative data

Endpoint:
short-term repeated dose toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
26 January 2017 - 28 August 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2017
Report date:
2017

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)
Version / remarks:
2009
Deviations:
no
GLP compliance:
yes
Limit test:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
2-Ethylhexyl (R)-2-(2-methyl-4chlorophenoxy)propionate
EC Number:
630-324-3
Cas Number:
861229-15-4
Molecular formula:
C18H27ClO3
IUPAC Name:
2-Ethylhexyl (R)-2-(2-methyl-4chlorophenoxy)propionate
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- batch No.of test material: CHP0006

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
Storage conditions: Room temperature (15 to 25 °C)

Test animals

Species:
rat
Strain:
Sprague-Dawley
Details on species / strain selection:
The rat is an animal model commonly utilized in this type of toxicity studies and is recommended by current testing guidelines, e.g. OECD 412. In addition, a historical database of this species and strain of rats (Sprague-Dawley CD® outbred), equally exposed by inhalation, is available in the laboratory for comparison.
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Envigo Dublin, Virginia
- Age at study initiation: approximately 9 weeks
- Weight at study initiation: 210 g to 286 g
- Fasting period before study: no
- Housing: Polycarbonate cages with a stainless steel mesh lid, nominally 2 or 3 per cage
- Diet: ad libitum: Teklad Global 16% Protein Rodent Diet (Certified), 2016C Envigo, Madison, Wisconsin
- Water: ad libitum: Potable water from the public supply (New Jersey-American Water Company, Cherry Hill, New Jersey) via an automated watering system
- Acclimation period: at least 6 days

DETAILS OF FOOD AND WATER QUALITY: There were no known contaminants in the feed and water that were expected to interfere with the results of this study.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-26
- Humidity (%): 30-70
- Air changes (per hr): no information
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
inhalation: aerosol
Type of inhalation exposure:
nose only
Vehicle:
air
Mass median aerodynamic diameter (MMAD):
>= 2.7 - <= 3.1 µm
Details on inhalation exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Flow through (ADG) snout-only exposure system

- Method of holding animals in test chamber: Animal restraint tube

- Source and rate of air: Dry air from in-house compressed air system – breathing quality

- System of generating particulates/aerosols:
Group 1 – Air control
Groups 2 to 4 – Micro atomizer manufactured by Envigo
One Micro atomizer with a fine needle for each group
Dynamic test item feed from disposable clinical syringe driven by syringe pump

- Temperature, humidity, pressure in air chamber: Monitored using Sunbeam and Springfield Apollo Humidity and Thermometer gauges as follows:
Frequency – continuous monitoring; documented at approximately 30 minute intervals
Sample location – gauges located in restraint tube on the exposure system
Sample position remained constant

- Air flow rate:
Inlet Generation Airflow:
Group 1 – 68.0 L/minute
Groups 2 to 4 – 4.0 L/minute
Dilution Airflow:
Dry air from in-house compressed air system – breathing quality
Flow – 64.0 L/minute per system (Groups 2 to 4)
A further 2.0 L/minute room airflow drawn passively into chamber via
tangential inlet port for each group (Groups 1 to 4)
Extract Airflow:
Drawn by in-house extract system
Drawn from base of exposure system
Flow – 70.0 L/minute per system
Filtered locally

- Method of particle size determination: Determined by cascade impaction
samples collected as follows:
Impactor type – Marple 290 Series (296 configuration)
Sample collection media – stainless steel substrates and glass fiber final stage filter
Sample flow – 3.0 L/minute
Sample volume – measured by wet-type gas meter
Sample frequency – minimum of 1 sample/test group/week
Sample location: Representative animal exposure position
Sample analysis: Gravimetric – Groups 2 to 4, Chemical (HPLC/UV) – Groups 2 to 4
MMAD and σg derived
Sample disposition
Substrates and final stage filters analyzed by FIA

Aerosol samples collected as follows:
-Filter type – glass fiber, held in an open face filter holder
-Sample flow – 2.0 L/minute
-Sample volume – measured by timed flowmeter
-Sample frequency – minimum of 3 samples/group/exposure
-Sample location: Representative animal exposure position
Sample analysis: Gravimetric – Groups 1 to 4; Chemical (HPLC/UV) – Groups 1 to 4
Sample disposition: Filters sent for chemical analysis by FIA – Exposure Days 1 to 4 and then weekly; filters not sent for analysis stored refrigerated (2 - 8ºC) an subsequently discarded after study completion
-Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Matrix: Filter papers; stainless steel slides
Calibration Range: 5.00 μg/mL to 100.00 μg/mL
Regression Type: Linear
Data Calculation: Peak area
Limit of Quantification: 5.00 μg/mL
Analytical Instrumentation: HPLC/UV Agilent Technologies
Type of Detection: UV
-Column Type Phenomenex Hypersil BDS C18 Supplied by Agilent
-Column Dimensions Length = 100 mm
Diameter = 4.6 mm
Particle Size = 5 µm
-Column Temperature 40°C
-Run Time 6.0 minutes
-Injection Volume 50 µL
Mobile Phase: Acetonitrile / Water (80 / 20, v/v)
Extraction Solvent /Sample Diluent: Acetonitrile / Water (70 / 30, v/v)
Duration of treatment / exposure:
4 weeks (+ 4 weeks test item-free recovery period)
Frequency of treatment:
6 hours once daily 5 days a week
Doses / concentrationsopen allclose all
Dose / conc.:
0 mg/L air
Dose / conc.:
0.02 mg/L air (nominal)
Remarks:
Exposures represent active ingredient, which represents approximately 0.013 mg/L
mecoprop-p acid equivalent
Dose / conc.:
0.05 mg/L air (nominal)
Remarks:
Exposures represent active ingredient, which represents approximately 0.033 mg/L
mecoprop-p acid equivalent
Dose / conc.:
0.2 mg/L air (nominal)
Remarks:
Exposures represent active ingredient, which represents approximately 0.130 mg/L
mecoprop-p acid equivalent
No. of animals per sex per dose:
28
Control animals:
yes, concurrent no treatment
Details on study design:
A three week preliminary inhalation investigation was conducted at target exposure levels of 0, 0.05, 0.22 and 1.0 mg/L to assess the toxicity and toxicokinetic profile of these exposure levels of MCPP-p 2-EHE to rats when administered via nose-only inhalation. The levels for the preliminary investigation were selected based on the results of non-inhalation studies of multiple phenoxy compounds where weight gain impairment and other changes to liver and kidney weights and histopathology were observed at approximately 0.3 mg/kg/day that would approximate an inhalation level of 1.0 mg/L. Only males were evaluated in this study because prior non-inhalation test results showed the male to be more sensitive to the test item than the female.

Training for dosing:
The animals on study were acclimated to the method of restraint for 3 days (10 minutes on Day 1, 30 minutes on Day 2 and 60 minutes on Day 3) within the 7 days preceding their initial test item exposure.


Animals were restrained (individual plastic exposure tubes) during the exposure administration procedures for a maximum of 420 minutes per day. This daily period of restraint included the 360 minutes of exposures during which interruptions for technical reasons were expected. This daily period of restraint also included the pre-exposure and post-exposure intervals in which the animals were placed in or removed from the plastic exposure tubes.
Positive control:
None

Examinations

Observations and examinations performed and frequency:
DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Animals were removed from their cages and examined twice pretest and weekly during the study period (after exposure on exposure days). Examinations included observations of general condition, skin and fur, eyes, nose, oral cavity, abdomen and external genitalia as well as evaluations of respiration.

BODY WEIGHT: Yes
- Time schedule for examinations: Non-fasted body weights were recorded for all animals twice pretest and twice weekly during the exposure period (prior to exposure on exposure days). During the recovery period, non-fasted
body weights were recorded weekly. Terminal, fasted body weights were obtained just prior to necropsy.

FOOD CONSUMPTION: Yes
Food consumption was measured (weighed) weekly (once every 7 days), beginning one week prior to treatment.

OPHTHALMOSCOPIC EXAMINATION: Yes
All animals were examined pretest and during the 4th week of the exposure period. Only animals which were within normal limits at the pretest examination were placed on test. Lids, lacrimal apparatus and conjunctiva were examined visually. The cornea, anterior chamber, lens, iris, vitreous humor, retina and optic disc were examined by indirect ophthalmoscopy. The pupils of each animal were dilated prior to examination using tropicamide ophthalmic solution.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: at the end of the exposure period
- Anaesthetic used for blood collection: Yes, isoflurane anesthesia
- Animals fasted: Yes
- How many animals: 10 animals/group
- Parameters checked: Hemoglobin (HGB), Hematocrit (HCT), Red blood cell count (RBC), Platelet count (PLT), Mean corpuscular volume (MCV), Mean corpuscular hemoglobin (MCH), Mean corpuscular hemoglobin concentration (MCHC), Red cell distribution width (RDW), Total white blood cell count (WBC), Reticulocyte count (RETIC), Differential white blood cell count, Neutrophils (ANEU), Lymphocytes (ALYM), Eosinophils (AEOS), Basophils (ABASO), Monocytes (AMONO), Large unstained cells (ALUC), Prothrombin time (PT), Activated partial thromboplastin time (APTT)

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at the end of the exposure period
- Animals fasted: Yes
- How many animals: 10 animals/group
- Parameters checked: Aspartate aminotransferase (AST), Alanine aminotransferase (ALT), Alkaline phosphatase (ALKP), Blood urea nitrogen (BUN), Creatinine (CREAT), Glucose (GLU), Triglycerides (TRIG), Total protein (TP), Albumin (ALB), Total bilirubin (TBILI)
Sodium (NA+) , Potassium (K+) , Chloride (Cl-), Calcium (Ca++), Inorganic phosphorus (PHOS)

URINALYSIS: Yes
- Time schedule for collection of urine: Urine was collected into ice-chilled containers overnight (approximately 12 to 16 hours)
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Not specified
- Parameters checked: pH, Protein, Glucose (GLU), Ketones (KET), Bilirubin (BIL), Occult blood (BLD), Appearance (APP), Specific gravity (Sp.G.), Volume (VOL)
When the protein result was ≥100 mg/dL, microscopic examination of the urine sediment was performed on centrifuged urine samples via manual microscopy and the following cellular
elements identified: Sperm (SPM), Red blood cells (RBC), White blood cells (WBC), Epithelial cells (EPC), Casts (CAST), Amorphous matter (AMOR), Triple phosphate (Trip/Phos), Other crystals (Oth/Cryst)

OTHER:
Body Temperature
Body temperature was recorded for 5 randomly selected animals/group shortly after the first exposure (within 1 hour) and after an exposure during the last week of exposure (within 1 hour). Body temperatures were recorded via rectal probes.

Sacrifice and pathology:
GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes
Statistics:
If Bartlett's test for variance homogeneity was not significant at 1% level, then parametric methods were applied. If the F1 approximate test for monotonicity of exposure-response was not significant at the 1% level, Williams' test for a monotonic trend was applied. If the F1 test was significant, suggesting that the exposure-response was not monotone, Dunnett's test was performed instead. If Bartlett's test was significant at 1% level, then logarithmic and square-root transformations were tried. If Bartlett's test was still significant, then non-parametric methods were applied to mean ranks. If H1 approximate test for monotonicity was not significant at 1% level, Shirley's test for a monotonic trend was applied. If H1 test was significant, then Steel's test was performed instead.
If Jonckheere-Terpstra test was significant at the 5% level, then direction of trend was established and one-tailed step-down testing in this direction was performed. If the Jonckheere-Terpstra test was not significant at the 5% level, then the Kruskal-Wallis test was applied. If the Kruskal-Wallis test was significant at 5% level, the test-item treated groups were compared to the control using exact Wilcoxon rank sum tests, otherwise, no further comparisons were made. For pre-treatment data, a Kruskal-Wallis test was performed. If test was significant at 5% level treated groups were compared to control using exact Wilcoxon rank sum tests. Comparisons involving only two groups were performed using Wilcoxon rank sum tests.
For comparisons involving more than two groups, if Cochran-Armitage test was significant at 5% level, then the direction of the trend was established and one-tailed step-down testing in this direction was performed. If the Cochran-Armitage test was not significant at 5% level, then the χ2 test was applied. If the χ2 test was significant at 5% level, test-item treated groups were compared to control using Fisher’s Exact tests, otherwise, no further comparisons were made.

Results and discussion

Results of examinations

Clinical signs:
no effects observed
Description (incidence and severity):
There were no test item-related effects on clinical signs.
Mortality:
no mortality observed
Body weight and weight changes:
no effects observed
Description (incidence and severity):
There were no test item-related effects on body weights.
Food consumption and compound intake (if feeding study):
no effects observed
Description (incidence and severity):
There were no test item-related effects on food consumption.
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
no effects observed
Description (incidence and severity):
There were no test item-related effects on ocular findings.
Haematological findings:
effects observed, non-treatment-related
Description (incidence and severity):
There were no MCPP-p-2-EHE-related hematology changes at any exposure level at study termination (Day 29). All differences between control and treated mean values, including those that were statistically significant, were considered not MCPP-p-2-EHE related as they lacked a exposure level relationship and/or there was general overlap between individual control and treated values.
Clinical biochemistry findings:
effects observed, non-treatment-related
Description (incidence and severity):
There were no MCPP-p-2-EHE-related clinical chemistry changes at any exposure level at study termination (Day 29). All differences between control and treated mean values, including those that were statistically significant, were considered not MCPP-p-2-EHE related as there was general overlap between individual control and treated values.
Urinalysis findings:
no effects observed
Description (incidence and severity):
There were no MCPP-p-2-EHE-related urinalysis changes at any exposure level at study termination (Day 29).
Behaviour (functional findings):
not examined
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
effects observed, non-treatment-related
Description (incidence and severity):
Terminal necropsy: All organ weight changes, including statistically significant changes in pituitary weights at 0.20 ml/L, were considered not to be test item-related because they were sporadic, independent of exposure level, small in magnitude and/or did not have macroscopic or microscopic correlates.
Recovery Necropsy: There was a statistically significant increase in pituitary weight in Group 4 due to one animal with a much higher pituitary weight. All other animals were comparable to controls and the other groups. The higher weight in one animal is considered to be incidental and not test-item related.
Gross pathological findings:
no effects observed
Description (incidence and severity):
There were no test item-related macroscopic findings. All macroscopic findings occurred sporadically or at a similar incidence and severity in the control and test item exposed groups and were considered incidental and due to biological variability.
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Terminal Necropsy:
Larynx
Minimal to slight squamous hyperplasia of the laryngeal respiratory epithelium occurred at ≥ 0.05 mg/L and exhibited an exposure-related increase in incidence and severity. Squamous hyperplasia was located in the anterior larynx along the medial aspect of the arytenoid cartilages. Minimal to slight epithelial alteration was present at ≥ 0.02 mg/L and was located in the anterior ventral larynx at or near the base of the epiglottis. Epithelial alteration is considered to be the initial stage of a generally concentration-dependent transformation from pre-existing epithelium to full laryngeal squamous metaplasia (see table 1 "information on results)
Thymus
Four of 10 animals in the 0.20 mg/L exposure group had minimal to moderate atrophy of the thymus which correlated with a macroscopic observation of small thymus and a trend for lower weight compared to controls. Given the absence of other indicators of stress, the biological significance of this finding is unclear. All other microscopic findings occurred sporadically or at similar incidence and severity in control and test item treated groups and were considered incidental and due to biological
variability.
Recovery Necropsy:
Following an up to 4 week recovery period, the absence of squamous hyperplasia and its precursor change (epithelial alteration) in the larynx was indicative of full recovery of both findings. Full recovery was seen after 1 week.


Histopathological findings: neoplastic:
not examined

Effect levels

Key result
Dose descriptor:
NOAEC
Effect level:
0.2 mg/L air
Based on:
test mat.
Sex:
male
Basis for effect level:
other: highest dose tested

Target system / organ toxicity

Key result
Critical effects observed:
no

Any other information on results incl. tables

Table 1: Test item-related findings in the larynx

Group/sex

1M

2M

3M

4M

Exposure (mg/L)

0

0.02

0.05

0.20

 

 

 

 

 

Hyperplasia, squamous cell, squam.epith.

 

 

 

 

Minimal

0

0

0

o

Slight

0

0

1

1

Total

0

0

1

3

 

 

 

 

 

Alteration, epithelial, resp. epithelium

 

 

 

 

Minimal

0

5

7

5

Slight

0

0

0

3

Total

0

5

7

8

 

 

 

 

 

Number of tissues examined

10

10

10

10

 

Table 2: Target and mean achieved aerosol concentrations were as follows

Group

Target

Aerosol Concentration (mg/L)

               Gravimetric               Analytical

1

0 (air only)

0.000

0.000

 

 

2

0.02

0.020

0.023

 

 

3

0.05

0.054

0.047

 

 

4

0.20

0.190

0.170

 

 

No MCPP-p-2-EHE was detected in Group 1 samples. Mean achieved gravimetric concentration for Group 2 was at the target, for Group 3 was 8% above target and for Group 4 was 5% below

target. Mean achieved analytical concentration for Group 2 was 15% above target, for Groups 3 and 4 were 6% and 15% below target, respectively. On occasions, during the study, aerosol concentration individual and /or daily mean values were greater than 15% (above or below target).

 

Table 3: Particle size distribution measurements were as follows:

Group

MMAD (µm)      GSD

MMAD (µm)    GSD

 

       Gravimetric

         Analytical

2

3.0                   1.66-1.76

3.1                 1.64-1.91

3

2.5                   1.71-1.84

2.7                 1.73-1.79

4

2.7                   1.63-1.84

2.8                 1.54-1.81

The MMAD values for gravimetric and chemical analysis results showed that the delivered particle size was respirable to the rats.

 

Applicant's summary and conclusion

Conclusions:
Under the conditions of this study and based on the histopathology findings, the NOAEC was considered to be the high exposure level of 200 mg/m3.
Executive summary:

Male Sprague-Dawley CD rats (28/group) were exposed by nose-only inhalation for 6 hours, once daily, 5 days per week with 0 (air only), 0.02, 0.05 or 0.20 mg/L MCPP-p-2-EHE for 4 consecutive weeks. At the end of the treatment period, 10 animals/group were euthanized and necropsied and the remaining 18 animals/group were held for an up to 4-week treatment free period. Following a 1, 2 or 4 week recovery period, 6 animals/group were euthanized and necropsied at each interval. Parameters evaluated during the study were: viability, clinical observations, ophthalmology, body weights, body temperature, food consumption, clinical pathology (end of exposure period), organ weights, macroscopic observations and microscopic pathology.

There were no unscheduled decedents. All animals survived until their scheduled termination. Inhalation exposures of MCPP-p 2-EHE to rats for 4 weeks at target exposure levels of 0.02, 0.05 and 0.20 mg/L resulted in no adverse effects on clinical signs, body weights, food consumption, clinical pathology parameters, organ weights or macroscopic pathology. Four-weeks repeat inhalation exposure of male rats to MCPP-p 2-EHE was associated with squamous hyperplasia in the larynx at ≥ 0.05 mg/L and epithelial alteration ≥ 0.02 mg/L, with complete recovery after a one week recovery period. Laryngeal squamous hyperplasia and epithelial alteration are considered to be adaptive non-specific response to chronic irritation. An expert international workshop on laryngeal squamous metaplasia concluded that laryngeal epithelial alteration of minimal to slight severity should be considered non-adverse as they generally regress following a sufficient recovery period after exposure, do not progress over time and are not associated with laryngeal dysfunction.

In conclusion, under the conditions of this study and based on the histopathology findings, the NOAEC was considered to be the high exposure level of 200 mg/m3.