Maleic anhydride (Butenedioic Anhydride, Toxilic Anhydride, 2,5-Dioxofuran) is an organic compound with the formula C₂H₂(CO)₂O. It appears as colourless crystals or a white solid with a choking, acrid smell. It melts at 58°C and is corrosive. It dissolves in water to form maleic acid and also dissolves in most organic solvents.
Maleic anhydride is mainly used to produce unsaturated polyester resins for making boats, vehicles, buildings, pipes, and electrical products. It is also used in making lube oil adhesives, which extend oil-change intervals and improve engine efficiency. Additionally, it is used in copolymers, pesticides, other organic compounds, and Diels-Alder syntheses.
Maleic anhydride breaks down easily in soil and does not strongly bind to soil particles, allowing it to leach into groundwater, where it breaks down naturally. In the air, it reacts quickly and does not persist long. It does not accumulate in the environment and is unlikely to affect the global environment.
Maleic anhydride is released during its manufacturing, transportation, storage, and use. There are no natural sources of it in the environment. Most exposure occurs in workplaces, through spills, emissions, or vent gases. It can also be released into the atmosphere during its manufacture, transport, or use.
The main ways people are exposed to maleic anhydride are:
Breathing in maleic anhydride can cause respiratory irritation, burning in the throat, coughing, tearing, headaches, eye irritation, and corneal burns (which heal within 48 hours). In guinea pigs, it can cause bronchial asthma. Tests on animals show moderate to high toxicity when ingested and moderate toxicity from skin exposure.
Long-term exposure to maleic anhydride can cause chronic bronchitis, asthma-like attacks, lung swelling, upper respiratory irritation, eye irritation, and skin irritation in workers. Some people may develop allergies, making them sensitive to lower concentrations. In animals, it has caused nose and eye irritation, respiratory issues, kidney problems, and weight changes.
The EPA has not set a Reference Concentration (RfC) for maleic anhydride. The Reference Dose (RfD) is 0.1 mg/kg/day, based on kidney damage in rats. The California Environmental Protection Agency (CalEPA) has a chronic inhalation reference level of 2 x 10⁻⁴ mg/m³, a safe concentration below which harmful effects are unlikely.
No data is available on maleic anhydride’s effects on human reproduction or development. In rats, it showed no harmful effects on the offspring when given through the stomach or diet.
There is no information on whether maleic anhydride causes cancer in humans. Studies in rats showed no increase in tumours. The EPA has not classified maleic anhydride for its potential to cause cancer due to insufficient testing.
Use enclosures, local exhaust ventilation, or other controls to keep airborne levels low. If dust, fumes, or mist is created, ensure ventilation keeps exposure below limits.
For handling maleic anhydride, use:
For large spills, use:
OSHA: The Occupational Safety & Health Administration has set a Permissible Exposure Limit (PEL) for maleic anhydride of:
ACGIH: The American Conference of Governmental Industrial Hygienists has set a Threshold Limit Value (TLV) for maleic anhydride of 0.25 ppm, 1 mg/m3 TWA
NIOSH: The National Institute for Occupational Safety and Health has set a Recommended Exposure Limit (REL) for maleic anhydride of: 0.25 ppm TWA
Safe Work Australia: Safe Work Australia has established a Time Weighted Average (TWA) concentration for maleic anhydride of: 0.25ppm, 1 mg/m3
