Chemical Exposure as a Risk Factor for Hearing
- Slides: 27
Chemical Exposure as a Risk Factor for Hearing Loss: Implications for Occupational Health Thais C. Morata, Ph. D. Hearing Loss Prevention Team tmorata@cdc. gov The findings and conclusions in this presentation are those of the author and do not necessarily represent the views of the National Institute for Occupational Safety and Health. 1
Before the 1980’s No systematic research effort on auditory effects of chemicals, but isolated reports: - Poisoning: accidents or abuse - Occupational exposures (painters, printers, metal, chemical, leather industry workers, etc. ) - Environmental exposures (air and water contamination) 2
Schacht J, Hawkins JE. 2006 Sketches of otohistory. Part 11: Ototoxicity: drug-induced hearing loss. Audiol Neurootol. 2006; 11(1): 1 -6. 3
Bergstrom & Nystrom, 1986 Scand Audiol. 1986; 15(4): 227 -34. 4
Features of NIHL/Ototoxicity General descriptors • Bilateral, symmetrical, and irreversible • Onset in the high-frequency range, progress rate determined by risk factors • Cochlear, or with a cochlear component • History of exposure 5
Ototoxicity of therapeutic drugs • Antimalarial • Non-steroidal antiinflammatory • Aminoglycosides • Antimicrobial • Loop diuretics • Antineoplastic • Chelating agents Mostly: ü Vastly studied ü Effects restricted to cochlea ü Use monitored, i. e. , knowledge of intake Approaches: ü Substitution ü Antioxidants 6
Ototoxicity of environmental chemical exposures Mostly: ü Relatively few studies • Metals ü Effects not restricted to the cochlea • Solvents ü Use poorly monitored, i. e. , poor • Asphyxiants knowledge of exposure history • Pesticides ü Confounded by noise Approaches: üSubstitution/control of exposure üAntioxidants 7
Selected key publications reporting effects • Metals – Trimethyltin (Fechter et al, Crofton et al. ) – Methyl mercury (Konshi et al. , Ison et al. , Rice et al. ) – Lead (Discalzi et al) – Pesticides Perry & May J Agromedicine. 2005; 10(2): 4955. 8
Selected key publications reporting effects • Chemical asphyxiants – Carbon Monoxide (CO) + noise (Fechter et al) – Hydrogen Cyanide + noise (Fechter et al) – Potassium Cyanide (Konishi et al. , Evans & Klinke, Fechter et al. ) • Acrylonitrile (Fechter et al. , Pouyatos et al. ) 9
Selected key publications reporting effects • Organic solvents – Toluene (Pryor et al. , Sullivan et al. , Johnson et al. , Crofton et al, Campo et al. , Morata et al. , Fechter et al. ) – Ethyl benzene (Cappaert et al. ) – Styrene (Campo et al. , Crofton et al. , Pryor et al. , Morata et al, Sliwinska-Kowalska et al ) – Xylene (Pryor et al. , Crofton et al, 1994) – Trichloroethylene (Crofton et al. , Fechter et al. , Muijser et al. ) – N- Hexane (Rebert et al. , Nylen et al. , ) – Carbon disulfide (Sulkowski, Morata, Chang et al. ) – Solvent mixtures (Rebert et al. , Crofton et al. , Morata et al. , Jacobsen et al. , Kim et al. , Sliwinska-Kowalska et al) 10
2006 ICOH Milano • Special Session (June 14 th) • Mini-Symposium (June 15 th) • Other presentations dispersed in noise or chemical sessions 11
In the 1990’s 12
1998 -2006 TLVs® and BEIs®: Notes, Noise “Exposure to certain chemicals may also result in hearing loss. In settings in which there may be exposure to noise as well as toluene, lead, … …. periodic audiograms are advised and should be carefully reviewed. ” 13
ACOEM Noise-induced Hearing Loss EVIDENCE-BASED STATEMENT, JOEM 45(6) 2003 “Clinicians evaluating cases of possible noise-induced hearing loss should keep in mind the following clinical concerns: … …Coexposure to ototoxic agents, such as solvents, heavy metals and tobacco smoke, may act in synergy with noise to cause hearing loss”. 14
Standards Australia-New Zealand AS/NZS 1269: 2005 Occupational Noise Management/Informative Appendix on Ototoxic Agents requiring hearing tests for those exposed to ototoxic agents http: //www. standards. com. au/catalogue/ script/search. asp 15
US Army Regulation 1998 -2004 Dept. of the Army Pamphlet 40 -501 Hearing Conservation Program: Requires consideration of ototoxic chemical exposures (including toluene) for program inclusion, particularly when in combination with marginal noise (¶ 3 -3). https: //134. 11. 61. 26/CD 4/Publications/DA/DA%20 Pam%2040 -501%2019981210. pdf Fact Sheet 51 -002 -0903 suggests Action Level for chemicals for inclusion in Hearing Conservation Program. http: //chppm-www. apgea. army. mil/documents/FACT/51 -002 -0903. pdf 16
Legislation The European Community directive on noise (2003/10 EC noise) requires that the interaction between noise and workrelated ototoxic substances, and noise and vibration be taken into account in the risk assessment of exposed populations (Article 4 of Section II) . http: //europa. eu. int/eur-lex/pri/en/oj/dat/2003/l_04220030215 en 00380044. pdf 17
Legislation Countries (Australia, New Zealand, Brazil) started to accept link between chemical exposure and hearing loss in compensation cases Brazil Decree no. 3048/ May 6, 1999 Australia http: //www. workcover. nsw. gov. au/Publicati ons/Workers. Comp/Injury. Management/Permi mpair. htm 18
Remaining challenges 1 - Number of chemicals and combinations Lab studies Damage Mechanism Administration Route Field Studies Priority List & Rationale Identify Risk Populations Data over Exposure Range Rationale: Magnitude of exposed populations, chemical’s ototoxicity, general toxicity, as well as nephro- or neurotoxicity. Morata et al. , 2003 19
Remaining challenges 2 - Dose-response, NOEL, LOEL, Action Level, Response Level • Chronic effect/ role of peak exposures • Biomarkers 20
Remaining challenges 2 - Analysis strategies Groups: • Distribution of hearing loss to be compared from groups with different exposure conditions • Comparing mean thresholds between groups does not always allow distinction between the effect of each agent (noise or chemical); risk ratios are needed. 21
2 - Analysis strategies • Pure tone audiometry – Requires large population, or – Requires complaint of speech difficulty or other difficulty inconsistent w/ thresholds • Need to consistently define hearing loss and change from baseline • Need good reference data from unexposed populations • Criteria for excluding age/confounders • Consideration of non-occupational exposures 22
Remaining challenges 3. Appropriate metrics Individual cases: • Ototoxicity or neurotoxicity/Cochlear vs. retrocochlear? Tests to complement puretone audiometry are needed • Complaints of hearing difficulties not compatible with audiometric result • Other complaints associated with neurotoxicity (balance, vision, etc). 23
3. Appropriate metrics Availability of gold standard or screening tests? Not yet (Morata and Little, 2002) • Length of test • Administration time • Ease of analysis • Sensitivity/specificity (validity) • Utility for retrospective vs. prospective or longitudinal studies 24
Impact on Preventive Practices & Research • Recommended limits have not taken ototoxic properties or combined exposures into consideration • Controlling noise and hearing protectors insufficient for preventing hearing loss • Eligibility to Hearing Loss Prevention Programs 25
Remediation • Reduce hazardous exposures – Engineering controls – Protective equipment (e. g. respirators, gloves) • Education of the potentially affected population 26
NIOSH, Publication Dissemination http: //www. cdc. gov/niosh/homepage. html pubstaft@cdc. gov http: //www 2 a. cdc. gov/niosh-comments/nora-comments/input. asp 27
- Managing economic exposure and translation exposure
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