Phthalic anhydride

May 1994
Immediately Dangerous to Life or Health Concentrations (IDLH)

CAS number: 85–44–9

NIOSH REL: 6 mg/m3 (1 ppm) TWA

Current OSHA PEL: 12 mg/m3 (2 ppm) TWA

1989 OSHA PEL: 6 mg/m3 (1 ppm) TWA

1993-1994 ACGIH TLV: 6.1 mg/m3 (1 ppm) TWA

Description of substance: White solid (flake) or a clear, colorless, mobile liquid (molten) with a characteristic, acrid odor.

LEL: . . 1.7% (10% LEL, 10,500 mg/m3)

Original (SCP) IDLH: 10,000 mg/m3

Basis for original (SCP) IDLH: Because no data on acute inhalation toxicity are available on which to base an IDLH for phthalic anhydride, the chosen IDLH is based on repeated exposure data. AIHA [1967] reported that exposure of rats and rabbits to 10,000 mg/m3 for 4 hours/day for several days produced a 25% fatality rate [Malten and Zielhuis 1964].

Short-term exposure guidelines: None developed


Lethal dose data:

Species Reference Route LD50




Adjusted LD Derived value
Rat Biofax 1970 oral 4,020 ----- 28,140 mg/m3 2,814 mg/m3
Mouse Izmerov et al. 1982 oral 1,520 ----- 10,500 mg/m3 1,050 mg/m3
Cat Marhold 1986 oral 800 ----- 5,600 mg/m3 560 mg/m3
Rat Patty 1963 oral 800-1,600 ----- 5,600 -11,200 mg/m3 560 - 1,120 mg/m3
Mouse Zhilova & Kasparov 1969 oral 2,210 ----- 15,470 mg/m3 1,547 mg/m3

Other animal data: It has been reported that exposure of rats and rabbits to 10,000 mg/m3 for 4 hours/day for several days produced a 25% fatality rate [Malten and Zielhuis 1964].

Human data: It has been reported that an exposure of 30 mg/m3 is associated with conjunctivitis, while 25 mg/m3 is associated with signs of mucous membrane irritation [Baader 1955]. It has been stated that phthalic anhydride has similar toxic effects (i.e., irritation of the skin, eyes, and upper respiratory system) as maleic anhydride, but has reduced potency [ACGIH 1991].

Revised IDLH: 60 mg/m3

Basis for revised IDLH: Based on acute toxicity data in animals [Biofax 1970; Izmerov et al. 1982; Malten and Zielhuis 1964; Marhold 1986; Patty 1963; Zhilova and Kasparov 1969], a value between 600 and 3,000 mg/m3 would have been appropriate. However, the revised IDLH for phthalic anhydride is 60 mg/m3 (i.e., 10 times the NIOSH REL) based on acute inhalation data in humans [Baader 1955] and an analogy to maleic anhydride [ACGIH 1991] which has a revised IDLH that is 10 times its NIOSH REL. This may be a conservative value due to the lack of relevant acute toxicity data for workers exposed to concentrations above 30 mg/m3.


1. ACGIH [1991]. Phthalic anhydride. In: Documentation of the threshold limit values and biological exposure indices. 6th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, pp. 1263-1264.

2. AIHA [1967]. Phthalic anhydride. In: Hygienic guide series. Am Ind Hyg Assoc J 28:395-398.

3. Baader EW [1955]. Diseases due to phthalic acid and its compounds. Arch Gewerbepath Gewerbehyg 13:419-453 (in German).

4. Biofax [1970]. Phthalic anhydride. Northbrook, IL: Biofax Industrial Bio-Test Laboratories, Inc.

5. Izmerov NF, Sanotsky IV, Sidorov KK [1982]. Toxicometric parameters of industrial toxic chemicals under single exposure. Moscow, Russia: Centre of International Projects, GKNT, p. 322.

6. Malten KE, Zielhuis RL [1964]. Alkyd resins. In: Industrial toxicology and dermatology in the production and processing of plastics. Amsterdam, The Netherlands: Elsevier Publishing Company, pp. 59-70.

7. Marhold J [1986]. Prehled Prumyslove Toxikologie, Organicke Latky. Prague, Czechoslovakia: Avicenum, p. 322 (in Czechoslovakian).

8. Patty FA, ed. [1963]. Industrial hygiene and toxicology. 2nd rev. ed. Vol. II. Toxicology. New York, NY: Interscience Publishers, Inc., pp. 1822-1823.

9. Zhilova NA, Kasparov AA [1969]. Phthalic anhydride and n-nitrosodiphenylamine (Vulcalent A). Chem Abstr 71:280.

Page last reviewed: December 4, 2014