CAREX Canada

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CAS No. 106-46-7

Wikimedia Commons, p-Dichlorobenzene^[1]

IARC Monograph Vol. 73, 1999 (Group 2B)

General Information

para-Dichlorobenzene is a white to colourless crystalline solid with a mothball-like odour.^[2] It may also be referred to as p-dichlorobenzene, 1,4-dichlorobenzene or PDCB.^[3] There are numerous other synonyms and product names; see HSDB for more information.^[3]

p-Dichlorobenzene has been classified by IARC as a Group 2B carcinogen, possibly carcinogenic to humans. p-Dichlorobenzene is carcinogenic in experimental animals. Oral administration of PDCB caused increased incidences of hepatocellular carcinomas and adenomas in mice, as well as increased incidence of renal tubular adenocarcinomas in male rats.^[4,5]

Additionally, exposure to PDCB can cause painful irritation of the eyes, skin and nasal cavity, as well as headache, coughing, shortness of breath, drowsiness, dizziness, nausea, vomiting, skin irritation, and liver damage.^[3,5]

PDCB has been ranked by CAREX Canada as Group B (possible high priority) for both the occupational and environmental settings. Prioritization was based on the carcinogenicity and other toxic properties of the substance, the prevalence of exposure in Canada, and the feasibility of assessing exposure.

Regulations and Guidelines

Occupational Exposure Limits (OEL)

Canadian Jurisdictions	OEL (ppm)
Canada Labour Code	10
BC, AB, MB, ON, NL, PE, NB, NS	10
SK	10 15 [stel]
QC, NT, NU, YK*	75 110 [stel]
Other Jurisdictions	OEL (ppm)
ACGIH 2010 TLV	10

ppm = parts per million

stel = short term exposure limit (15 min. maximum)

TLV = Threshold Limit Value (8 hour maximum)

Canadian Environmental Guidelines

Health Canada’s Drinking Water Guidelines set out a Maximum Acceptable Concentration (MAC) of 0.005 mg/L for PDCB in drinking water.^[6] PDCB was not included in other Canadian government environmental guidelines reviewed.^[7-9]

Canadian Agencies/Organizations

PDCB is included in Health Canada’s Domestic Substance List (DSL) as a low priority substance with exposure risk already managed.^[10] It was not included other Canadian government chemical listings reviewed.^[11,12]

Main Uses

p-Dichlorobenzene is used primarily as a moth repellent and space deodorant.^[2,4] p-Dichlorobenzene is also used as a chemical intermediate in the production of other chemicals, including polyphenylene sulphide and 1,2,4-trichlorobenzene.^[2,4]

There are several other minor uses for PDCB, including: pesticide against certain tree-boring insects and ants; fungicide for tobacco seeds, leather and some fabrics; disinfectant; animal repellent; intermediate chemical in pigment and dye production; ingredient in the manufacturing of certain pharmaceuticuals and resin-bonded abrasives.^[2,5]

In Canada, PDCB is listed as an active ingredient in 10 current and 8 historical products registered with the Pest Management Regulatory Agency (PMRA).^[13] All products listed were mothballs or air deodorizers.

Canadian Production and Trade

Canada was a net exporter of p-dichlorobenzene in 2009.^[15] The majority of p-dichlorobenzene was exported to the US and Jamaica.^[15]

Production and Trade

Activity	Quantity	Year
Domestic consumption	3,500 t	1993^[14]
Export*: Mainly to US, Japan	1,177 t of ‘dichlorobenzene, o-dichlorobenzene, p-dichlorobenzene’	2009^[15]
Import*: Mainly from US, China	801 t of ‘dichlorobenzene, o-dichlorobenzene, p-dichlorobenzene’	2009^[15]

t = tonne

*Product categories presented include isomers of dichlorobenzene.

Occupational Exposures

Inhalation is the most important route of occupational exposure to p-dichlorobenzene, although dermal exposure can also occur.^[2,5] The main occupations exposed include workers involved in the production and processing of PDCB.^[2,4,5] Exposure may also occur in workplaces where para-dichlorobenzene is used, such as in mothball and resin-bonded abrasive wheel manufacturing plants.^[5] Historically, PDCB had been measured in workplace indoor air at levels up to 700 ppm.^[2,4,5] Air concentrations were found to be higher in p-dichlorobenzene manufacturing plants compared to plants that used the chemical in their production processes.^[5]

CAREX Canada is reviewing whether it is feasible to prepare exposure estimates for Canadian workers exposed to p-dichlorobenzene. This will likely depend on availability of exposure data.

Environmental Exposures

Sources of environmental exposure include industrial emissions, incinerators, and use of the chemical as a deodorizer and insect and animal repellent.^[2,5] Because of its high volatility and the dispersive nature of its uses, almost all p-dichlorobenzene used is expected to be released into the atmosphere.^[2,14]

In Canada, the daily intake of p-dichlorobenzene for the general population is expected to range from 0.1 to 2.1 μg/kg of body weight.^[14] The most significant route of exposure for the general public is via inhalation of contaminated air.^[2,5] Air testing conducted in 23 locations across Canada between 1988 and 1990 found that 99% of the samples had detectable levels (>0.1 μg/m³) of p-dichlorobenzene.^[14] The average concentration was 0.92 μg/m³ and the highest concentrations (up to 15.7 μg/m³) were found in industrial areas.^[14]

Indoor air concentrations of para-dichlorobenzene may be one to three orders of magnitude higher than outdoor concentrations if household products containing PDCB are used.^[5] One study found that, depending on the season, the mean indoor concentrations of PDCB in approximately 200 Canadian homes ranged from 10.54 to 35.75 μg/m³.^[16]

p-Dichlorobenzene has been found in various foods, including meat, fish, poultry, egg, baked goods, fruits and vegetables, butter, milk, and soft drinks.^[5] Concentrations in most foods are less than 10 μg/kg.^[4,5] Low levels (<1 μg/L) of p-dichlorobenzene have also been found in some drinking water samples in Canada.^[14]

Searches of environmental and consumer product databases yielded the following results on current potential for exposure to PDCB in Canada:

NPRI Reported Releases and US Household Products

NPRI 2009^[17]
Search Term: para-Dichlorobenzene
Category	Quantity	Industry
Released into Environment	3.8 t	Chemical manufacture and refining (2 companies in total)
Disposed of	2.8 t
Sent to off-site recycling	None