Review of Environmental Fate and Effects of Selected
Phthalate Esters

5 Diethyl Phthalate (DEP)

5.1 Physico-chemical properties
5.1.1 Water solubility
5.1.2 Octanol-water partition coefficient
5.1.3 Summary
5.2 Environmental concentrations and fate
5.2.1 Concentrations in the environment
5.2.2 Abiotic degradation
5.2.3 Biodegradation
5.2.4 Bioaccumulation
5.2.5 Summary and conclusion
5.3 Effects
5.3.1 Toxicity to micro-organisms
5.3.2 Toxicity to algae
5.3.3 Toxicity to invertebrates
5.3.4 Toxicity to fish
5.3.5 Estrogenic effects
5.3.6 Summary and conclusions
5.4 Environmental hazard classification
5.5 PNEC for the aquatic environment
 

DEP is used as a plasicizer in plastics, food packaging application. DEP is a dye application agent, and a diluent in polysulfide dental impression materials solvent; wetting agent; camphor substitute; used in perfumery; alcohol denaturant and as a component in insecticidal sprays /6/.

5.1 Physico-chemical properties

DEP (C₁₂H₁₄O₄), CAS No.: 84-66-2, with an alkyl chain length of 2,2 /1/ is a clear, stable, odourless liquid. The molecular weight is 222.2 g/mol. DEP has a melting point of about -40.5°C and a boiling point at 298°C. The density is 1.118 g/ml and the vapour pressure is 1·10^-3 mmHg at 25°C /1/.

5.1.1 Water solubility

DEP is a low molecular weight phthalate. Several aqueous solubility data on DEP are referred to in the ranging from 400 to 7028 mg/l. The solubility has been calculated to 260.3 mg/l /7/. In a literature review by Staples et al. /1/, it was concluded that a water solubility of about 1100 mg/l was the most likely value based on available evidence.

5.1.2 Octanol-water partition coefficient

Reported log K_ow values are ranging from 2.21 to 3.00. A log K_ow of 2.47 has been calculated /7/. According to Staples et al. /1/, the most likely log K_ow value based on available evidence was concluded to be 2.38.

5.1.3 Summary

The physico-chemical properties on DEP are summarized in Table 5.1.

Table 5.1
Physico-chemical properties of Diethyl Phthalate (DEP)

5.2 Environmental concentrations and fate

5.2.1 Concentrations in the environment

The content of DEP in wastewater and sewage sludge from Danish treatment plants has been measured at one occasion during recent years. An overview of the results is given in Table 5.2.

Table 5.2
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As no data were available on measurements in inlet and outlet waste water, it is not possible to derive any mass balances.

No data are available.

5.2.2 Abiotic degradation

Wolfe et al. (1980) /2/ measured the hydrolysis rate constant of DEP and estimated a half-life of 8.8 years at pH 7. The hydrolysis half-life at neutral pH and 25°C range is estimated to 2.9 years /7/.

No experimental data on photodegradation of DEP are available. Estimated photodegradation half-lives in the atmosphere are in the range from 1.8 to 18 days /4, 7/. In the aquatic environment only insignificant photodegradation is expected /1/.

5.2.3 Biodegradation

Staples et al. (1996) /1/ refer to an investigation by Changming & Kang (1990) /13/ showing a degradation of 99.2% after 6 days of incubation.

By use of an acclimated inoculum, Sugatt et al. (1984) /14/ found a biodegradability of 95% of DEP after 28 days of incubation. Staples et al. (1996) /1/ refer to a study of Aichinger et al. (1992) /15/ using acclimated inocula demonstrating a degradability of 93%.

Staples et al. (1996) /1/ have reviewed the biodegradability of DEP and referred to numerous studies showing a high degree of primary biodegradability - in general between 90% and 100%.

In a simulation of a biological sewage treatment plant, Patterson & Kodukala (1981) /47/ determined 79-98% removal of DEP.

Staples et al. (1996) /1/ refer to a few tests on anaerobic biodegradability of DEP showing a primary biodegradability of 64% to 100% and an ultimate biodegradability of 0% to 76% at 35-37°C and incubation for up to 70 days.

Hattori et al. (1975) /16/ demonstrated a 100% primary degradability of DEP after 6 days in freshwater in a river die-away test, and 14-68% after 14 days in marine waters.

5.2.4 Bioaccumulation

For DEP, only one bioaccumulation study performed with fish was found. A total BCF of 117 for Bluegill Sunfish (Lepomis macrochirus) was reported by Barrows et al. (1980) /17/ in a flow-through experiment and feeding ad libitum. Exposure concentration: 8.7 µg/l. Exposure period is not known.

5.2.5 Summary and conclusion

Hydrolysis and photodegradation are not significant degradation routes of DEP in the aquatic environment.

DEP is readily biodegradable in standard laboratory tests and, hence, the substance is expected to be mineralized rapidly in the aerobic part of a sewage treatment plant. The studies of anaerobic biodegradability indicate a potential for mineralization of DEP during anaerobic treatment of sludge.

DEP has a moderate bioaccumulation potential demonstrated by both log K_ow » 2.4 and the experimentally derived BCF value of 117 for fish.

5.3 Effects

5.3.1 Toxicity to micro-organisms

The toxicity studies with micro-organisms are summarized in Table 5.3. The table contains data on both bacteria and protozoa.

Table 5.3
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From the above results, DEP seems to have relatively low toxicity to micro-organisms.

5.3.2 Toxicity to algae

The toxicity studies with DEP for freshwater and marine algae are summarized in Table 5.4.

Table 5.4
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The toxicity data obtained on the different algae species seem to be in close agreement except the 96 h test on effects on the growth rate of Gymnodinium breve where a relatively low EC₅₀ value was found.

5.3.3 Toxicity to invertebrates

The short-term toxicity data on DEP to freshwater and marine invertebrates are presented in Table 5.5 and the long-term toxicity data on DEP to freshwater and marine invertebrates are presented in Table 5.6.

Table 5.5
link to table

Table 5.6
link to table

As seen from the tables, NOEC values of 13 mg/l and 25 mg/l, respectively, were obtained in 21 d reproduction tests with Daphnia magna. However, a lower NOEC value was obtained in a 96 h mortality test with the marine crustacean Mysidopsis bahia (2.7 mg/l, measured concentration).

5.3.4 Toxicity to fish

The short-term toxicity data on DEP to freshwater and marine fish are presented in Table 5.7. No long-term toxicity studies with fish were found for DEP.

Table 5.7
link to table

5.3.5 Estrogenic effects

In an investigation by Harris et al. (1997) /62/, DEP was shown to have weak estrogenic activity in an in vitro recombinant yeast screen test, with a relative potency of approx. 5·10⁷ times less than 17b-estradiol.

5.3.6 Summary and conclusions

DEP has been shown acutely toxic (EC₅₀ or LC₅₀ values) to algae, crustaceans and fish in the range 7.6-131 mg/l, however, with most values in the range 20-40 mg/l irrespective of the trophic level investigated. DEP is thus, solely based on aquatic toxicity data, considered harmful to aquatic organisms. The NOEC values obtained in crustaceans and fish acute toxicity studies range from 1.7-46 mg/l. In long-term studies with algae and Daphnia magna NOEC-values of 3.7-25 mg/l were determined.

In an investigation by Harris et al. (1997) /62/, DEP was shown to have weak estrogenic activity in an in vitro recombinant yeast screen test, with a relative potency of approx. 5·10⁷ times less than 17b-estradiol.

5.4 Environmental hazard classification

DEP has been shown acutely toxic (EC₅₀ or LC₅₀ values) to algae, crustaceans and fish in the range 7.6-131 mg/l. The marine crustacean Mysidopsis bahia seems considerably more sensitive than Daphnia magna.

NOEC levels in chronic toxicity tests with algae were in the range 3.7-25 mg/l. Compared to the NOEC levels derived in the acute toxicity tests with crustaceans and fish, no further toxicity was achieved in these long-term tests.

DEP is readily biodegradable in standard laboratory tests and, hence, the substance is expected to be mineralized rapidly in the aerobic part of a sewage treatment plant. The studies of anaerobic biodegradability indicate a potential for mineralization of DEP during anaerobic treatment of sludge.

DEP seems to have relatively low toxicity to micro-organisms.

DEP has a moderate bioaccumulation potential demonstrated by both log K_ow » 2.4 and the experimentally derived BCF value of 117 for fish.

The water solubility of DEP is » 1000 mg/l which is well above the cut-off value of 1 mg/l.

Considering the criteria for environmental hazard classification (EEC 1993) and the above evaluation of the environmental fate and effect of Diethyl phthalate, it is proposed that DEP should not be classified as dangerous for the aquatic environment.

5.5 PNEC for the aquatic environment

Toxicity data are available on short-term tests with bacteria, protozoa, algae, crustaceans and fish. All toxicity data are more or less in the same range with an EC₅₀ for algae at 3.0 mg/l and NOEC for crustaceans at 2.7 mg/l as the lowest short-term toxicity values. Long-term toxicity data are available on algae and crustaceans with a NOEC for algae at 3.7 mg/l as the lowest. An assessment factor of 50 for the two long-term NOEC should be used for deriving a PNEC_aquatic and considering the fact that the substance is readily biodegradable but has a moderate bioaccumulation potential and has a weak estrogenic activity, a PNEC_aquatic = 0.01 mg/l is proposed.