PESTICIDES – POSSIBLE CARCINOGEN (IARC 2B)
- A pesticide used to repel moths, and protect against tree-boring insects
- Associated cancers: Liver and kidney cancers (animal studies only)
- Most important route of exposure: Inhalation
- Uses: Moth repellant and space deodorant
- Occupational exposures: Primarily in workers involved in its production, as well as those working in buildings where it is used to repel insects
- Environmental exposures: Via contaminated air from industrial emissions and incinerators, and via PDCB’s use as a deodorizer and insect and animal repellant
- Fast fact: p-Dichlorobenzene can also irritate the eyes, skin and nasal cavity, and cause shortness of breath, nausea, vomiting, and liver damage, especially at higher concentrations.
para-Dichlorobenzene is a white to colourless crystalline solid with a mothball-like odour. It may also be referred to as p-dichlorobenzene, 1,4-dichlorobenzene, or PDCB. There are numerous other synonyms and product names; see the Hazardous Substances Data Bank (HSDB) for more information.
p-Dichlorobenzene has been classified by the International Agency for Research on Cancer (IARC) as Group 2B, possibly carcinogenic to humans. p-Dichlorobenzene causes cancer 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.[3,4]
Additionally, exposure to PDCB can cause painful irritation of the eyes, skin, and nasal cavity. It can also cause headache, coughing, shortness of breath, drowsiness, dizziness, nausea, vomiting, skin irritation, and liver damage.[2,4]
Regulations and Guidelines
Occupational exposure limits (OEL)[5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]
|Canadian Jurisdictions||OEL (ppm)|
|Canada Labour Code||10|
|AB, BC, MB, NB, NL, NS, ON, PE||10|
|SK, NT, YT, NU||10
|Other Jurisdictions||OEL (ppm)|
|ACGIH 2020 TLV||10|
ppm = parts per million
stel = short term exposure limit (15 min. maximum)
ACGIH = American Conference of Governmental Industrial Hygienists
TLV = threshold limit value (8 hour maximum)
Canadian environmental guidelines and standards*
|Drinking Water Guidelines (Canada) and Standards (ON, QC, SK)||MAC = 0.005 mg/L||1987-2020
|Ontario Ambient Air Quality Criteria||24 hour: 95 µg/m3||2016|
|Government of Canada’s Indoor Air Reference Levels||60 µg/m3 (critical effect: nasal lesions)||2018|
|Quebec’s Clean Air Regulation||4 minute limit: 730 µg/m3
1 year limit: 160 µg/m3; Prohibited discharge into the air if the concentration of para-dichlorobenzene exceeds the standard
|BC’s Contaminated Sites Regulation, BC Reg 375/96||Sets soil standards for the protection of human health:
Agricultural and low density residential sites: 4,500 μg/g
Urban park and high density residential sites: 9,000 μg/g
Commercial sites: 30,000 μg/g
Industrial sites: 800,000 μg/g
Drinking water: 5 µg/L
Sets vapour standards for the protection of human health:
*Standards are legislated and legally enforceable, while guidelines (including Ontario ambient air quality criteria) describe concentrations of contaminants in the environment (e.g. air, water) that are protective against adverse health, environmental, or aesthetic (e.g. odour) effects
mg/L = milligrams per litre
µg/m3 = micrograms per cubic metre
µg/g = micrograms per gram
|Canada-Ontario Agreement on Great Lakes Water Quality and Ecosystem Health||Tier 2 chemical: potential for causing widespread impacts, or that have already caused local adverse impacts on the Great Lakes Basin Ecosystem||2015|
|Health Canada||DSL – low priority substance (already risk managed)||2006|
|Environment Canada’s National Pollutant Release Inventory||NPRI Part (Threshold Category): 1A, Reportable to NPRI if manufactured, processed, or otherwise used at quantities greater than: 10 tonnes; 5, Reportable to NPRI if released at quantities greater than: 1 tonne of 10-tonne total VOC air release.||2016|
|National Classification System for Contaminated Sites||Rank: “High hazard”||2008|
p-Dichlorobenzene was not included in other Canadian government guidelines, standards, or chemical listings reviewed.
p-Dichlorobenzene is used primarily as a moth repellent and space deodorant.[1,3] It is also used as an intermediate in producing other chemicals, including polyphenylene sulphide and 1,2,4-trichlorobenzene.[1,3]
There are several other minor uses for PDCB, such as: a pesticide against certain tree-boring insects and ants; a fungicide for tobacco seeds, leather, and some fabrics; a disinfectant; an animal repellent; an intermediate chemical in producing pigment and dye; an ingredient in manufacturing certain pharmaceuticals and resin-bonded abrasives.[1,4]
There are four products listed with PDCB as an active ingredient registered with the Canadian Pest Management Regulatory Agency (PMRA). Of these, three are registered for domestic use. All products listed were mothballs or air deodorizers.
Environmental Exposures Overview
Sources of environmental exposure to p-dichlorobenzene include industrial emissions, incinerators, and use of the chemical as a deodorizer and insect and animal repellent.[1,4] Because of its high volatility and the dispersive nature of its uses, almost all PDCB used is expected to be released into the atmosphere.[1,35]
The most significant route of exposure to PDCB for the general public is by inhaling contaminated air.[1,4] 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 PDCB. The highest concentrations were found in industrial areas.
Indoor air concentrations of PDCB may be one to three orders of magnitude higher than outdoor concentrations if household products containing PDCB are used.
p-Dichlorobenzene has been found in various foods, including meat, fish, poultry, egg, baked goods, fruits and vegetables, butter, milk, and soft drinks. Concentrations in most foods are less than 10 μg/kg.[3,4] Low levels (<1 μg/L) of PDCB have also been found in some drinking water samples in Canada.
Searches of Environment Canada’s National Pollutant Release Inventory (NPRI) and the US Consumer Product Information Database yielded the following results on current potential for exposure to PDCB in Canada:
NPRI reported releases
|Substance name: ‘p-Dichlorobenzene’|
|Released into Environment||0.441 t||Chemical manufacture(1 facility)|
|Sent to off-site recycling||None|
|US Consumer Products 2016|
|Search Term||Quantity||Product Type|
|‘p-Dichlorobenzene’||10||Pesticides, moths (9), toilet bowl deodorizer (1)|
t = tonne
Occupational Exposures Overview
Inhalation is the most important route of occupational exposure to p-dichlorobenzene, although dermal exposure may also occur.[1,4]
The main occupations exposed to PDCB include workers involved in its production and processing.[1,3,4] Exposure may also occur in workplaces where PDCB is used, such as in mothball and resin-bonded abrasive wheel manufacturing plants. Air concentrations were found to be higher in p-dichlorobenzene manufacturing plants compared to plants that used the chemical in their production processes.
CAREX Canada has not prioritized para-Dichlorobenzen for exposure estimate development. This is because there is a lack of exposure monitoring data in the Canadian Workplace Exposure Database on which to base an estimate.
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