Thin and short chrysotile fibres: an additional hazard?

Transcription

1 Thin and short chrysotile fibres: an additional hazard? Requested by R.S.A Srl Balangero to Interdepartmental Centre G. Scansetti for Studies on Asbestos and Other Toxic Particulates University of Torino - Italy Università di Torino Chiara Groppo, Francesco Turci, Maura Tomatis, Roberto Compagnoni Bice Fubini European Conference on Asbestos Monitoring and Analytical Methods Venice, 5-7 December 2005

2 Qualitative and quantitative determination of chrysotile short fibres in the soil of Balangero former asbestos mine Objectives: Are there short fibres (fibrils: length < 5 µm, diameter < 0.2 µm) in the crushed stone of former chrysotile mine in Balangero? Do anthropic activities influence the presence of chrysotile fibrils in soil? Does an increased risk of dispersion exist in the presence of short fibres in soil?

3 Examined soils Stone dump, Corio side S1 East zone: crushed stone from excavation used for the formation of summit steps. high soil movement S2 East zone: crushed stone undisturbed. no soil movement Former mine of San Vittore (Balangero) S3 Central zone: soil from surface reprofiling. low soil movement (footsteps)

4 Soil analysis Soil samples Separation and enrichment phases Filtering Scanning Electronic Microscopy and EDS analysis

5 Fibres separation 1. Some soil portions were dried in a non ventilated oven (24h, 100 C) mg of dry soil were weighted 3. The soil has been recursively (10 times) suspended in water (100 ml) and the supernatant was separated and collected into a graduated cylinder 4. Suspension of fine particulate was stirred and then sedimented for 2 hrs. in a graduated cylinder (1 litre, Ø = 6 cm; h = 34 cm) ml of clear suspension were pipetted from the top of the cylinder 6. Three identical aliquots (5 ml each) were extracted from the 50 ml suspension and then filtered on cellulose acetate membrane filter (Ø = 47 mm; pore size = 0.20 µm)

6 Filters preparation and equipments Filters were gold coated as to obtain the maximum resolution. The membrane diaphanization step was skipped in order not to loose any fibres possibly present on the filter. Instruments: a. SEM Leica Stereoscan with EDS microprobe (Dept. of Chemistry I.F.M. University of Torino) b. SEM Stereoscan 360 (Cambridge Instruments) with EDS microprobe (Dept. of Mineralogical and Petrological Sciences Univ. of Torino)

7 Electron microscopy images 3 filters were created for each soil sample 100 images were recorded at 3000 X for each filter In order to have an overall view of the filter, some low magnification images were recorded In order to correctly measure the fibril dimension, some fields at higher magnification (up to X) were also recorded Some as ten fibres per filter underwent elemental EDS analysis

8 Sample: 1 high anthropic activity 2000 X

9 Sample X

10 Sample X

11 Sample 2. no anthropic activity 2000 X

12 Sample X Nanometric diameters

13 Sample 3: low anthropic activity 2000 X

14 Sample X Nanometric diameters

15 Macroscopic results General observations The 3 soil samples showed a different behaviour during the sedimentation process: a) Soil 1 soil movement: high (machines) fine particle suspension was turbid for a long time b) Soil 2 soil movement: none fine particle suspension was turbid for a short time c) Soil 3 soil movement: low (footsteps) fine particle suspension showed a intermediate sedimentation time

16 Microscopic results 1. Morphological observation and elemental analysis (EDS) indicates that only serpentinite minerals (chrysotile and antigorite) are present on filters (no contamination from other asbestos) 2. A wide dimensional range is observed: a. Non-fibrous particles (likely antigorite) size is about some tens µm. b. Fibrous particles (both chrysotile and antigorite) divided in two dimensional classes: i) Regulated fibres (d = µm; l = l 5-20 µm) ii) Thin and Short fibres (d = nm; l = 1-10 µm) 3. Thin and Short fibres have a rather homogenous diameter, whilst length is quite variable. 4. A constant nanometric diameter indicates that the observed fibres are fibrils of chrysotile.

17 Quantitatively, the Thin and Short fibres appear equally present in all of the three examined soil samples.

18 Are fibrils more dangerous than longer fibers? Literature data have always indicated long thin fibers as the most potent ones in causing mesotheliomas

19 the carcinogenic effect of asbestos is dependent upon the fiber's size (lenght >8 µm, diameter < 0.25 µm) Stanton et al., Natl Cancer Inst. 67(5): the nature of the mineral and the nature of active surface sites influence the carcinogenic potency of asbestos fibers,. Bonneau et al., 1986b. Environ Res 41: ; Fubini, and Otero Aréan, Chem. Soc. Rev. 28: ;Kane et al., IARC Scientific Publication No Lyon, France: IARC p. 11. Kamp, D. W., and Weitzman, S.A Thorax 54: ; Hardy, J. A., and Aust, A. E Chem. Rev. 95: the carcinogenic effect of asbestos also depends upon biopersistence Moolgavkar et al., 2001 Inhal. Tox. 2001, 13,

20 1994 short fiber (lenght < 2 µm) were cleared more rapidly (by macrophages ingestion) than the longer ones Churg et al., 1994 Ann Occup Hyg. 38(4):625-33, Churg et al., 1991 Cancer. 67(7): thin asbestos fibers should not be excluded from those contributing to the induction of human malignant mesothelioma Suzuki and Yuen Ann NY Acad Sci 982: Dodson et al., 2003 Am. J. Ind. Med., 44:

21 Conclusions All the examined soils from San Vittore mine contain chrysotile fibrils. No quantitative differences in fibrils among the observed soils. Literature data do not indicate that Thin and Short chrysotile fibres may represent an increased risk because of their dimensions.