UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

Date: July 19, 2012 

OFFICE OF CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

SUBJECT: Ethoprop, Immunotoxicity study in Rats 

PC Code: 041101 

Decision No.: 457676 

Petition No.: N/A 

Risk Assessment Type: N/ A 

TXR No.: 0056382 

MRID No.: 48632501 

DP Barcode: 396215 

Registration No.: N/ A 

Regulatory Action: N/A 

Submission No.: N/ A 

CAS No.: 13194-48-4 

40 CFR: N/A 

FROM: Y ung G . Y ang, PhD . . t .:L (I d" <..:7 / .. Lv~ - t¥ 

Risk Assessment Branch VI 

Health Effects Division (7509 P) 

THROUGH: F~ ecia Fort, Chief -4 . g . , ~'--..J! Risk Assessment Branch VI ..,.,...-j....Jl}JICJ~Cfl..r 

Health Effects Division (7509 P) 

TO: Monica Wait 

RMIB3 

Pesticide Re-Evaluation Division (7508P) 

And 

Kit Farwell, DVM 

Risk Assessment Branch VII 

Health Effects Division (7509P) 

I. CONCLUSIONS 

The immunotoxicity study in rats for Ethoprop (MRID 48632501) has been reviewed. 

It is classified as acceptable/guideline and satisfies guideline requirements for an 

immunotoxicity study (OPPTS 870.7800). 

1 
II. BACKGROUND and ACTION REQUESTED 

An immunotoxicity study on Ethoprop (MRID 48632501) has been submitted. RAB VI 

was asked to review and prepare a DER for this study. 

III. RESULTS AND DISCUSSION 

The immunotoxicity study in rats for Ethoprop (MRID 48632501) has been reviewed. 

The DER is attached and an executive summary is as follows: 

EXECUTIVE SUMMARY: In an immunotoxicity study (MRID 48632501), Ethoprop 

(96.6% a.i., Batch no. PEA4000032) was administered to male Sprague-Dawley 

(Crl:CD(SD)) rats (10/group) in diets at dose levels of 0, 5, 15, or 30 ppm (equivalent to 

0.4, 1.2, or 2.43 mg/kg/day, respectively) for 4 weeks. On Day 25, all animals in all 

groups received an intravenous injection of 2x 108 sheep red blood cells in 0.9% saline at 

the dose volume of 1.0 ml/animal. The positive control group consisted of 8 males 

received cyclophosphamide (50 mg/kg) by intraperitoneal injection on Day 27. 

The animals were monitored for mortality and for treatment related symptoms twice 

daily. Body weights were recorded on Day (-7), Day (-4), Day (1) and then twice weekly 

until necropsy. Food consumption was recorded daily. Detailed clinical observations 

were done prior to the test substance administration and once every week till necropsy. 

During Week 4, blood samples were taken without fasting from the retro-orbital sinus 

from all animals under isoflurane anesthesia for blood (plasma and red blood cell) 

cholinesterase (ChE) analysis. On Day 29, animals were killed by carbon dioxide 

asphyxiation. All anjmals were subject to the detailed necropsy. Brains were processed 

and examined for cholinesterase activity. Spleens, thymus and brain from animals were 

weighed. Splenic tissues were used as the sources of splenocytes for conducting 

immunotoxicology investigations. 

There were no treatment related clinical signs, no effect on body weight and food and 

water consumption at dietary concentrations up to 30 ppm. However, there were 

statistically significant reductions of erythrocyte acetylcholinesterase activity at 5 

(p<0.05), 15 and 30 ppm (p<0.01). The percentage reduction for RBC ChE was 18%, 

56% and 71% at 5, 15 and 30 ppm, respectively. There was a 13% reduction of brain 

acetylcholinesterase at 30 ppm. No treatment related effect on organ weights and 

macroscopic pathology was found. 

The systemic toxicity LOAEL is 5 ppm (0.4 mg/kg/day) based on reduced red blood 

cell cholinesterase activity, the systemic toxicity NOAEL is not established(< 0.4 

mg/kglday). 

Primary T-cell dependent antibody response to sheep RBC was analyzed by modified 

Jeme Plaque Forming Cell assay. There was no statistically significant decreased in both 

the specific activity (PFC/ 1 06 cells) and total activity (PFC/spleen) in treated groups 

when compared to the vehicle control group. There was a high inter-individual variability 

noted in all the treatment groups as well as in the control group. Evaluation of individual 

2 
animal data of this study did not show any trend or distribution that would demonstrate 

significant suppression of anti-SRBC PFC response. Animals in positive control group, 

showed a statistically significant (p<O.OO 1) decrease of PFC response to a challenge with 

SRBCs in compared to the vehicle control group. This confirmed the ability of the test 

system to detect immunosuppressive effects and confirmed the validity of the study 

design. 

The Natural Killer (NK) cells activity was not evaluated in this study. The toxicology 

database for Ethoprop does not reveal any evidence of treatment related effects on the 

immune system. The overall weight of evidence suggests that the chemical does not 

directly target the immune system. Under HED guidance a NK cell activity assay is not 

required at this time. 

Under conditions of this study, the immunotoxicity NOAEL is 30 ppm (equivalent to 

2.43 mg/kg/day), the highest tested dose. The LOAEL is not established (>2.43 

mg/kg/day). 

This immunotoxicity study is classified acceptable/ guideline and satisfies the guideline 

requirement for an immunotoxicity study (OPPTS 870.7800) in rats. 

3 
Etho ro I 041101 

Immunotoxicity (2011) Page 1 of9 

OPPTS 870.7800 I DACO 4.8 I OECD None 

EPA Reviewer: Khin Swe Oo, MD. DABT Signature: _ __ """""''":----:----

Toxicology and Epi~emiology Branch, Health Effects Division (7509P)hte: 7j ~~ Jt ot'!J. . EPA Secondary Reviewer: Yung G. Yang, PhD Signature: ~ 6: ~ -c:7 

Risk Assessment Branch VI, Health Effects Division (7509P) Date: 7;/ l/2:9 1 vTemplate version 09/11 

TXR #: 0056382 

DATA EVALUATION RECORD 

STUDY TYPE: Immunotoxicity- 4 weeks Oral (Dietary) Study; OPPTS 870.7800 

PC CODE: 041 101 DP BARCODE: D 396215 

TEST MATERIAL (PURITY): Ethoprop (96.6% w/w) 

SYNONYMS: Ethoprophos; 0-ethyl-S,S-dipropyl phosphorodithioate. 

CITATION: Arrowsmith W. (2011). Ethoprop: 4 -Week Dietary Immunotoxicity Study in 

Male Sprague-Dawley Rat. Huntingdon Life Sciences, Woolley Road, Alconbury, Huntingdon, 

Cambridgeshire PE 28 4HS, UK. Project ID BDG0050. MRID 48632501, Unpublished. 

SPONSOR: AMV AC Chemical Corporation, 4100 E. Washington Blvd., Los Angeles, CA 

90023, USA. 

EXECUTIVE SUMMARY: In an immunotoxicity study (MRID 48632501), Ethoprop (96.6% 

a.i., Batch no. PEA4000032) was administered to male Sprague-Dawley (Crl:CD(SD)) rats 

(10/group) in diets at dose levels of 0, 5, 15, or 30 ppm (equivalent to 0.4, 1.2, or 2.43 

mg/kg/day, respectively) for 4 weeks. On Day 25, all animals in all groups received an 

intravenous injection of2x108 sheep red blood cells in 0.9% saline at the dose volume of 1.0 

ml/animal. The positive control group consisted of 8 males received cyclophosphamide (50 

mg/kg) by intraperitoneal injection on Day 27. 

The animals were monitored for mortality and for treatment related symptoms twice daily. Body 

weights were recorded on Day (-7), Day (-4), Day (1) and then twice weekly until necropsy. 

Food consumption was recorded daily. Detailed clinical observations were done prior to the test 

substance administration and once every week till necropsy. During Week 4, blood samples 

were taken without fasting from the retro-orbital sinus from all animals under isoflurane 

anesthesia for blood (plasma and red blood cell) cholinesterase (ChE) analysis. On Day 29, 

animals were killed by carbon dioxide asphyxiation. All animals were subject to the detailed 

necropsy. Brains were processed and examined for cholinesterase activity. Spleens, thymus and 

brain from animals were weighed. Splenic tissues were used as the sources of splenocytes for 

conducting immunotoxicology investigations. 

There were no treatment related clinical signs, no effect on body weight and food and water 

consumption at dietary concentrations up to 30 ppm. However, there were statistically 

significant reductions of erythrocyte acetylcholinesterase activity at 5 (p<0.05), 15 and 30 ppm 

(p<0.01). The percentage reduction for RBC ChE was 18%, 56% and 71% at 5, 15 and 30 ppm, 

respectively. There was a 13% reduction of brain acetylcholinesterase at 30 ppm. No treatment 
Ethoprop I 041101 

Immunotoxicity (2011) Page 2 of 9 

OPPTS 870.7800 I DACO 4.8 I OECD None 

related effect on organ weights and macroscopic pathology was found. 

The systemic toxicity LOAEL is 5 ppm (0.4 mglkg/day) based on reduced red blood cell 

cholinesterase activity, the systemic toxicity NOAEL is not established(< 0.4 mglkg/day). 

Primary T-cell dependent antibody response to sheep RBC was analyzed by modified Jeme 

Plaque Forming Cell assay. There was no statistically significant decreased in both the specific 

activity (PFC/106 cells) and total activity (PFC/spleen) in treated groups when compared to the 

vehicle control group. There was a high inter-individual variability noted in all the treatment 

groups as well as in the control group. Evaluation of individual animal data of this study did not 

show any trend or distribution that would demonstrate significant suppression of anti-SRBC PFC 

response. Animals in positive control group, showed a statistically significant (p<O.OOI) decrease 

of PFC response to a challenge with SRBCs in compared to the vehicle control group. This 

confirmed the ability of the test system to detect immunosuppressive effects and confirmed the 

validity of the study design. 

The Natural Killer (NK) cells activity was not evaluated in this study. The toxicology database 

for Ethoprop does not reveal any evidence of treatment related effects on the immune system. 

The overall weight of evidence suggests that the chemical does not directly target the immune 

system. Under HED guidance a NK cell activity assay is not required at this time. 

Under conditions of this study, the immunotoxicity NOAEL is 30 ppm (equivalent to 2.43 

mglkglday), the highest tested dose. The LOAEL is not established (>2.43 mglkglday). 

This immunotoxicity study is classified acceptable/ guideline and satisfies the guideline 

requirement for an immunotoxicity study (OPPTS 870.7800) in rats. 

COMPLIANCE: Signed and dated GLP, Quality Assurance, and Data Confidentiality 

statements were provided. 
Ethoprop I 041101 

I. MATERIALS AND METHODS 

A. MATERIALS: 

1. Test material: Ethoprop 

Immunotoxicity (2011) Page 3 of9 

OPPTS 870.7800 I DACO 4.8 I OECD None 

Description: Clear light yellow liquid 

Lot/Batch#: PEA4000032 

Purity: 96.6% (w/w) 

Compound Stability: Stored deep frozen approximately at -20°C pending use. 

CAS # of TGAI: 13194-48-4 

2. Vehicle and/or positive control: Rat and Mouse No.1 Maintenance Diet. Positive control 

group received cyclophosphamide monohydrate 50mg/kg, (Lot/Batch no. not reported), via 

intraperitoneal injection on Day 27 (2 days before termination). 

3. Test animals: 

Species: Rats, male 

Strain: Sprague-Dawley Crl: CD(SD) 

Age/weight at the start of treatment: 49-56 days; 233- 329 grams 

Source: Charles River (UK) Ltd. 

Housing: Housed five animals per cage. 

Diet: Rat and Mouse No.1 Maintenance Diet, ad libitum 

Water: Public water supply ad libitum 

Environmental conditions: Temperature: 19-23°C 

Humidity: 40-70% 
Ethoprop I 041101 

Acclimation period: 

B. STUDY DESIGN: 

Immunotoxicity (2011) Page 4 of9 

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Air changes: Positive air pressure, not re-circulate 

Photoperiod: 12 hrs dark/12 hrs light 

13 days 

1. In life dates - Experiment Start: April1, 201 1 End: June 10, 2011 

2. Animal assignment: 

Table 1. Study Design 

Group Dietary Treatment Dietary Cone. Achieved dosage No. of 

No. (ppm) (m_glkglday) animals 

1 Vehicle Control 0 0 10 

2 Ethoprop 5 0.4 10 

3 Ethoprop 15 1.2 10 

4 Ethoprop 30 2.43 10 

5 Positive control (CPH)b -- 50° 8 

• Data obtamed from pages 11 of the study report (MRID 48632501). 

• b Cyclophosphamide (CPH) was given to positive control group by intraperitoneal injection (50 mg/kg, 

5mg/mL, lOmllkg) on Day 27. 

3. Dose selection: It was reported that the dose levels were selected based on the findings from 

previous 28 day dietary toxicity studies (WIL-21199 and WIL-21200). In Project WIL -

21200, the dietary concentrations used were 7.5, 15, and 30 ppm, and found low RBC ChE 

activity in males at 7. 5 ppm. In Project WIL - 21199, the dietary concentrations were, 0 .2, 

0.5, and 1 ppm; and no treatment related findings at any dose level. 

4. Diet preparation and analysis: Diet was prepared weekly by preparing the premix and 

mixing it with an appropriate amount of basal diet to achieve the final concentrations. 

Prepared diet was stored deep frozen approximately at -20°C pending use. 

Results of Diet Analysis: 

Homogeneity analysis: CV <2%. Accuracy within 5% ofthe nominal concentration 

Stability analysis: The mean analyzed concentration remained within 9% of the initial time 

zero. 

Concentration analysis: Concentration analysis showed ( + 10% to - 15%) of nominal 

concentrations. 

5. Statistics: It was reported that, treatment groups were compared using pairwise Fisher's 

Exact tests (Fisher 1973) for each dose group against the control. If Bartlett's test for 

variance homogeneity (Bartlett 1937) was not significant at the 1 %level, parametric _.,. 

analysis (the FI approximate test) was applied. If the F 1 approximate test was significant, 

Dunnett's test (Dunnett 1955, 1964) was performed instead. If Bartlett's test was significant 

at the 1 % level, then logarithmic and square-root transformations were tried. If Bartlett's test 

was still significant, then non-parametric tests were applied. If the HI approximate test for 
Ethoprop I 041101 

Immunotoxicity (2011) Page 5 of 9 

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monotonicity of dose-response was not significant at the 1 %level, Shirley's test for a 

monotonic trend (Shirley 1977) was applied. For organ weight data, analysis of covariance 

was initially performed using terminal bodyweight as covariate. If the within group 

relationship between organ weight and bodyweight was significant at the 1 0% level, then the 

treatment comparisons were made on adjusted group means in order to allow for differences 

in bodyweight which might influence the organ weights. 

Fisher's Exact tests (Fisher 1973) was performed for cholinesterase data if 75% of the data 

(across all groups) were the same value. Treatment groups were compared with control group 

with pairwise comparisons. 

C. METHODS: 

1. Observations: 

The animals were monitored for morbidity and for treatment related symptoms twice daily. 

Detailed clinical observations were done before the test substance administration and once 

every week till necropsy. 

2. Body weight: 

Body weights were recorded before test substance administration (Days -7 and -4) and then 

twice weekly from Day 0 until necropsy. 

3. Food/water consumption and compound intake: 

Food consumption was recorded weekly. Water consumption was observed daily. 

4. Sacrifice and pathology: On Day 29, animals were sacrificed by carbondioxide 

asphyxiation. 

a. Gross necropsy: all animals were subjected to a necropsy; brain, spleen and thymus were 

weighed. Spleen samples were taken for immunotoxicology investigation and brain was 

processed and examined for cholinesterase activity. 

b. Tissue preparation/histopathology: histology was not performed. 

5. Immunotoxicitv: 

a. Plague Forming Cell (PFC) Assay: T-lymphocyte-dependent antibody response to sheep 

red blood cells is evaluated with PFC assay. Animals were exposed to the test substance for 

4 weeks except vehicle control and positive control groups. On Day 25, all animals in all 

groups were injected intravenously into the tail vein with sheep red blood cell (2x 1 0

8 SRBC) 

in 09% saline (1.0 ml/animal). On Day 27, animals in positive control group were treated 

with immunosuppressant cyclophosphamide 50 mg/kg (5mg/ml solution at lOml/kg b.w.) via 

intraperitoneal injection. 

At termination, the spleens from the animals were removed and a single cell suspension was 

prepared from each animal by mechanical dissociation. Cells were counted and diluted to an 

appropriate concentration for the assay. The spleen cells were then mixed with an agar matrix 
Ethoprop I 041101 

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containing a suspension of the SRBCs and guinea pig serum complement. This mixture was 

poured into Petri dishes, allowed to set and incubated for up to 3 hours. Individual B 

lymphocytes secreting antibodies to SRBCs formed small foci where antibody-dependent, 

complement-mediated lysis occurred. The number of lytic plaques for each animal was 

determined and group mean responses calculated. 

b. Natural Killer (NK) Cells Activity Assay: NK cells assay was not performed. 

II. RESULTS: 

A. OBSERVATIONs: 

1. Clinical signs of toxicity: There were no treatment related signs and symptoms in treated 

groups. 

2. Mortality: There were no premature deaths. 

B. Body weight and weight gain: No treatment related effects on body weight and body 

weight gain (Table 2). 

TABLE 2. Average body weights and body weight gains during 28 days of treatment 

Ethoprop Body weights (g ± SD) 

Dose (ppm) Day 1 Dayl5 

0( vehicle control) 272±20.8 373±27.4 

5 274±26.1 376±40.1 

IS 288±23.2 381±35.9 

30 245± 14.5 370±20.3 

Data obtamed from page 33 m the study report. 

n = l 0 animals per group. 

Day22 

410±32. 1 

414±48.5 

420±40.6 

406±24.0 

Day29 

438±33.3 

446±50.0 

45 1±44.4 

433±26.1 

C. FOOD/WATER CONSUMPTION AND COMPOUND INTAKE: 

1. Food consumption: No differences in food consumption in all groups. 

Total weight gain 

(g ± SD) 

(Days 1-29) 

165±23.9 

172±29.0 

163±25.5 

153± 15.3 

2. Water consumption: There was no effect of treatment on water consumption. 

3. Compound consumption: included in Table 1. 

4. Food efficiency: Did not report. 

D. GROSS NECROPSY: No treatment related macroscopic changes at necropsy. 

1. Organ weight: There were no brain, thymus and spleen weight differences in treated groups 

when compared to the vehicle control group (Table 3). 
Ethoprop I 041101 

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Table 3. Mean terminal body weight and Organ weights, Mean±SD 

Dose Group Body weight (g) Brain (g) Spleen (g) Thymus (g) (ppm) 

Vehicle Control 436±33 2.04±0.09 0.862±0.197 0.489±0.138 

5 445±50 2.00±0.07 0.915±0.192 0.481±0.163 

15 449±45 2.07±0.08 0.952±0.145 0.454±0.1 09 

30 433±26 2.17±0.3 0.850±0.136 0.465±0.111 

InformatiOn was obtamed from page 36 of the study report 

2. Histology: No report on histology 

3. Blood and brain cholinesterase: Erythrocyte acetylcholinesterase activity was statistically 

significantly reduced in a dose-related manner in all treated groups when compared to the vehicle 

control group (18%, 56% and 71% reduction at 5, 15 and 30 ppm groups, respectively). Brain 

acetylcholinesterase activity was significantly reduced at 30 ppm (p<O.Ol) (Table 4). 

Table 4. Blood and brain cholinesterase (ChE) activities 

Dose Group (ppm) Blood ChE (U/L) 

0 1832.5*±364.2 

5 1497.5±496.3 

15 797.5**±272.7 

30 522.5**±248.7 

Data extracted from page 35 of the study (n=lO) 

*P<0.05; ** p<O.Ol 

E. IMMUNOTOXICITY TESTS: 

Brain ChE (U/kg) 

2415 5±907 .2 

23425±1109.1 

23260±984.3 

21 090**±1 013.5 

1. Plague forming cell assay (PFC): There were no statistically significant changes in the PFC 

response to sheep red blood cells, in all treated groups when compared to the vehicle control 

group (Table 5). There was a high inter-individual variability noted in all the treatment groups 

as well as in the control group. Evaluation of individual animal data of this study did not show 

any trend or distribution that would demonstrate significant suppression of anti-SRBC PFC 

response (Figures 1 and 2). Treatment with cyclophosphamide resulted in almost complete 

reduction of the PFC response, both as PFC/106 cells or PFC/spleen (p<O.OOl). 

Table 5. Results of plaque forming cell assay (mean± SD) 

Group (ppm) Cells/spleen 

(107

) 

PFC/106 cells PFCispleen 

0 37.94±16.94 657.8±217.2 251642±128579 

5 33.89±17.76 611.8±611.8 193082±114327 

15 41.13±17.1 6 826.3±733.9 269062±116755 

30 33 .61± 12.45 525.0±296.0 193996±165671 

Positive control 9.89 ... ±3.28 23.8 ... ±17.7 2231'"±1576 

Data extracted from page 115 of study report . 

.. p<O.Ol. ••• p<O.OOI. 
Ethoprop I 041101 

Immunotoxicity (2011) Page 8 of 9 

OPPTS 870.7800 I DACO 4.8 I OECD None 

Fieure 1: Individual animal data of specific activity (PFC/106 cells) 

3000.0 

2500.0 

.. 

'ii 

Q 

2000.0 

~ 

i 1500.0 

u 

... 

0.. 1000.0 

500.0 

0.0 

0 

Key: 

Group I • Conlrol, 0 ppm 

Group 2 ~ ETHOI>KOP. S ppm 

Group 3 = ETiiOPROP, 15 ppm 

Group 4 ~ E'IHOPROP, JO ppm 

• 

. 

• 

T 

• 

Group S - Cyclophosphamide, SO mt/k{'. 

• 

• • 

• • 

• • • 

T l .L 

• • • .... 

2 3 Mole group 4 5 

Data extracted from page 113 of the study report. 

Fieure 2: Individual animal data of total activity (PFC/spleen) 

600000 

500000 

c 

: 400000 

ii. 

.. 

! 300000 

u 

... 

0.. 

200000 

100000 

0 

0 

Key: 

Group 1 - Conrr<>l, 0 ppm 

Gr<>up 2 = ETHOPROP, S prm 

Group 3 • ETHOPROP, 15 ppm 

Group 4 = ETHOPROP, 30 ppm 

• 

• 

• 

• 

• 

• 

• 

• 

• 

Group S = Cyclophosphamide, SO mglkg 

• 

• • 

• 

• • 

• 

... •• 

• f 

• 

• 

2 3 M .. •group 

Data extracted from page 114 of the study report. 

• 

• 

• 

-

• 

i 

• 

4 5 

2. NK cell activity assay: Did not perform NK cell assay. 

III.DISCUSSION AND CONCLUSIONS: 

A. INVESTIGATORS' CONCLUSIONS: It is concluded that dietary administration of 

Ethoprop to male Sprague-Dawley rats at 5, 15 and 30 ppm for four weeks caused no 

toxicologically significant findings. There was no suppression of immune function. The NOAEL 

for immunotoxicity was greater than 30 ppm (> 2.43 mg/kg/day). 
Ethoprop I 041101 

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OPPTS 870.7800 I DACO 4.8 / OECD None 

B. REVIEWER COMMENTS: In an immunotoxicity study (MRID 48632501), Ethoprop 

(96.6% a.i., Batch no. PEA4000032) was administered to male Sprague-Dawley (Crl:CD(SD)) 

rats (10/group) in diets at dose levels ofO, 5, 15, or 30 ppm for 4 weeks. On Day 25, all animals 

in all groups received an intravenous injection (by bolus) of2x108 sheep red blood cells in 0.9% 

saline at the dose volume of 1.0 ml/animal. The positive control group consisted of 8 males 

received 50 mglkg cyclophosphamide (CPH) by intraperitoneal injection on Day 27. 

There were no treatment related effects on clinical signs, body weight, food, and water 

consumption at dietary concentrations up to 30 ppm. However, there were statistically 

significant reductions of erythrocyte acetylcholinesterase activity at 5 (p<0.05), 15 and 30 ppm 

(p<O.Ol). The percentage reduction for RBC ChE was 18%, 56% and 71% at 5, 15 and 30 ppm, 

respectively. There was a 13% reduction of brain acetylcholinesterase activity at 30 ppm. No 

treatment related effect on organ weights and macroscopic pathology was found. 

The systemic toxicity LOAEL is 5 ppm (0.4 mg/kg/day) based on reduced red blood cell 

cholinesterase levels, the systemic toxicity NOAEL is (<0.4 mglk.g/day). 

Primary T-cell dependent antibody response to sheep RBC was analyzed by modified Jeme 

Plaque Forming Cell assay. There was no statistically significant decreased in both the specific 

activity (PFC/1 06 cells) and total activity (PFC/spleen) in treated groups when compared to the 

vehicle control group. There was a high inter-individual variability noted in all the treatment 

groups as well as in the control group. Animals in positive control group, showed a statistically 

significant (p<O.OOl) decreased PFC response to a challenge with SRBCs in compared to the 

vehicle control group. This confirmed the ability of the test system to detect immunosuppressive 

effects and confirmed the validity of the study design. 

The Natural Killer (NK) cells activity was not evaluated in this study. The toxicology database 

for Ethoprop does not reveal any evidence of treatment related effects on the immune system. 

The overall weight of evidence suggests that the chemical does not directly target the immune 

system. Under HED guidance a NK cell activity assay is not required at this time. 

Under conditions of this study, the immunotoxicity NOAEL is 30 ppm (equivalent to 2.43 

mglkglday), the highest tested dose. The LOAEL is not established (>2.43 mglkglday). 

C. STUDY DEFICIENCIES: Body weight, body weight changes, and organ weights of the 

positive control (cyclophosphamide) group was not reported.