Review of Environmental Fate and Effects of Selected
Phthalate Esters

4 Dimethyl Phthalate (DMP)

4.1 Physico-chemical properties
4.1.1 Water solubility
4.1.2 Octanol-water partition coefficient
4.1.3 Summary
4.2 Environmental concentrations and fate
4.2.1 Concentrations in the environment
4.2.2 Abiotic degradation
4.2.3 Biodegradation
4.2.4 Bioaccumulation
4.2.5 Summary and conclusion
4.3 Effects
4.3.1 Toxicity to micro-organisms
4.3.2 Toxicity to algae
4.3.3 Toxicity to invertebrates
4.3.4 Toxicity to fish
4.3.5 Estrogenic effects
4.3.6 Summary and conclusions
4.4 Environmental hazard classification
4.5 PNEC for the aquatic compartment
 

DMP is used as a plasticizer in latex, cellulose acetate film and plastics. DMP is as a constituent of rubber, coating agents, safety glass, moulding powders, insect repellents and perfumes. DMP leaches to the environment from tubings, dishes, paper, containers by general use of plastics and the above listed products /6/.

4.1 Physico-chemical properties

DMP (C₁₀H₁₀O₄), CAS No.: 131-11-3, with an alkyl chain length of 1,1 /1/ is a colourless liquid. The molecular weight is 194.2 g/mol. DMP has a melting point of 0°C and a boiling point at 282°C /6/. The density is 1.192 g/ml and the vapour pressure is 2·10^-3 mmHg at 25°C /1/.

4.1.1 Water solubility

DMP is a low molecular weight phthalate. Several aqueous solubility data on DMP are referred to in the literature. Independent experimental measurements are generally in good agreement and believed to be reliable for lower molecular weight molecules. Literature values range from 2810 to 4320 mg/l. The solubility has been calculated to 2179 mg/l /7/. In a literature review by Staples et al. /1/, it was concluded that a water solubility of about 4200 mg/l was the most likely value based on available evidence.

4.1.2 Octanol-water partition coefficient

Fairly consistent log K_ow values are seen in the literature for lower molecular weight phthalates as DMP. Reported log K_ow values are only ranging from 1.46 to 1.90. A log K_ow value of 1.56 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 1.61.

4.1.3 Summary

The physico-chemical properties on DMP are summarized in Table 4.1.

Table 4.1
Physico-chemical properties of Dimethyl Phthalate (DMP)

4.2 Environmental concentrations and fate

4.2.1 Concentrations in the environment

The content of DMP 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 4.2.

Table 4.2
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As no data were available on measurements in inlet and outlet waste water, it was not possible to derive any mass balances.

No data available.

4.2.2 Abiotic degradation

Wolfe et al. (1980) /2/ measured the hydrolysis rate constant of DMP and estimated a half-life of 3.2 years at alkaline conditions. The hydrolysis half-life at neutral pH and 25°C is estimated to 2.7 years /7/.

No experimental data on photodegradation of DMP are available. Estimated photodegradation half-lives in the atmosphere are in the range from 9.3 to 93 days /4, 7/. DMP in pure water is photodegraded by irradiation with UV light with a half-life of 13 hours /11/. However, in the aquatic environment only insignificant photodegradation is expected /1/.

4.2.3 Biodegradation

The ready biodegradability of DMP was determined in the OECD 301C test resulting in a degradation of 90-98% /12/.

Staples et al. (1996) /1/ refer to an investigation by Changming & Kang (1990) /13/ showing a degradation of 99.6% after 4 days incubation.

Sugatt et al. (1984) /14/ using an acclimated inoculum demonstrated a biodegradability of DMP of 86% after 28 days. Staples et al. (1996) /1/ refer to a study of Aichinger et al. (1992) /15/ using an acclimated inoculum demonstrating a degradability of 96%.

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

Howard (1989) /11/ refers to studies on the biodegradation of DMP in sewage treatment plants demonstrating that the total removal frequently approached 100% while mineralization ranged between 58 and 88%.

Staples et al. (1996) /1/ refer to studies showing anaerobic primary biodegradation at 30-37°C in the range from 18% to 100% and anaerobic ultimate biodegradation in the range from 41% to 100%.

Hattori et al. (1975) /16/ demonstrated 100% primary degradation after 8 days in freshwater in a river die-away test, but only 0-32% after 7-14 days in marine waters.

4.2.4 Bioaccumulation

For DMP, only one bioaccumulation study performed with fish was found. A total BCF of 57 for Bluegill Sunfish (Lepomis macrochirus) was reported by Barrows et al. (1980) /17/ (exposure concentration: 8.7 µg/l; test procedure: flow through; exposure period: not known). The low bioaccumulation potential is in conformity with the log K_ow » 1.6.

4.2.5 Summary and conclusion

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

DMP 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 DMP during anaerobic treatment of sludge.

DMP has a low bioaccumulation potential demonstrated by both log K_ow » 1.6 and the experimentally derived BCF value of 57 for fish.

4.3 Effects

4.3.1 Toxicity to micro-organisms

The toxicity studies with micro-organisms are summarized in Table 4.3. The table contains data on both bacteria and protozoa.

Table 4.3
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From the above results, DMP seems to have relatively low toxicity to micro-organisms.

4.3.2 Toxicity to algae

The short-term toxicity studies with DMP for freshwater and marine algae are summarized in Table 4.4.

Table 4.4
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The toxicity data obtained on the different algae species seem to be in close agreement, except for the tests with Chlorella pyrenoidosa and Gymnodinium breve, which show higher effect concentrations. The relatively high EC₅₀ value (142 mg/l) in the 6-day test Selenastrum capricornutum can be attributed to experimental problems during the relatively long exposure period or to the biodegradability of the substance.

4.3.3 Toxicity to invertebrates

The short-term toxicity data on DMP to freshwater and marine invertebrates are presented in Table 4.5 and the long-term toxicity data on DMP to freshwater and marine invertebrates are presented in Table 4.6.

Table 4.5
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Table 4.6
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The toxicity data obtained with the different crustacean species are in close agreement except for the test with Paratanytarsus parthenogenica.

4.3.3.Toxicity to fish

The short-term toxicity data on DMP to freshwater and marine fish are presented in Table 4.7 and the long-term toxicity data on DMP to freshwater and marine fish species are presented in Table 4.8.

Table 4.7
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Table 4.8
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From the results obtained by Springborn Bionomics (1987) /43/ with Pimephales promelas, it can be seen that no further toxicity is obtained when the exposure period is increased from 96 h to 144 h. This indicates that steady state conditions and thus the maximum toxicity of DMP are reached during a 96 h test period.

4.3.5 Estrogenic effects

No data are available.

4.3.6 Summary and conclusions

DMP seems to have a relatively low toxicity to micro-organisms.

DMP has been shown acutely toxic (EC₅₀ or LC₅₀ values) to algae, crustaceans and fish in the range 26-377 mg/l, however, with most values in the range 25-50 mg/l irrespective of the trophic level investigated. DMP is thus, solely based on aquatic toxicity data, considered harmful to aquatic organisms.

NOEC levels in chronic toxicity tests with crustaceans and fish were both close to 10 mg/l. Compared to the NOEC levels derived in the acute toxicity tests no further toxicity was achieved in the long-term tests.

No data are available in which the estrogenic effect of DMP has been evaluated.

4.4 Environmental hazard classification

DMP has been shown acutely toxic (EC₅₀ or LC₅₀ values) to algae, crustaceans and fish in the range 26-377 mg/l, however, with most values in the range 25-50 mg/l irrespective of the trophic level investigated.

NOEC levels in chronic toxicity tests with algae, crustaceans and fish were all close to 10 mg/l. Compared to the NOEC levels derived in the acute toxicity tests no further toxicity was achieved in the long-term tests.

DMP 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 DMP during anaerobic treatment of sludge.

DMP is bioaccumulative in aquatic biota, which is demonstrated by the experimentally derived BCF value of 57 for fish.

The water solubility of DMP is » 4200 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 effects of Dimethyl phthalate, it is proposed that DMP should not be classified as dangerous to the aquatic environment.

4.5 PNEC for the aquatic compartment

Long-term NOECs for three trophic levels are available, all of them in the same concentration range. The lowest NOEC available is the 21 d NOEC for Daphnia magna at 9.6 mg/l. Considering the fact that the substance is readily biodegradable and with a low bioaccumulation potential, an assessment factor of 10 is proposed for the derivation of a PNEC_aquatic resulting in a proposed PNEC_aquatic = 1 mg/l.