Bis(2-butoxyethyl) ether

Endpoint summary

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

Weight of evidence approach is applied to derive the skin sensitization potential of DEGDBE. The applied method comprise

a) LLNA on DEGDBE and assessment on the reliability

b) In-vitro data on DEGDBE

c) Skin sensitization of DEGDBE by grouping of DEGDBE with other structurally related glycol ethers

d) Conclusion

Each method will be separately discussed.

a) LLNA on DEGDBE and assessment on the reliability

DEGDBE was investigated for its sensitization potential by use of LLNA. The SI > 3 was obtained. However, in the supplementory experiment, it could be demonstrated that the red blood cell count was reduced in mice that were treated according to the dosing scheme of LLNA.

Attributable to the treatment method, it can be assumed:

- the regional exposure burden near to the draining lymph node must be significantly higher, especially shortly after the treatment;

- the regional level of damaged red blood cells could be significantly higher.

Removal of senescent and damaged red blood cells occurs by spleen and lymph nodes. The question arisen from the findings in the LLNA with DEGDBE is that whether a regionally increased level of damaged red blood cells could be associated with regional lymph node activation. With respect to this question two relevant experiments were found in the literature:

- Oehmichen M. et al., 1982:

Rabbits were treated with autologous red blood cells intracerebrally and the time dependency of red blood cell degradation in the brain as well as in the cervical lymph nodes was investigated.

In the brain tissue at the injection site no significant extracellular degradation of the red blood cells was observed. Within 24 hours after treatment the neutrophilic leukocytes, monocytes and erythrophages began to increase. Fourth day onwards, active digestion of red blood cells could be observed. Erythrophages disappeared ca. 30 days after treatment. 

Severe cervical lymph node swelling occurred shortly after treatment. In the cervical lymph nodes free red blood cells and/or phagocytes containing red blood cells or cell debris were found. The findings of histologic investigation indicate that non-phagocytized red blood cells arriving at the lymph nodes were ingested rapidly by lymph node macrophages.

Neither red blood cells nor hemosiderin were demonstrated in the inguinal lymph nodes after treatment, confirming the regional lymph node activation as the primary degradation mechanism of regionally applied autologous red blood cells.

- Simon G.T. et al., 1975:

Rats were intramuscularly treated with autogenic and xenogenic red blood cells and the red blood cell degradation in spleen and diverse lymph nodes in the body were investigated with electron microscopy and immunoferritin technique.

Five minutes after the intramuscular injection, red blood cells appeared focally in the nearby draining lymph node, where they were phagocytized and degraded rapidly. No changes were found in spleen and mesenteric- and axillary lymph nodes. 

Both autogenic and xenogenic red blood cells were phagocytized by lymph node macrophages indiscriminately. For autogenic red blood cells the affected lymph nodes returned to normal in two days, while for xenogenic red blood cells further morphological changes could be observed.

In likewise manner, it can be concluded that the regional treatment with DEGDBE may be associated with regionally elevated level of damaged red blood cells and regional lymph node activation.

In conclusion, it is likely that the increased lymph node weight and enhanced cell-proliferation in the draining lymph node in LLNA with DEGDBE is the consequence of hemolytic activity of DEGDBE. The findings in LLNA may not reflect the true skin sensitization potential of DEGDBE.

b) In-vitro data on DEGDBE

In-vitro skin sensitization test (BASF Project No.:64V0555/12A277)

A combination of several in vitro methods addressing key steps of the adverse outcome pathway was conducted to assess the skin sensitizing potential of DEGDBE.

protein reactivity (DPRA; BASR Project No.: 64V0555/12A274)

activation of keratinocytes (LuSens; BASR Project No.: 64V0555/12A276)

activation of dendritic cells (MUSST; BASR Project No.: 64V0555/12A275) .

The tests were performed as described in Bauch et al. 2012. The results of the individual studies are summarized in Table 2. No effect was found in DPRA and MUSST, whereas enhanced activation for keratinocytes was found. Based on the validated weight of evidence approach1, the study director assessed DEGDBE as a no skin sensitizer.

 

Table 2: Results obtained in in-vitro skin sensitization tests.
Test method	Test result	Test evaluation
Protein reactivity (DPRA)	no significant effect	negative
Keratinocte activation assay (LuSens)	significant LuSens activation	positive
Dendritic cell line activation assay (MUSST)	no significant effect	negative

c) Skin sensitization of DEGDBE by grouping of DEGDBE with other structurally related glycol ethers

c1) Category approach justification:

The skin sensitization potential of DEGDBE is to be assessed by read-across consideration. Three structurally related glycol ethers are identified as suitable surrogates. Together with DEGDBE, a category building is proposed to increase the robustness of the read-across consideration.

c1-1) Category members and chemical structures: the similarity in their structure is given by presence of butoxylated ethylene glycol at terminal position (Butyl-O-CH₂-O-).

Ethylene glycol butyl ether (EGBE)* CAS 111-76-2	Butyl-O-CH2-OH
Diethylene glycol butyl ether (DEGBE)* CAS 112-34-5	Butyl-O-CH2-O-CH2-OH
Diethylene glycol dibutyl ether (DEGDBE)** CAS 112-73-2	Butyl-O- CH2-O-CH2-O-Butyl
Polyethylene glycol dibutyl ether (PolyEGDBE)*** CAS 31885-97-9	Butyl-O- CH2-O-CH2-O-CH2-O-Butyl

* EGBE and DEGBE are extensively investigated substances and reviews on their toxicity profiles are available in public domain (i.e. EU Risk Assessment Report, 2-Butoxyethanol (EGBE), CAS 111 -76 -2, 2008; Opinion on Diethylene Glycol Monobutyl Ether (DEGBE), SCCP/1043/06, 2006). **target chemical. ***Clariant own data, details provides in corresponding endpoint sutdy record.

c1-2) The proposed grouping is justified by the common mode of action, namely systemic exposure to 2-butoxyacetic acid (2-BAA) and/or butoxyethoxyacetic acid (BEAA):

EGBE: 2-BAA is the major urinary metabolite (summarized in EU risk assessment, 2008)

- DEGBE: BEAA is the major urinary metabolite (Deisinger et al. 1989)

- DEGDBE: in 28-day study (Clariant own data) the urinary 2-BAA determination was incorporated; 750 mg/kg bw external dose level corresponded to 1400 mg/L 2-BAA in urine.

- PolyEGDBE: no experimental data is available; BEAA and/or 2-BAA as metabolite can be reasonably assumed due to the observed RBC reduction.

c1 -3) The proposed grouping is justified by the comparable toxicity profiles, which reflects the toxicity action of 2-BAA and/or BEAA. Both metabolites are known to induce hemolysis (Udden 2002; Udden 2005).

- EGBE: hemolytic action demonstrated in acute and repeated dose toxicity studies (summarized in EU risk assessment, 2008)

- DEGBE: i.e. in 2 and 13 week oral toxicity studies (Johnson et al. 2005)

- DEGDBE: in 28-day study (Clariant own data) RBC reduction and hematuria was evident.

- PolyEGDBE: in dose-range finding study for OECD 422 (Clariant own data), RBC reduction was evident.

c2) Skin sensitization potential of DEGDBE based on read-across

No significant skin sensitization potential can be assigned based on grouping of DEGDBE and structurally related glycol ethers, which includes DEGDBE (target chemical), EGBE (CAS 111 -76 -2), DEGBE (112 -34 -5), and PolyEGDBE (31885 -97 -9).

The data availability on each members are as shown in the table.

Table: Data availability for the endpoint skin sensitizing
Category members	Test methods
	Human repeated insult patch test	Guinea Pig maximization test	Local lymph node assay	In-vitro tests comprising three key steps of adverse outcome pathway
EGBE	negative	negative	-	-
DEGBE	-	-	positive	negative
DEGDBE	-	negative	-	-
PolyEGDBE	-	-	negative	-

d) Conclusion on the skin sensitization potential of DEGDBE

The justification for the evaluation of the result of LLNA for DEGDBE as " not reliable" is provided. The approach to assess the skin sensitization potential for DEGDBE based on the in-vitro day and on the grouping of substances is considered to be sufficiently reliable. Therefore, DEGDBE is considered to be of low sensitization potential .

Based on the weight of evidence approach using the dicussions provided under a), b) and c), the DEGDBE is considered to be a non-skin sensitizer.

Migrated from Short description of key information:
No significant skin sensitization potential can be assigned for DEGDBE.

Justification for selection of skin sensitisation endpoint:
Weight of evidence approach is used. The data set comprises one LLNA and a battery of in-vitro studies for DEGDBE and five studies for three read-across supporting substances.

Justification for classification or non-classification

DEGDBE is a non-skin sensitizer based on the weight of evidence approach. The data used for the evaluation comprises studies on DEGDBE as well as studies on read-across substances. Further mechanistical consideration was applied to assess the reliability of the existing data on DEGDBE.

No classification is warranted.