Chemicals and hearing loss california industrial hygiene conference december 4 2006
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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:

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Chemicals and hearing loss california industrial hygiene conference december 4 2006 l.jpg

Chemicals and Hearing LossCalifornia 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 l.jpg
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


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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)


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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.


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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

Ototoxins

  • Drugs

    • Aminoglycosides

    • Loop diuretics

    • Anti-neoplastic agents

    • ASA

    • Quinine compounds

  • Others

    • Chem. warfare nerve agents

    • Organophosphate (pesticide)

    • Paraquat (pesticide)

  • Metals

    • * Mercury and derivatives

    • * Lead and derivatives

    • * Arsenic (atoxyl)

    • * Manganese

    • Trimethyltin (organic tin)

    • Cobalt

  • Asphyxiants

    • ** Carbon Monoxide

    • * Cyanide

Army ID:* potential ** high-priority


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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)


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Problems caused by solvents Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug.

  • 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


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Many other causes of Hearing Loss Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug.

  • 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


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Hearing Conservation Programs Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug. (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)


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Questions with integrating into solvent exposure in HCP Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug.

  • Which solvents to include?

  • Excessive exposure levels?

  • Best audiometric test battery?

    • Location of damage - Retrocochlear hearing loss

    • Efficient Monitoring Program


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2002 Best Practices Workshop Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug. 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


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Current knowledge Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug.

  • 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


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Mechanistic Research Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug. 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


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Rationale for Inclusion of Chemicals Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug. 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


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Exposure Issues Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug.

  • 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


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Response Level and Action Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug.

  • 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)


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Other Issues Identified Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug.

  • 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


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Key points – Take home message Keith, RW., Scandinavian Journal of Work, Environment & Health, 19(4): 245-54, 1993 Aug.

  • 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


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