What is HCCPD?

Hexachlorocyclopentadiene (HCCPD), also known as C-56, is a colourless organochlorine compound used as a precursor in the manufacture of several cyclodiene pesticides. It is a reactive diene that is inexpensive and industrially significant. However, many of its derivatives are persistent organic pollutants (POPs), raising environmental and health concerns.

What is HCCPD used for?

HCCPD is not used directly by consumers, but it plays a key role in the manufacturing of various industrial products. These include:

• Pesticides (especially older organochlorine-based ones)
• Flame-retardant compounds
• Shock-resistant plastics and non-burning resins
• Dyes, esters, ketones, and fluorocarbons

Most HCCPD found in the environment is released during its production, processing, or disposal, rather than from consumer end-use.

In the Environment

HCCPD can enter the air, water, and soil, but its fate depends on environmental conditions:

• In air:

It is released as a vapour during manufacturing but quickly breaks down due to sunlight and atmospheric reactions. Around half is removed in under one day.

• In water:

HCCPD has low water solubility (2.1 mg/L or 2 ppm) and readily evaporates from surface water. Sunlight degrades it rapidly, breaking down half the compound in just four minutes under light exposure.

• In soil:

HCCPD binds to organic matter, such as decaying plants and animals. In sandy soils, however, it can leach down to groundwater—especially when solvents like gasoline, acetone, or paint thinners are present.

Microorganisms in soil can degrade HCCPD, with half of the chemical breaking down in 1–2 weeks, although the byproducts of this degradation are not well understood.

• In wildlife:

Small amounts of HCCPD can accumulate in fish, but there's no clear evidence of bioaccumulation in plants, animals, or dairy products.

Sources & Routes of Exposure

Source of Exposure

You're most likely to be exposed to HCCPD if you:

• Live near hazardous waste sites where HCCPD or its derivatives were disposed of
• Work in chemical manufacturing facilities that produce or use HCCPD
• Handle pesticides made from HCCPD or treat related industrial waste

Other sources include:

• Soil treated with pesticides like endosulfan or pentac, which may contain HCCPD as an impurity
• Landfills containing older pesticides such as aldrin, chlordane, dieldrin, endrin, heptachlor, or isodrin
• Drinking water, but only rarely—HCCPD might form as a byproduct during chlorination if humic acids are present

While it’s not commonly found in food, minimal exposure could occur from eating fish caught in contaminated water.

Routes of Exposure

HCCPD can enter the human body through:

• Inhalation (main route in occupational settings)
• Skin absorption
• Ingestion
• Eye and skin contact with vapour or liquid forms

Health Effects

Acute Effects

HCCPD is highly toxic and acts as a severe irritant to the eyes, skin, and respiratory tract. Exposure may cause:

• Inhalation: Coughing, chest pain, difficulty breathing, tearing, sneezing, and excessive salivation.
• Skin contact: Burns, blisters, and irritation.
• Other symptoms: Nervousness, headaches, and abdominal cramps.

Animal studies support these effects:

• Inhalation: Extremely toxic to rats.
• Oral exposure: Moderately toxic.
• Dermal contact: High to extreme toxicity.

Chronic Effects

Although human data is limited, animal studies suggest chronic exposure can affect the:

• Lungs
• Liver
• Kidneys
• Blood

The U.S. EPA Reference Concentration (RfC) is 0.0002 mg/m³, based on respiratory effects in rats. The Reference Dose (RfD) is 0.006 mg/kg/day, based on gastrointestinal lesions in animals.

Reproductive and Developmental Effects

There is no human data available on reproductive or developmental toxicity.

Animal studies via gavage exposure show no birth defects, and no data exists for inhalation exposure.

Carcinogenicity

Long-term epidemiological studies have not found an increase in cancer-related deaths among exposed workers.

The National Toxicology Programme (NTP) found no carcinogenic activity in rats or mice following a 2-year inhalation study.

As a result, the EPA classifies HCCPD as a Group D: Not Classifiable as to Human Carcinogenicity.

Safety

First Aid Measures

Eyes:

Rinse immediately with water for at least 15 minutes; seek medical attention.

Skin:

Remove contaminated clothing and flush skin for at least 15 minutes; seek medical aid.

Inhalation:

Move to fresh air. If breathing is difficult, provide oxygen. Use barrier resuscitation devices if needed. Medical help is urgent.

Ingestion:

Do not induce vomiting. Seek immediate medical attention and contact poison control.

Important: Avoid direct mouth-to-mouth resuscitation if ingestion or inhalation of HCCPD is suspected.

Firefighting Measures

• Protective Gear: Use a self-contained breathing apparatus (SCBA) and full protective clothing.
• Reactivity: May release toxic and corrosive gases when heated or exposed to water.
• Do NOT use water directly on HCCPD fires.
• Extinguishing agents: Use foam, dry chemical, or carbon dioxide.

Exposure Controls and Personal Protection

Engineering Controls

• Use under a chemical fume hood.
• Ensure eyewash stations and safety showers are readily available.

Personal Protective Equipment

• Eye protection: Chemical safety goggles (OSHA 29 CFR 1910.133 or EN166 compliant).
• Skin: Chemical-resistant gloves and full-body protective clothing.
• Respiratory: Use a respirator meeting OSHA (29 CFR 1910.134) or EN 149 standards when necessary.

Regulation

United States

• OSHA: The Occupational Safety & Health Administration has established limits on exposure to HCCPD in order to protect workers exposed on the job. The limit is 0.01ppm in the air for an 8-hour workday over a 40- hour workweek.
• NIOSH: The National Institute for Occupational Safety and Health (NIOSH) suggests the same limit for workplace air.
• EPA has recommended guidelines on how much HCCPD can be present in drinking water. The maximum contaminant levels (MCL) and maximum concentration level goal (MCLG) for drinking water are 50 ppb. 
• EPA recommends that exposures in children should not exceed 2 ppm in water for 10-day periods or no more than 0.7 ppb for up to 7 years. 
• If adults are exposed for more than 7 years, the EPA recommends that exposure levels should not exceed 50 ppb.
• HCCPD has been named a hazardous substance by EPA. If quantities equal to or greater than one pound are released to the environment, the National Response Centre for the federal government must be told immediately. 

Australia

• Safe Work Australia: Safe Work Australia has established a time weighted average concentration for HCCPD of 0.1ppm and 0.11 mg/m3 over an 8-hour workday.