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Ethephon (CASRN 16672-87-0)

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0297

Ethephon; CASRN 16672-87-0

Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data, as outlined in the IRIS assessment development process. Sections I (Health Hazard Assessments for Noncarcinogenic Effects) and II (Carcinogenicity Assessment for Lifetime Exposure) present the conclusions that were reached during the assessment development process. Supporting information and explanations of the methods used to derive the values given in IRIS are provided in the guidance documents located on the IRIS website.

STATUS OF DATA FOR Ethephon

File First On-Line 08/22/1988

Category (section)
Status
Last Revised
Oral RfD Assessment (I.A.) on-line 03/01/1991
Inhalation RfC Assessment (I.B.) no data
Carcinogenicity Assessment (II.) no data

_I.  Chronic Health Hazard Assessments for Noncarcinogenic Effects

_I.A. Reference Dose for Chronic Oral Exposure (RfD)

Substance Name — Ethephon
CASRN — 16672-87-0
Primary Synonym — 2-Chloroethylphosphonic acid
Last Revised — 03/01/1991

The oral Reference Dose (RfD) is based on the assumption that thresholds exist for certain toxic effects such as cellular necrosis. It is expressed in units of mg/kg-day. In general, the RfD is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. Please refer to the Background Document for an elaboration of these concepts. RfDs can also be derived for the noncarcinogenic health effects of substances that are also carcinogens. Therefore, it is essential to refer to other sources of information concerning the carcinogenicity of this substance. If the U.S. EPA has evaluated this substance for potential human carcinogenicity, a summary of that evaluation will be contained in Section II of this file.

__I.A.1. Oral RfD Summary

Critical Effect
Experimental Doses*
UF
MF
RfD

Plasma ChE inhibition

16-Day Human Study

Union Carbide, 1977a

NOEL: None

LEL: 0.5 mg/kg/day

100
1
5E-3
mg/kg/day

*Conversion Factors -- none

__I.A.2. Principal and Supporting Studies (Oral RfD)

Union Carbide Agricultural Products Company, Inc. 1977a. MRID 00066931. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

In this human study, 10 humans/sex were orally dosed with ethephon at 0.5 mg/kg/day for 16 days, followed by a recovery period of 29 days. Dose related effects occurred in plasma cholinesterase activity, but not in red blood cell cholinesterase activity. The effect was reversible within 15 days. A statistically significant decrease in plasma cholinesterase activity also occurred in the control group (approximately 71 to 83% of initial control values) at the same periods of analysis reported for the test subjects, but the test subjects demonstrated a larger decrease (approximately 56 to 49% of paired initial values) than the control group. When the control group and test groups were compared by the Wilcoxon Rank Sum Test, the results were statistically significant (p<0.05). In addition, no dose related effects occurred in hematology, blood chemistry, or urine analyses.

__I.A.3. Uncertainty and Modifying Factors (Oral RfD)

UF — An uncertainty factor of 10 was used to account for the intraspecies differences. An additional UF of 10 was used to account for the lack of an established NOEL for plasma cholinesterase inhibition.

MF — None

__I.A.4. Additional Studies/Comments (Oral RfD)

Data Considered for Establishing the RfD

1) 16-Day Study - human: Principal study - see previous description; no core grade

2) 28-Day Study - human: NOEL=none; LEL=1.8 mg/kg/day (average of 2.2 mg/kg/day effect level in males and 1.5 mg/kg/day for females; dose related effects on diarrhea, urgency of bowel movements, urinary urgency, stomach cramps, and either loss or increase in appetite in the absence of plasma or RBC cholinesterase inhibition); no core grade (Union Carbide, 1972)

3) 104-Week Feeding (oncogenic) - rat: Systemic NOEL=300 ppm (15 mg/kg/day); Systemic LEL=3000 ppm (150 mg/kg/day) (HDT; plasma and RBC ChE inhibition); core grade supplementary (Union Carbide, 1978)

4) 2-Year Feeding - dog: NOEL=none; LEL=30 ppm (0.75 mg/kg/day; LDT) (plasma ChE inhibition); RBC ChE was inhibited at the MDT (300 ppm) and HDT (1000-3000 ppm, depending on day of administration; Smooth muscle hypertrophy was noted at the MDT and HDT; Body weight and efficiency of food consumption were reduced at HDT; core grade supplementary (Union Carbide, 1977b)

5) Teratology - rat: Embryo/fetal and Maternal NOEL=600 mg/kg/day; Embryo/fetal and Maternal LEL=1800 mg/kg/day (maternal death (56%) and equivocal teratogenicity); core grade minimum (Union Carbide, 1980)

6) Teratology - rabbit: Embryo/fetal NOEL=50 mg/kg/day; Embryo/fetal LEL=100 mg/kg/day (resorption); Maternal NOEL=100 mg/kg/day, Maternal LEL=250 mg/kg/day (decreased food consumption, and increased gut histopathology and mortality); core grade minimum (Union Carbide, 1981b)

Other Data Reviewed:

1) 78-Week Feeding/(oncogenic) - mouse: Systemic NOEL=30 ppm (4.5 mg/kg/day); Systemic LEL=300 ppm (45 mg/kg/day) (plasma ChE inhibition in males and females); Systemic NOEL=none; LEL=30 ppm (4.5 mg/kg/day for RBC ChE inhibition in females); core grade supplementary (Union Carbide, 1985)

Data Gap(s): Chronic Rat Feeding Study, Chronic Dog Feeding Study, Rat Reproduction Study

__I.A.5. Confidence in the Oral RfD

Study — Low
Database — Medium
RfD — Low

The critical study is of low quality and is given a low confidence rating. The database is given a medium to low confidence rating due to the lack of adequate chronic studies. Low confidence in the RfD follows.

__I.A.6. EPA Documentation and Review of the Oral RfD

Source Document — This assessment is not presented in any existing U.S. EPA document.

Other EPA Documentation — Pesticide Registration Standard, March 1988; Pesticide Registration Files

Agency Work Group Review — 03/23/1988

Verification Date — 03/23/1988

Screening-Level Literature Review Findings — A screening-level review conducted by an EPA contractor of the more recent toxicology literature pertinent to the RfD for Ethephon conducted in September 2002 did not identify any critical new studies. IRIS users who know of important new studies may provide that information to the IRIS Hotline at hotline.iris@epa.gov or (202)566-1676.

__I.A.7. EPA Contacts (Oral RfD)

Please contact the IRIS Hotline for all questions concerning this assessment or IRIS, in general, at (202)566-1676 (phone), (202)566-1749 (FAX) or hotline.iris@epa.gov (internet address).

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_I.B. Reference Concentration for Chronic Inhalation Exposure (RfC)

Substance Name — Ethephon
CASRN — 16672-87-0
Primary Synonym — 2-Chloroethylphosphonic acid

Not available at this time.

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_II.  Carcinogenicity Assessment for Lifetime Exposure

Substance Name — Ethephon
CASRN — 16672-87-0
Primary Synonym — 2-Chloroethylphosphonic acid

This substance/agent has not undergone a complete evaluation and determination under US EPA's IRIS program for evidence of human carcinogenic potential.

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_III.  [reserved]
_IV.  [reserved]
_V.  [reserved]


_VI.  Bibliography

Substance Name — Ethephon
CASRN — 16672-87-0
Primary Synonym — 2-Chloroethylphosphonic acid
Last Revised — 03/01/1991

_VI.A. Oral RfD References

Union Carbide Agricultural Products Company. 1972. MRID No. 00036510. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Union Carbide Agricultural Products Company. 1977a. MRID No. 00066931. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Union Carbide Agricultural Products Company. 1977b. MRID No. 00060359, 00147357. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Union Carbide Agricultural Products Company. 1978. MRID No. 00060358, 00144558. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Union Carbide Agricultural Products Company. 1980. MRID No. 00063745. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Union Carbide Agricultural Products Company. 1981. MRID No. 00085755. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

Union Carbide Agricultural Products Company. 1985. MRID No. 00081634, 00165591. Available from EPA. Write to FOI, EPA, Washington, DC 20460.

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_VI.B. Inhalation RfC References

None

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_VI.C. Carcinogenicity Assessment References

None

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_VII.  Revision History

Substance Name — Ethephon
CASRN — 16672-87-0
Primary Synonym — 2-Chloroethylphosphonic acid

Date
Section
Description
08/22/1988 I.A. Oral RfD summary on-line
03/01/1991 I.A.4. Citations added
03/01/1991 VI. Bibliography on-line
01/01/1992 IV. Regulatory Action section on-line
04/01/1997 III., IV., V. Drinking Water Health Advisories, EPA Regulatory Actions, and Supplementary Data were removed from IRIS on or before April 1997. IRIS users were directed to the appropriate EPA Program Offices for this information.
12/03/2002 I.A.6. Screening-Level Literature Review Findings message has been added.

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_VIII.  Synonyms

Substance Name — Ethephon
CASRN — 16672-87-0
Primary Synonym — 2-Chloroethylphosphonic acid
Last Revised — 08/22/1988

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