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EC number: -
CAS number: -
Assessment of Aquatic Toxicity Based on Assessment of Hydrolysis Products
Based on experiences with attempting to design and conduct appropriate
studies to investigate the ecotoxicity of alkyl and aryl phosphites, it
was determined that conducting aquatic toxicity studies on tris
2-propylheptyl phosphite (T2PHP) in algae, daphnia and fish would not be
possible. This conclusion is consistent with OECD Guidance Document #23
entitled “Guidance Document on Aquatic Toxicity Testing of Difficult
Substances and Mixtures” (OECD 2000) because of the inherent
physical/chemical properties of the test substance (i.e., extremely poor
water solubility and hydrolysis). Based on the expert approach that was
developed for other alkyl and aryl phosphites, it was concluded that,
since direct measurements of the ecotoxicity of the parent test
substance (T2PHP) would not feasible, the evaluation should focus on
quantifying the toxicity of the combination of hydrolysis by-products of
T2PHP– namely 2-propylehptanol and phosphorus acid.
It is possible to quantitatively predict the maximum theoretical
concentration of hydrolysis by-products and resulting toxicity of the
solution of these by-products based on the known toxicity of the
individual by-products, assuming additive toxicity. To achieve this,
measured and calculated aquatic toxicity values for the individual
primary hydrolysis by-products of T2PHP (2-propylehptanol and phosphorus
acid) were identified. Using the estimated water solubility of T2PHP of
2.1 x 10-8 mg/L, the maximum theoretical concentrations of the
individual hydrolysis by-products in water were calculated. These
maximum estimated concentrations were then compared to the aquatic
toxicity values for the hydrolysis products and ratios for each were
summed to develop a maximum theoretical solution toxicity. A derived
solution toxicity value of 1.0 would be considered to be equivalent to a
toxicity value for an “aged” (hydrolyzed) solution. The further this
value is below 1, the lower the anticipated ecotoxicity hazard.
Based on the following stoichiometry:
one mole T2PHP (mw= 502.8 g/mole) yields two moles 2-propylheptanol
(158.3 mw = g/mole) and one mole phosphorous acid (mw= 82.00 g/mole)
At its aqueous solubility limit of 2.1 x 10-11 g/L = 4.1 x 10
-14 moles/L (2.1 x 10-11 g/L ÷ 502.8 g/mole), T2PHP would hydrolyse to
1.2 x10 -13 moles/L 2-propylheptanol and 4.1 x 10-14 moles/L phosphorous
acid. These molar concentrations equate to mass concentrations of 1.9 x
10-8 mg 2-propylheptanol/L and 3.4 x 10 -9 mg phosphorous acid/L
These values are orders of magnitude below the NOECs and PNECs for
2-propylheptanol and phosphorus acid suggesting that T2PHP will not
result in environmental hazards based on its hydrolysis products.
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