Can Amphibole Fibers or Particles Contribute to Mesothelioma

Can Amphibole Fibers/Particles Contribute to Mesothelioma and Other Asbestos Related Diseases in Northeast Minnesota? Philip M. Cook, Ph.D. Senior Research Chemist U.S. Environmental Protection Agency National Health and Environmental Effects Research Laboratory Duluth, Minnesota This presentation does not represent U.S. EPA policy or risk assessment conclusions. Some data and interpretations presented are preliminary and have not yet been published in peer reviewed research journals. Dust exposures associated with taconite mining present one of the most complex health risk assessment problems imaginable. Biwabik Iron Formation Amphiboles are uniquely present near the Duluth complex Definitions Associated with Mineral Crystal Habits in Rocks (and potential to produce microscopic fibers when crushed) • asbestos – a commercial term applied to fibrous minerals, usually having a columnar growth pattern and properties suitable for use in industrial processes • asbestiform – crystallized with properties associated with asbestos (high tensile strength, flexible, high aspect ratio, columnar habit, easily separable fibers, durable faces) • fibrous – gives the appearance of consisting of fibers • acicular – needlelike • cleavage – ability to break along preferred crystal orientations Adapted from T. Zoltai, 1981 Potentially Fibrous Minerals in the Biwabik formation • Amphiboles in metamorphosed iron formation (east) Cummingtonite – grunerite (Mg,Fe)7Si8O22(OH)2 Actinolite – ferroactinolite Ca2(Mg,Fe)7Si8O22(OH)2 • Sheet silicates in unmetamorphosed iron formation (west) Minnesotaite (Fe,Mg)3Si4O10(OH)2; iron rich talc Greenalite (Fe)2-3Si2O5(OH)2; iron serpentine Stilpnomelmane K(Fe,Mg)8(Si,Al)12(O,OH)27⋅n(H2O) Of these minerals, only the amphiboles appear to have documented health effects in humans at this time. The large quartz content of taconite is an additional inhalation health risk factor to consider. Why investigate amphiboles? • Unresolved issue since 1973 – Reserve Mining Case • Research in 1980s supported concern for inhalation hazards. • Libby MT vermiculite problems re-ignited involvement of EPA in assessing health risks associated with “asbestos-like fibers”. Research under the Libby Action Plan is on-going. • The State of Minnesota has requested U.S. EPA to provide data and models that may result in an improved cancer risk based community air quality standard for amphibole fibers. • Epidemiological data reported by MDH in December 2007 indicates that 36 of 58 mesothelioma deaths among taconite workers employed prior to 1983 appear to be associated with work experience at the two mines with amphibole fibers. • MSHA monitoring data indicate that fiber concentrations have been historically greater at these two mines. Inhaled mineral particle shapes and size distributions are affected by crystal structure, growth habits in rocks, intensity and duration of rock crushing, and particle transport and sorting over time. Amphiboles consist of a double chain silicate structure with preferred cleavage on {110} planes. Iron rich amphibole minerals with calcium and magnesium are associated with east range taconite. A Major Complication for Risk Assessors: Mineral Fibers Have Diverse Origins and Properties When Removed from Rocks Chrysotile asbestos cross-fiber vein Amphibole crystals in taconite (iron ore) - ferroactinolite replacing hornblende 5 cm Ferroactinolite – SEM – what is the habit? P. Morton, U. M. D. Geology Dept. Asbestiform amphibole from the Dunka Pit used by LTV/Erie Mining Co. This is probably ferroactinolite Measures of Small Sizes • millimeter (mm) 10-3 m • micrometer (µm) 10 -6 m • nanometer (nm) 10 -9 m • angstrom (Å) 10-10 m DNA is 2 nm wide in contrast to nanoparticles which are 1-100 nm wide (0.001-0.1 µm) Mineral fibers* can be as thin as 20 nm (0.02 µm) *for microscopic particles “fiber” is defined as any particle having parallel sides and a length to width (aspect) ratio ≥ 3.0 C=C 1.33 Å Si–O 1.63 Å Thin, short fibers may require separation from coarse particles to be seen by TEM Reserve Mining dry cobb tailings <2 µm fraction 2 µm EPA circa 1978 Amphibole fiber* in Silver Bay air sample – circa 1975 Calibration of XRD Mass Concentration to TEM Fiber Concentration XRD measurement of amphibole mass concentrations in community air from one week high volume air samples: a two year record for three sites Conceptual Model for development of methods for prospective assessment of health risks associated with exposures to mineral and synthetic fibers p es -r Effects toxicology re la t iv se do e Dose in tissues po te nc ie s Exposures fa t e/t ra res epidemiology Key question: what dose in tissues/lung should not be exceeded? Temporal exposure issues - lifetime, short term, early life stages nsp ort se on pir ati ret on en tio n/c lea ra nc e Sources n tra slo n tio ca The thin fibers (≤ 0.1 µm) are in the nanoparticle range Systemic Distribution of Nanoparticles Oberdörster et al., Environ. Health Perspect. 113: 823-839, 2005 20 Operational Dosimetry Modeling • “Dose” Internal body amount: Deposited or retained Defined as associated with toxicity to evaluate “dose-response” relationships • “Metric” Measurement: mass, number, surface area Scale same as observation or response endpoint (e.g., lung region versus local, specific cell type) • “Model” Mimic or describe important processes Simulate different exposure scenarios Draft U.S. EPA Libby Amphibole Risk Assessment Science Conceptual Model Exposure Internal Dose Biologically Effective Dose Early Biological Effect Effect Noncancer Cancer Exposure Altered Structure / Function Clinical Disease Prognostic Significance TB Deposition LA Exposure PU Deposition Retained TB Dose Retained PU Dose Inflammation and Cellular Proliferation Remodeling Interstitial fibrosis Lung Tumors Human Health Risk Pleural fibrosis Mutation of Normal Cells Clonal Expansion of Mutated Cells Remodeling Inflammation and Cellular Proliferation Translocated Dose to Pleura Mutation of Normal Cells Clonal Expansion of Mutated Cells Mesothelioma Susceptibility Intratracheal and Intrapleural Exposures of Fischer-344 Rats • The primary objective was to determine relative potencies of different fiber types for carcinogenesis. • Initial studies included two samples of amphibole from taconite ore in Minnesota - ferroactinolite (fibrous) and grunerite (non-fibrous). • Amosite was a positive control. • Details of bioassays and effects provided in Coffin et al. Toxicology Letters, 1982. • Details of quantitative dose-response analysis provided in Cook et al. Toxicology Letters, 1982. • Similar IT and IP studies were later performed with crocidolite, chrysotile, erionite, fiber glass, and other mineral fibers. PRIMARY TUMORS 5 % TUMORS 4 LUNG 3 LUNG 2 1 PLEURA PLEURA 0 0 A F G F/A ReP: 7.8 104 <200 11.6 <2.7 G/A ReP: <0.7 Amosite is reference fiber for relative potency so a number > 1.0 indicates greater potency Intratracheal instillation of amphibole fibers into Fisher rats. Retained fiber dose in lungs over two years obtained for interpretation of relative carcinogenicities. Cook et al. and Coffin et al. Toxicology Letters 1982 1 µm The ferroactinolite fibers partially dissolved and split longitudinally while residing in rat lung tissues over time. Particle from human lung tissue: dissolution of talc appears to release amphibole fibers What you typically see through the microscope (bivariate) does not fully describe fiber morphology. Aspect ratios for amphibole fibers: typically the width observed is 2-5 times the thickness or third dimension of the fiber lying on a membrane filter. For ferroactinolite fibers, marginal 3:1 aspect ratios equated to length to thickness ratios that averaged about 15:1. L W T Question: what is the biologically relevant aspect ratio? Mean Shapes and Sizes of Fiber Types (shapes based on TEM measurements of thickness) Amosite Grunerite Crocidolite Ferroactinolite Exposure 628 f/ng 40 f/ng 3360 f/ng 54 f/ng Rat Lung One Year 205 f/ng 31 f/ng 464 f/ng 411 f/ng Mean Shapes and Sizes of Fiber Types Chrysotile Glass Erionite Exposure 21000 f/ng 5660 f/ng 850 f/ng Rat Lung One Year 5490 f/ng 436 f/ng In Vitro Dissolution Studies Sample Preparation: Grinding & Sieving Synthetic Lung Lining Fluid Acid incubation Environmental Sample EM Grid Counting and Analysis EM Grid kd kd Ferroactinolite sample used in rat intratracheal exposures Ferroactinolite sample after acid leaching equal to 1 year in lungs 5 µm 5 µm Amphibole particles observed to split into thinner fibers in rat lungs are observed to behave similarly in accelerated acid leaching assay. Conceptual Model for Carcinogenic Potency - Pott, 1978 Reference Doses Calculated with Alternative LxW Bin Based Relative Carcinogenicity Factors (RCFs) 600 Million fibers/lungs for 5% tumors -IT 500 400 300 200 100 0 Amosite * Pott RCFs Cook RCFs Croc. Ferroact Ferroact. Year 1 * For Cook RCFs, Amosite and Crocidolite at 1 year Ferroactinolite at 1 year. Update – total fiber surface area appears to provide even greater equality in potency for the three amphibole samples. NHEERL DATA BASE CONTENT • 42 unique mineral and synthetic fiber samples • 270 individual sample TEM analysis files • Effects studies represented – EPA, Stanton et al., Wagner et al., Davis et al., others associated with UICC samples • Number of effective particles measured – 1,186,046 • Values measured for every particle – length, width, SAED/particle identity, shape category (e.g. fiber), area multiplier. • Additional measurements for selected particles – EDS elemental composition, thickness. • Sample associated parameters – origin, mass analyzed, filter area, TEM grid area examined, leaching condition, etc. DATA BASE CONTENT Basic Types of Samples • Fiber exposure samples – fibers/mass sample in exposure – Intratracheal, Intrapleural, Inhalation, Intraperitoneal, in vitro • Whole lung samples – fibers/lungs over time • Extra-pulmonary tissue samples for fiber translocation measurements – fibers/g tissue or /organ over time • Leached fiber exposure samples to simulate alteration over time in lung and other tissues • Methods development and QA samples Potential Data Base Benefits • High quality data generated by one laboratory. • Routine calculations of fiber or total particle number, mass, or surface area concentrations for total sample or any set of defined L x W categories. • Applicability to exposures from many studies – improving, standardizing dose metrics across studies possible. • Emphasizes tissue burden dose over time. • Data for simulation of in vivo alteration of fiber samples over time and bio-durability. • Ability to test relative potency values for specified fiber length x width categories, and total surface area. • Describe fiber size relationships associated with translocation from lung or pleura over time. The Stanton Study and EPA Reanalysis • Stanton et al. 1981 has frequently been cited as evidence for long fiber potency. • An unconventional approach was used for calculating particle concentrations in rat pleural exposures which were characterized as order of magnitude estimates. • Although Stanton et al. found log # fibers > 8 µm long and ≤ 0.25 µm wide to best correlate with incidence of pleural sarcoma, significant correlations were found for other fiber size categories. • Our preliminary statistical analysis in 1985 using EPA TEM data indicated fiber thinness was a strong morphological descriptor of potency. This is consistent with total fiber surface area now being tested. • The EPA TEM data for 30 Stanton Samples allows testing of alternative relative potency modes to determine additive contributions of all fiber types and sizes with consideration of in vivo durability effects on carcinogenicity. Stanton et al. (1981) Samples 1 0.9 0.8 PROBABILITY OF TUMOR C = crocidolite G = glass D = dawsonite L = aluminum oxide S = silicon carbide A = attapulgite P = titanate T = talc M = tremolite W = wollastonite H = halloysite O= amosite M M O C P D D S P C C CG C G G L G G DG C L D C D 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 W C L C C L HG HCW G ADDW ACGPT LTGGGG LTTGG CWTTGG G L G G G L C T 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 LOG NUMBER PARTICLES MEASURING < 0.25 µm x 8 µm PER MICROGRAM Stanton et al. Samples Reanalyzed by EPA 1 0.9 0.8 PROBABILITY OF TUMOR C = crocidolite G = glass D = dawsonite L = aluminum oxide S = silicon carbide A = attapulgite P = titanate T = talc M = tremolite W = wollastonite H = halloysite O= amosite M M O C P D D S C C C C L D C L D C D 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 W C L W DWD P L CW L 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 LOG NUMBER PARTICLES MEASURING < 0.25 µm x 8 µm PER MICROGRAM Preliminary data - analysis in progress EPA Re-analysis of 30 Stanton Samples Preliminary data - analysis in progress EPA Re-analysis of 30 Stanton Samples Preliminary data - analysis in progress EPA Re-analysis of 30 Stanton Samples Preliminary data - analysis in progress EPA Re-analysis of 30 Stanton Samples Outlier – high surface area and low % tumors – but low biodurability Exposure 2 Months in Tissue Simulation Dawsonite 6 – Stanton 13% Tumor Probability Exposure 1 Year in Tissue Simulation 2 Years in Tissue Simulation Dawsonite 7 – Stanton 68% Tumor Probability Other respirable and biodurable silicate particles may contribute to taconite health risks • All taconite workers appear to be exposed to quartz particles and non-amphibole silicates. • There do not appear to be toxicological data on potentially fibrous silicates like minnesotaite which have been mentioned as possible contributors to pulmonary disease since the 1970s (T. Zoltai and others). • Preoccupation with “cleavage fragments” may be a real hindrance to determination of all the factors which contribute to asbestos associated diseases. Inhalation of quartz with asbestos potentiates mesothelioma production in rats - Davis et al. 1991 50 A denom a A denocarcinom a P leural m esotheliom a 40 13 % Tumor 30 9 8 20 6 4 4 6 3 3 4 2 10 1 1 0 0 il e ls tr o ot on ys 0 rtz ua ite Q os m Q m os A it e + ua rtz hr + C C C hr ys ot i le A Conclusions for Amphibole Fiber Risks Associated with Taconite • Toxicology data for amphiboles, including the detailed data for ferroactinolite, support the historical concerns for amphibole fibers and the need to account for the contributions of the short fibers which predominate in most exposure data. Total fiber surface area is potentially an effective and practical dose metric (TEM or equivalent SEM) for relating human exposures to health risks. Relating risks to internal/tissue doses over time is feasible with application of a basic human fiber dosimetry model to relate inhaled fibers to tissue doses over time. EPA’s Libby Action Plan related research plan is poised to facilitate development of these approaches. The biological and physical-chemical bases for assertions that cleavage fragments lack potency are very weak. However, if the cleavage fragment distinction is valid, effects associated with taconite may have to be attributed to a few particles out of many respired. • • • •