Review of Environmental Fate and Effects of Selected
Phthalate Esters

8 Diisononyl Phthalate (DINP)

8.1 Physico-chemical properties
8.1.1 Water solubility
8.1.2 Octanol-water partition coefficient
8.1.3 Summary
8.2 Environmental concentrations and fate
8.2.1 Concentrations in the environment
8.2.2 Abiotic degradation
8.2.3 Biodegradation
8.2.4 Bioaccumulation
8.2.5 Summary and conclusion
8.3 Effects
8.3.1 Toxicity to micro-organisms
8.3.2 Toxicity to algae
8.3.3 Toxicity to invertebrates
8.3.4 Estrogenic effects
8.3.6 Summary and conclusions
8.4 Environmental hazard classification
8.5 PNEC for the aquatic compartment
 

8.1 Physico-chemical properties

DINP (C₂₆H₄₂O₄), CAS No.: 28553-12-0 and 68515-48-0, with an alkyl chain length of 9,9 /1/ is a colourless oily liquid. The molecular weight is 418.6 (418.6-432.6). DINP has a melting point of about -48°C and a boiling point at 440°C /1, 7/. The density is 0.97 g/ml and the vapour pressure is <5.0·10^-7 mmHg at 25°C.

8.1.1 Water solubility

DINP is a high molecular weight phthalate. Evidence indicates that many of the measured water solubilities for high molecular weight phthalates esters reported in the literature are erroneously too high. The water solubility is calculated to be 2.31^-5 mg/l /7/ while, in the literature, several aqueous solubility data on DINP range from 7.8·10^-5 to 0.0006 mg/l. 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.

8.1.2 Octanol-water partition coefficient

For high molecular weight phthalates as DINP, the HPLC method for determination of K_ow values cannot be used. Log K_ow values for DINP have thus been calculated by use of SPARC by USEPA /117/ and a value of 10.0 has been estimated while a value of 9.37 has been estimated in EPIWIN (1994) /7/. In a review by Staples et al. /1/, a log K_ow of >8.0 has been concluded as being the most likely value based on available evidence.

8.1.3 Summary

The approximate physico-chemical properties on DINP are summarized in Table 8.1.

Table 8.1
Physico-chemical properties of Diisononyl Phthalate (DINP)

8.2 Environmental concentrations and fate

8.2.1 Concentrations in the environment

The content of DINP in wastewater and sewage sludge from Danish treatment plants has been measured during recent years. An overview of the results is given in Table 8.2.

Table 8.2
link to table

It is the general picture that a high removal of DINP from the waste water is found during the wastewater treatment. However, mass balances show that most of the amount in the inlet water is found in sludge /9/, which roughly indicates that the degradation of DINP is limited and that DINP is adsorbed to and follows the sludge.

No data are available.

8.2.2 Abiotic degradation

No experimental data on the hydrolysis of DINP 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 DINP are available. Estimated photodegradation half-lives in the atmosphere are in the range from 0.2 to 2 days /4, 7/. In the aquatic environment, only insignificant photodegradation is expected /1/.

8.2.3 Biodegradation

Scholz et al. (1997) /65/ investigated the ready biodegradability of DINP in the Modified Sturm test (OECD 301B) and found a degradation of 79% after incubation for 28 days. Staples et al. (1996) /1/ refer to studies showing an ultimate biodegradation of <1-70% after incubation for 28 days.

When using an acclimated inoculum, Sugatt et al. (1984) /14/ demonstrated a biodegradability of DINP of 62% after 28 days.

Staples et al. (1996) /1/ refer to studies with DINP showing a primary biodegradability of more than 95% 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 DINP. During a 3-week acclimation phase in a SCAS test, an average daily primary degradation of 68% was found and, in a succeeding die-away test, a primary degradability of more than 90% was found after 5 days of incubation.

No data are available.

Johnson et al. (1984) /68/ investigated the biodegradation of DINP in sediment which had been pre-exposed for 28 days before the start of the experiment. After 28 days of incubation, a primary degradation of 1% was determined under aerobic conditions and less than 1% under anaerobic conditions. Further experiments demonstrated that the same degree of degradation (1.2-1.6% after 28 days) was reached at various exposure concentrations from 0.02 to 10 mg/l. Finally, increasing degradation was observed with increasing temperature from about less than 1% at 12°C to more than 2% at 28°C.

8.2.4 Bioaccumulation

For DINP, only one bioaccumulation study performed with molluscs was found. A total BCF of 1844 was reported by Solbakken et al. (1985) /118/ (the exposure concentration was 61 mg/l and the test procedure was static).

8.2.5 Summary and conclusion

DINP seems to be efficiently removed from waste waters based on the low outlet concentrations compared to inlet concentrations in sewage treatment plants. However, mass balances show that most of the amount in the inlet water is found in sludge, which indicates that the degradation of DINP is limited and that DINP is adsorbed to and follows the sludge.

Hydrolysis and photodegradation are not significant degradation routes of DINP 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 a simulation test of a sewage treatment plant, a high primary biodegradability was found. This is inconsistent with the above conclusions based on measurements in full-scale wastewater treatment plants. In a sediment-water system, very low rates of primary biodegradation were found under both aerobic and anaerobic conditions.

DINP is bioaccumulative in aquatic biota, which is demonstrated by the experimentally derived BCF value of 1844 for molluscs.

8.3 Effects

8.3.1 Toxicity to micro-organisms

No toxicity with micro-organisms could be found.

8.3.2Toxicity to algae

One toxicity study with algae was found. The results are presented in Table 8.3.

Table 8.3
link to table

From the above results, DINP seems to have no acute or chronic toxicity to algae. The effect concentrations measured are, however, far above the water solubility of the substance.

8.3.3 Toxicity to invertebrates

The short-term toxicity data on DINP to freshwater and marine invertebrates are presented in Table 8.4 and the long-term toxicity data on DINP to freshwater and marine invertebrates are presented in Table 8.5.

Table 8.4
link to table

Table 8.5
link to table

From the above results, DINP 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) of the test animals or microdroplets which may adhere to the surface of the animals. The effect concentration measured is far above the water solubility of the substance.

8.3.4 Toxicity to fish

Only short-term toxicity data exist on fish. The toxicity data on DINP to freshwater and marine fish are presented in Table 8.6.

Table 8.6
link to table

DINP 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.

8.3.5 Estrogenic effects

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

8.3.6 Summary and conclusions

The results from ecotoxicology tests vary with a factor of up to 3. The reason for the variability should most probably be sought in experimental difficulties arising from the low water solubility of DINP. 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.

DINP shows no acute toxicity to either algae, crustaceans or fish. Toxicity was observed in a long-term test with Daphnia magna (LOEC = 0.089 mg/l, NOEC = 0.034 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 above 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 /121/. However, taking the relatively high biotransformation of phthalatic esters into account, steady state conditions will probably never be reached for which reason maximum toxicity of DINP will never be seen.

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

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

8.4 Environmental hazard classification

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

Toxicity of DINP was observed in a long-term test with Daphnia magna (NOEC = 0.034 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. No chronic or long-term tests performed with fish were available.

DINP is readily biodegradable in laboratory tests.

DINP is bioaccumulative in aquatic biota, which is demonstrated by the experimentally derived BCF value of 1844 for fish.

The water solubility of DINP 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 of Diisononyl phthalate, it is proposed that DINP should not be classified as dangerous to the aquatic environment. However, it has to be noted that DINP is highly bioaccumulative.

8.5 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.