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Description of key information

Short description of key information on bioaccumulation potential result: 
Rat liver microsomes initiated the metabolisation of simple alkyl phenols to quinone methides.
Short description of key information on absorption rate:
Exposure of human skin, in vitro, to concentrations of up to 10% NPE result in minimal exposure. The percentage dose absorbed was concentration dependant (ca. 1% for a 0.1% solution, 0.1% for a 1% solution and 0.01% for a 10% solution).

Key value for chemical safety assessment

Absorption rate - dermal (%):
1

Additional information

See attached Document for structures.

Toxicokinetic Assessment of Phenol, heptyl derivs., EC# 276-743-1

 

The toxicokinetic profile of phenol, heptyl derivs., EC# 276-743-1, is based on physical chemical property and toxicity data on the substance and absorption, distribution, metabolism and/or excretion data on structurally similar substances. No experimentally derived ADME data are available on this substance.

 

Substance Characterization

 

Analytical characterizations show that this substance meets the definition of a UVCB. The representative chemical structure of this substance is illustrated in Figure 1. This substance is chemically described as 4-heptylphenol, branched. It consists primarily of a phenol group that is alkylated at the para position (number 4 carbon) on the ring.

 

 

Figure 1. Representative structure of EC# 276-743-1

 

 

This substance contains both mono- and di-alkylated heptylphenol isomers. However, the mono isomers represent nearly 90% of this UVCB’s composition. The predicted structures are shown below (Figure 2).

 

 

 

Structure 1:             OC1=CC=C(C(C)(C)CC(C)C)C=C1

 

 

Structure 2:             CC(C)C(C(C)C)C1=CC=C(O)C=C1

 

 

Structure 3:             OC1=C(C(C)C(C)C(C)C)C=C(C(C)(C)CC(C)C)C=C1

 

 

Structure 4:             OC1=C(C(C)(CC(C)C)C)C=C(C(C)(C)CC(C)C)C=C1

 

 

Structure 5:             OC1=C(C(C)C(C)C(C)C)C=C(C(C)C(C)C(C)C)C=C1

 

 

Figure 2. Predicted mono- and di-alkylated heptylphenol structures

 

Physical Chemical Properties

 

Molecular weight, water solubility, log Kow, and vapor pressure are key physical chemical properties for assessing the toxicokinetics of a substance. This substance is a clear amber viscous liquid. It has a relatively low molecular weight (192.3). Physical chemical testing shows that it is slightly soluble in water (42.1 mg/l), is moderately hydrophobic (log Kow 4.5), and has a low vapor pressure (2.6 x 10-1Pa @ 25° C). Hydrolysis studies show that it is stable at pH 4 but exhibits limited hydrolysis at pH 7 to 9.

 

Exposure Routes

 

The potential for exposure to this substance is limited by its use and physical chemical properties. The dermal contact is considered to be the primary route of occupational exposure. Inhalation exposure is expected to be limited because this substance has a relatively low vapor pressure (OECD 2003: negligible <1 Pa; ECHA R15.5: low < 0.1 Pa). Oral exposure is not an anticipated route of exposure to workers or the general public.

 

Absorption

 

Dermal

 

The dermal absorption of this substance is expected to be limited. While the substance is slightly soluble and small enough (MW is < 500) for it to be absorbed, the log Kow for this substance (4.79) is outside the optimal range of 1 to 2 (Guidance Document on Dermal Absorption, European Commission, Health and Consumer Protection Directorate-General. Sanco/222/2000 rev. 7, March 19, 2004). Studies with other alkyl phenols indicate that skin penetration over 8 hours is only 1% of the applied dose (Monteiro-Riviere, et al, 2000).

 

Results of an acute dermal toxicity study in rabbits also indicate that dermal absorption of this substance is limited. Animals were given a single dermal dose of 2,000 mg/kg and observed for systemic and local effects for 14 days. The predominant finding was necrosis and severe edema of the skin followed by body weight loss, which was noted in a number of animals at day 7 and 14 observations. One animal that exhibited body weight loss died at day 12 following exposure. No clinical signs were observed that were indicative of systemic effects, and no gross pathological abnormalities were observed.

 

Inhalation  

 

Because this substance has a relatively low vapor pressure (2.6 x 10-1Pa @ 25° C; OECD 2003: negligible <1 Pa; ECHA R15.5: low < 0.1 Pa), the potential for inhalation exposure and uptake via the lungs is not expected. However, if this substance reaches the respiratory tract, the physical chemical properties and its bioavailability, as inferred from the oral toxicity data, indicates that uptake will occur likely by means of micellar solubilization.

 

Oral

 

Absorption in the gastrointestinal tract also is influenced by the water solubility, lipophilicity, and molecular weight of a chemical. Because this substance is slightly soluble in water (42.19 mg/l), slightly hydrophobic (log Kow 4.5), and has a relatively low molecular weight (192.3), it is expected to be absorbed. 

 

Results of acute and repeat dose oral toxicity studies in rats provide direct evidence that this substance is absorbed. In single dose studies using 2,000 mg/kg or 5000 mg/kg of this substance, death ensues as early as day 1 post exposure. Because of the strong corrosive/irritant nature of this substance and the observation of gross pathology changes (spleen and liver) only at 2000 mg/kg, it is not clear to what degree the cause of deaths following a single dose is due to local versus systemic toxicity. However, a 28-day repeat dose study and a reproduction/developmental screen study clearly show that this substance is absorbed causing test material-related effects at 450 mg/kg/day and 160 mg/kg/day, respectively.

 

Distribution

 

Once this substance is absorbed, it is expected to be distributed via the blood to the liver and other tissues. Due to its moderate lipophilic nature it is predicted to be absorbed by cells of the organs and tissues that it contacts. The 28-day repeat dose and reproduction/developmental screen studies also provide direct evidence that this substance is distributed to and absorbed by the liver, kidneys, thymus, and seminal vesicles at very high doses (450 mg/kg/day for 28 days) and the liver and kidneys at lower doses (150 mg/kg/day, up to 51 days)1.

 

1Microscopic pathological evaluation of the liver, kidneys, thymus, and seminal vesicles was conducted in both the 28-day repeat dose and reproductive/development screen studies.

 

Metabolism

 

Based on the structures in Figure 2, this UVCB substance is expected to be metabolized via a number of metabolic pathways. Alkylphenols are known to undergo both Phase I and Phase II reactions (Thompson et al, 1995). Both the alkyl side chains(s) and the aromatic ring are subject to oxidative metabolism to form a semi-quinone. Alkyl phenols also are known to undergo glucuronidation with the glutathione moiety attached to the benzylic carbon on the alkyl side chain.

 

Elimination

 

Because of the hydroxyl and alkyl structural characteristics of this substance, Phase I and Phase II metabolic by-products are expected to be eliminated via renal and/or biliary excretion.

 

References

 

Monteiro-Riviere NA, Van Miller, JP, Simon G, Joiner RL, Brooks JD and Rivere JE (2000). Comparativein vitropercutaneous absorption of nonylphenol and nonylphenol ethoxylates (NPE-4 and NPE-9) through human, porcine and rat skin, Toxicol. and Indust. Health 16:49-57.

 

Thompson DC, Perera K and London R (1995). Quinone methide formation from para isomers of methylphenol (creosol), ethylphenol, and isopropylphenol: relationship to toxicity, Chem. Res. Toxicol. 8:55-60.

Discussion on bioaccumulation potential result:

Test compounds (2 mM each) were dissolved in DMSO and added to pre-incubated rat liver slices (30 min at 37°C in 20 mL glass scintillation vials containing 2.5 mL Krebs-Hepes buffer (pH 7.4)) at a volume of 25 µL (1% v/v) and incubated for up to 6 h. Toxicity was measured as loss of intracellular potassium using a flame photometer ( liver slices removed at appropriate time intervals dried, washed and acidified before centrigugation for 10 minutes and dilution with water). Microsoms for metabolite formation were prepared from similar rat livers to those used from the slice assays. Incubation at 37°C was performed for various time periods and stopped by acidification. Metabolism was analysed using HPLC, MS and Proton NMR.

Results

A single glutathione conjugate peak was detected for each compound. Peaks were not observed in absence of glutathione. The rate of formation of the glutathione peak mirrors the toxicity of the parent material. Splitting of the conjugate peak shows two distinct forms suggesting diastereomeric conjugates. MS confirmed that the conjugates are monoglutathione conjugates where the glutathione is attached to the benzylic carbon. This is consistent with the formation of reactive quinone methide intermediates

Conclusions

Rat liver microsomes initiated the metabolisation of simple alkyl phenols to quinone methides.

Discussion on absorption rate:

Method and materials

Percutaneous absorption of ring-labelled 14C-NP (1%), 14C-NPE-4 and 14C-NPE-9 (0.1, 1.0, 10%) applied in polyethylene glycol (PEG-400) or water (NPE-9) only using in vitro flowthrough diffusion cells containing split thickness human, pig and rat skin was assessed. Absorption into perfusate, as well as disposition into stratum corneum and skin was assessed.

Results

In all species, the fraction of the dose absorbed was dependant upon concentration of the applied dose with increased absorption efficiency seen at lower concentrations. In all dosing scenarios the bulk of the dose remained on the surface and did not penetrate the stratum corneum even after 8 h.

Conclusions

Exposure of human skin to concentrations of up to 10% NPE result in minimal exposure. The percentage dose absorbed was concentration dependant (ca. 1% for a 0.1% solution, 0.1% for a 1% solution and 0.01% for a 10% solution). There were no large species differences for absorption seen in the study.

In the case of NPE, an absorbed flux of 0.1 µg/0.32 cm2/8 h or 0.3 µg/cm2/8 h is a more accurate estimate of absorption for all doses up to 10%