Analyses of ratios of cobalt and nickel between respirable and inhalable dust

Status:

completed 04/2021

Aims:

A dissertation produced at the IFA studying the ratio between inhalable and respirable dust fractions and their constituents in various working areas discussed the possibility of converting values for inhalable dust into those for respirable dust. The dissertation drew upon all 15,120 data records concerning parallel measurements of respirable and inhalable dust available in the MEGA exposure database (measurement data on exposure to hazardous substances at the workplace) as at November 2016. The scope for performing conversions for dust constituents was also discussed during the dissertation project. The data records were comparatively small, numbering 57 and 126 pairs of measured values for cobalt and nickel respectively. Their validity was therefore limited.

Substance-specific information is particularly relevant for the setting of new limit values. For example, a fixed factor for conversion of the cobalt content from respirable to inhalable dust was proposed by Subcommittee III of the AGS Committee for Hazardous Substances during discussion of a new limit. This conversion factor was scrutinized critically with reference to the conversion function presented in the dissertation. In addition, the conversion functions for the nickel content stated in the forthcoming report on nickel and formally recognized (BK) occupational diseases are an important source of support for case managers at the German Social Accident Insurance Institutions.

The principal objective of this project was to develop a method for converting the elemental fractions of cobalt and nickel in inhalable and respirable dust based upon the procedure described in the dissertation. The results are to be published.

Activities/Methods:

In recent years, numerous parallel measurements of respirable and inhalable dust conducted by the metrological services of the German Social Accident Insurance Institutions have also included specific analysis of the metal content. Considerably more data records are therefore now available for analysis than was the case at the end of 2016. In the first step of this project, a fresh analysis was to be carried out with reference to all data records available for the two metals in the MEGA exposure database, including the data available to date from 2020: 1/2020; 645 (Ni), 240 (Co). The results were to be used to update the conversion functions in the dissertation. In addition, a means was to be developed for conversion for discrete, activity-specific, heuristic groups. Following completion of the analyses, the results are to be summarized in the nickel report on formally recognized occupational diseases, and published internationally.

Results:

Parallel measurements of nickel and cobalt for the period from 2011 to 2020 were analysed by means of the SPSS Statistics software application. The new analysis considered 639 parallel measurements for cobalt and 551 for nickel. This significantly larger number of available value pairs enabled activity groups to be created for each substance. Activity-specific (heuristic) groups were also extracted. For cobalt, five activity groups (surface treatment, high temperature processing, filling/transport/sorting/storage, machining/abrasive techniques and forming) and two heuristic groups (welding and grinding) were formed which describe the data record in more detail and reveal improved correlation coefficients (0.860 ≤ R ≤ 0.925). Three activity groups (high temperature processing, filling/transport/sorting/storage and machining/abrasive techniques) and a total of seven activity-selective heuristic groups were formed for nickel. For these heuristic groups, the influence of the abrasive content in particular had to be taken into account for activities involving materials containing nickel.

With one exception, the conversion functions in all groups are power functions exhibiting no linear relationship between the concentrations of the constituent substance arising in the different time fractions. The exception is the welding group, of which the grinding time fraction is < 5%“. Where the grinding time fraction in welding is < 5%, the nickel concentrations are seen to exhibit a linear relationship. During the analyses of the two constituents, the influence of the type of sampling (personal/stationary), the sampling system used and physically impossible values (constituent concentrations at which the content was greater in the respirable dust than in the inhalable dust) upon the measured values was also examined. The type of sampling and the selected sampling system have no influence on the results. Pairs of values in which the concentrations of cobalt or nickel in the inhalable dust fraction were lower than in the respirable dust concentration were not considered in the analysis.

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