Review of Environmental Fate and Effects of Selected
Phthalate Esters

9 Diisodecyl Phthalate (DIDP)

9.1 Physico-chemical properties
9.1.1 Water solubility
9.1.2 Octanol-water partition coefficient
9.1.3 Summary
9.2 Environmental concentrations and fate
9.2.1 Concentrations in the environment
9.2.2 Abiotic degradation
9.2.3 Biodegradation
9.2.4 Bioaccumulation
9.2.5 Summary and conclusion
9.3 Effects
9.3.1 Toxicity to micro-organisms
9.3.2 Toxicity to alga
9.3.3 Toxicity to invertebrates
9.3.4 Toxicity to fish
9.3.5 Estrogenic effects
9.3.6 Summary and conclusions
9.4 Environmental hazard classification
9.5 PNEC for the aquatic compartment
 

9.1 Physico-chemical properties

DIDP (C₂₈H₄₆O₄), CAS No.: 26761-40-0 and 68515-49-1. DIDP is not a pure compound but a mixture of phthalates with side chains of average length 10,10 /6/. The molecular weight is about 446.7 (432.7-446.7) g. DIDP has a melting point of about -46°C and a boiling point at 463°C /1, 7/. The density is 0.961 g/ml and the vapour pressure is <5.0·10^-7 mmHg at 25°C /1/.

9.1.1 Water solubility

DIDP is a high molecular weight phthalate. Evidence indicates that many of the measured water solubilities for high molecular weight phthalate esters reported in literature are erroneously too high. In the literature, several aqueous solubility data on DIDP range from 7.4·10^-6 to <0.00013 mg/l. The solubility has been calculated to be 2.24·10^-6 /7/. In a literature review by Staples et al. /1/, it was concluded that a water solubility of <0.001 mg/l was the most likely value based on available evidence.

9.1.2 Octanol-water partition coefficient

For high molecular weight phthalates as DIDP, the HPLC method for determination of K_ow values cannot be used. Log K_ow values for DIDP have thus been calculated by use of SPARC by USEPA /117/ and a value of 10.0 has been estimated while a value of 10.36 has been calculated in /7/. In a review by Staples et al. /1/, a log K_ow of >8.0 has, however, been concluded as being the most likely value based on available evidence.

9.1.3 Summary

The approximate physico-chemical properties on DIDP are summarized in Table 9.1.

Table 9.1
Physico-chemical properties of Diisodectyl Phthalate (DIDP)

9.2 Environmental concentrations and fate

9.2.1 Concentrations in the environment

No data are available.

9.2.2 Abiotic degradation

No experimental data on the hydrolysis of DIDP are available. The hydrolysis half-life at neutral pH and 25°C range is estimated to 3.4 years /7/.

No experimental data on photodegradation of DIDP are available. The photodegradation half-life in the atmosphere is estimated to 0.2 days /7/. In the aquatic environment only insignificant photodegradation is expected /1/.

9.2.3 Biodegradation

The ready biodegradability of DIDP was determined in the OECD 301C test resulting in a degradation of 42% after 14 days of incubation /12/. Lundberg (1994) /118/ refers to a degradation of 30-100% of DIDP in the OECD 301C after 14 days of incubation. Staples et al. (1996) /1/ refers to two studies showing an ultimate biodegradation of 67% after 28 days of incubation.

When using an acclimated inoculum, Sugatt et al. (1984) /14/ demonstrated a biodegradability of DIDP of 56% after 28 days of exposure.

Staples et al. (1996) /1/ refer to studies with DIDP showing a primary biodegradability of 42% by employing a non-acclimated inoculum and 68->99% by using acclimated inocula.

Lundberg (1994) /118/ refers to a study for the Chemical Manufacturers Association on degradation of DIDP. During a 3-week acclimation phase in a SCAS test, an average daily primary degradation of 68% was found and, in a succeding die-away test, a primary degradability of more than 90% was found after 9 days of incubation.

No data are available.

In a sediment-water system, Johnson et al. (1984 /68/, cited by Lundberg 1994 /118/) found a mineralization of 1% after 28 days of incubation at 22°C.

9.2.4 Bioaccumulation

In the review given by Staples et al. (1996) /1/, several bioaccumulation studies with molluscs, crustaceans and fish are reported. Below, a number of studies on bioaccumulation of DIDP referred to in Staples et al. (1996) /1/ are given.

Brown & Thompson (1982a) /122/ determined the total BCF for Mytilus edulis, BCF values of 3977 and 2998 were found (exposure concentration: 4.4 and 41.7 µg/l, respectively; test procedure: flow through; exposure period: not known).

For crustaceans, only data on Daphnia magna exist. Brown & Thompson (1982b) /123/ determined the total BCF in static renewal tests and found the following BCF values: 90 (exposure concentration: 100.4 µg/l); 128 (exposure concentration: 32.6 µg/l); and 147 (exposure concentration: 9.6 µg/l).

Japan CITI (1992) /124/ found a total BCF for carp (Cyprinus carpio) of <3.6 to <14.4 (test procedure: flow through; exposure concentration: 0.1-1.0 µg/l; exposure period: not known).

9.2.5 Summary and conclusion

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

DINP exhibits a borderline ready biodegradability with some test results showing a mineralization greater than the pass level and some below the pass level. In simulation of a sewage treatment plant, a high primary biodegradability was found. No data are available on degradation under anaerobic conditions. In a sediment-water system, a very low primary biodegradation was seen under aerobic conditions.

DIDP is bioaccumulative in aquatic biota, which is demonstrated by the experimentally derived BCF value of up to 4000 for molluscs.

9.3 Effects

9.3.1 Toxicity to micro-organisms

Only one study with micro-organisms (protozoa) was found. The results of the test are given in Table 9.2.

Table 9.2
link to table

No toxicity of DIDP to protozoans was found. The NOEC value given is far above the water solubility of the substance.

9.3.2 Toxicity to algae

One toxicity study with algae was found. The results are presented in Table 9.3.

Table 9.3
link to table

From the above results, DIDP seems to have no acute or chronic toxicity to algae. The effect concentration measured is far above the water solubility of the substance.

9.3.3 Toxicity to invertebrates

The short-term toxicity data on DIDP to freshwater and marine invertebrates are presented in Table 9.4 and the long-term toxicity data on DIDP to freshwater and marine invertebrates are presented in Table 9.5.

Table 9.4
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Table 9.5
link to table

From the above results, DIDP seems to have no acute toxicity to crustaceans while a slight toxicity was observed in a 21 d survival test with Daphnia magna. Due to the low solubility of the substance, the effect observed may in part be ascribed to an indirect effect such as floating (entrapment) or microdroplets which may adhere to the surface of the animals. The effect concentration measured is far above the water solubility of the substance.

9.3.4 Toxicity to fish

Only short-term toxicity data exist on fish. The toxicity data on DIDP to freshwater and marine fish are presented in Table 9.6.

Table 9.6
link to table

DIDP showed no acute toxicity in any of the acute toxicity tests performed. The NOEC values given are all far above the water solubility of the substance.

9.3.5 Estrogenic effects

Meek et al. (1997) /103/ measured changes in the reproductive organs in female rats. It was shown that DIDP did not produce estrogenic activity. However, it has to be noted that the conclusions made are based on unpublished data.

9.3.6 Summary and conclusions

The results from ecotoxicology tests vary with a factor of up to 10. The reason for the variability should most probably be sought in experimental difficulties arising from the low water solubility of DIDP. The formation of microdroplets, surface films and adsorption to surfaces of the test organisms lead to difficulties in maintaining steady exposure concentrations and/or cause direct physical effects.

DIDP shows no acute toxicity to either algae, crustaceans or fish. Toxicity was observed in a long-term test with Daphnia magna (NOEC = 0.03 mg/l). However, the toxicity observed is expected to be ascribed mainly to an indirect effect such as floating (entrapment) or microdroplets which may adhere to the surface of the animals.

Although no acute toxicity was observed at or below the water solubility of the substance in any of the tests performed, it has to be noted that the maximum toxicity of a substance will only be seen when steady state conditions have been achieved during the exposure time. With a log K_ow value of approx. 8, it can be estimated that steady state conditions in a fish test will not be reached before 1300 days of exposure. However, taking the relatively high biotransformation of phthalate esters into account, steady state conditions will probably never be reached and maximum toxicity of DIDP will thus probably never be seen.

As no chronic toxicity tests with fish are available, it can not be excluded that DIDP may cause long-term adverse effects at or below the water solubility of the substance in aquatic organisms (caused by direct or indirect effects).

DIDP did not show any changes in the reproductive organs of female rats /103/.

9.4 Environmental hazard classification

No acute toxicity is observed at or below the water solubility level of DIDP (<0.001 mg/l).

Slight toxicity was observed in a long-term test with Daphnia magna (NOEC = 0.03 mg/l). However, the toxicity observed is thought to be ascribed mainly to an indirect effect such as floating (entrapment) or microdroplets which may adhere to the surface of the animals. No chronic or long-term tests performed with fish were available.

DIDP is readily biodegradable in laboratory tests.

DIDP is bioaccumulative in aquatic biota, which is demonstrated by the experimentally derived BCF value of up to 4000 for molluscs.

The water solubility of DIDP is < 0.001 mg/l, which is well below 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 Diisodecyl phthalate of, it is proposed that DIDP should not be classified as dangerous to the aquatic environment. However, it has to be noted that DIDP is highly bioaccumulative.

9.5 PNEC for the aquatic compartment

No acute toxicity has been measured at concentrations at or below the solubility limit. Weak toxic effects were found in one test at a concentration far above the solubility limit. The available data do not allow a derivation of a PNEC_aquatic