Triphenyl phosphate

Endpoint summary

Additional information

A large number of data are available to evaluate the acute toxicity of TPP on fish, daphnia and algae. However, only those that were performed to today's standard testing guidelines or showed sufficient reliable results are appropriate for use in aquatic hazard assessment.

 

It should be noted that due to the instability of TPP in water, the aquatic effects data cover not only the toxicity of TPP but also the toxicity of the degradation products. This is particularly relevant for tests with longer exposure periods.

 

Acute Toxicity to Fish

Several acute fish tests were performed according to the U.S. guideline EPA-660/3-75-009. Mayer et al. (1981) reports static test results with 96 h-LC50 values of 0.4 mg/l for Oncorhynchus mykiss and 0.32 - 0.56 mg/L for the marine species Cyprinodon variegatus (both nominal concentrations). Further acute fish toxicity data were generated in studies on killifish (Oryzias latipes) and goldfish (Carassius auratus) (Sasaki et al, 1982), Oncorhynchus mykiss (Palawski et al, 1983) and Lepomis macrochirus (Huckins et al, 1991). These studies reported LC50 values that are broadly comparable with those reported in the key study by Mayer et al. (1981) presented here.

 

Acute Toxicity to Invertebrates

A test on the acute toxicity of TPP to Daphnia magna was conducted according to the US guideline EPA-660/3-75-009. Static exposure for 96 hours resulted in a LC50 value of 1.0 mg/L (nominal concentration) (Mayer et al., 1981). Lower effective concentrations were found for another crustacean, Mysidopsis bahia, in a test on the acute toxicity as well conducted according to US guideline EPA-660/3-75-009. Static exposure for 96 hours resulted in a LC50 value of 0.18 - 0.32 mg/L (nominal concentration) (Mayer et al.,1981).

 

Further invertebrate toxicity studies investigated the acute effects of TPP on scud (Gammarus pseudolimnaeus) and midge larvae (Chironomus riparius) (Huckins et al., 1991). The results of these studies are broadly consistent with the findings of the key studies identified for this endpoint. Further, Lo and Hsieh (2000) investigated the toxicity of TPP to golden apple snail (Pomacea canaliculata) and reported a relatively lower toxicity than is identified for crustaceans in other studies (72 hr LC50: 38.2 mg/L).

 

Acute Toxicity to Algae

Mayer et al. (1981) determined the toxicity of TPP (no information on purity) to Selenastrum capricornutum using a method recommended by the United States Environmental Protection Agency (USEPA, 1971). The 96h-EC50 was determined to be 2 mg/L. Millington et al. (1988) investigated the toxicity of TPP to algae with different growth media (Bolds basal medium = BBM, OECD and US-EPA media) according to OECD guideline 201 (modified). Selenastrum capricornutum as well as Scenedesmus subspicatus showed 72 h-LOEC values on growth of 0.5 mg/L with BBM, 1.0 mg/L with OECD medium, and 5.0 mg/l with EPA medium. Chlorella vulgaris did not show any effect at 5.0 mg/L growing on any of the media.

 

Since a 96 hour algae study can be considered to be a multigenerational test, NOECs were also derived for this study, applying a factor of 2 on the LOEC (Guidance on information requirements and chemical safety assessment, Chaper R.10, 2008). Thus the 72 h-NOEC for Chlorella vulgaris is determined with 2.5 mg/L, and for Selenastrum capricornutum as well as Scenedesmus subspicatus with 0.25 to 2.5 mg/L, depending on the growth medium used.

 

Chronic Toxicity

Long-term (chronic) toxicity data are available for fish, Daphnia and algae. The lowest relevant long-term value, the LC10 of 4.80 µg/L was determined in an OECD TG 234 (2021) study on Dani rerio for the endpoint post hatch survivability. This value is used for the derivation of the PNECaqua.

 

In the key long-term fish toxicity study, a 30 d-LOEC of 0.055 mg/L was determined for the development of sac fry stage of Oncorhynchus mykiss regarding the endpoints length and weight (Sitthichaikasem, 1978). From the test raw data an EC10 of 0.037 mg/L was calculated, equipollent to the NOEC (Guidance on information requirements and chemical safety assessment, Chaper R.10, 2008). 

Two supporting studies have been identified. In a long-term flow through tests with sac fry stage of Oncorhynchus mykiss a 90 d-NOEC >= 0.0014 mg/L based on measured triphenyl phosphate concentrations was determined for the endpoints eye cataract, vertebral collagen amount, survival, and growth (Mayer et al., 1981). This is lower than the LC10 of 0.0048 mg/L in the OECD TG 234 study (2021). However, since the NOEC value in the paper by Mayer et al (1981) is a ‘greater than or equal to’ value, it is arguably more of an artefact of the test concentrations used than a definitive NOEC. Indeed, Mayer et al (1981) also reported a NOEC (based on survival) for fathead minnows (Pimephales promelas) exposed to TPP in a flow-through study over 30 days of between 0.087 and 0.230 mg/L. By examining the acute toxicity data reported in the same paper, it can be seen that fathead minnows display a similar level of sensitivity to TPP as rainbow trout (96h LC50 values of 0.66 and 0.4 mg/L for fathead minnows and rainbow trout, respectively). Assuming the same sensitivity for the chronic test, it can be estimated that the NOEC for rainbow trout would be at least 0.05 mg/L (i.e. 0.087 x (0.4/0.66)). This calculation provides confidence that the true NOEC for rainbow trout is considerably greater than 0.0014 mg/L and provides further support that the LC10 value of 0.0048 mg/L is a reliable basis for the aquatic PNEC.

 

Endocrine disrupter testing in aquatic vertebrates - in vivo

Several in vivo studies on ED properties of Triphenyl phosphate with fish were identified and are listed in chapter 6.1.8. These studies are relevant and sufficiently reliable to be used in the ED assessment. However, all have short-comings such as incomplete or non-transparent data report. None of them is adequate to conclude on potential ED properties of the substance as such but all have to be evaluated in a weight-of-evidence approach. 

A Fish Sexual Development Test (OECD 234; GLP compliant) was performed and no endorine-related effect of the test item triphenyl phosphate was identified. This is the most relevant and a fully reliable study, robustly reported in Chapter 6.1.8