Environmental ‘Low Dose’ Mesotheliomas and Their Relationship to Domestic Exposures-Preliminary Report

Crocidolite is a fibrous mineral with unusual crystallography in that the fiber width varies according to geographical origin. The fibers from the mining areas of Western Australia and the Cape Province, in South Africa are ‘thin’ compared to those from Bolivian and some other mines. Regardless, the mineral is a well known causative agent for mesothelioma. The literature contains many reports of the disease occurring as a consequence of so called environmental exposures due to what some believe to be ‘low’ dose, ambient exposure. However, closer examination of these exposure conditions generally reveals an unrecognized (or simply ignored) strong domestic (para-occupational) exposure component. Oftentimes, the importance of such domestic exposures is not considered since they too are thought to be too low to contribute to risk. We have, for the first time, applied state of the art measurement methods to evaluate domestic (shake out) conditions created by workers in a historical unregulated crocidolite-cement based operating plant in Bolivia. Our results show that exposures can reach levels more usually associated with historic occupational exposures. The reason for studying the exposures in such a plant is that epidemiological studies have shown that ‘thin’ crocidolite fibers are associated with a high mesothelioma risk while exposure to the ‘thick’ Bolivian fibers are associated with a much lessened mesothelioma risk.


Introduction
Crocidolite is a fibrous mineral with unusual crystallography in that the fiber width varies according to geographical origin and it may be a unique mineral in this respect.This property was first studied by Shedd (1985) from the US Bureau of Mines who showed that the fiber dimensions of crocidolites from crocidolite mining regions in Western Australia and the Cape Province, in South Africa are 'thin' compared to those from Bolivian and some other mines.
Crocidolite is a major cause of the tumor mesothelioma and the relevance of fiber width to its pathogenicity has been reviewed by the authors (Ilgren et al., 2012a).
Environmental mesotheliomas are said to arise under 'low dose' conditions without occupational or para-occupational (domestic) exposure.In truth, environmental mesotheliomas thus labeled are actually domestic mesotheliomas which arise after high dose exposures (Browne & Wagner, 2001).Whilst there is strong evidence to suggest domestic exposures associated with asbestos disease are consistent with high occupational exposure levels (Sawyer, 1979;Browne, 1983;Gardner & Saracci, 1989;Gibbs, Jones, Pooley, Griffiths, & Wagner, 1989;Castleman, 1988 (Note 1); Huncharek, Capotorto & Muscat, 1989;Gaensler, McCloud, & Carrington, 1985;Newhouse, 1991 personal commun), data from direct measurements of historical operating facilities are lacking (Health Effects Institute, 1991).It is commonly presumed levels of exposure in households are lower than those in the workplace, though measurements are not available documenting such levels.We thus document, for the first time, using modern measurement methods in a fully operational historic unregulated manufacturing plant, that the exposures produced during domestic ('shake out') activities, are indeed very high.Taken together, these data provide further evidence that environmental mesotheliomas as currently defined do not exist (Browne & Wagner, 2001).

Study Location
Bolivia has several small crocidolite mines spread along both flanks of the headwaters of the Minasmayu river in the Alto Chapare District in the Cochabamba Department, Bolivia (Mindat, 2013).

Simulation Study and Measurement Details
A shake out simulation study was done in the setting of a historical crocidolite manufacturing plant.The operating conditions, lay out and other details of the plant as well as the methods used for fiber collection and measurement have already been described in detail (Ilgren, Van Orden, Lee, Kamiya, & Hoskins, 2012;Van Orden, Lee, Zock, Sanchez, & Kamiya, & Ilgren, E., 2012;Van Orden, Lee, Zock, & Sanchez, 2012).A worker sieving crocidolite in the fiberizing unit of the plant six days a week, 8 hours a day, was asked to put on new work clothes in the morning before coming to work.He wore a personal sampler throughout the day.The company changing room was cleaned at the start of the day.It was closed until all work at the plant was done 8 hours later.The worker from the sieving department then changed his clothes in the changing room at 5:00 pm and shook them out continuously for two minutes.A sampler was placed less than one foot from his breathing zone and another was placed three meters away at the same height on the other side of the changing room.

Findings
The concentrations recorded from the personal sampler and those found during shake out are shown below (Table 1).All of the readings are well into the occupational range.The fiber size dimensional profiles from each sample are also shown (Table 2) are not statistically different.Background concentration data were not available so the lowest reading in the plant has been used in its place.This was from a sample taken upwind of a worker drilling a crocidolite panel (Table 1).

Table 1 .
Observed PCM and TEM fiber concentrations (f/ml) for samples collected following the shake out of work clothes.(July2011)(also see[11])