Document BRdzOJdej2aEjGGzym1aXrrGj

Crystalline Silica: Update on Toxicology, Regulation & Other Issues September 30, 2005 Tom Hethmon Rinker Materials Corporation Crystalline Silica Silicon dioxide (SiO2). Silica exists in two forms: amorphous & crystalline. Polymorphs: quartz, tridymite (rare) & cristobalite (rare). Key Polymorphs Alpha & beta quartz Cristobalite Tridymite Keatite Coesite Stishovite Moganite Natural Occurrence of Crystalline Silica Most common mineral in the Earth's crust Crystalline Silica Occurrence Sand Gravel Limestone* Slate Granite Pumice Sandstone Shale Schist Quartzite Obsidian Conglomerates Siltstone Silt Gneiss Marble* Rhyolite Breccia General Dust Sources in the U.S. Sources of Fugitive Dust Percentage of Total Dust (PM1o) Generation Unpaved roads 28% Construction 23% Agriculture 19% Paved roads 15% Wind erosion 5% Mining/Quarrying 1% Crystalline Silica Exposures Occurrence in Industry Pulmonary Toxicology Particle size is critical. Peak dust inhalation occurs with particles having a diameter of 0.5 to 3 microns (^m). RCS is invisible to the human eye. Pulmonary clearance mechanisms: macrophages & the mucociliary escalator. Silicosis Defined Progressive form of diffuse, nodular, interstitial, pulmonary fibrosis resulting from the inhalation of respirable crystalline silica (RCS). Symptoms: shortness of breath, reduced pulmonary function, chronic cough, may also involve fever & weight loss. Cardiac complications in advanced cases. Treatment: No specific treatment. Cessation of exposure. Smoking cessation if relevant. Antibiotics. Anti tuberculosis drugs. Lung transplant is rarely attempted. Crystalline Silica: Silicosis Defined Chronic (simple) silicosis: Most common form. Caused by exposure to respirable crystalline silica over periods that are generally longer than 20 years. Often more prominent in the upper lobes. Nodules are usually small (< 1 cm). Usually involves exposures to dusts containing less than 30% RCS concentrations. Silicosis is often confused with other dust disease miliary tuberculosis, siderosis, sarcoidosis, coal miner's pneumoconiosis, etc. Crystalline Silica: Silicosis Defined Accelerated silicosis: Occurs after exposure to higher concentrations of RCS over shorter periods relative to the chronic form, e.g., 5 - 15 years. Inflammation, scarring and symptoms occur faster than in chronic silicosis. Acute silicosis: Results from short-term exposure to very high concentrations of RCS. Can occur after massive exposures of several weeks to less than two years. Medical Surveillance Occupational history. Medical examination. Chest x-ray. Pulmonary function test (PFT). Less common: baseline TB skin test. Pulmonary Function Testing (PFT) PFT testing can only find defects consistent with silica exposure and that can be found in many other diseases. There is no PFT that can diagnose silicosis. More sophisticated testing available: diffusing capacity. Chest X-Rays Routine chest x-rays may or may not find silicosis when an employee is beginning to have symptoms. Symptoms are non-specific (cough, shortness of breath, etc). Only when the typical findings of silicosis are present can the diagnosis be comfortably made. Chest x-rays, however, can identify employees who have early disease, and allow for intervention. CT-scans may be useful. Silicosis may progress after removal from exposure. Normal vs. Silicotic Lung Normal Advanced chronic silicosis Toxicology of Crystalline Silica Particle surface characteristics affect fibrogenic activity, e.g., freshly cleaved particle potency. Quartz is not mutagenic, i.e., negative Ames test. Reproductive & developmental effects unknown. Mechanisms of action: cellular inflammation, nodule formation, suppressed immune function, alveolar proteinosis. Carcinogenicity: direct genotoxic effect for quartz not established. Autoimmune Disease Immune activation by occupational exposure to RCS may be linked to scleroderma, rheumatoid arthritis, polyarthritis, mixed connective tissue disease, lupus erythematosus, polymyositis, fibritosis & glomerulonephritis. Some research suggests that *10% of silicotics will develop clinically detectable autoimmune disease or "abnormal immune tests". The cellular mechanism that leads from RCS exposure to these autoimmune diseases is not known and has not been clinically substantiated. Crystalline Silica Epidemiology Lung cancer standard mortality ratios (SMR's) for crystalline silica have slight but consistent elevations. The relationship between silica and lung cancer in the absence of silicosis is unclear. Some studies have verified the exposure response relationship between silicosis and tuberculosis, etc. Confounding factors, e.g., tobacco, poorly controlled or assessed in most studies. Criteria for Carcinogenicity Strength of association (high relative risk) Dose response relationship ^ Consistency of findings ^ Temporal cogency (exposure before disease) ^ Biological plausibility & experimental evidence Control of confounding & bias Specificity Carcinogenicity Designations Suspect lung carcinogen: - OSHA: - MSHA: Suspected No designation - ACGIH: - IARC: - NIOSH: A2 (Suspected) 1 (Confirmed in humans) Potential (human) Historical Exposure Assessment Different sampling methods used: konimeter, impinger, gravimetric without size selection, gravimetric analysis with cyclones, x-ray diffraction. Conversion factors have been proposed, but correlation between dust particle number and size is difficult. Until recently, different criteria were used to define the respirable fraction of RCS, e.g., ISO, ACGIH. Current consensus: 50% cut point for particles of 4 ^m aerodynamic diameter. U.S. Silicosis Mortality 1968 - 2002 Distribution of Silicosis Deaths Medsciape www.medscape.com! FIGURE Z Geographic cfstrilxition of age-adjusted silicosis mortality rates', by county--National Occupational Respiratory Mortality System, United States, 1968-2002 >0-4 >4 -1 Par million persons aged >15 years. Rates were not calculated for counties with fewer than live deaths Source: MMWR 20Q5 Centers Far D sea&e Contiral and Prevention (GDC) Exposure Limits & Guidelines Agency OSHA MSHA NIOSH ACGIH Country U.S. U.S. U.S. U.S. Limit (mg/m3) 0.1* 0.1 0.05 0.05 *10 mg/m3/(% SiO2+ 2) Averaging 8-hour TWA 8-hour TWA 8-hour TWA 8-hour TWA Proposed Regulation: OSHA Published a draft proposed standard 10/03. SBREFA review subsequently conducted. General industry, maritime & construction versions. Reduction in PEL, e.g., construction: PEL 0.1 mg/m3 0.075 mg/m3 0.05 mg/m3 Action Level 0.05 mg/m3 0.04 mg/m3 No separate AL Proposed Regulation: OSHA Engineering & work practice: primary controls Employee rotation unacceptable (carcinogen) Exposure assessment & regulated areas Two options for sampling: - (1) If PEL = 0.05 mg/m3 trigger for quarterly sampling - (1) If PEL > 0.075 mg/m3 semiannual sampling - (2) Periodic enough to ensure proper controls Designated competent persons Respiratory protection & other PPE. Housekeeping & hygiene Medical surveillance, education & training Proposed California OSHA PEL Air Contaminants Advisory Committee (ACAC). Recommended reduction in PEL to 0.01 mg/m3. Applies to all forms of respirable crystalline silica. Based on risk assessment work from S. Africa. Recommendation forwarded to CDOSH (OSHA). ACGIH TLV NIC 2004 Would reduce the TLV from 0.05 to 0.025 mg/m3. Applicable to quartz and cristobalite. "Intended to prevent pulmonary fibrosis that may be a risk factor for lung cancer." A2 suspect carcinogen designation. "Evidence that levels of silica exposure leading to fibrosis are required for increase risk for lung cancer." ACGIH is currently being sued over its TLV process. ASTM E1132-99a "Standard Practice for Health Requirements Relating to Occupational Exposure to Respirable Crystalline Silica." Voluntary consensus standard. OSHA & MSHA required to considered. Judicial notice. Comprehensive control structure: - Exposure assessment - Engineering, administrative & PPE controls - Hygiene facilities - Respiratory medical surveillance & medical protection - Worker training & education - Warning signs & labels Does not include a recommended exposure standard. Current Sampling Methodologies NIOSH 7500: Pre-tarred PVC filter w/ 10 mm cyclone with x-ray diffraction. Most widely used and recognized. (NIOSJH 7500 = OSHA 142). LOD: 0.005 mg. NIOSH 7601: Visible absorption spectrophotometry. Does not differentiate between quartz, cristobalite and tridymite. NIOSH 7602: Infrared spectrophotometry. Can distinguish between quartz and cristobalite, but not tridymite. LOD: 0.005 mg. Watch for interferences, e.g., silicates, feldspars, micas, potash, graphite, etc. Air Sampling Challenges Are the existing crystalline silica standards consistent? Recent research looked at crystal morphology, surface area, particle size distribution, elemental composition for <4.5 ^m Silver Bond B, <10 ^m Silver Bond B, NIST 1878, NIST 1878a. Used a variety of laboratories and reference methods. Differences were significant. Publication to follow. Air Sampling Challenges Airborne concentrations of RCS below 0.05 mg/m3 collected via 1.7 lpm cyclone and analyzed by x-ray diffraction or IR offer insufficient precision and accuracy. NIOSH: "..current methods do not meet appropriate accuracy criterion to quantify exposures at concentrations below 0.05 mg/m3." Issues: Dust loads below 40 ^g, limits of detection, overall RSD as measured by NIOSH PAT program. Litigation: Recent Developments Silica the second wave following asbestos litigation. 2005: Judge Janis Graham presiding over multidistrict litigation in Corpus Christi, Texas. Sent 90 cases representing 10,000 plaintiffs back to their states of origin. Called into question plaintiff's evidence of injury. Expected to have wide-ranging consequences on mass tort litigation involving silica. Adding momentum to state legislative efforts to require prima facie evidence of injury to justify litigation. Tort Reform Legislation Florida "Asbestos & Silica Compensation Fairness Act of 2005" Requires plaintiffs to make prima facie showing of physical impairment based on specific medical criteria for nonmalignant asbestos, asbestos-related lung cancer claim and certain silica-related disease. Two disease rule: claims arising from a nonmalignant condition and cancer are separate actions. No punitive damages awarded for silica-related claims. No damages for "fear of cancer" claims. Dust Exposure Controls Material substitution (e.g., sandblasting) Isolation (enclosures) Process modification Ventilation (general vs local) Suppression (water) Administrative procedures (time, rotation) Personal protective equipment (respirators) Most desirable Least desirable Special Case: Sandblasting Must use silica substitute, e.g., garnet. Requires air-line respirator. Process Control/Design Mobile & Fixed Equipment Enclosures Road Dust Suppression Conveyor Drop Points Drop box Covered conveyors Truck-borne Dust 3.9m WSNTmtfl WOBTIKTW! Truck wash Vacuuming & Wet Sweeping Respiratory Protection Respirator type based on silica air concentration. Air-purifying vs air-supplying. Requires medical qualification & fit-testing. A View to the Future Increasing regulation at the state & federal level. On-going & unresolved debate over dose response. Increasing focus on ambient issues. Watch for "mixed dust pneumoconiosis." Improved screening & diagnosis techniques. Improved epidemiology. Thank You for Your Attention Comments, questions, additions?