The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has evaluated boric acid and tetraborates. Available publications are described in detail.
MAK values for boric acid and tetraborates of 10 mg boric acid/m3 I (1.8 mg boron/m3) or 5 mg disodium tetraborate pentahydrate/m3 I (0.75 mg boron/m3; also valid for other tetraborates and their hydrates) were established on the basis of the acute irritation effect to the respiratory tract. Additionally a potentially relevant systemic effect is a possible reproductive damage (effect on male fertility and embryotoxicity), only to be expected at concentrations above about 30 mg boron/m3. Exposures at such high levels have not been described even under worst case occupational hygienic conditions.
Due to the main local irritant effect the biological threshold values can only be derived from a correlation with the air concentration. There is a quantitatively comparable relationship between the total boron intake and its urinary excretion. The boron excretion caused by background exposure is subject to considerable variations, therefore the occupational exposure is obtained from the difference in boron excretion between post‐shift and pre‐shift urine. From this, for an exposure at the level of the MAK values, 8.5 mg boron/g creatinine is obtained as shift increment for urinary boron excretion in the case of boric acid and 4 mg boron/g creatinine in the case of borates. These values refer to the individually determined difference between the boron concentration in post‐shift and pre‐shift urine. Owing to the fact that local irritation is the main effect and that there is no systemic toxicity at this concentration, no biological tolerance value (BAT value) was derived.