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Description of key information

Key value for chemical safety assessment

Additional information

No studies on toxicokinetics are available for the reaction mass of tert-butylphenyl diphenyl phosphate and di-tert-butylphenyl phenyl phosphate. The available toxicity studies provide no or little information. Therefore the assessment is primarily based on physicochemical properties, supported by some toxicological indications.

 

Physical/chemical properties

The physical/chemical properties that are of importance to assess the toxicokinetics behaviour of multi-constituent are:

  • Water solubility – approx. 116 microgram/L
  • Molecular weight – 326 -438 g/mol
  • Log Kow – 5.61 for the main constituent (C4), 3.85 for TPP and > 6.5 for C8 & C12
  • Vapour pressure - 0.00108 Pa (20°C) (based on the read-across: reaction mass of t-butylphenyldiphenyl phosphate and bis-t-butylphenylphenyl phosphate and triphenyl phosphate).

 

Absorption

Based on log Kow, the substance of concern is relatively highly lipophilic and therefore oral/GI-absorption by passive diffusion is expected to be limited. Reasonably micellular solubilisation will be the major mechanism for absorption, also because it has a low water solubility and a moderate low molecular weight. Oral acute toxicity studies indicate some visible adverse effects in GI-tract, adrenals, testes and lungs. This indicate that absorption has occurred, although it gives no indication of the amount of absorbed substance.

Due to the low vapour pressure of the reaction mass, respiratory exposure is unlikely to occur on a large scale. However, when respiratory exposure has occurred, absorption will be similar to oral absorption.

Due to its lipophilic character, the dermal penetration of the reaction mass of t-BuPDPP and di-t-BuPPP into the stratum corneum will be high. Because of its low water solubility the rate of penetration from the stratum corneum into the epidermis is likely to be low. This would be supported by the outcome of the skin sensitization study (LLNA), in which the SI was >3 in all concentrations tested, however, no dose-response was observed. One theoretical explanation might be that the majority of the dermal applied substance stays in the local stratum corneum and only a small fraction has been absorbed into the epidermis.

 

Distribution, metabolism and excretion

Based on the physical chemical properties the substance will be distributed into cells and to a lower extent into the extracellular spaces. Due to its highly lipophilic character it is anticipated that the substance would tend to be accumulated in adipose tissues and in lipophilic layers like the stratum corneum. In one study (Sauerhoff, 1981) a significantly higher concentration of phosphates was found in the urine of exposed animals. This was theoretically clarified by excretion of metabolites. There is no indication of metabolism rate and excretion rates.

 

Conclusion:

It is assumed that the substance of concern can be absorbed after oral and respiratory exposure, but the amount of absorption cannot be predicted based on the currently available information. Dermal absorption is considered to be very low, but accumulation in the stratum corneum is expected. No information is available about the distribution, metabolism and excretion.

For risk assessment purposes, absorption via the oral and inhalation route are assumed to be similar, based on the absence of effects in 90-day studies via both routes. For dermal absorption, it was assumed as a worst-case that absorption was similar to oral absorption.