Zinc sulphide

Endpoint summary

Description of key information

Non-human information
The repeated dose toxicity of water soluble zinc sulphate and zinc monoglycerolate has been examined in a total of 3 subchronic oral feeding studies. Due to the different dosing regimens, the lowest NOAEL was determined to be 31.5 mg/kg bw/day of zinc monoglycerolate which equals a total zinc exposure of approximate 13 mg/kg bw/day. The zinc NOAEL derived from the feeding studies with zinc sulphate was determined to be 104 mg Zn/kg bw/day in mice and approximately 53.5 mg/kg bw/day in rats. At higher doses the most important effects in the rats were the development of hypocupremia, and significant changes in the pancreas (i.e., focal acinar degeneration and necrosis) and a decreased number of pigmented macrophages in spleen.
No longer term inhalation studies allowing to derive a robust NOEL for the inhalatory exposure of the respective zinc compounds has been identified. In a short term 3-day inhalation study with guinea pigs, a concentration of 2.3 mg ultrafine ZnO/m3 (3 hours/day) resulted in changes in neutrophils and activities of lactate dehydrogenase and alkaline phosphatase in the pulmonary fluid. At higher concentrations increased protein concentration, neutrophils, and enzyme activities in lung lavage fluids were seen, together with significant centriacinar inflammation of the pulmonary tissue. Inhalatory doses of 2.7 mg ultrafine ZnO/m3 for 5 days 3hours/day did not alter the lung function parameters in guinea pigs, but at 5 and 7 mg ultrafine ZnO/m3 exposure according to a similar pattern, a gradual decrease in total lung capacity, vital capacity and reduction of the carbon monoxide diffusing capacity was seen in combination with inflammatory changes and edema. The relevance of the findings in studies with ultra-fine zinc oxide fumes is unclear with respect to commercial grade zinc oxide, as the latter is of much larger particle size and can have different toxicological characteristics.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEL

13.3 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEC

2.7 mg/m³

Study duration:

subacute

Species:

guinea pig

Additional information

The biological activities of zinc compounds are determined by their ability to release zinc under the respective exposure conditions. Hence, information on the effects of systemically available zinc allows the repeated dose toxicity assessment across all those zinc compounds covered in this safety report.

Non-human information

The repeated dose toxicity of water soluble zinc sulphate and zinc monoglycerolate has been examined in a total of 3 subchronic oral feeding studies. Due to the different dosing regimens, the lowest NOAEL was determined to be 31.5 mg/kg bw/day of zinc monoglycerolate which equals a total zinc exposure of approximate 13 mg/kg bw/day. The zinc NOAEL derived from the feeding studies with zinc sulphate was determined to be 104 mg Zn/kg bw/day in mice and approximately 53.5 mg/kg bw/day in rats. At higher doses the most important effects in the rats were the development of hypocupremia, and significant changes in the pancreas (i.e., focal acinar degeneration and necrosis) and a decreased number of pigmented macrophages in spleen.

No longer term inhalation studies allowing to derive a robust NOEL for the inhalatory exposure of the respective zinc compounds has been identified. In a short term 3-day inhalation study with guinea pigs, a concentration of 2.3 mg ultrafine ZnO/m³(3 hours/day) resulted in changes in neutrophils and activities of lactate dehydrogenase and alkaline phosphatase in the pulmonary fluid. At higher concentrations increased protein concentration, neutrophils, and enzyme activities in lung lavage fluids were seen, together with significant centriacinar inflammation of the pulmonary tissue. Inhalatory doses of 2.7 mg ultrafine ZnO/m³for 5 days 3hours/day did not alter the lung function parameters in guinea pigs, but at 5 and 7 mg ultrafine ZnO/m³exposure according to a similar pattern, a gradual decrease in total lung capacity, vital capacity and reduction of the carbon monoxide diffusing capacity was seen in combination with inflammatory changes and edema. The relevance of the findings in studies with ultra-fine zinc oxide fumes is unclear with respect to commercial grade zinc oxide, as the latter is of much larger particle size and can have different toxicological characteristics.

Human information

Upon supplementing men and women with 150 mg Zn/day (as zinc sulphate capsules), women appeared to be more sensitive than men to the effects of high zinc intake: clinical signs such as headache, nausea and gastric discomfort were more frequent among women and women but not men had decreased activities of serum ceruloplasmin and ESOD. In some earlier oral studies in which humans were supplemented with moderately high amounts of zinc (50 mg Zn/day), a reduction in ESOD activity was also observed and again women appeared to be more sensitive to this effect. Hence, a reduction in ESOD was thought to be a sensitive indicator of copper status. However, in more recent and more sophisticated studies using the same dose level, ESOD was only marginally reduced (without a correlation with changes in copper balance), while findings on more specific copper deprivation signs (decreased serum ceruloplasmin and platelet cytochrome c oxidase) indicated that a sub-optimal intake of zinc was more effective than a moderately high intake of zinc in inducing changes associated with a decreased copper status in postmenopausal women. Given this, and the degree of the observed ESOD reduction in comparison to the natural variability in its activity, the zinc-induced decrease in ESOD activity is considered to have marginal biological significance, if any and also because it may not have been caused by an interference with copper metabolism as deep tissue SOD increases as a function of zinc exposure was observed.

Overall, it can be concluded that from studies in which humans were supplemented with zinc (as zinc gluconate), that women are more sensitive to the effects of high zinc intake and that a dose of 50 mg Zn/day is the human NOAEL. This equals a daily exposure of 0.83 mg/kg bw. At the LOAEL of 150 mg Zn/day, clinical signs and indications for disturbance of copper homeostasis have been observed.

Repeated dose toxicity: via oral route - systemic effects (target organ) cardiovascular / hematological: other; digestive: pancreas

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

Justification for classification or non-classification

Zinc is essential for human growth and development, neurological functions and immunocompetence. The main clinical manifestations of zinc deficiency are growth retardation, delay in sexual maturation or increased susceptibility to infections (SCF, 2003). Health specialists recommend supplementing the diet with zinc in case human diet is zinc deficient. The maximum allowable daily intake has been established to be 50 mg zinc per day. Hence no classification is required.