Triboron trimethyl hexaoxide

Endpoint summary

Description of key information

TMBX is hydrolytically unstable and breaks down to form methanol and boric acid in the presence of water, these species can be expected to be found in the body fluids and tissues following absorption by any route of administration. Therefore, an assessment of acute toxicity potential was conducted taking account of the hydrolysis breakdown products of TMBX.

Acute oral, dermal and inhalation studies have been performed with boric acid. Experimental data showed low acute toxicity to boric acid. The mean of the male and female values were obtained from the key study (oral route; Keller 1962). The LD50 is equivalent to 658.9 mg B/kg bw.

LD50 values of >2000 mg/kg were recorded for both oral and dermal routes and > 2 mg/L for the acute inhalation study. The highest attainable inhalation concentration was 2.12 mg/L.

Boric acid is of low acute toxicity. Although some of the acute oral studies were not of modern standards and were performed prior to the introduction of GLP, they are reproducible across a number of studies and species and of acceptable quality. For acute dermal and acute inhalation some studies do meet the modern GLP standard.

In rats, LD50 values for methanol after single oral administration range from 1187 to 2769 mg/kg bw, depending on the concentration of the aqueous solution used (BASF 1975, concentrations 15 to 35%, not further specified).

In Rhesus monkeys orally dosed with 6000 mg/kg bw, the retina and the optic papilla showed extended oedema, and the pupils were wide and non-responsive. Six of 8 animals exhibited cystic degeneration of the outer retinal granular layer, and in one animal there was evidence of significant demyelinisation of the optic nerve. Histological lesions were seen in the putamen and nucleus caudatus in 3 of 8 animals. All of these effects were most pronounced after early compensation of acidosis using bicarbonate application, because the monkeys generally did not survive those high doses of methanol but after early treatment with bicarbonate (Potts, 1955; Potts et al., 1955).

There was no evidence of marked acidosis in 12 Rhesus monkeys (28 applications) after sublethal doses up to 6000 mg/kg bw. Specifically, there was no hyperventilation, no increase in urinary excretion of organic acids, or shift in serum bicarbonate. Blindness was seen in only one surviving monkey dosed with 9000 mg/kg bw; the effect was transient four days after exposure. The LD50 was between 7000 and 9000 mg/kg bw (Cooper and Felig, 1961).

Dermal:

Methanol is classified as acute toxic Cat.3 (H301,H311,H331) according to the EU Regulation 1272/2008. Therefore, animal testing regarding acute dermal toxicity is not necessary.

In rabbits, a dermal LD50 of about 17,000 mg/kg bw was found. No further details were reported (Rowe and McCollister, 1981).

 

Human data:

Due to misuse of methanol in the production of alcoholic beverages oral ingestion is the most frequent route of poisoning, death and blindness from methanol. However, there are also case reports from percutaneous absorption or vapor inhalation having elicited the methanol acute toxic syndrome.

A blood level of 500 mg/L methanol in acutely poisoned patients is generally regarded as an indication for hemodialysis. This blood concentration can transiently be achieved in an adult person (70 kg) by ingestion of 0.4 mL methanol/kg bw (Kavet and Nauss, 1990). Generally in humans, transient central nervous system (CNS) effects appear at blood methanol levels of 200 mg/L and serious ocular symptoms appear above 500 mg/L ranging from mild photophobia, misty or blurred vison to markedly reduced visual acuity and total blindness (Kavet and Nauss, 1990; Dethlefs and Naraqi, 1978). Acute methanol intoxication evolves in a well-defined pattern. First, a mild depression of the CNS occurs which is followed by an asymptomatic latent period commonly lasting 12 to 14 hours. Clinical symptoms include headache, dizziness, nausea and vomiting, abdominal pain, and labored, periodic breathing and mag progress to coma and death from respiratory failure (Kavet and Nauss, 1990).

The minimal acute methanol dose to humans that can result in death is considered to be 300 to 1000 mg/kg by ingestion. Fatalities have occurred in untreated patients with initial methanol blood levels in the range of 1500 to 2000 mg/L (IPCS/WHO, 1997). In general, coma, seizures and prolonged acidosis were poor prognostic signs (Naraqi et al., 1979). Such high and potentially lethal blood methanol levels are less likely to be achieved from inhalation exposure. Exposure to 0.26 mg/L methanol for 4 hours was without significant physiologic effects in human volunteers (Muttray et al., 2001).

 

In conclusion, there are two dominating acute effects from methanol: blindness and metabolic acidosis. For the latter, formate is considered to be the ultimate toxicant in acute methanol intoxication in humans. Acidosis and ophthalmologic changes are typical effects in primates. They do not occur in rodents or rabbits, which are able to remove formate more efficiently. In these animals, CNS depression, narcosis and death are the leading symptoms of intoxication. Although the mechanism for optic nerve damage from exposure to methanol has not been established, potential mechanisms and the possible role of formate are discussed in section 5.10.3.

Although the lethal dose of methanol is high for most experimental animals (> 2000 mg/kg bw after single oral administration) these data are not employed for classification. The classification is only based upon the experiences in humans and classifies methanol as acutely toxic by oral, dermal and inhalative exposure and, furthermore, as capable of inducing serious irreversible effects upon single exposure by all of these routes.

Upon hydrolysis TMBX yields 34.1 g of methanol and 65.9g of boric acid per 100g of the parent substance. The oral ATE for TMBX is calculated as 293 mg/kg based upon a converted ATE point estimate of 100 mg/kg bw for methanol (Acute oral category 3). Boric acid is disregarded as the derived LD50 value is above the oral limit does of 2000mg/kg bw.

 

The dermal ATE for TMBX is calculated as 879.8 mg/kg based upon a converted ATE point estimate of 300 mg/kg bw for methanol (Acute dermal category 3). Boric acid is disregarded as the derived LD50 value is above the oral limit does of 2000mg/kg bw.

No inhalation toxicity is expected for TMBX based upon its vapour pressure and the low likelihood of generation of aerosol or droplets during its use.

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study, limited documentation, acceptable for assessment.

Principles of method if other than guideline:

Study performed according to internal company standards (BASF-test) before actual guideline was adopted.

GLP compliance:

no

Test type:

standard acute method

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Route of administration:

oral: gavage

Vehicle:

water

Details on oral exposure:

VEHICLE
- Concentration in vehicle: 15 - 35 %

Doses:

551-1285, 808-1885, 1187-2769 mg/kg bw (corresponding to 15 - 35 % aqueous solution)

No. of animals per sex per dose:

10

Control animals:

not specified

Details on study design:

- Duration of observation period following administration: 7 days

Statistics:

no data

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 1 187 - 2 769 mg/kg bw

Remarks on result:

other: 15 to 35% aqueous solution

Mortality:

No mortality was observed in any dose group.

Clinical signs:

Apathy, staggering, dyspnea, latero-abdominal position, atony, to some extent slight exsiccosis

Body weight:

no data

Gross pathology:

No pathological findings after post-observation period of 7 days.

Other findings:

no data

Reference 2

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

No data

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Meets generally accepted scientific standards with acceptable restrictions.

Qualifier:

according to guideline

Guideline:

other: No data

Deviations:

not specified

Principles of method if other than guideline:

Boric acid was administered orally by gavage to six groups of five male and five female albino Sprague-Dawley rats. The test material was administered as a 50 % w/v suspension in 0.5 % aqueous methyl cellulose at dosage levels of 2.0; 2.5; 3.16; 3.98; 5.01 and 6.31 g/kg bw. Rats were fasted for a period of 3 to 4 h prior to dosage. Animals were observed for mortality and toxic effects at 1, 2, 4, and 24 h and once daily after for a total of 14 days. At teh end of the observation period the surviving animals were weighed sacrificed and autopsies were performed.

GLP compliance:

no

Remarks:

Study pre-dates GLP

Test type:

standard acute method

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: Males: 267 - 302 g; Females: 214 - 248 g

Route of administration:

oral: gavage

Vehicle:

other: 0.5 % aqueous methyl cellulose

Details on oral exposure:

VEHICLE
- Concentration in vehicle: 50 % w/v

MAXIMUM DOSE VOLUME APPLIED: 3450 - 4080 mg/kg bw

Doses:

2.0; 2.5; 3.16; 3.98; 5.01 and 6.31 g/kg bw.

No. of animals per sex per dose:

Five animals/group; no further data

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days
- Necropsy of survivors performed: Yes
- Other examinations performed: Clinical signs

Statistics:

Litchfield and Wilcoxon

Sex:

male

Dose descriptor:

LD50

Effect level:

3 450 mg/kg bw

Based on:

test mat.

95% CL:

2 950 - 4 040

Remarks on result:

other: mg boric acid/kg

Sex:

female

Dose descriptor:

LD50

Effect level:

4 080 mg/kg bw

Based on:

test mat.

95% CL:

3 640 - 4 560

Remarks on result:

other: mg boric acid/kg bw

Mortality:

No data

Clinical signs:

Symptoms include sings of CNS depression, ataxia, convulsions, laboured breathing or rapid respiration; blood crust around nose, marked diarrhoea and ptosis.

Body weight:

No data

Gross pathology:

Autopsies indicated congestion of lungs, kidneys and adrenals; inflammation of the pyloric portion of stomach and small intestine.

Other findings:

No data

Interpretation of results:

GHS criteria not met

Conclusions:

The acute oral LD50 of boric acid for male albino rats was 3450 (2950 - 4040) mg boric acid/kg, equivalent to 604 mg B/kg bw. In female albino rats the acute oral LD50 of boric acid was 4080 (3640 - 4560) mg boric acid/kg, equivalent to 714 mg B/kg bw.

Reference 3

Endpoint:

acute toxicity: oral

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

Methanol is classified as acute toxic Cat.3 (H301,H311,H331) according to the EU Regulation 1272/2008. Therefore, animal testing regarding acute oral toxicity is not necessary. In addition, rodent models are not suitable for assessing the huamn toxicity of methanol. Further informaiton on the human toxicity of methanol is presented in section 7.10.3.

Reason / purpose for cross-reference:

data waiving: supporting information

Reason / purpose for cross-reference:

data waiving: supporting information

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

293 mg/kg bw

Acute toxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Acute toxicity: via dermal route

Link to relevant study records

Reference

Reference 1

Endpoint:

acute toxicity: dermal

Type of information:

experimental study

Adequacy of study:

key study

Study period:

No data

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline study.

Qualifier:

according to guideline

Guideline:

other: FIFRA (40 CFR 163)

Deviations:

no

GLP compliance:

no

Remarks:

Study pre-dates GLP

Test type:

fixed dose procedure

Limit test:

yes

Species:

rabbit

Strain:

New Zealand White

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan F. Plummer
- Weight at study initiation: 1623 - 2922 g

Type of coverage:

semiocclusive

Vehicle:

physiological saline

Details on dermal exposure:

TEST SITE
- Area of exposure: The skin of all animals was abraded longitudinally every 2 - 3 cm, deep enough to penetrate the stratum corneum, but not cause bleeding.
- % coverage: > 10 % of body surface implied
- Type of wrap if used: Semi occlusive


REMOVAL OF TEST SUBSTANCE
- Washing (if done): Moist towel
- Time after start of exposure: 24 h


TEST MATERIAL
- For solids, paste formed: Yes


VEHICLE
- Amount applied: Substance moistened with 1.5 mL saline

Duration of exposure:

24 h

Doses:

Dosage to 2 g/kg

No. of animals per sex per dose:

5/sex/group

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days
- Necropsy of survivors performed: Yes
- Other examinations performed: Clinical signs, histopathology

Statistics:

Not applicable - limit test.

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 2 000 mg/kg bw

Based on:

test mat.

Mortality:

No deaths occurred

Clinical signs:

Clinical changes were limited to transient diarrhoea in 2 rabbits and some incidences of erythema (9), and oedema (30), atonia (2), desquamation (4), necrosis, and other evidence of irritation at 23 and ~70.5 h after treatment.

Body weight:

No data

Gross pathology:

No gross necrospy findings were observed. Observations included one animal with gas filled intestine, one animal with pale yellow-coloured kidneys and 5 animals with enlarged or swollen fallopian tubes.

Other findings:

No data

Gross necropsy findings in male and female rabbits at the end of the observation period:

Gross Necropsy Findings	Dosage at 2 g/kg
Number of animals necropsied	10
No gross necropsy findings	5
Intestine
Gas-filled	1
Kidneys
Pale yellow coloured	1
Fallopian tubes
Enlarged or swollen	4
Pale	1
External
Diarrhoea stains	1

Interpretation of results:

not classified

Conclusions:

The study was performed according to FIFRA (40 CFR 163). The LD50 > 2000 mg/kg bw indicating no acute dermal toxicity. No deaths occurred. Clinical changes were limited to erythema, oedema, atonia, desquamation, necrosis and some incidences of skin irritation at more than 24 h of treatment.

Reference 2

Endpoint:

acute toxicity: dermal

Data waiving:

other justification

Justification for data waiving:

other:

Justification for type of information:

Methanol is classified as acute toxic Cat.3 (H301,H311,H331) according to the EU Regulation 1272/2008. Therefore, animal testing regarding acute dermal toxicity is not necessary. In addition, rodent models are not suitable for assessing the huamn toxicity of methanol

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

879.8 mg/kg bw

Justification for classification or non-classification

Upon hydrolysis TMBX yields 34.1 g of methanol and 65.9g of boric acid per 100g of the parent substance. The oral ATE for TMBX is calculated as 293 mg/kg based upon a converted ATE point estimate of 100 mg/kg bw for methanol (Acute oral category 3). Boric acid is disregarded as the derived LD50 value is above the oral limit does of 2000mg/kg bw.

 

The dermal ATE for TMBX is calculated as 879.8 mg/kg based upon a converted ATE point estimate of 300 mg/kg bw for methanol (Acute dermal category 3). Boric acid is disregarded as the derived LD50 value is above the oral limit does of 2000mg/kg bw.

No inhalation toxicity is expected for TMBX based upon its vapour pressure and the low likelihood of generation of aerosol or droplets during its use.

The resulting classification for TMBX according to the criteria set out in 1272/2008/EC is acute toxicity category 3 (oral , dermal) H301 H311.

In addition, based upon the proportion of methanol (>10g/100g TMBX) expected to yield from the gastic hydrolysis following oral exposure, the classification of Single Target organ toxicity -Single exposure Category 1 should be assigned to TMBX for the affected organs optic nerve and central nervous system.