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Neurotoxicity

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Description of key information

The findings in a neutrotoxicological screening battery performed as part of the 90-day repeat oral dose study with ammoniumm bromide indicates that effects observed are probably reversible as evidenced in the four week recovery period at doses ≥225 mg/kg bw/day in both sexes.
Studies with sodium bromide give an NOAEL = 80 mg/kg bw/day (equivalent to 62.1 mg (Br-) /kg bw/day).

Key value for chemical safety assessment

Effect on neurotoxicity: via oral route

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEL
80 mg/kg bw/day

Additional information

Sodium bromide is an inorganic salt that dissociates to its composite ions in aqueous solutions at environmental pH and temperature. Comparison of the available data on the various bromide salts have shown that the bromide ion is the relevant ion for determination of the toxicological profile with simple cations such as potassium, sodium or ammonium, that are ubiquitous in nature, having little or no influence on the bromide ion properties. It is therefore justified to read-across data from other inorganic bromide salts to sodium bromide.

A neurotoxicologigal screening battery was performed as part of the 90 -day repeat oral dose study (Barton et al 2007) on ammonium bromide. The findings noted during the detailed neurotoxicity examination (included viability, clinical signs, detailed functional observations) consisted of increased limpness, decreased alertness, increases in landing foot splay and decreases in fore and hind limb grip strength. At the low dose (100 mg/kg bw/day) the findings were limited to slight limpness in 3 males; of these, only one showed the finding on more than one occasion. Functional alterations were noted in both sexes at ≥225 mg/kg bw/day. All of these effects had reversed following the 4 week recovery period, except for hind limb grip strength in females at 750 mg/kg bw/day. It was considered that all neurotoxicological effects were probably reversible.

Sodium bromide neurotoxicity in the mouse.

Motility was increased and evasion time decreased upon administration of sodium bromide while treadmill activity was decreased. Bodyweight decreases were noted for the highest three dose groups.

Multivariate analysis of all 11 variables measured indicate that no significant effects were noted for the 400 ppm dose group while for the 1200 ppm dose group significant changes were noted at a small range of time points. Higher dosages gave clear and statistically significant changes in many variables over a larger range of time points, both during and after sodium bromide administration. The effect limit based on behavioural variables and body weight therefore lies between 400 and 1200 ppm sodium bromidein mice.

Sodium bromide neurotoxicity in the rat.

The criterion of errors shows a positive relationship between the number of errors and the strength of the bromide-dosage. The criterion of time shows that the 120 mg/kg bw/day group which received the largest dose of bromide was significantly slower than each of the other groups but the other groups did not differ among themselves. All groups reached the same level of performance before the 25thday of the test. The fact suggested that in the maze-test the deleterious effects of the bromide appear in the rate of learning rather than in the performance finally attained.

 LOAEL: 120 mg/kg bw/day - significantly slower navigation of the maze for rats (equivalent to 93.1 mg (Br-)/kg bw/day)

NOAEL: 80 mg/kg bw/day (equivalent to 62.1 mg (Br-) /kg bw/day)

Justification for classification or non-classification

Based on a NOAEL of 80 mg/kg bw/day, Sodium bromide is not classified as neurotoxic.

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