A retrospective analysis of nickel exposure data at a South African base metal refinery

Abstract

Background: Nickel compounds are classified as a known human carcinogen causing lung and nasal cancer and nickel is a common cause of allergic contact dermatitis. Refinery workers in base metal refineries are occupationally exposed to soluble nickel and controlling nickel exposure is, therefore, essential. Control measures improved over time and consequently resulted in trends in soluble nickel exposure, which can be identified with a retrospective analysis of the exposure data. Aims and objectives: This study aimed to analyse soluble nickel exposure data from a South African base metal refinery in order to identify trends in the exposure data during 1982 until 2014 in two tankhouses (i.e. Copper and Nickel Tankhouse). Furthermore, it aimed to identify specific trends in soluble nickel exposure within the sections inside the tankhouses and occupations, and to determine the number of excursions above the Time Weighted Average, Occupational Exposure Limit (TWA-OEL) for each of the different sections, as well as the different occupations. Finally, the effect of process changes on soluble nickel exposure was evaluated in both tankhouses. Methods: Soluble nickel exposure data from two tankhouses (i.e. Copper and Nickel Tankhouse) of the base metal refinery were obtained and grouped into area and personal measurements. Exposure data were presented in an exposure matrix, which described exposure profiles for each of the pre-determined categories (sections inside tankhouses: Centre, East, West bays, North and South end, Contractor’s tea room, Overhead crane and occupation categories: Cell worker, Crane driver, Supervisor, Miscellaneous activities) independently. One-way analyses of variances (ANOVA) were conducted to identify significant differences in exposures over time, and the trends were illustrated with linear regression graphs. Differences between sections inside the tankhouses as well as the different occupations were furthermore evaluated with Honest Significant Difference (HSD) Tukey tests, and the percentage of measurements above the TWA-OEL (0.1 mg/m3) set by the Mine Health and Safety Act (MHSA) were calculated. Results: Significant downward trends (p ≤ 0.0001) were identified in area exposure data in the Copper Tankhouse between 1982 and 2011. Area exposure in the Copper Tankhouse decreased with a factor of 29 between 1982 and 1986. However, after 1986 no significant downward trend was identified in area exposure. Furthermore, personal exposure decreased with a factor of three between 1991 and 2014 in the Copper Tankhouse, consequently, significant downward trends were identified in personal exposure (p ≤ 0.0001). An eight-fold reduction in soluble nickel exposure of Cell workers and Crane drivers were identified, while a significant increase (p ≤ 0.05) in exposure were identified for Supervisors when exposure increased with a factor of seven between 2001 and 2010. No significant trends were identified in area and personal exposure in the Nickel Tankhouse. Exposures measured for the Miscellaneous category and Supervisors were significantly different (p ≤ 0.05) from Cell workers and Crane drivers. The highest percentage of OEL exceedances were determined for Cell workers (Copper Tankhouse, 64%; Nickel Tankhouse, 32%) and Crane drivers (Copper Tankhouse, 64%; Nickel Tankhouse, 19%), if Supervisors in the Nickel Tankhouse with limited measurements were not taken into account. The substantial decrease in area soluble nickel exposure (1982 – 1986) can be attributed to the polypropylene bead which were increased inside the electrowinning cells in 1986, and recent significant decreases in personal exposure in the Copper Tankhouse can be attributed to the movement of nickel production to the Nickel Tankhouse during 2009. Conclusion: Significant downward trends in soluble nickel exposure inside the Copper Tankhouse were identified and may be ascribed to the implementation of various control measures and process changes. No exposure trend was established in the Nickel Tankhouse, as only four years of exposure data were available. A comprehensive exposure assessment is recommended to establish accurate exposure profiles for categories in which high soluble nickel exposure was identified (i.e. Supervisors and Contractor’s tea room). Furthermore, six measurements, quarterly, per occupation are recommended, due to the significant differences between the occupations. Finally, due to the carcinogenic effects of nickel compounds it is recommended to control exposure to the lowest possible level