Alcohols, C20-22, reaction products with phosphorus oxide (P2O5)

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics

Data waiving:

other justification

Justification for data waiving:

other:

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:

No systemic adverse effects have been noted after single-dose and repeat-dose oral exposure in animals. This does not enable to conclude whether the substance is not absorbed by oral route, or is absorbed but non-toxic. However, the components of the UVCB being chemically related to absorbable molecules such as phosphates and fatty alcohols, an extensive oral absorption is almost certain.
Absorption upon inhalation is undetermined in the absence of studies involving inhalation of the substance. The substance is manufactured as flakes or pellets (no grinding is performed), so under these actual exposure conditions the possibility of absorption after inhalation is virtually null.
No systemic adverse effects have been noted in animals after single-dose dermal exposure and after induction and challenge dermal applications . This does not enable to conclude whether the product is not absorbed by dermal route, or is absorbed but non-toxic. However, the molar mass (299–407 g/mol for individual components of the product), the very high lipophilicity (log Kow ranging 8.6 -9.7 for individual components of the product) and the very low water solubility (≤ 1 mg/L) may be expected to considerably limit the dermal penetration of the product. Furthermore, the substance is manufactured as flakes or pellets (no grinding is performed), so under these actual exposure conditions the dermal absorption is virtually null.

Absorption of Phosphoric acid alkyl esters:
Oral absorption
Phosphoric acid alkyl esters are expected to undergo hydrolysis to aliphatic alcohols and Phosphoric acid in the gastro-intestinal tract by intestinal phosphatases. Thus, the gastro-intestinal absorption of Phosphoric acid alkyl esters is assumed to play a minor role compared to the absorption of the metabolites aliphatic alcohols and Phosphoric acid.
This is supported by data collected by the Dutch Committee on Updating of Occupational Exposure Limits on Tributyl Phosphate (Health Council of the Netherlands, 2005): “After administration of oral doses of tributyl phosphate of 156 mg/kg bw, the parent compound was detected in the gastrointestinal tract, the blood, and the liver within 30 to 60 minutes. Following a single dose, the highest amount was found in the gastrointestinal tract (not quantified), and 5.7% of the dose was detected in the other tissues (no further information given).”
Long chain aliphatic alcohols can be expected to be orally absorbed depending on their chain-length. As stated in the OECD SIDS Initial Assessment Report on long chain alcohols, aliphatic alcohols “orally administered aliphatic alcohols […] show a chain-length dependant potential for gastro-intestinal absorption, with shorter chain aliphatic alcohols having a higher absorption potential than longer chain alcohols.” (OECD SIDS, 2006)
Phosphate is an essential nutrient which is absorbed in the small intestine via passive diffusion (paracellular transport) as well as via active transport by sodium-dependent phosphate co-transporters (Sabbagh et al, 2011).
“Net absorption from a mixed diet has been reported to vary between 55-70% in adults (Lemann 1996; Nordin, 1986) and between 65-90% in infants and children (Ziegler and Fomon, 1983). There is no evidence that, contrary to calcium, absorption efficiency varies with dietary intake. Phosphate absorption is greatest in jejunum and takes place by a saturable, active transport mechanism, facilitated by 1,25-dihydroxyvitamin D, as well as by passive diffusion (Chenet al., 1974).”(EFSA, 2005)
The oral absorption of Phosphoric acid alkyl esters and their metabolites is considered to be 100%.

Dermal absorption
The maximum steady state penetration rate (which is the highest exposure risk for a chemical) of Phosphoric acid alkyl esters and Phosphoric acid were predicted from in vitro measurements by Marzulli et al. (1965), also cited in a Chemical Hazard Information Profile on Tri(alkyl/alkoxy) Phosphates by Sigmon and Daugherty, 1985:
substance Dermal penetration rate µg/cm²/min Dermal penetration rate recalculated tomg/cm²/h
Trimethyl phosphate 1.47 0.0882
Triethyl phosphate 1.12 0.0672
Tri(isopropyl) phosphate 0.78 0.0468
Tri-n-propyl phosphate 0.65 0.039
Tri-n-butyl phosphate 0.18 0.0108
Phosphoric acid, 8.5% 0.003 0.00018
In human the average maximum steady state rate of penetration of Tri-n-butyl phosphate through the anterior forearm skin was 0.10 μg/cm²/min (= 0.006mg/cm²/h). No further details are available (Marzulli et al., 1965).
From these data it can be concluded, that the dermal penetration rate of Phosphoric acid alkyl esters decreases with increasing chain length. It can be further assumed that ionised forms as Phosphoric acid mono- and dialkyl esters have a lower dermal penetration rate than Phosphoric acid trialkyl esters (see Guidance on information requirements and chemical safety assessment, Chapter R.7c). Based on that, the maximum steady state penetration rate of the registered substance will be lower than 0.01 mg/cm²/h.
No data are available on the dermally absorbed fraction of Phosphoric acid alkyl esters. Thus is is assumed that the dermal absorption is 100%.

Details on distribution in tissues:

There are no data on distribution after exposure to the product: product levels in organs and tissues were not determined, and no target organ or tissue was identified in the absence of adverse effects in all the studies performed.
No accumulation of the product is expected based on the various metabolic pathways which can be expected for the product.

Distribution of Phosphoric acid alkyl esters:
As Phosphoric acid alkyl esters are assumed to be efficiently hydrolysed to aliphatic alcohols and Phosphate, the distribution of the parent compound does not play a major role.
According to EFSA (2005) “approximately 70% is present as organic phosphates, such as in the phospholipids of red blood cells and in the plasma lipoproteins. The other 30% is present as inorganic phosphate, of which 15% is protein bound. About 50% of the inorganic phosphate is in the soluble divalent cation form (HPO42-), the remaining as the monovalent anion (H2PO4-, 10%) and the trivalent cation (PO43-, <0.01%), or as HPO42-complexed with sodium, calcium and magnesium salts. These anion forms are interconvertible and effective buffers of blood pH and involved in regulation of the whole body acid-base balance. […]
Serum Pi [= inorganic phosphate] in normal adults varies between 0.97-1.45 mmol/L (3.0-4.5 mg/dL), and shows a slight increase with increasing phosphorus intakes (Heaney, 1996). Hyperphosphatemia, associated with clear clinical symptoms, has only been reported in patients with end-stage renal disease, i.e. when glomerular filtration rate (GFR) has decreased below 20% of the adult value (FNB, 1997).” (EFSA, 2005)
“The long chain aliphatic carboxylic acids are efficiently eliminated and aliphatic alcohols are therefore not expected to have a tissue retention or bioaccumulation potential (Bevan, 2001). Longer chained aliphatic alcohols within this category may enter common lipid biosynthesis pathways and will be indistinguishable from the lipids derived from other sources (including dietary glycerides)” (OECD SIDS, 2006).

Metabolism
In the three in vitro genotoxicity tests (see 5.7), the addition of liver microsome fraction (S9 mix) had no influence on cytotoxic and genotoxic effects of the product (however two of these tests did not include the maximal recommended concentration). There is therefore no conclusion concerning a possible liver metabolism of the unchanged components of the UVCB. Such a metabolism can not be excluded, in particular for the metabolites of the components.
The 1-eiconasol (C20) and 1-doconasol (C22) inside the UVCB (confidential data) may be hypothesised to undergo acido-basic and oxido-reductive reactions of the terminal -OH in exposed organisms, in their gut (after oral exposure) and at systemic level. They may therefore notably turn into fatty acids, and then possibly undergo the same metabolism as endogenous fatty acids, leading to physiological molecules and complete degradation.
The alkylphosphates (C20, C22) inside the UVCB (confidential data) may be hypothesised to undergo acido-basic and oxido-reductive reactions of the terminal phosphate in exposed organisms, in their gut (after oral exposure) and possibly at systemic level (if systemic absorption occurs). They may also, most likely, be de-phosphated and therefore follow the same metabolism as 1-eiconasol and 1-doconasol.

Metabolism of Phosphoric acid alkyl esters:
Phosphoric acid alkyl esters are hydrolysed unspecifically by phosphatases, e.g. acid phosphatase or alkaline phosphatase. Both enzymes are found in most organisms from bacteria to human. Alkaline phosphatases are present in all tissues, but are particularly concentrated in liver, kidney, bile duct, bone, placenta. In human and most other mammals three isoenzymes of Alkaline phosphatase exist: intestinal ALP, placental ALP, tissue non-specific ALP (present in bone, liver, kidney, skin).
Seven different forms of Acid phosphatase are known in humans and other mammals. These are also present in different tissues and organs (predominantly erythrocytes, liver, placenta, prostate, lung, pancreas).
Phosphate as such is not metabolised. It “is an essential dietary constituent, involved in numerous physiological processes, such as the cell’s energy cycle (high-energy pyrophosphate bonds in adenosine triphosphate [ATP]), regulation of the whole body acid-base balance, as component of the cell structure (as phospholipids) and of nucleotides and nucleic acids in DNA and RNA, in cell regulation and signalling by phosphorylation of catalytic proteins and as second messenger (cAMP). Another important function is in the mineralization of bones and teeth (as part of the hydroxyapatite)” (EFSA, 2005).
Linear and branched primary aliphatic alcohols are oxidised to the corresponding carboxylic acid, with the corresponding aldehyde as a transient intermediate. The carboxylic acids are further degraded via acyl-CoA intermediates in by the mitochondrial beta-oxidation process. Branched aliphatic chains can be degraded via alpha- or omega-oxidation (see common text books on biochemistry).
“The long chain aliphatic carboxylic acids are efficiently eliminated and aliphatic alcohols are therefore not expected to have a tissue retention or bioaccumulation potential (Bevan, 2001). Longer chained aliphatic alcohols within this category may enter common lipid biosynthesis pathways and will be indistinguishable from the lipids derived from other sources (including dietary glycerides) (Kabir, 1993; 1995a,b).
A comparison of the linear and branched aliphatic alcohols shows a high degree of similarity in biotransformation. For both sub-categories the first step of the biotransformation consists of an oxidation of the alcohol to the corresponding carboxylic acids, followed by a stepwise elimination of C2 units in the mitochondrial β-oxidation process. The metabolic breakdown for both the linear and mono-branched alcohols is highly efficient and involves processes for both sub-groups of alcohols. The presence of a side chain does not terminate the β-oxidation process, however in some cases a single Carbon unit is removed before the C2 elimination can proceed.” (OECD SIDS, 2006)

Details on excretion:

No abnormal odor was noted in animal studies. There is therefore no indication of a noteworthy expiratory excretion of the product and/or its degradation products. However, when considering the putative metabolism of the components of the UVCB, it seems reasonable to predict a minor expiratory excretion of volatile carbon compounds.
No gastro-intestinal clinical signs and no coloration of feces were noted after repeated oral exposure to the product. There is therefore no conclusion concerning a possible fecal excretion of the product and/or its metabolites. However, when considering the putative metabolism of the components of the UVCB, it seems reasonable to predict a fecal excretion of the degradation products related to fatty acid metabolism.
Neither clinical signs evocative of coloration of urine (e.g. coloured litter) nor microscopic effects on kidneys were noted after repeated oral exposure to the product. There is therefore no conclusion concerning a possible urinary excretion of the product and/or its metabolites. Considering the components of the UVCB, an urinary excretion of the phosphate group (upon dephosphatation) can be predicted.
There are no data (notably distribution data to mammary glands) enabling to conclude on a possible excretion into milk

Accumulation an elimination of Phosphoric acid alkyl esters:
“The long chain aliphatic carboxylic acids are efficiently eliminated and aliphatic alcohols are therefore not expected to have a tissue retention or bioaccumulation potential (Bevan, 2001). Longer chained aliphatic alcohols within this category may enter common lipid biosynthesis pathways and will be indistinguishable from the lipids derived from other sources (including dietary glycerides)” (OECD SIDS, 2006).
The metabolites of Phosphoric acid alkyl esters - Phosphate and aliphatic alcohols, which are oxidised to the corresponding fatty acids - enter normal metabolic pathways and are therefore indistinguishable from Phosphate and lipids from other sources. Phosphate levels are regulated by parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D. Excess absorbed Phosphate is renally excreted (EFSA, 2005).
Thus, a detailed examination of the excretion pathways seems not necessary.

Applicant's summary and conclusion

Executive summary:

Absorption by oral route is expected to be good. For the substance per se, absorption by respiratory route is undetermined and absorption by dermal route is most probably limited; furthermore for both routes, absorption is virtually null for workers at the manufacturing steps as the test product is in the form of flakes or pellets.

Distribution is undetermined but no accumulation of the product is expected.

Liver metabolism is unsure.

Elimination is expected to be mainly fecal (fatty acids and metabolites), and urinary (phosphate) and expiratory (organic volatiles) to a minor extent. The possibility of excretion into milk is undetermined.