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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

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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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OtotoxinsOrganic 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)

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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 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 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 (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

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 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

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 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 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

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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

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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)

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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

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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