Re: Mortality among workers in the geothermal power plants at Larderello, Italy. Am. J. Ind. Med. 35:536–539, 2000.*
Authors: Merler Enzo , Silvestri Stefano , Mauro Luigi , Campinoti Graziano 
Published: October 2004

We would like to comment of the article by Pira et al. [1999]. The authors present the results of a mortality study of a cohort of 3,946 male workers, employed between 1950 and 1990 in a geothermal electric plant located in the Pisa Province (Italy) and run by the Italian Electric Company (ENEL), followed for the same period for the identification of their mortality (even if the hypothesis under study is that exposures to carcinogenic agents, including asbestos, which implies long latency periods, have occurred). Apart from two deaths due to primary pleural tumors, no cancer excesses were detected and the authors stated that the study provides "reassuring information". As far as primary pleural tumors are concerned, "There was no overall excess mortality" and "death rates were not significantly above unity...although two deaths from pleural cancer were observed among workers exposed to asbestos".

Two points seem worth mentioning. The company (ENEL) was accustomed to using large amounts of crocidolite (considering that de‐insulation and renovation were regularly required) to cover engines, and this led to an excess of mesotheliomas among workers of thermoelectric power plants in Italy [Crosignani, 1995]. At the geothermal power plant under study, in addition to crocidolite used for the insulation of turbines, amosite was used for the steam pipe coverings. The workers of the geothermal power plant were exposed to these specific commercial asbestos types, not generically to "asbestos", as the authors quoted throughout their contribution. That amosite was used in the insulation of ducts is very well known [see e.g., Rossi et al., 1995]. The steam pipes extended for hundreds of kilometers, in several places passing near residential areas, and have a diameter between 300 and 800 mm; hundreds of tons of amosite have been used. Firms and contract workers were employed for both insulation and de‐insulation of ducts, so that the number of subjects occupationally exposed to asbestos exceeded the sample population studied by Pira et al., which is restricted to factory workers. Work on pipes was performed without protection and workers were not informed about the risk. When renovation of ducts was required, large amounts of friable amosite were abandoned everywhere. Finally, the company decided to insulate the cellars of the houses of their employees living in the area, several of which are now in poor condition of maintenance, with amosite sprayed all over.

Since 1988, we have monitored the occurrence of mesothelioma, through an active search of cases in the entire Tuscany Region, through a project called Regional Archive of Malignant Mesotheliomas. The identification is followed by interviews aimed at identifying exposures to known risk factors, especially to asbestos.

The two cited cases of primary pleural tumors occurred before 1990, have been histologically diagnosed as mesothelioma and they died in 1985 and 1988 respectively, in the last years of the observation period. From 1990, the year in which Pira's follow‐up period ended, to 1998, we identified five additional confirmed cases of pleural mesotheliomas (one by means of cytology, four by histology) among the employees of the ENEL study base. Whereas for primary pleural tumors the Pira study reports an RR of 1.4 (95% CI 0.57‐5.02) in the overall cohort and an RR of 4 (95%CI 0.61‐18.06) among those exposed to ⩾5,000 fibers/year, the RR of mesothelioma based on seven mesothelioma cases among these ENEL workers (assuming a certain increase in the person‐years), should be no less than 3.9 (95%CI 1.56‐8.02) for the overall cohort, and no less than 11.67 (95%CI 4.69‐24.04) among those exposed to ⩾5,000 fibers/year.

The occurrence of additional cases of mesothelioma in recent years is not surprising, considering that exposures have occurred mainly from the 1950s to 1980s and long latencies are needed for the development of mesotheliomas.

We are definitely concerned about the large amount of amosite and crocidolite used by this company and the high mesothelioma cancer risks already detected among these ENEL workers, and what should be expected to occur in the next years among the exposed local population, inclusive of the general population of the area. We believe that "reassuring" messages are wrong and misleading.