Phthalic anhydride

Endpoint summary

Additional information

The kinetic of the hydrolysis of phthalic anhydride was studied to be 30.5 seconds at pH 7.24 at 25°C (Andres, 2001). The main hydrolsis product is phthalic acid.

In the atmosphere a half-life of 21.4 d for phthalic anhydride is estimated due to reaction with photochemically produced hydroxyl radicals, considering an OH-concentration of 500,000 radicals/cm³ as a 24-h average (Bayer Industry Services, 2004). For the main hydrolysis product phthalic acid a half-life of 13 d is estimated (Bayer Industry Services, 2004). The atmospheric half-life of phthalic anhydride is only of theoretical intrest, as any decomposition of the substance in water is not considered by the program. Therefore, the atmospheric half-life of 13 days of phthalic acid is taken into account for further assessment.

Experiments on photochemical transformations of phthalic anhydride in various aquatic media were conducted in a photochemical reactor and in natural sunlight (Bajt, 1992). The photochemical reactions of phthalic anhydride, which hydrolyses to phthalic acid in water, showed polymerisation to polyphenyl. Kinetic studies of photochemical transformations of phthalic anhydride in all aqueous media revealed the occurrence of first order reactions with different rate constants. The half-lives of phthalic anhydride were 3.9 h (distilled water), 6.3 h (riverine water), 6.8 h (artificial sea water), and 9.6 h (natural sea water) under anaerobic conditions. In an irradiation experiment with phthalic acid, the hydrolysis product of phthalic anhydride, a first order rate constant (k/hours ) for photooxidation in sea water was determined to be 0.75. That is equivalent with a half-life of 0.93 hours (Armstrong, 1968).

In a modified MITI test comparable to OECD TG 301 C the biodegradation of phthalic anhydride was investigated (MITI, 1992). After 2 weeks 85 % degradation of the test substance was determined. Therefore, phthalic anhydride is classified as readily biodegradable. The biodegradation of phthalic anhydride was also investigated with activated sludge obtained from the waste water treatment plant of the Kashima petroleum and petrochemical industrial complex in Japan. The test was performed in a "fill-and-draw" type apparatus with aeration cylinders and is regarded as a test on inherent biodegradability. TOC and COD were monitored during the test. After 24 hours, 33 % degradation was measured with COD and 88 % with TOC (Matsui, 1975, 1988). Based on this result, phthalic anhydride is regarded as inherently biodegradable.

Assessing the bioaccumulation potential in aquatic organisms, a BCF has been calculated with the BCF Program (v 2.15) taking the octanol-water partition coefficient in account. Using the log KOW of 1.6 for phthalic anhydride, the calculated BCF is 3.4 (Bayer Industry Services, 2004a). For the hydrolysis product phthalic acid, a BCF value of 3.2 is calculated by using the log KOW of 0.73 (Bayer Industry Services, 2004b). These results indicate no significant potential for bioaccumulation of phthalic anhydride and phthalic acid in aquatic organisms.

In green house studies 14C-phthalic acid was applied to soil planted with wheat (Triticum aestivum)/corn (Zea mays) or soybeans (Glycine max)/tall fescue (Festuca arundinacea). For phthalic acid the bioaccumulation ratios were 0.013 for plants and 0.0046 for seeds. TLC analysis showed that the percent of the extractable 14C still in phthalic acid, was 5 % in corn and fescue, 15 % in soybean, 9 % in wheat plants, and the highest for wheat seed (47 %) (Dorney et al., 1985). This study demonstrates the relatively low potential for accumulation of phthalic acid in plants.

The distribution of phthalic anhydride between the organic phase of soil or sediments and the porewater was calculated by using QSAR with the PCKOC program (v 1.66). A Koc of 11 for phthalic anhydride (Bayer Industry Services, 2004a) was calculated. Von Oepen (1991) investigated the sorption capacity of three different soils by batch equilibrium studies for the hydrolysis product phthalic acid similar to the OECD TG 106 . The soils used for testing were an acidic forest soil, an agricultural soil and a sublimnic soil. The sorption equilibrium was reached within 16 hours. Sorption coefficients between 2 and 31 were determined.

The Henry's law constant (HLC) of phthalic anhydride is estimated as 0.64 Pa m³/mol at 25 °C (Bayer Industry Services, 2004). For the hydrolysis product of the phthalic anhydride, phthalic acid, the HLC is estimated as 2.21 x 10-7 Pa m³/mol (Bayer Industry Services, 2004).

Calculation of the distribution of phthalic anhydride in the environment according to the Mackay fugacity model, is not suitable because the substance hydrolyses rapidly in water. The Mackay model does not consider degradation reactions, hence the Mackay equilibrium distribution of phthalic anhydride in the environment is not appropriate.

The distribution of the hydrolysis product phthalic acid in a "unit world" was calculated according to the Mackay fugacity model level I (Bayer Industry Services, 2004) based on the physico-chemical properties. The main target compartment for phthalic acid is water with 99.91 %, followed by soil and sediment with 0.042 and 0.043%, respectively.