Chemicals and Hearing Loss California Industrial Hygiene Conference December 4, 2006

1
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

2
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

3
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)

4
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.

5
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

• 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
6
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)

7
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

8
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/susceptibili
  ty
• Medical contributions to poor hearing health

9
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)

10
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

11
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

12
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

13
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

14
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

15
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

16
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 gt85dB A SPL, hearing
  protection, remove from noise
• New training needs for exposed population
• HCP initial and annual (effects, purpose
  testing protection)

17
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

18
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