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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

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
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
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
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

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

slide6

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
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
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
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
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
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
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
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
slide14
Rationale for Inclusion of Chemicalsguide 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
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
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
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
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
ad