Module 4: Metals And The Lung - Lecture (Continued)

AIRWAYS DISEASE:

Chronic obstructive pulmonary disease (COPD):

Chronic airways diseases are very common in the general population, which makes the diagnosis of occupational causation difficult. Tobacco smoking is the most common cause in the population and there is little if anything to separate effects due to tobacco from those due to occupational exposures.

The most common form of COPD is cough and phlegm (chronic bronchitis) which may occur without airflow obstruction (also known now as COPD stage 0). Once there is chronic airflow obstruction, the condition is COPD proper (stages 1 onwards).

Occupational COPD is about to become a compensatable condition under COIDA, and the responsibility will be on occupational medical practitioners to know the literature and to be able to make an informed diagnosis.

Cough and phlegm with or without lung function loss is a non-specific response to a variety of intermittent or chronic irritant exposures in industry. Population studies, including in South Africa, show an association between both chronic bronchitis and symptoms of airways obstruction and "having ever been exposed to dust, fumes, vapours or strong smells".

With regard to metal exposures, for example, in welders and in iron and steel workers, the literature (mostly cross-sectional studies) is consistent in showing an increase in cough and phlegm but less so in demonstrating lung function loss.

Emphysema:

Emphysema, a subset of COPD, is mainly a smoking disease and is not a common occupational disease. Of the metals, cadmium is reported as being capable of causing emphysema.

Asthma:

The best documented metallic cause of asthma is platinum salts, particularly in South Africa with its large and growing platinum mining and refining sector. The antigenic form is a complex salt of platinum produced in the refining, not the mining, process.

The mechanism of the asthma is via IgE production, which means that a skin prick test (or RAST) can be used in screening for platinum hypersensitivity (even before symptoms occur).

Local experience shows that a large proportion of the refinery workforce becomes sensitised and/or develops symptoms of platinum salt sensitivity - 41% within the first 24 months in one study. Smoking increases the risk of sensitisation. The longer the exposure persists after the onset of asthma, the less likely is the asthma to reverse after exposure ceases.

Other metals causing occupational asthma are cobalt, nickel and chromium. (Note that nickel and chromium are very common causes of allergic contact dermatitis, but via a different mechanism from that of asthma).

Chrome asthma is due the hexavalent form (chromium VI). Exposure may occur in situations where the chrome exposure is apparent, for example chrome plating, or in settings not specifically associated with chrome use, such as in stainless steel welding and construction (chromates in cement).

"Potroom asthma", occurring in aluminium smelters, is another condition of relevance in South Africa, because of the two smelters at Richard's Bay and another one possibly to be built at Coega. This form of asthma is thought not to be due to aluminium, but to the fluorides used in the process.

Vanadium is used for hardening steel and as a colouring agent. Vanadium is mined in South Africa at Steelpoort in Mpumalanga, in a complex process that produces various forms of vanadium, of which vanadium pentoxide dust is an important exposure. Vanadium is known to be a respiratory tract irritant, but a recent study at the South African plant suggests that it is also a cause also of occupational asthma. (Irsigler et al. S Afr Med J 1999; 35:366-374).

Occupational asthma due to metals is reported fairly frequently to SORDSA, including that due to platinum, vanadium, chrome and nickel and hard metal. Welding fumes is another category of exposure in which metals may be involved in causation of occupational asthma.