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. 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

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/susceptibility • 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 =>85dB 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