Dermal nickel exposure associated with coin handling and in various occupational settings: assessment using a newly developed finger immersion method

Abstract

The role of nickel in causing hand dermatitis in some occupations has been difficult to assess due to problems with reliable measurement of the exposure to nickel in the workplace and lack of a definitive threshold for nickel allergic contact dermatitis. It is not uncommon to find nickel allergy on patch testing but it is difficult to determine whether this is of relevance to occupational nickel exposure or simply a reflection of past exposure to nickel-plated jewellery or other nonoccupational nickel exposure. To devise a simple and reproducible method to quantify the amount of nickel on the skin and to apply the technique to measure dermal nickel exposure in various occupational settings. A rapid and simple sampling procedure was developed for determination of nickel on the skin of workers potentially exposed to nickel by exposing individuals to nickel-releasing coins and measuring exposure by immersing the exposed thumbs and index fingers directly into graduated sample tubes containing ultrapure water and aqueous nickel extracts. The solutions were analysed by inductively coupled plasma-optical emission spectrometry after stabilization with nitric acid. The method shows advantages over alternatives such as wipe testing and tape stripping in terms of extraction efficiency, speed and ease of operation in the field. A pilot survey of dermal nickel exposure for workers in several occupational settings was conducted. The study suggested that a 'normal' level of nickel on the skin is <10 ng cm(-2). Coin handling induced an appreciable increase in the amount of nickel on the skin within 2 min. Experiments indicated a linear relationship between coin handling (exposure time) and measured dermal nickel levels following standardized coin handling. A pilot survey, conducted among cashiers, shop assistants, bar staff, hairdressers and workers in the nickel industry revealed dermal nickel concentrations ranging from <0.9 to 7160 ng cm(-2). The levels of nickel on the skin of cashiers, shop assistants, bar staff and hairdressers were below the threshold level for water-soluble ionic nickel for occluded exposure at which 10% of nickel-allergic subjects react (0.01% or 100 parts per million, equivalent to 530 ng cm(-2)) and the five-times higher threshold for unoccluded exposure (500 parts per million). The levels in some nickel platers and nickel refinery workers approached or exceeded these levels. However, few cases of nickel dermatitis are observed in plating and refinery facilities, perhaps due to immune tolerance, self-selection or, for refinery workers, exposure to water-insoluble rather than water-soluble nickel compounds. The elicitation threshold for water-soluble nickel compounds cannot be compared directly with dermal exposure to water-insoluble nickel compounds as the latter release a significantly lesser amount of nickel ions. We describe a reproducible, simple and rapid procedure for the assessment of nickel levels in occupationally exposed individuals.