IN-DEPTH REVIEW |
Concerns for asthma at pre-placement assessment and health surveillance in platinum refining—a personal approach
41 Blackhorse Lane, Hitchin, Hertfordshire SG4 9EG, UK
Correspondence to: Peter J. Linnett, 41 Blackhorse Lane, Hitchin, Hertfordshire SG4 9EG, UK. Tel: +44 1462433095; e-mail: peterj.linnett{at}btinternet.com
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Abstract |
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 Top Abstract IntroductionPre-placement considerationsPre-placement medical...Mechanism of allergy to...SurveillanceFrequency of monitoringSummaryConflicts of interestReferences |
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Platinum, a noble metal, is inert in the body and has an important use in medical applications. It is used in autocatalysts to control harmful vehicular emissions and the catalytic effects improve efficiencies of pharmaceutical and petrochemical processes. The refining process involves exposure to halogeno complex salts of platinum which are potent allergens. They induce symptoms typical of a type I allergy, the most significant of which is asthma. Platinum refining not only exposes employees to the risk of sensitization to these salts but also to respiratory irritants. Inhalation of these aggravates pre-existing asthma. The increasing incidence of asthma in the community requires that prospective employees for platinum refining be assessed carefully to establish their respiratory health status in relation to the risk of sensitization or aggravation of pre-existing asthma. Routine medical surveillance has been shown to reduce persistence of asthma in sensitized workers who cease exposure to the platinum salts upon diagnosis. Skin prick test using dilute platinum salt solutions can detect sensitization at an early stage and this has become the mainstay of surveillance programmes as it is objective and reproducible as well as predictive for the development of symptoms when exposure is allowed to continue. Symptoms are not sensitive or specific. Smoking is a significant risk factor.
Keywords Medical surveillance; occupational asthma; platinum refining; platinum salts
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Introduction |
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TopAbstractIntroductionPre-placement considerationsPre-placement medical...Mechanism of allergy to...SurveillanceFrequency of monitoringSummaryConflicts of interestReferences |
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Platinum, being inert in biological media, has widespread uses in medical applications, e.g. stents, and by its catalytic properties makes a valuable contribution to the control of vehicular emissions, thereby reducing the particulates and respiratory irritants released into the environment. The platinum group metals (PGM) which include palladium, rhodium, iridium, ruthenium and osmium are noble metals and refining is performed by a chemical process which initially requires that they be dissolved in concentrated acids before further treatment by which they are separated from each other and purified. The medium in which this occurs is aggressive and difficult to contain and the problems of containment may be aggravated by the catalytic effect of these metals.
The acid used for dissolution of the PGMs is either aqua regia, a mix of concentrated nitric and hydrochloric acids, or concentrated hydrochloric acid through which a stream of chlorine is passed. This process produces a halogeno complex salt of platinum. The final stage of refining is precipitation of platinum as ammonium hexachloroplatinate which undergoes thermal reduction to produce a metallic sponge. The halogeno complex salts of platinum are extremely potent allergens and the risk of sensitization has been high, being in the range of 25–90% [1–4]. This is a marked contrast from experience with non-halogenated complex salts which have been tolerated at a similar level of exposure without sensitization [1].
Apart from the exposure dose [4] an important risk factor is smoking which conveys a relative risk of 
5 [1–4]. Atopy, as demonstrated by a positive skin prick test reaction to common aeroallergens, while excluding subjects with a history of asthma or eczema, was reported to carry a relative risk of 2 (2.29, CI 0.88–5.99) [2] but in recent years this has not shown to hold (personal observation). Other genetic factors have been described [5].
The work environment necessarily includes a number of respiratory irritants including chlorine, hydrochloric acid and ammonia. Many other hazardous substances may be present and these can aggravate pre-existing asthma even though exposure is controlled below current workplace exposure limits.
Occupational asthma (OA) due to platinum salts is a reportable disease but the scale of the industry in UK and the medical surveillance programmes are such that, though several cases of sensitization are detected each year, there are very few cases of OA reported. However, the rationale for the surveillance programme does provide a model which may have application to other industries which have similar challenges. The approach to medical surveillance of workers exposed to platinum salts has been described [6,7] and this paper provides an update and justification for the recommendations.
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Pre-placement considerations |
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TopAbstractIntroductionPre-placement considerationsPre-placement medical...Mechanism of allergy to...SurveillanceFrequency of monitoringSummaryConflicts of interestReferences |
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Pre-placement medical examination is concerned with identifying pre-existing respiratory disease particularly asthma, which may be aggravated both by the work exposures and the risk of sensitization. Eczema or other dermal conditions are also aggravated by the work environment and increase the risk of sensitization.
In the past, the policy was that atopic subjects should not be employed where there was a high risk of sensitization, though smokers were employed. This policy has been reversed and atopics are employed, though smokers are not knowingly recruited to work where there is significant exposure to chloroplatinates and the consequent risk of sensitization to the platinum salts is high. In this context the cumulative risk of sensitization is still significant over the first 5 years of employment. This policy requires an honest response from the applicant who must understand the risk and consequence of dishonesty. If there is doubt, a smokerlyzer test will be performed but this is only useful if the subject has smoked recently. Determination of cotinine levels in urine would be a more accurate test. The studies do not show how long the relative risk continues after cessation of smoking. There are probably several factors involved and when smokers quit in order to be considered for employment, they are required to demonstrate that they are non-smoking, without nicotine replacement for 3 months, as this also gives time to show that the habit has stopped.
When atopics, as demonstrated by skin prick test, were excluded from employment, most of those with asthma and eczema were excluded but now, with the change in policy, there is a risk of accepting asthmatics into the workplace where they face both the risk of sensitization and OA, as well as aggravation of their asthma from inhalation of respiratory irritants.
With the increasing incidence of asthma in the community it has become necessary to explore the circumstances and history of this diagnosis and this has to be considered in relation to the risk assessment for the work to be performed. The following describe most of the situations that occur and the action taken.
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Pre-placement medical questionnaire and examination |
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TopAbstractIntroductionPre-placement considerationsPre-placement medical...Mechanism of allergy to...SurveillanceFrequency of monitoringSummaryConflicts of interestReferences |
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In a general health questionnaire the applicants are asked if they have ever had asthma, allergies, eczema or dermatitis. In addition, at the medical examination direct questions are asked, viz:
Have you ever had tightness in your chest or difficulty in breathing during exercise?
Have you ever had a wheeze or whistling in your chest during exercise?
Have you ever had tightness in your chest or difficulty in breathing in freezing cold air during a winter night?
Have you ever had wheeze or whistling in your chest when breathing in freezing cold air during a winter night?
Have you ever used an inhaler?If anyone admits to symptoms of allergic rhinitis, further questions are asked to check whether there are any asthma symptoms directly associated with inhaling the allergen and also to detect if there is an increase in non-specific bronchial hyper-responsiveness which may be apparent on inhalation of cold air or after exercise for a short time after the allergen exposure.
The following considerations apply in deciding on the suitability for employment in platinum refining:
- (i) Persistent asthma on treatment is not acceptable.
- (ii) Childhood asthma with no recurrence since early teens still has a 25% likelihood of recurrence. If the applicant is young, in his/her early 20s, and has no experience of working in an industrial environment with respiratory irritants, the risk is considered unacceptable. However, if the applicant is much older, in his/her late 30s or older, and has been able to tolerate other industrial environments, the risk of reactivating asthma is assumed to be much lower and this is acceptable.
- (iii) If there has been a very occasional wheeze which has not needed medical attention and is associated with high allergen levels, e.g. only during a bad hay-fever season, then this is acceptable.
- (iv) If there has been an occasional wheeze, not more than once a year, which only occurs after coryza or viral infection, does not persist for >2 or 3 days and has not required medication, and there are no symptoms of bronchial hyper-responsiveness, this is acceptable if spirometry is normal.
- (ii) Childhood asthma with no recurrence since early teens still has a 25% likelihood of recurrence. If the applicant is young, in his/her early 20s, and has no experience of working in an industrial environment with respiratory irritants, the risk is considered unacceptable. However, if the applicant is much older, in his/her late 30s or older, and has been able to tolerate other industrial environments, the risk of reactivating asthma is assumed to be much lower and this is acceptable.
Skin prick test with chloroplatinates is done to ensure a baseline negative status at commencement of employment. Sensitization cannot occur in the absence of exposure but in the past some applicants have been found to have been sensitized during their post-graduate university work, or may have been sensitized by work in other platinum refineries.
Spirometry is performed to European Respiratory Society standards. Acceptable values are not more than 2 residual standard deviations below the European Coal and Steel Community predicted values for forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1) (1 l). FEV1 to FVC ratio should exceed 70%. We do not normally test after use of a bronchodilator.
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Mechanism of allergy to platinum salts |
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TopAbstractIntroductionPre-placement considerationsPre-placement medical...Mechanism of allergy to...SurveillanceFrequency of monitoringSummaryConflicts of interestReferences |
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Allergy to complex salts of platinum was well described by Hunter et al. [8] and the mechanism investigated by Pepys et al. [9,10]. It is a type I allergy with immediate reaction to inhalation or contact with the complex halogeno salts of platinum which in the workplace are almost all chloroplatinates. The allergenic potential of the platinum compounds is related to the number of leaving halide ions in the platinum complex [11]. Complex platinum salts are soluble in dilute hydrochloric acid but not all soluble platinum compounds are allergenic; thus, the workplace exposure limit (WEL) which applies to these has a specific entry in EH40/2005 for ‘halogeno-platinum compounds’ (complex co-ordination compounds in which the platinum atom is directly co-ordinated to halide groups) which includes an entry as ‘sensitizer’, thus differentiating these compounds from other soluble platinum compounds though both groups have a similar WEL of 0.002 mg/m3.
Skin prick test reactivity with dilute solutions of chloroplatinates correlates well with symptoms and provocation tests [9]. The skin prick test is objective, reproducible and quantifiable and thus is an essential part of the surveillance routine.
When exposure to platinum salts continues at the same level which has resulted in sensitization, a positive skin prick test is 100% predictive for the development of symptoms [4].
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Surveillance |
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TopAbstractIntroductionPre-placement considerationsPre-placement medical...Mechanism of allergy to...SurveillanceFrequency of monitoringSummaryConflicts of interestReferences |
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Four follow-up studies have demonstrated the benefit of early identification of sensitization to the platinum salts. In a platinum refinery in the UK, surveillance was performed at 3-month intervals and all cases of sensitization ceased exposure on diagnosis. Follow-up studies were conducted 1 and 2 years later demonstrating a reversion of skin test reactivity in sensitized subjects and no difference in spirometry on exercise or cold air inhalation in comparison with a group of workers who had a similar duration of exposure but who remained unsensitized [12]. In a South African study where workers only ceased exposure when symptoms were admitted, which in some cases was up to a year after sensitization had been demonstrated by a positive skin prick test,
10% of the subjects continued to have demonstrable asthma when seen 1 and 2 years later [13]. A prospective study in Germany during which surveillance was performed initially after 6 months and then annually showed a decline in skin test reactivity and symptoms on follow-up of sensitized cases [14]. A study in the USA at a facility that did not have routine medical surveillance showed that asthma could continue for as much as 5 years after cessation of exposure in a significant number of workers who admitted they had asthma for as long as 5 years before being tested and ceasing exposure [15]. There are three main components in the medical surveillance: skin prick test, enquiry for symptoms and spirometry.
The skin prick test reaction using chloroplatinates is objective and reproducible. It is specific and, in the absence of symptoms, it is predictive for the development of the allergy. Skin prick testing using serial dilutions can demonstrate increasing or decreasing sensitivity and for sensitized cases can indicate if control of exposure is effective.
Symptoms elicited at routine surveillance are not specific and not sensitive. In a prospective study in which a modification of the Medical Research Council questionnaire was administered every 3 months, the questions which correlated best with the allergy were (R. J. Dowdeswell, personal communication):
Since your last examination has your chest felt tight or your breathing been difficult? Has your chest sounded wheezy or whistling?When someone does present with allergic symptoms, then enquiry needs to be made to establish the extent and relationship to work exposures. They are then very relevant to the diagnosis but not so helpful in screening.
Spirometry performed as part of the screening test very seldom identifies a case of allergy to platinum salts as the bronchospasm has resolved when the subject is seen. The benefit of routine spirometry includes the following:
- (i) Performance often improves after the initial pre-placement medical examination as the subject becomes more familiar with the technique.
- (ii) It provides a recent baseline against which to compare a subsequent trace if symptoms are reported.
- (iii) It is a reminder to the employee of the concern for respiratory health.
- (ii) It provides a recent baseline against which to compare a subsequent trace if symptoms are reported.
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Frequency of monitoring |
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TopAbstractIntroductionPre-placement considerationsPre-placement medical...Mechanism of allergy to...SurveillanceFrequency of monitoringSummaryConflicts of interestReferences |
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When routine surveillance was introduced, skin prick tests were performed every 3 months. Thus, no case of sensitization would have had symptoms for longer than 3 months. If done at this frequency, there is a good outcome on long-term follow-up studies [12]. When the frequency is reduced to 12 months, the outcome is also favourable but skin prick test positive reactions are more likely to persist [14]. There was a similar experience when workers with positive skin tests were allowed to continue with exposure until they declared symptoms, which in some cases was up to 12 months after becoming sensitized [13]. The longer the symptoms are present before cessation of exposure the more likely there is persistence of asthma and skin test reactivity for several years after exposure has ceased [15].
When exposure is infrequent and the risk of sensitization is historically low then testing at 12-month intervals is appropriate but when exposure is regular and frequent and the risk of sensitization is high, testing every 6 months probably provides as good a prognosis as does testing every 3 months and is practicable.
Employees who are at a risk of sensitization should be reminded regularly of the need to report symptoms as soon as they occur and not to wait until they are due to attend for their next surveillance appointment.
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Summary |
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TopAbstractIntroductionPre-placement considerationsPre-placement medical...Mechanism of allergy to...SurveillanceFrequency of monitoringSummaryConflicts of interestReferences |
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Halogeno complex salts of platinum are very potent allergens provoking type I allergic symptoms in workers who handle them. The cumulative risk of sensitization for new employees in platinum refining remains high.
Smoking as declared at pre-placement medical examination carries a relative risk of 5 for sensitization to the platinum salts. When the attributable risk of sensitization is high, employment of smokers may increase the risk to an unacceptable level.
Respiratory irritants in the workplace may trigger bronchospasm in asthmatic subjects. Eczema is aggravated by the irritant environment and predisposes to sensitization.
Early diagnosis and cessation of exposure as soon as sensitization is identified have been shown to be effective in preventing persistence of bronchial hyper-responsiveness.
For detection of allergy to halogeno complex salts of platinum, the skin prick test is an objective and reproducible technique for identifying sensitization and monitoring of cases. It forms the mainstay of the medical surveillance programme.
Symptoms are non-specific and non-sensitive for surveillance though integral to diagnosis. Spirometry is not helpful at routine surveillance though is essential in diagnostic evaluation.
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Conflicts of interest |
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TopAbstractIntroductionPre-placement considerationsPre-placement medical...Mechanism of allergy to...SurveillanceFrequency of monitoringSummaryConflicts of interestReferences |
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None declared.
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References |
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TopAbstractIntroductionPre-placement considerationsPre-placement medical...Mechanism of allergy to...SurveillanceFrequency of monitoringSummaryConflicts of interestReferences |
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