Chemicals And Hearing Loss
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Chemicals And Hearing Loss






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    Chemicals And Hearing Loss Chemicals And Hearing Loss Presentation Transcript

    • Chemicals and Hearing Loss California Industrial Hygiene Conference December 4, 2006 LT Anne M. Jarrett, M.A., CCC-A Occupational Audiologist, MSC, USN Hearing Conservation Program Naval Medical Center San Diego
    • Hearing in the Work Environment
      • Important for understanding:
        • Individually and others in the work environment
          • critical orders
          • warning and alerting signals (including listening to equipment sounds)
        • Productivity
          • general directions
          • Job related communication between coworkers
      • Hearing can be difficult in the work environment
        • poor acoustical environments
          • noise, distance, reverberation, distractions
          • work space, intercoms, meetings, telephones, walkie-talkie
        • Compounded by any underlying hearing loss
    • Workers in the United States
      • 30 million individuals in the labor force who are exposed to hazardous noise
      • 9.5 million individuals who may be exposed to organic solvents
      • 1988 – Nat. Institute for Occup. Safety & Heath (NIOSH)
        • began studying the solvents and HL
      • 1998 - National Occupational Research Agenda (NORA)
        • included noise + chemicals topic
      • 2001 - NIOSH
        • made available grants for investigating
      • 2002 - NIOSH Best Practices Workshop
      • (Effects of Chemicals & Noise on Hearing)
    • Work Environments with Solvents
      • Painting
      • Printing
      • Boat Building
      • Construction
      • Furniture Making
      • Manufacturing of metal, leather, and petroleum products
      • Cause: Spills, explosions/fires, industrial wastes, water contamination, occupational environment, etc.
    • Ototoxins
      • Organic solvents
        • ** Toluene (printing)
        • ** Xylenes (plastics)
        • ** Styrenes (plastics)
        • ** Trichloroethylene (degrease)
        • * Carbon Disulfide (textile)
        • * Stoddard/white spirits
        • * N-hexane
        • Fuels (JP-8 fuel)
        • Ethyl benzene
        • Perchloroethylene
        • Butyl Nitrite
        • Methylene chloride
      • Metals
        • * Mercury and derivatives
        • * Lead and derivatives
        • * Arsenic (atoxyl)
        • * Manganese
        • Trimethyltin (organic tin)
        • Cobalt
      • Asphyxiants
        • ** Carbon Monoxide
        • * Cyanide
      Army ID: * potential ** high-priority
      • Drugs
        • Aminoglycosides
        • Loop diuretics
        • Anti-neoplastic agents
        • ASA
        • Quinine compounds
      • Others
        • Chem. warfare nerve agents
        • Organophosphate (pesticide)
        • Paraquat (pesticide)
    • Morata,TC., Dunn,DE., Kretschmer, LW., Lemasters, GK., Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug.
      • Paint and print industries - risk of hearing loss
        • Unexposed (no noise or solvent)
        • Noise exposed only – hearing loss risk 4x
        • Toluene solvent only – hearing loss risk 5x
        • Toluene solvents and noise –hearing loss risk 11x
        • Controls: previous exposure to noise and/or chemicals, medical and audiological history, age, length of employment, recreational exposure, and military service
        • Tests: puretones, immittance (tympanograms, reflexes, reflex decay)
    • Problems caused by solvents
      • Hearing Loss
        • Sensorineural Hearing Loss - Inner Ear
          • Tuning (clarity and loudness)
          • Testing: common audiometric procedures (Puretones, Speech, Other)
        • Central/Retrocochlear Hearing Loss - Brainstem and Cortex
          • Processing (transmission, cognition, varying degrees of tuning and loudness)
          • Testing:
            • Speech Processing (interrupted speech, speech in noise, temporal integration)
            • Evoked Potentials (brainstem or cortical potentials),
            • DPOAE: Contra-lateral suppression (efferent testing)
            • Reflex and Reflex Decay
            • Modified Puretone: masking level difference, gap detection, duration pattern, pitch pattern, temporal integration, high frequency audiometry, step size less 5dB
            • Questionnaire on speech discrimination difficulties or other auditory problems that are inconsistent with thresholds
      • Disequilibrium, Headaches, Vision Problems, Neurological
    • Many other causes of Hearing Loss
      • Accumulative noise exposure
        • occupational and recreational
      • Disease Processes
        • outer, middle, inner ear and combinations
      • Accidents
      • Ototoxic exposure that are medical
      • Aging
      • Genetics: anatomical and sensitivity/susceptibility
      • Medical contributions to poor hearing health
    • Hearing Conservation Programs (HCP)
      • Most HCP have no mandate for chemical exposure
        • American Conference of Industrial Hygienists (ACGIH)
          • Advise Monitoring
        • US Army (1998):
          • Initiation enrollment when there is excessive exposures to ototoxins (1 of 13 solvents)
          • Monitoring (same as noise exposure)
    • Questions with integrating into solvent exposure in HCP
      • Which solvents to include?
      • Excessive exposure levels?
      • Best audiometric test battery?
        • Location of damage - Retrocochlear hearing loss
        • Efficient Monitoring Program
    • 2002 Best Practices Workshop Comb. Effects of Chem. & Noise on Hearing
      • NORA – Nat. Occupational Research Agenda
      • NIOSH – Nat. Institute for Occupational Safety and Health
      • NHCA – Nat. Hearing Conservation Association
      • Goal:
        • Review current knowledge
        • Determine how to address chemical exposures in hearing loss prevention efforts
      • Next Slides:
      • Main Results of the Workshop
    • Current knowledge
      • Yes, enough evidence that solvents alone and solvents combined with noise exposure cause hearing, but more research is needed
      • Research does not capture all conditions/questions to outline a new national guideline for Hearing Conservation Programs
    • Mechanistic Research guide research to determine auditory risk - affect
      • Understand the mechanisms by which chemicals affect the auditory system. Lead to a prediction of which chemicals to target by preventive efforts
      • Issues:
        • Species respond differently – clues to the mechanism of ototoxicity
        • Toxic interactions – manipulate exposure parameters
        • Physical or other factors considerations
          • Health status, genetics, and age of participants
    • Rationale for Inclusion of Chemicals guide research on specific solvents and establish recommendations for best practices
      • Magnitude of exposed population
      • Evidence of chemical's ototoxicity, general toxicity, and neurotoxicity
      • Chemical produces reactive oxygen species (free radicals) or glutathione depletion -cellular injury
        • Glutathione –antioxidant that limits cell damage
    • Exposure Issues
      • Methods for administering chemicals
        • inhalation, dermal, injection sites
      • Methods for evaluating exposures
        • Task-based exposures assessments
          • experienced, specifically trained control variables)
        • Comprehensive noise measurements
        • Biomarkers for type of cell damage in the ear
        • Personal protective use
        • Target workers who have held their jobs
      • Methods for assessing auditory effects
        • Approach that discerns peripheral vs. central systems
        • No gold standard auditory test battery
    • Response Level and Action
      • Concentration level at which protective action (i.e.. enrolled in HCP) should be initiated
        • What actions for various solvents
          • Intervals between testing
            • HCP= annually
          • Alert/Criteria signal
            • HCP = puretones significant threshold shift
          • Alternatives Evaluation/control exposure
            • HCP = NIOSH 8 hour TWA =>85dB A SPL, hearing protection, remove from noise
          • New training needs for exposed population
            • HCP = initial and annual (effects, purpose testing & protection)
    • Other Issues Identified
      • Information Dissemination
      • Database (IH, HCP)
      • Other research questions
        • Development of standardized case history
        • Interactions that modify the effects (smoking)
        • Occurrence of tinnitus
        • Incorporating neurological tests periodical medical evaluations
        • Antioxidant therapy impact on preventive strategies
    • Key points – Take home message
      • Keep updated on new research findings and guidelines
      • Review exposures in current work area and workers
      • No standard yet but it is coming
      • Hearing is:
        • Complex (when damaged causes many problems)
        • Painless (often taken for granted)
        • Effects others (not just the hearing impaired)
        • Permanent (except for many OM and ME problems)
        • Accumulative and Progressive
        • Often preventable