Phosphonic acid, mixed C12-20-alkyl and C14-18-unsatd. alkyl derivs.

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics

Type of information:

other: Expert statement

Adequacy of study:

key study

Study period:

January 2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: On the basis of experimental data and considering general principles and knowledge the basic toxicokinetic properties were concluded with sufficient certainty.

Reason / purpose for cross-reference:

reference to other study

Objective of study:

absorption

distribution

excretion

metabolism

Qualifier:

no guideline available

Principles of method if other than guideline:

The basic toxicokinetic behaviour was assessed based on the known properties of the submission item by applying generally known and accepted principles.

GLP compliance:

no

Preliminary studies:

Physicochemical properties influencing the toxicokinetics are the water insolubility (< 0.1 mg/L), the irrelevantly low vapour pressure (0.00043 Pa at 25 °C), the very high lipophilicity (Log Kow > 9.4), the molecular weight range between 369.25 and 605.5 g/mol and the absence of any dissociation, pH-effects, corrosive or irritant properties.
No treatment related changes were observed in the 28 d repeated dose subacute toxicity or in the subacute oral reproduction/developmental toxicity study in rats (NOAEL ≥ 1000 mg/kg bw per d) and an acute dermal toxicity test (up to 2000 mg/kg bw).
The submission item is deemed to show low bioaccumulation and was found readily biodegradable.

Type:

absorption

Results:

Orally and dermally low; inhalation negligible

Type:

distribution

Results:

Widely with tendency to shift into fatty tissues

Type:

metabolism

Results:

Intense, therefore any accumulation unlikely

Type:

excretion

Results:

Predominantly unchanged via faeces

Details on absorption:

It is generally accepted that the optimal level of lipophilicity for the transepithelial passage is about Log Kow 3.5 while excessive hydrophoby is expected to result in low intestinal epithelial permeability and in low oral absorption. The lack of dissociation in the range of 0-14 pH supports the assumption that no speciation will influence the fugacity of the submission item. Due to the absence of irritating properties it can be expected that the submission item will not produce any local effects, which could increase the permeability. The assumption of low oral absorption is supported by the absence of subacute rodent toxicity as no difference to the control was observed in two independent studies. Accordingly low dermal absorption is supported by the absence of effects in the acute dermal toxicity study up to 5000 mg/kg bw. Inhalation seems an irrelevant route of exposure due to the negligible vaporization. The formation of any airborne particles is unlikely in the supported uses. In summary orally and dermally low absorption can be expected, while inhalation is considered an irrelevant exposure route.

Details on distribution in tissues:

The molecular weight range of the submission is in a comparatively low range, which is associated with generally wide distribution. The water insolubility in combination with the lack of dissociability will lead to a tendency of partitioning into fatty tissues and organs. Thus wide tissue distribution with tendency to shift into fatty tissues can be assumed.

Details on excretion:

Due to the water insolubility, kidney elimination will play an insignificant role, while unchanged excretion in the faeces seems likely. Only an insignificant fraction is expected to be exhaled due to the low vapour pressure.

Details on metabolites:

Read-across to comparable compounds suggests important metabolization, which is supported by the finding of microbial transformation leading to ready biodegradation. Similar chemicals show low BCF however having high Kow values (see waiving justification for aquatic bioaccumulation). Therefore a high metabolic rate can be expected. The UVCB may undergo a cleavage from activated phospholipases in long-chain alcohols. Alcohols could thereafter be oxidized by the alcohol dehydrogenase to aldehyde and by aldehyde dehydrogenase enzymes to fatty acids. In the liver the fatty acids are expected to be broken down by β-oxidation. This assumption is supported by the OECD QSAR Toolbox version 3.0 results (CATABOL algorithm) for low and high molecular weight representatives of the UVCB, where hydrogenphosphonates and the respective alcohols, aldehydes and carbonic acids were predicted. Therefore intense metabolism seems likely and low half-lives in biota can be expected.

Executive summary:

The basic toxicokinetic behaviour of the test item can be assessed based on the known properties and available toxicity studies of the submission item by applying generally known and accepted principles including QSPR calculation. Physicochemical properties influencing the toxicokinetics are the water insolubility (< 0.1 mg/L), the irrelevantly low vapour pressure (0.00043 Pa at 25 °C), the very high lipophilicity (Log Kow > 9.4), the molecular weight range between 369.25 and 605.5 g/mol and the absence of any dissociation, pH-effects and corrosive or irritant properties. No treatment related changes in the test animals were observed during the 28 d repeated dose subacute toxicity or in the oral reproduction/developmental toxicity study in rats (NOAEL > 1000 mg/kg bw /d) and an acute dermal toxicity test indicating no effects up to 2000 mg/kg bw. The submission item is deemed to show low bioaccumulation in aquatic food chains and was found readily biodegradable.

Absorption: It is generally accepted that the optimal level of lipophilicity for the transepithelial passage is about Log Kow 3.5 while excessive hydrophoby is expected to result in low intestinal epithelial permeability and in low oral absorption. The lack of dissociation in the range of 0-14 pH supports the assumption that no speciation will influence the fugacity of the submission item. Due to the absence of irritating properties it can be expected that the submission item will not produce any local effects, which could increase the permeability. The assumption of low oral absorption is supported by the absence of subacute rodent toxicity as no difference to the control was observed in two independent studies. Accordingly low dermal absorption is supported by the absence of effects in the acute dermal toxicity study up to 2000 mg/kg bw. Inhalation seems an irrelevant route of exposure due to the negligible vaporization. The formation of any airborne particles is unlikely in the supported uses. In summary orally and dermally low absorption can be expected, while inhalation is considered an irrelevant exposure route.

Distribution: The molecular weight range of the submission is in a comparatively low range, which is associated with generally wide distribution. The water insolubility in combination with the lack of dissociability will lead to a tendency of partitioning into fatty tissues and organs. Thus wide tissue distribution with tendency to shift into fatty tissues can be assumed.

Metabolism: Read-across to comparable compounds suggests important metabolization, which is supported by the finding of microbial transformation leading to ready biodegradation. Similar chemicals show low BCF however having high Kow values (see waiving justification for aquatic bioaccumulation). Therefore a high metabolic rate can be expected. The UVCB may undergo a cleavage from activated phospholipases in long-chain alcohols. Alcohols could thereafter be oxidized by the alcohol dehydrogenase to aldehyde and by aldehyde dehydrogenase enzymes to fatty acids. In the liver the fatty acids are expected to be broken down by β-oxidation. This assumption is supported by the OECD QSAR Toolbox version 3.0 results (CATABOL algorithm) for low and high molecular weight representatives of the UVCB, where hydrogenphosphonates and the respective alcohols, aldehydes and carbonic acids were predicted. Therefore intense metabolism seems likely and low half-lives in biota can be expected.

Excretion: Due to the water insolubility, kidney elimination will play an insignificant role, while unchanged excretion in the faeces seems likely.

Reference 2

Endpoint:

dermal absorption

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

Study period:

January 2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Generally accepted equations for the approximation of determinants of dermatological and systemic penetration after topical application (Kp and Jmax) were used.

Justification for type of information:

QSAR prediction: migrated from IUCLID 5.6

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

other: EPA U.S. (2004). Risk Assessment Guidance for Superfund (RAGS), Volume I: Human Health Evaluation Manual (Part E, Supplemental Guidance for Dermal Risk Assessment). Document References EPA/540/R/99/005, OSWER 9285.7-02EP and PB99-963312.

Deviations:

yes

Remarks:

In addition to the guideline generally accepted Jmax estimation and evaluation schemes were used

Principles of method if other than guideline:

The DERMWIN v2.01 software estimates the dermal permeability coefficient (Kp) or skin permeability coefficient, which is a flux value normalized for concentration [cm/h]. It represents the rate at which a chemical penetrates the skin. A general equation for approximation of the value, used in as well in DEREK (rulebase software, Lhasa Ltd) has been published by Potts & Guy (1992). The Kp estimation methodology used in DERMWIN is taken directly from the EPA (2004) document (and supplemental Excel spreadsheet) and represents a minor refinement of the general equation. The estimation methodology in DERMWIN v2.01 is an update of the method and equations used in previous versions of DERMWIN that were based on the EPA (1992) document. A correction of the Kp calculation taking into account the contribution of living skin layers (viable epidermis and dermis) according to Cleek & Bunge (1993) has been proposed for very lipophilic chemicals.
Another determinant of dermatological and systemic penetration after topical application is the dermal delivery or flux of solutes into or through the skin. The maximum dose of a solute able to be delivered over a given period of time and area of application is defined by its dermal maximum flux, Jmax. Kroes et al (2007) demonstrate that Jmax can be derived from the Kp and the water solubility. Magnusson et al (2004) found the molecular weight to be the dominant determinant of Jmax and proposes another estimation method. Jmax should be a constant as long as the chemical is at its maximum thermodynamic activity in the vehicle, i.e. that it is a saturated solution or the pure compound (Kroes et al 2007). Kp and Jmax are derived by these methods and evaluated by the scheme proposed by Kroes et al (2007).
- EPA U.S. Environmental Protection Agency (1992). Dermal Exposure Assessment: Principles and Applications. U.S. EPA Exposure Assessment Group, Office of Health and Environmental Assessment, Washington, DC, U.S.A., Interim Report Self-published January 1992, Document Reference EPA/600/8-91/011B. 389 p.
- EPA U.S. Environmental Protection Agency (2004). Risk Assessment Guidance for Superfund (RAGS), Volume I: Human Health Evaluation Manual (Part E, Supplemental Guidance for Dermal Risk Assessment). U.S. EPA, Office of Superfund Remediation and Technology Innovation, Washington, DC, U.S.A., Self-published July 1994, Document References EPA/540/R/99/005, OSWER 9285.7-02EP and PB99-963312. 156 p. (Available online at: http://www.epa.gov/oswer/riskassessment/ragse/index.htm)

GLP compliance:

no

Absorption in different matrices:

QSPR calculation
Dermal permeability coefficient (Kp):
Equation 1, DERMWIN v2.1: 1.48 to 31.45 cm/h for high and low molecular weight representative structures, respectively
Equation 2, Potts & Guy (1992): 2.62 to 72.51 cm/h for high and low molecular weight representative structures, respectively
Equation 3, Cleek & Bunge (1993): 0.10 to 0.14 cm/h for high and low molecular weight representative structures, respectively - used for Jmax calculation according to Kroes et al (2007).

Dermal maximum flux (Jmax):
Equation 4, Kroes et al (2007): 1.0 to 1.4 pg/(cm²∙h) for high and low molecular weight representative structures, respectively (based on corrected Kp, Cleek & Bunge 1993)
Equation 5, Magnusson et al (2004): 0.62 pg/(cm²∙h) to 11,386 pg/(cm²∙h) for high and low molecular weight representative structures, respectively

Dermal absorption category:
The UVCB clearly falls into the “low” skin absorption category and the worst case default absorbed dose per 24 h can be expected not to exceed 10 % of the neat UVCB.

Resulting dose:
For a standard person (1.75 m body height, 75 kg body weight, 1.84 m² body surface) for 24 h in contact with the pure UVCB on 10 % of his body surface, the absorbed dose would be as low as 0.6 μg/kg bw according to Equation 5 (Kroes et al 2007).

Conclusions:

Estimated dermal permeability coefficient, Kp ca. 0.10 to 0.14 cm/h and dermal maximum flux, Jmax ca. 1.0 to 1.4 pg/(cm²∙h); “low” skin absorption category and worst case absorption rate not exceeding 10 % per 24 h

Executive summary:

To assess on the dermal absorption of the test item generally accepted equations for the approximation of determinants of dermatological and systemic penetration after topical application (Kp and Jmax) were used. The calculations were made with the extrema of the molecular weights (MW) contained.

Three methods were used for the computation of the dermal permeability coefficient (Kp). The dermal maximum flux (Jmax) was estimated on the basis two independent approaches, one starting from the most reliable Kp values and considering water solubility while the second one uses MW as sole determinant.

The calculations suggest that high lipophilicity correction is relevant for the UVCB, which is supported by applicability domain considerations. The accordingly estimated Kp (calculated using Kow and MW) ranges from 0.10 to 0.14 cm/h and the Jmax from 1.0 to 1.4 pg/(cm²∙h) for high and low molecular weight representative structures, respectively. The model using only MW predicts a larger range, whereof the upper extreme value keeps however clearly below 0.1 μg/(cm²∙h), which represents the reference value for categorization.

Considering the Log Kow and MW above 5 and 300 g/mol, respectively, the results clearly place the UVCB in the “low” skin absorption category and the worst case default absorbed dose per 24 h can be expected not to exceed 10 % of the neat UVCB.

Description of key information

Absorption: Orally and dermally low; inhalation negligible
Distribution: Widely with tendency to shift into fatty tissues
Metabolism: Intense, therefore any accumulation unlikely
Excretion: Predominantly unchanged via faeces

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

No experimental data from a toxicokinetic study are available. Therefore the toxicokinetic properties are assessed on the basis of known properties and available toxicity studies of the submission item by applying generally known and accepted principles including QSPR calculation. Physicochemical properties influencing the toxicokinetics are the water insolubility (< 0.1 mg/L, Fox & White 2012, Harlan Report no. 41103263), the irrelevantly low vapour pressure (0.00043 Pa at 25 °C, Tremain & Atwal 2011, Harlan Report no. 41103264), the very high lipophilicity (Log Kow > 9.4, Fox & White 2012, Harlan Report no. 41103263), the molecular weight range between 369.25 and 605.5 g/mol and the absence of any dissociation (waiving argumentation), pH-effects (Flanders 2012, Harlan Report no. 41103491, measured in test media solutions with vehicle) and corrosive or irritant properties (Gabriel 1974, Biosearch Reports on Primary Skin Irritation Study - Rabbits and Report on Primary Eye Irritation - Rabbits). No treatment related changes in the test animals were observed during the 28 d repeated dose subacute toxicity (Dunster & Watson 2012, Harlan Report no. 41103273) or in the oral reproduction/developmental toxicity (Toot 2012, WIL Research Report no. WIL-168198) studies in rats (NOAEL > 1000 mg/kg bw per d in both experiments) and an acute dermal toxicity test (Sanders 2011, Harlan Report no. 41103266) indicating no effects up to 2000 mg/kg bw. The submission item is deemed to show low bioaccumulation in aquatic food chains (waiving argumentation) and was found readily biodegradable (Clarke 2011, Harlan Report no. 41103271).

Absorption: It is generally accepted that the optimal level of lipophilicity for the transepithelial passage is about Log Kow 3.5 while excessive hydrophoby is expected to result in low intestinal epithelial permeability and in low oral absorption. The lack of dissociation in the range of 0-14 pH supports the assumption that no speciation will influence the fugacity of the submission item. Due to the absence of irritating properties it can be expected that the submission item will not produce any local effects, which could increase the permeability. The assumption of low oral absorption is supported by the absence of subacute rodent toxicity as no difference to the control was observed in two independent studies. Accordingly low dermal absorption is supported by the absence of effects in the acute dermal toxicity study up to 2000 mg/kg bw. To quantify the assumed low dermal absorption, generally accepted equations for the approximation of determinants of dermatological and systemic penetration after topical application (i. e. the dermal permeability coefficient Kp and the dermal maximum flux, Jmax) were used to assess the dermal absorption potential of the submission item. The results clearly place the UVCB in the “low” skin absorption category and the worst case default absorbed dose per 24 h can be expected not to exceed 10 % of the neat UVCB. In summary orally and dermally low absorption can be expected. Inhalation seems an irrelevant route of exposure due to the negligible vaporization. The formation of any airborne particles is unlikely in the supported uses. In summary orally and dermally low absorption can be expected, while inhalation is considered an irrelevant exposure route.

Distribution: The molecular weight range of the submission is in a comparatively low range, which is associated with generally wide distribution. The water insolubility in combination with the lack of dissociability will lead to a tendency of partitioning into fatty tissues and organs. Thus wide tissue distribution with tendency to shift into fatty tissues can be assumed.

Metabolism: Read-across to comparable compounds suggests important metabolization, which is supported by the finding of microbial transformation leading to ready biodegradation. Similar chemicals show low BCF however having high Kow values (see waiving justification for aquatic bioaccumulation). Therefore a high metabolic rate can be expected. The UVCB may undergo a cleavage from activated phospholipases in long-chain alcohols. Alcohols could thereafter be oxidized by the alcohol dehydrogenase to aldehyde and by aldehyde dehydrogenase enzymes to fatty acids. In the liver the fatty acids are expected to be broken down by β-oxidation. This assumption is supported by the OECD QSAR Toolbox version 3.0 results (CATABOL algorithm) for low and high molecular weight representatives of the UVCB, where hydrogenphosphonates and the respective alcohols, aldehydes and carbonic acids were predicted. Therefore intense metabolism seems likely and low half-lives in biota can be expected.

Excretion: Due to the water insolubility, kidney elimination will play an insignificant role, while unchanged excretion in the faeces seems likely. Only an insignificant fraction is expected to be exhaled due to the low vapour pressure.