2-ethylhexyl diphenyl phosphate

Endpoint summary

Additional information

Acute toxicity Data:

2 -Ethylhexyl (diphenyl)phosphate has acute toxicity data for fish (rainbow trout and fathead minnow), invertebrates (two midge species and the water flea Daphnia magna), and algae (two green algae and one diatom species) (see Table 2).

For fish, acute 96-h LC50 values from four studies ranged from 1.3 to 15 mg/L. For invertebrates, acute 48-h LC50 or EC50 values from four studies ranged from 0.15 to 0.67 mg/L. For algae, acute 72-h or 96-h EC50 values from four studies ranged from 0.12 to >0.40 mg/L. Across all acute aquatic studies with 2EHDPP, effects were only reported at concentrations in excess of the water solubility of 0.0506 mg/L at 21 deg.C.

 

Chronic toxicity Data:

Chronic toxicity data for fish (rainbow trout), invertebrates (D. magna), and green algae are also available for 2 -Ethylhexyl (diphenyl)phosphate (see Table 2).

 

For fish, a 71-day early life stage test was conducted with rainbow trout. A flow-through test design was employed that exposed a range of concentrations (0 to 0.60 mg/L nominal) to eggs and fry over the course of the test. Endpoints were egg hatching success, growth and development, behavior, and survival. No effects on any endpoint were reported except for survival. However, survival was only affected at concentrations above the water solubility. The solubility of 2EHDPP in water is 0.0506 mg/L at 21 deg.C. The average temperature in the water during the test was about 12 deg.C and ranged as low as 6 deg.C. The solubility of 2EHDPP would be even lower than 0.0506 mg/L at the much lower temperature of 12 deg.C. Therefore, there were no effects from 2EHDPP on rainbow trout eggs or fry at or below the water solubility.

 

For invertebrates, a 21-day life-cycle test was conducted with D. magna and 2EHDPP. A flow-through test design was employed that exposed a range of concentrations (0 to 0.15 mg/L) to daphnids beginning with <24-h old neonates through adult reproduction. Endpoints included survival throughout the 21-day test and cumulative young produced per female during reproduction. Effects on survival were only found at a nominal concentration of 0.15 mg/L (mean measured concentration of 0.075 mg/L), in excess of the water solubility. This is consistent with the finding from the short term range finding study that found daphnids entrapped on the surface at 0.036 mg/L and mortality at concentrations of 0.06 to 0.28 mg/L, all exceeding the measured water solubility of 0.0506 mg/L. Egg production was reported to be reduced at the nominal concentration of 0.075 mg/L that exceeds the water solubility (mean measured 0.043 mg/L). Because daphnids were found entrapped at 0.036 mg/L after only 24 hours and some mortality occurred only at concentrations that exceeded the water solubility, undissolved test material may have been present at nominal concentrations as low as 0.036 mg/L. These data suggest that 2EHDPP is not toxic to daphnids at or below the water solubility. 

 

Additional Testing withDaphnia magnausing a structural analog

To further support the aquatic toxicity assessment of 2EHDPP, the results from a chronic D. magna life cycle test conducted with a structural analog compound were examined.

Isodecyl diphenylphosphate (IDDPP, CAS RN 29761-21-5) is a structural analog of 2EHDPP. As shown in the attached figure, both materials are diphenyl esters of phosphoric acid. Each molecule has an alkyl group attached to the diphenyl phosphate group. For 2EHDPP, the alkyl group consists of a branched C8 chain. For IDDPP, the alkyl group consists of a C8 chain with two methyl groups attached to the terminal carbon. As expected for the slightly larger substance, the water solubility of IDDPP is slightly lower (0.0112 mg/L) than for 2EHDPP (0.0506 mg/L) and the log Kow is slightly higher (6.11 vs. 5.87). Both materials are oily liquids that are poorly soluble. Aquatic toxicity information from one material can support the assessment of the other material as structural analogs.

 

A 21-day life cycle test was conducted with IDDPP at the limit of its water solubility (0.0112 mg/L). The limit test was based on OECD Guideline 211 and was conducted under full GLP. No effects on survival, adult length, days to first brood, or eggs per female were observed at the mean measured concentration of 0.00609 mg/L. As a structurally analogous compound, the results of this Daphnia LC study with IDDPP further support the conclusion that 2EHDPP is not toxic to aquatic organisms at or below its water solubility.

 

In conclusion, the acute and chronic aquatic toxicity of 2EHDPP has been tested with fish, invertebrates and algae. The assessment of the chronic aquatic toxicity of 2EHDPP is further supported by a high quality D. magna life cycle test that was conducted with a structurally analogous compound, isodecyl diphenyl phosphate (IDDPP, CAS RN 29761-21-5). The weight-of-evidence across all the studies is that no aquatic toxicity was found for 2EHDPP at or below the measured water solubility of 0.0506 mg/L at 21 deg.C.

 

Klimisch Scores:

Because of the ability of oily liquids such as 2EHDPP to entrap or foul daphnids during testing at or in excess oftheaqueous solubility, all studies that test ed above solubility or that report entrapment or the presence of undissolved test material should be scored as either Klimisch 3, not valid or Klimisch 4, not assignable. Since test concentrations were not measured for any of the acute fish or invertebrate studies and two of the algae studies, they are assigned a Klimisch score of 3. Two of the algae studies and all of the chronic studies analyzed test concentrations and are therefore assigned Klimisch scores of 4.All of these studies may be considered generally supportive of the conclusion that 2EHDPP is not toxic to aquatic organisms in short or long term tests at or below the water solubility.

The available studies for the aquatic toxicity of 2EHDPP are listed in the table below:

Table 2. Aquatic toxicity data for S141.
	Result	Comment	Reference	Flag and Klimish score
ACUTE STUDIES
Fish
Rainbow trout Salmo gairdneri	96-h LC50: 15 mg/L	Effects only observed at concentrations >solubility	Griffen et al. (1979a)	Supporting- K3
Rainbow trout Salmo gairdneri	96-h LC50 = 1.3 mg/L	Effects only observed at concentrations ≥solubility	Sousa et al. (1978a)	Supporting- K3
Fathead minnow Pimephales promelas	96-h LC50: 14 mg/L	Effects only observed at concentrations >solubility	Griffen et al. (1979b)	Supporting- K3
Fathead minnow Pimephales promelas	96-h LC-50: 6.7 mg/L	Effects only observed at concentrations ≥solubility	Sousa et al. (1978b)	Supporting- K3
Invertebrate
Water flea Daphnia magna	48-h EC50: 0.38 mg/L	Effects only observed at concentrations ≥solubility	LeBlanc and Cary (1979)	Supporting- K3
Water flea Daphnia magna	48-h EC50: 0.15 mg/L	Effects only observed at concentrations ≥solubility	Wilson and LeBlanc (1979)	Study not in the list
Midge Chironomus tentans	48-h LC50: 0.67 mg/L	Effects only observed at concentrations >solubility	Calvert et al. (1982a)	Supporting- K3
Midge Paratanytarsus parthenogenetica	48-h LC50: 0.50 mg/L	Effects only observed at concentrations ≥solubility	Renaudette et al. (1982)	Supporting- K3
Algae
Green algae Selenastrum capricornutum	72- EC50: 0.226 mg/L	Effects only observed at concentrations >solubility	Hughes and Williams (1995a)	Supporting-K3
Green algae Scenedesmus subspicatus	72- EC50: 0.120 mg/L	Effects only observed at concentrations >solubility	Hughes and Williams (1995b)	Supporting-K3
Green algae S. capricornutum	96- EC50: 0.20 mg/L	Effects only observed at concentrations >solubility	Hollister (1979a)	Supporting-K3
Diatom Navicula pelliculosa	72-h EC50: >0.40 mg/L (Range-finding study only)	Effects only observed at concentrations >solubility	Carolina Ecotox (1994)	Supporting-K3
CHRONIC STUDIES
Fish
Rainbow trout Salmo gairdneri	71-d NOEC (LOEC): 0.0211 (0.0508) mg/L	Effects only observed at concentration ≥solubility   Study performed at 10 to 12 deg.C. At these temperatures, the solubility in water would be even lower than the 0.0506 mg/L measured at 21 deg.C.	Adams et al. (1981)	WoE- K4
Invertebrates
Water flea Daphnia magna	21-d NOEC (LOEC): 0.018 (0.043) mg/L	Entrapment of daphnids noted at 0.036 mg/L during the range-finding study. This indicates the presence of undissolved test material and suggests that the solubility in water may be even lower than the measured value of 0.0506 mg/L.	Wilson and LeBlanc (1979), also cited in Adams & Heidolph (1985)	WoE- K4
Water flea Daphnia magna	21-d NOEC 0.00609 mg/L (time-weighted mean measured concentration based on the nominal water solubility limit of 0.011 mg/L)	No effects observed at the solubility limit of this structurally similar read-across compound Isodecyl diphenyl phosphate (IDDPP, CAS RN 29761-21-5)	Taylor (2013)	Key-K1
Algae
Green algae S. capricornutum	72- NOEC: 0.072 mg/L	Effects only observed at concentrations >solubility	Williams and Hughes (1995)	Supporting-K3
Green algae S. subspicatus	72- NOEC: 0.072 mg/L	Effects only observed at concentrations >solubility	Hughes and Williams (1995)	Supporting-K3