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Endpoint:
additional toxicological information
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Meets generally accepted scientific standards, well documented and acceptable for publication.

Data source

Reference
Reference Type:
publication
Title:
Nickel release from nickel particles in artificial sweat.
Author:
Midander K, Pan J, Wallinder IO, Heim K, Leygraf C.
Year:
2007
Bibliographic source:
Contact Dermatitis 56:325-330.

Materials and methods

Type of study / information:
Nickel levels and rates of nickel release from fine nickel powder particles immersed in artificial sweat.
Test guideline
Qualifier:
equivalent or similar to
Guideline:
other: The artificial sweat solution used for metal release immersion tests was prepared similar to EN1811.
Deviations:
yes
Principles of method if other than guideline:
The aim of this paper was to assess the amount of nickel released from nickel powder particles immersed in artificial sweat in order to simulate an occupational exposure scenario with nickel particles in contact with human skin as far as practicable. A worst-case scenario was created by measuring nickel release from a relatively small particle-sized (high surface area) nickel powder, in a relatively large volume of artificial sweat, during time periods relevant for an occupational scenario. The effect of particle loading and the time-dependent release process were studied and analyzed, in particular, with respect to specific surface area.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): nickel powder
- Substance type: commercially available Inco 123 nickel powder provided by Nickel Producers Environmental Research Association (NiPERA)
- Physical state: powder
- Other: particle size was 3-7 micrometers according to the material safety data sheet.
- Other: specific surface area was measured to be 0.43 square meters per gram by the Canadian Center for Mineral and Energy Technology (CANMET) using Brunauer Emmett Teller (BET) analysis.

Results and discussion

Any other information on results incl. tables

Particle loading had a significant influence on the released nickel concentration, though no linear correlation existed between the particle loading and the released amount of nickel.

  • At a given test volume, nickel release increased with increasing particle loading.
  • For the lowest particle loadings (I-IV), released nickel reached an almost steady-state concentration after 8 -12 hrs of immersion, although no steady-state condition was reached for the highest particle loading (V).
  • The highest particle loading, V (5 mg/cm2), resulted in a released concentration of 0.025 mg/mL after 12 hours of immersion, whereas a lower amount of particles, e.g. 5 times lower, III (1 mg/cm2), resulted in a concentration of 0.009 mg/mL, i.e. 64% lower compared to the highest loading.

Table 2. Released nickel from different particle loadings expressed in terms of concentration, amount of nickel released per bottom surface area of the test vessel and amount of nickel released per surface area of the loaded particles after 12 hours immersion in artificial sweat.

Particle loading   I  II  III  IV  V
 Ni concentration (mg/ml)  0.00041 +/- 0.00014  0.0027 +/- 0.00004  0.009 +/- 0.00034  0.02037 +/- 0.00031 0.02533 +/- 0.00031 
 Ni released bottom area test vessel (mg/cm2)  0.00021 +/- 0.00007  0.00136 +/- 0.00002  0.00452 +/- 0.00017  0.01023 +/- 0.00015  0.01273 +/- 0.00015
 Ni released particles surface area (mg/cm2)  0.00048 +/- 0.00017  0.00061 +/- 0.00004  0.00101 +/- 0.00003  0.00081 +/- 0.00001  0.0006 +/-0.00001

The released fraction of the total amount of nickel per total amount of nickel loaded showed no straightforward tendencies related to particle loading.

  • The three highest particle loadings (III-V) show an inverse behavior compared to observations of the nickel concentrations, with the lowest released fraction of nickel for the highest particle loading.
  • For most immersion time intervals, the lowest particle loading (I) resulted in a higher released fraction than the second lowest (II) and the highest particle loading (V).
  • Less than 0.5% of the total amount of loaded nickel was released into the solution for all nickel particle loadings studied.

Generally, the nickel release rate is initially high and decreases with time, reaching a relative steady-state level of 0.1 ug/cm2/hour or less for all particle loadings investigated.

  • Loading III (1 mg/cm2) showed the highest release rate throughout the immersion period, in particular during the first hour of immersion.
  • The end-point, in terms of total amount of released nickel, after 12 hours of immersion, clearly shows the range of nickel release from the different particle loadings.
  • The difference in total amount of released nickel is more than 60 times between the lowest (I) and the highest (V) loading.

XPS analysis: Oxygen and oxidized nickel was detected in the outermost surface layer on as-received nickel particles, indicative of a nickel oxide surface layer. In addition, the metallic nickel peak was observed, which implied a relatively thin (a few nanometers) surface oxide layer. The immersion in artificial sweat leads to a slight growth of the oxide film and a possible formation of hydroxides/oxy-hydroxides. No other contaminants or adsorbed species from the test medium were detected on the surface of the nickel powder.

Applicant's summary and conclusion

Conclusions:
The authors concluded that the study results can be used in the risk assessment process for direct and prolonged exposure to nickel metal powder, as may be found in certain occupational scenarios (e.g. nickel-producing and nickel-using facilities). The nickel release data can be used to estimate the amount of released nickel available for a given measured dermal exposure to nickel metal powder. This value can then be compared with the dermal nickel elicitation threshold to determine the risk of dermal nickel allergic contact dermatitis in nickel-sensitized individuals in that specific workplace.
Executive summary:

Study rated by an independent reviewer.