1,3,5-trioxane

Endpoint summary

Description of key information

In a 90 day gavage study (OECD 408) no adverse signs of toxicity were observed in rats treated in the highest tested dose level (NOAEL 300 mg/kg bw/day). 
In a 2 week inhalation study with rats signs of respiratory irritation were observed in all exposure group. Though no signs of systemic toxicity were observed. 

Key value for chemical safety assessment

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEC

3.62 mg/m³

Study duration:

subacute

Species:

rat

Additional information

Oral application:

In a 90 day oral study, rats were gavaged with trioxane dose levels of 30, 100, 300 mg/kg bw/day (RCC, 2002). The assay was performed according to the current OECD 408 guideline including recovery animals in the high and control dose. According to the guideline this study included a detailed macroscopic and microscopic analysis of all reproductive organs and endocrine glands (e.g. ovaries, testes, seminal vesicles).

No adverse signs of toxicity were observed in the highest tested dose level and therefore the NOAEL was identified as 300 mg/kg bw/day. Reticulocyte changes identified in high dose males were interpreted as an early sign of reduced erythropoiesis. Slight disturbance in iron metabolism was suggested by the lower spleen weights seen in high dose males. The mean spleen-to-body weight ratio was unchanged. Both effects were reversible at the end of the 4-week recovery periodand not interpreted as adverse.

In a 28-day study, doses of 40, 200, 1000 mg/kg bw/day were gavaged to rats (OECD Guideline 407). A NOAEL of 200 mg/kg bw (LOAEL 1000 mg/kg bw) was derived based on decreased leucocyte counts and alterations of clinical chemical parameters (e.g. increase in gamma-GT, decrease of glucose) (Hoechst AG, 1990). It should be emphazised that this value represents a very conservative NOAEL, since the adverse character of these effects is arguable. Reduction of absolute but not relative spleen weights was observed in high dose males and absolute and relative spleen weights in mid dose females. Due to lack of dose response, this effect was disregarded.  

 

The quality of study reporting and study performance of two older 2-year chronic exposure experiments in rats and cats was not according to current standards. Here both studies are reported for completness but their value for an assessment is limited.

Albino rats of mixed strains were administered trioxane at 200 or 870 mg/kg bw day in males and 310 or 1400 mg/kg bw day in females in daily feed for 104 weeks (Hoechst AG, 1966).

Non-neoplastic effects in rats were not considered to be treatment-related, since they appeared to affect the control and treated groups to a similar extent and incidence. No clear dose-response trends could be established in rats dying prematurely or in those sacrificed at study termination. Therefore the NOAEL in rats was determined to be 870 mg/kg/day in males and 1400 mg/kg/day in females (highest dose tested).

The NOAEL for cats was reported to be 22 mg/kg bw/day in males and 23 mg/kg bw/day in females (no test substance related findings in highest and single dose tested).

 

In 2 further oral repeated dose studies female rats were exposed to 190, 580 and 1160 mg/kg bw/day for 7 weeks (Sitarek and Baranski, 1990) and male rats to 850, 1700 mg/kg bw/day for 8 weeks (Baranski, 1984).

Reversible behavioral changes in the high dose and a dose- and time-dependent decrease in body weight gain were observed in all treated groups in the experiment with female rats. In the experiment with males, body weight gain was decreased and absolute and relative weights of liver, kidney and spermatic vesicle were increased. Histopathology of the testes revealed a dose dependent focal necrosis of the seminiferous epithelium. Additionally in females the oestrous cycle was significantly longer than in the control animals. This observation was reversible and was only observed in the high dose group in parallel to severe signs of maternal toxicity. Since reporting is limited and no data concerning significance or correlation to other parameters e.g. food uptake were provided, the value of these studies is very limited.

Repeated dose toxicity inhalation:

In a 2 week inhalation study, rats were whole body exposed to vapor concentrations of 0.38, 3.62 or 18.18 mg/l (Bio/Dynamics Inc., 1983). The test performance was according to current OECD-guideline 412 and the test atmosphere was verified analytically.

Signs of respiratory irritation (e.g. increased secretory responses) were observed in all exposure groups. In the high dose group respiratory impairment and histopathologically squamous metaplasia with necrosis and desquamation of the mucosa of the anterior nasal cavity was observed. Due to this reversible effect restricted to the upper respiratory tract, trioxane was legally classified as a respiratory irritant (R37, C&L 2002). According to GHS this would indicate classification as STOT_singlecategory 3 (H335, may cause respiratory irritation) (see acute toxicity).

For respiratory irritation a local LOAEC of 0.38 mg/l can be determined.

Decreased relative spleen weights were observed in all dose groups (in low dose only in males), though due to the lack of histopathology and absolute values in the study report no conclusion on the relevance of this observation can be made. 

Further signs of systemic toxicity were observed in the high dose group only (18.18 mg/l):

·       slight decrease of mean bw (13%)

·       changes in hematological parameters (e.g. increased hemoglobin, hematocrit and erythrocyte counts, decreased leucocyte counts),

·       changes in clinical chemical parameters (e.g. increase in serum GPT, total protein and albumin, decrease in glucose).

Based on these effects a systemic NOAEC of 3.62 mg/l can be determined. The adverse character of this effects is questionable and may, at least partly, be due to primary irritation of the respiratory tract.

 

Additional repeated dose studies are of such poor quality that they can not serve for a further refinement of the NOAEC. At the most the NOAEC_localfor respiratory irritation can be confirmed by an inhalation study with rats exposed to vapors of 0.05, 0.5 and 2.5 mg/l (Czajkowska and Krysiak, 1983). Signs of respiratory tract irritation (e.g. increased lymphocyte infiltration, tissue proliferation, metaplasia) were observed at the high dose level.

 

When comparing the 28-day key studies for both tested exposure routes (oral, inhalation), a good correlation in terms of target organ toxicity (e.g. hematopoetic system) was observed. Although, no severe sign of toxicity were identified which would result in a classification according to EU or GHS guidance.

 

 

Repeated dose toxicity: inhalation - systemic effects (target organ) respiratory: nose

Justification for classification or non-classification

According to Directive 67/548/EEC and Directive 1272/2008, no classification for systemic effects is indicated for the oral and inhalation route of exposure. For inhalation exposure signs of respiratory irritation require classification as a respiratory tract irritant (R37, C&L 2002). According to GHS this would indicate classification as STOT_singlecategory 3 (H335, may cause respiratory irritation).