N,N'-ethylenebis[N-acetylacetamide]

Endpoint summary

Description of key information

The repeated dose toxicity of TAED in the rat  has been evaluated following the oral, dermal and inhalation exposure route.  A NOAEL of 90 mg/kg bw/d was deduced from the 90-day oral gavage studies. The NOAEL in the 90-d dermal toxicity study was 2000 mg/kg bw/d. 90-day repeated exposure by inhalation to TAED dust at doses up to 99.7 mg/m³ did not cause any adverse effects in the rat lung, respiratory tract or nasal mucosa. 

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEL

90 mg/kg bw/day

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEL

2 000 mg/kg bw/day

Additional information

Repeated dose toxicity after oral administration of TAED

Subchronic oral toxicity was evaluated in groups of 10 male and 10 female Sprague-Dawley rats receiving TAED by gavage at daily dose levels of 0, 90, 250 and 800 mg/kg bw/d for 90 days (Potokar et al., 1987). A recovery control and high dose group consisting of 5 male and 5 female rats was terminated 28 days after the 90 day treatment period.

Mortality did not occur. Salivation observed in the animals of the high dose group was the only clinical finding. Water consumption was increased in males of the 250 and 800 mg/kg bw/d group and in all female test groups, whereas food consumption was not affected. Total body weight gain was decreased in male and female rats of all high dose groups. Slightly decreased haematocrit values in all male test groups and an increase in leukocytes in females of the high dose were observed. Changes in biochemical parameters considered to be compound-related comprised increased protein values in male and female rats of the high dose group and increased cholesterol values in female animals treated with 800 mg/kg bw/d. Eye examination revealed no compound related findings. At the dose level of 250 mg/kg bw/d relative liver and testes weights were significantly increased in male rats. At 800 mg/kg bw/d absolute and relative liver weights of both sexes and relative adrenal and testes weights in male rats were statistically significantly increased. No compound related macroscopically visible findings were present at necropsy. Histopathological examination revealed centrilobular hypertrophy of hepatocytes in all high dose animals. This effect reversed completely within the 28 day recovery period. In the animals of the low and mid dose group centrilobular hypertrophy was borderline in some rats and not considered a clear substance related effect, since this finding was also present in some control animals of the recovery group.

Substance related adverse effects occurred at the dose level of 800 mg/kg bw/d. The increased water consumption and increased relative testis weight without histopathological correlate seen at 250 mg/kg bw/d represent non-adverse effects. As increased liver weight in conjunction with centrilobular hypertrophy was found at this dose level, a conservative NOAEL of 90 mg/kg bw/d was derived from the study, even though the liver effects were reversible and can be interpreted as a consequence of metabolic adaptation not representing a clear adverse effect. The liver was determined to be the target organ based on changes in organ weight and microscopic pathology.

 

In a further 90-d oral toxicity study TAED was given to rats at dose levels of 0, 25, 500 and 1000 mg/kg bw/d (Wolfe and Borst, 2000). The spacing factor of 20 between low and mid dose represents a methodological flaw limiting the reliability of the study.

All animals survived and no treatment related clinical signs were noted. Biologically relevant body weight decrease (>10% and not within the normal range for rats of this age and strain) was seen at 500 and 1000 mg/kg bw/d and correlated with a decreased food consumption. Changes in clinical pathology parameters were of no clinical significance.

The liver was determined to be the target organ. An increase in absolute and relative liver weights was noted in the high and mid dose males and/or females accompanied centrilobular cytomegaly.

The study author did only derive NOELs and LOELs. However, a LOAEL of 500 mg/kg bw/d and a NOAEL of 25 mg/kg bw/d can be deduced for males and females based on microscopic changes in the liver and biologically relevant body weight decrease at 500 and 1000 mg/kg bw/d.

The NOAEL of 25 mg/kg bw/d is a result of the very wide spacing between the mid and low dose level. Given the adverse effects observed at 500 mg/kg bw/d it can be assumed that a higher NOAEL would have been obtained with a Guideline conform dose spacing.

In an 28-d oral gavage study in rats (Ullmann et al., 1989) the liver was also determined to be the target organ. A NOAEL of 200 mg/kg bw/d was derived based on pathological evidence for hepatic effects (hepatocellular hypertrophy) and on significant reductions on food consumption and body weights at the dose level of 1000 mg/kg bw/d.

 

Repeated dose toxicity after dermal administration of TAED

TAED when administered to Sprague-Dawley rats once daily for six hours to the skin by dermal application for 90 days at dose levels of 0, 20, 200, and 2000 mg/kg bw/d resulted in minimal centrilobular hypertrophy (cytomegaly) in 8/10 and 4/10 males and females, respectively, at the high-dose only (Wolfe and Okoth, 2000). The hypertrophy was not in conjunction with an increased liver weight. No other treatment-related findings were noted. Based on the effects in this study the NOEL is equal to or greater than 200 mg/kg bw/d.

The NOEL is a result of the large spacing factor of 10 between the high and mid dose level. Given that the centrilobular hypertrophy seen in 60 % of the animals dosed at 2000 mg/kg bw/d was of minimal severity, did not result in an increased liver weight, was fully reversible and represents an adaptive response, an actual NOEL close to 2000 mg/kg bw/d can be assumed and an NOAEL of 2000 mg/kg bw/d can be deduced from this study. This is supported by the theoretical dermal NOAEL of 2093 mg/kg bw/d which can be calculated from the oral NOAEL of 90 mg/kg bw/d taking into account the oral bioavailability of 100 % and the dermal penetration rate of 4.3 % for rat skin.

 

Repeated dose toxicity after inhalation of TAED

In a subacute inhalation toxicity study no adverse effects were found when 10 male and 10 female Wistar rats were exposed in inhalation chambers to TAED dust for 23 consecutive working days, 5 hours/day, at a mean TAED concentration of 283 mg/m³ (Pittermann, 1980).

 

In a subchronic inhalation study groups of 12 male rats were exposed in inhalation chambers to mean concentrations of TAED dust (< 3.5 µm) of 0, 12.2, 60.3 and 99.7 mg/m³ for 6 hours a day, 5 days a week, for 13 weeks (HERA members, 2002). A 13-week recovery group was included.

Mortality did not occur. The changes noted in some haematological and clinical chemical parameters were of no clinical significance. There were statistically significant increases in absolute and relative liver (all dose groups) and kidney weights (high and mid dose group) accompanied by centrilobular hypertrophy and eosinophilic droplets in the kidney composed of the normal male rat urinary protein alpha-2µ-globulin. All effects reversed completely during the 13-week recovery period.

A NOAEL for systemic effects could not be derived from this study as the whole body of the animals was exposed to TAED dust and the oral ingestion of unquantifiable amounts of substance would have occurred due to grooming.

Under the conditions of this study, repeated exposure by inhalation to TAED dust at doses up to 99.7 mg/m³ did not cause any adverse effects in the rat lung, respiratory tract or nasal mucosa.

Repeated dose toxicity: via oral route - systemic effects (target organ) digestive: liver

Repeated dose toxicity: dermal - systemic effects (target organ) digestive: liver

Justification for classification or non-classification

Repeated dose oral studies revealed that TAED reduces body weigh gain and causes reversible centrilobular hypertrophy in the liver at doses higher than 90 mg/kg bw/d due to the induction of metabolizing enzymes. This effect was also found in a 13-week whole body inhalation study. No adverse effects in the rat lung, respiratory tract or nasal mucosa were observed. Upon repeated dermal administration the same systemic effect of centrilobular hypertrophy was observed, however only at the highest dose tested (2000 mg/kg bw/d) and minimal in degree of severity.Based on these data, TAED is not subject to classification and labelling to Directive 67/548/EEC and Regulation 1272/2008/EC regarding repeated dose toxicity or target organ toxicity.