Hexachlorobenzene

Uses

Hexachlorobenzene is an industrial chemical associated with a wide range of chlorine chemistry processes. It is most often used to make other compounds, but has also been used as a wood preservative, a fungicide on grains and grain seeds, and an additive in explosives, as well as a part of the production process for rubber, aluminum, and dyes. Its fungicide use was permitted in the U.S. until 1965. There are currently no direct commercial uses of hexachlorobenzene in the U.S. However, it is still produced as a byproduct of the production of many other chemicals, and is a contaminant in many pesticides.

Health Effects

Hexachlorobenzene (HCB) is listed by EPA as a probable human carcinogen. It can damage the liver, kidneys, neurological system. and immune system. It may also damage the developing fetus if the mother is exposed. HCB is thought to be an endocrine disruptor.

An epidemic of porphyria cutanea tarda, a serious skin disease with associated neurological and liver damage, was seen in Turkish citizens who accidentally comsumed bread made with grain treated with HCB over a long period. Reduced growth and arthritic changes in limbs were seen in children who were exposed either directly or through breast milk.

In the Environment

HCB has a half-life in soil of 3 to 6 years. It will bioaccumulate in fish, marine mammals, birds, lichens, and animals that eat lichens (like caribou). It can also build up in wheat and vegetables. Human exposure is mostly through eating low levels of it in contaminated food -- it has been detected in food during market basket surveys.

Sources

Current releases of HCB are mainly from air and water discharges from chemical manufacturing processes, or from applications of pesticides that include it as a contaminant. It is also released by some waste incineration, and in waste water from non-ferrous metal production. There are also environmental reservoirs of the compound from old uses (for instance, contaminated sediments, or 84 known Superfund sites).

Unfortunately, recent air and water releases of HCB are not well enough known to permit detailed estimates of how many tons are released by each type of source. Two to five million pounds may be generated each year as a byproduct of chlorination chemical manufacturing processes. HCB is produced as a byproduct in the production of chlorine, carbon tetrachloride, perchloroethylene, trichloroethylene, ethylene dichloride, vinyl chloride, and 1,1,1-trichloroethane. Many of these are widely used chemicals; for instance, perchloroethylene is the principal solvent used in dry cleaning. It is produced along with, and may be found as a contaminant in, the pesticides atrazine, dimethyl tetrachloroterephthalate (DCPA), chlorothalonil, picloram, propazine, simazine, lindane, mirex, and pentachloronitrobenzene (PCNB).

EPA estimates that only 4,597 pounds of HCB were released to the air in 1990. For 1995, EPA's Toxic Release Inventory (TRI) reports 346 pounds of air releases, 6,458 pounds of water releases, 480 pounds of land releases, and 220 tons of HCB transferred as waste to other locations. 13 million tons of RCRA hazardous waste containing HCB was generated in 1995, but it is impossible to tell how much of this waste was HCB and how much was other ingredients.

References

* Environmental Protection Agency. 1990 Emissions Inventory of Section 112(c)(6) Pollutants: Polycyclic Organic Matter (POM), TCDD, TCDF, PCBs, Hexachlorobenzene, Mercury, and Alkylated Lead: Final Report. Office of Air and Radiation. April 1998.

* Environmental Protection Agency. National Primary Drinking Water Regulations: Technical Factsheet on: Hexachlorobenzene (HCB). Office of Ground Water and Drinking Water. January 1998.

* Environmental Protection Agency. Health Effects Notebook for Hazardous Air Pollutant -- Hexachlorobenzene Factsheet. Office of Air Quality Planning and Standards. May 1998.

* Agency for Toxic Substances and Disease Registry. ToxFAQ for Hexachlorobenzene. September 1997.

* Environmental Protection Agency. IRIS database for Hexachlorobenzene. Office of Research and Development. May 1998.

* Environmental Protection Agency. Toxic Release Inventory Database (1996 "frozen" version).

* Environmental Protection Agency. Biennial Reporting System Database (1995 final version).

* Environmental Protection Agency. Permit Compliance System Database (copy last updated in April 1997)

Detailed Sources of HCB Emissions

No detailed, overall breakdown of sources of HCB is available. However, EPA databases and other sources provide some guidance as to which types of industries may contribute most to HCB release.

Air releases

EPA estimates air releases for 1990 of HCB as follows (from EPA's 112(c)(6) 1990 emissions inventory document, Table 7-3):

The 1995 TRI database shows air releases of 305 pounds of HCB for the chlor-alkali industry, 246 pounds for the agricultural chemicals industry, and 15 pounds for cyclic crudes and intermediates.

Water releases

1995 TRI shows 6,344 pounds of water releases of HCB for the chlor-alkali industry and 114 pounds for agricultural chemicals. Unfortunately, TRI does not cover many kinds of water releasing facilities. To get an estimate of which industries might be involved in water releases of HCB, EPA's Permit Compliance System (PCS) database was searched for permits that included monitoring or effluent limits on HCB. Number of permits found in this database as of 1997 are listed below.

Type of Industry Number of water permits with limits on HCB

SEWERAGE SYSTEMS 216

(unknown) 195

INDUST. ORGANIC CHEMICALS NEC 103

PLSTC MAT./SYN RESINS/NV ELAST 79

CYCLIC CRUDES INTERM., DYES 25

INDUSTRIAL INORGANIC CHEMICALS 15

PETROLEUM REFINING 13

REFUSE SYSTEMS 10

SYN ORG FIBERS,EXCEPT CELLULOSE 10

ELEMENTARY & SECONDARY SCHOOLS 8

ALKALIES AND CHLORINE 7

PESTICIDES & AGRICULTURAL CHEM 6

Only industries with more than 5 permits were listed.

Hazardous waste

RCRA hazardous waste is generally supposed to be handled in ways that do not release it to the environment. However, industries that generate hazardous waste will often produce associated releases as well. The table of hazardous waste generation below was taken from the 1995 EPA Biennial Reporting System (BRS) database.