Technical Factsheet on: o-DICHLOROBENZENE
List of Contaminants
As part of the Drinking Water and Health pages, this fact sheet is part of a larger publication:
National Primary Drinking Water Regulations
Drinking Water Standards
MCLG: 0.6 mg/L
MCL: 0.6 mg/L
HAL: 1 to 10 day: 9 mg/L; Longer-term: 9 mg/L
Health Effects Summary
Acute: EPA has no data on the acute toxicity of o-dichlorobenzene which is relevant to the drinking water
Drinking water levels which are considered "safe" for short-term exposures: For a 10-kg (22 lb.) child
consuming 1 liter of water per day: upto a 7-year exposure to 9 mg/L.
Chronic: EPA has found o-dichlorobenzene to potentially cause damage to the nervous system, liver,
kidneys and blood cells from long-term exposure at levels above the MCL.
Cancer: There is inadequate evidence to state whether or not o-dichlorobenzene has the potential to
cause cancer from lifetime exposures in drinking water.
Usage Patterns
Production of o-dichlorobenzene has decreased since the 1970's: from 54.6 million lbs. in 1975 to an
estimated 43 million lbs. in 1991. In 1987 it was estimated that industries consumed o-dichlorobenzene
as follows: Organic synthesis (mainly for herbicides), 90%; toluene diisocyanate processing solvent, 5%;
solvent and miscellaneous uses, 5%.
The greatest use of o-dichlorobenzene is as a chemical intermediate for making agricultural chemicals,
primarily herbicides.
Other present and past uses include: solvent for waxes, gums, resins, wood preservatives, paints;
insecticide for termites and borers; in making dyes; as a coolant, deodorizer, degreaser.
Release Patterns
1,2-Dichlorobenzene's use in manufacturing and solvents may be significant sources of discharges into
water. Dichlorobenzenes also enter the water systems (raw and contaminated water) from the use of 1,2-
DCB as a deodorant in industrial wastewater treatment. Chemical waste dump leachates and direct
manufacturing effluents are reported to be the major source of pollution of the chlorobenzenes (including
the dichlorobenzenes) to Lake Ontario. The major source of 1,2-dichlorobenzene emission to the
atmosphere has been reported to be solvent applications which may emit 25% of annual production to the
From 1987 to 1993, according to EPA's Toxic Chemical Release Inventory, o-dichlorobenzene releases
to land and water totalled over240,000 lbs., of which nearly 172,000 lbs. was to land. These releases

were primarily from organic chemicals manufacturing industries which use it as an intermediate in
herbicide production. The largest releases occurred in New Jersey.
Environmental Fate
If released to soil, 1,2-dichlorobenzene can be moderately to tightly adsorbed. Experimental Koc values
of 280 to 320 were determined in silt loam soils containing less than 2 percent organic matter. In
equilibrium batch studies, a relatively strong adsorption of 1,2-dichlorobenzene to collected aquifer
material was observed. However, the detection of 1,2-dichlorobenzene in various groundwaters indicates
that leaching can occur. Volatilization from soil surfaces may be an important transport mechanism. It is
possible that 1,2-dichlorobenzene will be slowly biodegraded in soil under aerobic conditions. Chemical
transformation by hydrolysis, oxidation or direct photolysis are not expected to occur in soil.
If released to water, adsorption to sediment will be a major environmental fate process based upon
extensive monitoring data in the Great Lakes area and Koc values. Analysis of Lake Ontario sediment
cores has indicated the presence and persistence of 1,2-dichlorobenzene since before 1940. 1,2-
Dichlorobenzene is volatile from the water column with an estimated half-life of 4.4 hours from a model
river one meter deep flowing 1 m/sec with a wind velocity of 3 m/sec at 20 deg C; adsorption to sediment
will attenuate volatilization. It has been suggested that the three dichlorobenzene isomers may undergo
slow biodegradation in natural water. The dichlorobenzenes are not expected to be biotransformed in
anaerobic water conditions found in aquifers.
1,2-Dichlorobenzene is not expected to undergo significant hydrolysis in environmental waters. It is
reported to be resistant towards oxidation by peroxy radicals in aquatic media. In an isooctane solvent,
1,2-dichlorobenzene absorbs virtually no radiation above 300 nm; therefore, direct photolysis in the
environment should not be significant.
If released to air, 1,2-dichlorobenzene will exist predominantly in the vapor-phase and will react with
photochemically produced hydroxyl radicals at an estimated half-life rate of 24 days in a typical
atmosphere. Direct photolysis in the troposphere is not expected to be important. The detection of 1,2-
dichlorobenzene in rainwater suggests that atmospheric removal via wash-out is possible.
In a study of a representative green alga, the Iog10 bioconcentration factors (BCF) for 1,2-
dichlorobenzene was 4.17. Experimental BCF values of 66-560 have been reported and 1,2-
dichlorobenzene has been detected in trout from Lake Ontario. General population exposure to 1,2-
dichlorobenzene may occur through oral consumption of contaminated drinking water and food
(particularly fish) and through inhalation of contaminated air since 1,2-dichlorobenzene has been detected
in widespread ambient air.
Chemical/Physical Properties
CAS Number: 95-50-1
Color/ Form/Odor: Colorless liquid with pleasant, aromatic odor
M.P.: -17 C B.P.: 180.5 C
Vapor Pressure: 1.47 mm Hg at 25 C
Octanol/Water Partition (Kow): Log Kow = 3.38
Density/Spec, grav: 1.31 g/L at 20 C

Solubility: 0.14 g/L of water at 25 C; Slightly soluble in water
Soil sorption coefficient: Koc measured at 280 to 320 for loam soils; low to moderate mobility in soil
Odor/Taste Thresholds: N/A
Bioconcentration Factor: BCF measured at 270 to 560 in fish; expected to bioconcentrate in aquatic
Henry's Law Coefficient: 0.0012 atm-cu m/mole at 20 C
Trade Names/Synonyms: ortho Dichlorobenzol, Dilantin, Dowtherm E, Chloroben, Dilatin DB
Other Regulatory Information
-For Ground/Surface Water Sources:
Initial Frequency- 4 quarterly samples every 3 years
Repeat Frequency- Annually after 1 year of no detection
-Triggers - Return to Initial Freq. if detect at > 0.0005 mg/L
Reference Source	Method Numbers
EPA 600/4-88-039	502.2; 524.2
Treatment/Best Available Technologies: Granular Activated Charcoal and Packed Tower Aeration
Toxic Release Inventory - Releases to Water and Land, 1987 to 1993 (in pounds):

TOTALS (in pounds)

Top Five States*






Major Industries

Industrial Organics

Cyclic crudes, dyes

Alkalis, chlorine

Paper mills

Gum, wood chems.

* Water/Land totals only include facilities with releases greater than a certain amount - usually 1000 to
10,000 lbs.
For Additional Information

EPA can provide further regulatory or other general information:
EPA Safe Drinking Water Hotline - 800/426-4791
Other sources of toxicological and environmental fate data include:
Toxic Substance Control Act Information Line - 202/554-1404
Toxics Release Inventory, National Library of Medicine - 301/496-6531
Agency for Toxic Substances and Disease Registry - 404/639-6000