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Description of key information

The test substance did not cause immunotoxic effects in a reliable subacute oral study.

Key value for chemical safety assessment

Effect on immunotoxicity: via oral route

Link to relevant study records
immunotoxicity: short-term oral
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
17 October 2011 - 25 January 2012
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study
equivalent or similar to guideline
EPA OPPTS 870.7800
GLP compliance:
Limit test:
Route of administration:
oral: feed
Duration of treatment / exposure:
28 days
Frequency of treatment:
Dose / conc.:
4 000 ppm
Dose / conc.:
1 250 ppm
Dose / conc.:
400 ppm
No. of animals per sex per dose:
Control animals:
Trifloxysulfuron sodium administered ad libitum in the diet for up to 28 consecutive days to female B6C3F1 mice at dose levels of 400, 1250, and 4000 ppm resulted in a no-observed-effect-level (NOEL) for both the AFC assay (humoral immune response) and the NKC assay (innate immune response) of 4000 ppm (equivalent to 1066.6 mg/kg of body weight/day), the highest dose level evaluated.
Executive summary:

The test substance, trifloxysulfuron sodium (hereafter referred to as trifloxysulfuron), was offered ad libitum in the diet for up to 28 consecutive days to female B6C3F1 mice in Groups 2, 3, and 4 at dietary concentrations of 400, 1250, and 4000 ppm, respectively.
Ten mice/group (Subset A) were used for the splenic Antibody-Forming Cell (AFC) assay and 10 mice/group (Subset B) were used for the Natural Killer Cell (NKC) assay. Mice in the AFC positive control group (Group 5A) were administered the positive control substance, cyclophosphamide (CPS), via intraperitoneal injection (50 mg/kg/day) once daily for 4 consecutive days (study days 24 through 27). All AFC group mice (Groups 1A-5A) were immunized with an intravenous injection of sheep red blood cells (sRBC) on study day 24.
Mice in the NKC positive control group (Group 6B) were administered the positive control substance, anti asialo GM1, via a single intravenous injection (0.2 mL/animal) on study day 27, approximately 24 hours prior to the scheduled necropsy. The concurrent control groups (Groups 1A and 1B) and the positive control groups (Groups 5A and 6B) were offered the basal diet on a comparable regimen to the trifloxysulfuron-treated groups. All animals were euthanized on study day 28.

All animals were observed twice daily for mortality and moribundity. Clinical examinations were performed once daily for all animals. Detailed physical examinations were performed approximately weekly, and on the day of the scheduled necropsy. Individual body weights and food consumption were recorded approximately twice weekly. Complete necropsies were conducted on all animals. The liver, mesenteric lymph node, Peyer’s patches, spleen, and thymus were collected from all AFC- and NKC-designated animals at the scheduled necropsy, and the liver and spleen were weighed. In addition, the thymus was weighed from all NKC-designated animals. Spleens were placed in Earle’s Balanced Salt Solution (EBSS)/HEPES buffer and shipped to ImmunoTox®, Inc. After arrival at ImmunoTox®, Inc., spleen cell suspensions were prepared, spleen cell counts were performed, and the number of specific IgM antibody forming cells directed towards the sRBC antigen were determined for the AFC-designated animals to measure the humoral immune response using the splenic AFC assay. In addition, ImmunoTox®, Inc., personnel prepared the spleens from the NKC-designated animals to measure innate immunity using the NKC assay.

Mean achieved test substance consumption in the 0, 400, 1250, and 4000 ppm groups were 0.0, 94.8, 324.4, and 1066.6 mg/kg of body weight/day, respectively, over the entire 28-day study.
All animals survived to the scheduled necropsy. There were no trifloxysulfuron-related clinical observations, macroscopic findings, or effects on body weights, food consumption, or organ weights. There were no trifloxysulfuron-related effects on spleen cell numbers.
Trifloxysulfuron did not significantly suppress the humoral immune response when evaluated as either specific activity (AFC/106 spleen cells) or as total activity (AFC/spleen) of splenic IgM to the T-cell dependent antigen sRBC, and there were no trifloxysulfuron-related effects on NKC functional activity.
For the AFC positive control group, CPS, statistically significantly lower spleen weight, spleen cell numbers, specific activity, and total spleen activity of IgM antibody-forming cells were noted when compared to the vehicle control group. These effects were consistent with the known immunosuppressant effects of CPS and validated the functionality of the assay.
For the NKC positive control group, anti asialo GM1, statistically significantly lower
NKC activity at all effector:target ratios, except for the 6.25:1 effector:target ratio, were noted when compared to the vehicle control group. This effect was consistent with the known effects of anti asialo GM1 on NKC activity, which validated the functionality of the NKC assay.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
1 066.6 mg/kg bw/day
Study duration:

Effect on immunotoxicity: via inhalation route

Endpoint conclusion
Endpoint conclusion:
no study available

Effect on immunotoxicity: via dermal route

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

Justification for classification or non-classification