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2,4-Dichlorophenol (CASRN 120-83-2)

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2,4-Dichlorophenol; CASRN 120-83-2

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 2,4-Dichlorophenol

File First On-Line 01/31/1987

Category (section)
Last Revised
Oral RfD Assessment (I.A.) on-line 06/30/1988
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 — 2,4-Dichlorophenol
CASRN — 120-83-2
Last Revised — 06/30/1988

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*

Decreased delayed

Rat, Subchronic to

Exon and Koller, 1985

NOEL: 3 ppm (converted
to (0.3 mg/kg/day)

LOAEL: 30 ppm
(converted to
3.0 mg/kg/day)


*Conversion Factors -- Doses were estimated by the authors.

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

Exon, J.H. and L.D. Koller. 1985. Toxicity of 2-chlorophenol, 2,4- dichlorophenol and 2,4,6-trichlorophenol. In: Water Chlorination: Chemistry, Environmental Impact and Health Effects, Jolley et al., Ed. Vol. 5.

Female rats were exposed to 3, 30, or 300 ppm 2,4-dichlorophenol in drinking water from weaning age through breeding at 90 days, parturition, and weaning of pups. Ten randomly selected pups/group were weaned at 3 weeks and administered 2,4-dichlorophenol for an additional 15 weeks. The authors estimated the exposure to be approximately 0.3, 3.0, and 30.0 mg/kg bw/day for the low, medium, and high dose groups. Increases in serum antibody levels to keyhole limpet hemocyanin, as measured by an enzyme-linked immunosorbent assay (ELISA) were found to be treatment-related. The increase was statistically significant in the high-dose group, as were spleen and liver weights. Delayed-type hypersensitivity responses to bovine serum albumin in Freund's complete adjuvant were significantly decreased in those animals administered 3.0 mg/kg bw/day. The NOEL for 2,4-dichlorophenol was, therefore, determined to be 3 ppm or 0.3 mg/kg bw/day. This is substantially lower than the NOEL of 100 mg/kg bw/day reported by Kobayashi et al. (1972) for nonspecific liver changes in mice fed dichlorophenol in the diet for 180 days.

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

UF — A factor of 10 each was employed for extrapolation from animal data to humans and for protection of sensitive human subpopulations. Since the test animals were exposed both in utero and through milk before the 15-week administration in drinking water, an additional factor for use of a subchronic study was not considered necessary.

MF — None

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

Exon and Koller (1985) reported that exposure of dams to 300 ppm dichlorophenol resulted in a significant decrease in litter sizes.

__I.A.5. Confidence in the Oral RfD

Study — Low
Database — Low
RfD — Low

The study (Exon and Koller, 1985) used an adequate number of animals and measured very sensitive endpoints (immunological functions) in an appropriate manner. As these endpoints are not commonly used in derivation of human health risk evaluations, confidence in the study is rated low. Additional published studies did not look for the critical effects and did not support the magnitude of the NOEL/LOAEL. Therefore, confidence in the database is rated low. Low confidence in the RfD follows.

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

Source Document — U.S. EPA, 1985

The Drinking Water Criteria Document is currently undergoing review.

Other EPA Documentation — None

Agency Work Group Review — 11/06/1985, 01/22/1986

Verification Date — 01/22/1986

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 2,4-Dichlorophenol conducted in November 2001 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 — 2,4-Dichlorophenol
CASRN — 120-83-2

Not available at this time.

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_II.  Carcinogenicity Assessment for Lifetime Exposure

Substance Name — 2,4-Dichlorophenol
CASRN — 120-83-2

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 — 2,4-Dichlorophenol
CASRN — 120-83-2
Last Revised — 08/01/1989

_VI.A. Oral RfD References

Exon, J.H. and L.D. Koller. 1985. Toxicity of 2-chlorophenol, 2,4- dichlorophenol and 2,4,6-trichlorophenol. In: Water Chlorination: Chemistry, Environmental Impact and Health Effects, Jolley et al., Ed., Vol.5. (Chap. 25). Lewis Publishers, Chelsea, MI. p. 307-330.

Kobayashi, S., T. Fukuda, K. Kawaguchi, H. Chang, S. Toda and H. Kawamura. 1972. Chronic toxicity of 2,4-dichlorophenol in mice: A simple design for checking the toxicity of residual metabolites of pesticides. J. Med. Soc., Toho Univ., Japan. 19: 356-362.

U.S. EPA. 1985. Drinking Water Criteria Document for Chlorinated Phenols. Prepared by the Office of Health and Environmental Assessment, Environmental Criteria and Assessment Office, Cincinnati, OH for the Office of Drinking Water, Washington, DC.

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_VI.B. Inhalation RfC References


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_VI.C. Carcinogenicity Assessment References


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_VII.  Revision History

Substance Name — 2,4-Dichlorophenol
CASRN — 120-83-2

09/30/1987 I.A.2. Citation corrected
03/01/1988 I.A.1. Dose conversion clarified
03/01/1988 I.A.5. Confidence levels revised
03/01/1988 I.A.6. Documentation corrected
06/30/1988 I.A.7. Primary contact changed
08/01/1989 VI. Bibliography on-line
01/01/1992 IV. Regulatory actions updated
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 — 2,4-Dichlorophenol
CASRN — 120-83-2
Last Revised — 01/31/1987

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