Toxicology and Industrial Health

Occupational exposure of dental staff to elemental mercury vapor released from dental amalgam is an issue of concern because of the possible immunological and neurological adverse outcomes. Recently, studies have reported that inorganic mercury induces immunosuppression by decreasing the production of thymus gland hormone (thymulin). This study aimed at investigating mercury body burden in dental staff and the relation of this burden to the potential impact of mercury on thymus gland hormone level (thymulin). Besides, the work aimed at verifying mercury effect on nitric oxide synthetase as a possible mechanism of its immunotoxicity. The study population consisted of a group of dental staff (n = 39) [21 dentists and 18 nurses] and a matched control group (n = 42). Each individual was subjected to detailed occupational and medical history taking and to estimation of urinary mercury (U-Hg) and blood mercury (B-Hg) as indicators of mercury body burden and exposure, respectively. Measurement of total thymulin hormone blood level, and plasma level of nitrite and nitrate (indicators of nitric oxide) was also done. The study showed a significantly increased U-Hg and B-Hg levels in the dental staff compared to their controls. This elevation of mercury body burden was associated with significant reduction in thymulin hormone blood level and nitric oxide parameters. These results were more evident in the group of nurses compared to the dentists. In conclusion, our results show that dentists and dental nurses have significant exposure to mercury vapor and point to the negative impact of mercury on thymus gland functions and confirm the implication that the nitric oxide pathway is a possible mechanism for this impact. Moreover, the study raises attention to the importance of hygiene measures in reduction of exposure to mercury vapor released from dental amalgam.

ACGIH (2003) Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.
Agency for Toxic Substances and Disease Registry (ATSDR) (2003) Toxicological Profile for Mercury (update). Atlanta, GA: U.S. Department of public health and human services, public health service.
Amercican Dental Association (ADA) Council on Scientific Affairs (2003) Association report: dental mercury hygiene recommendations. J Am Dent Assoc 134: 14981499. Google Scholar Medline
Anderson G  Moore N  Owen J  Jenkinson E  (1996) Cellular interactions in thymocyte development. Annu Rev Immunol 14: 7399. Google Scholar Medline
Atesagaoglu A  Omurlu H  Ozcagli E  Sardas S  Ertas N  (2006) Mercury exposure in dental practice. Oper Dent 31: 666669. Google Scholar Medline
Bake MIa  Aulika B  Luse IIu  (2002) Risk for the influence of a chemical factor on dentists' health. Gig Sanit 4: 2930. Google Scholar
Consolini R  Legitimo A  Calleri A  Milani M  (2000) Distribution of age-related thymulin titres in normal subjects through the course of life. Clin Exp Immunol 121: 444447. Google Scholar Medline
Darbenne M  Savino W  (1994) Control of thymus physiology by peptidic hormones and neuropeptides. Immunol Today 15: 518523. Google Scholar Medline
Ding AH  Nathan CF  Stucher DJ  (1988) Release of active nitogen intermediate from mouse peritoneal macrophage comparison of activating cytokines and evidence of independent production. J Immunol 141: 24072412. Google Scholar Medline
Downing G  (1994) Multiple nitric oxide synthase systems in adult rat thymus revealed using NADPH diaphorase histochemistry. Immunology 82: 659664. Google Scholar Medline
Echeverria D  Heyer NJ  Martin MD  Naleway CA  Woods JS  Bittner AC  (1995) Behavioral effects of low-level exposure to elemental Hg among dentists. Neurotoxicol Teratol 17: 161168. Google Scholar Medline
El-Kholy F  Ibrahim N  El-Yasaky M  (1999) Exposure to mercury vapor and impact on health in the dental profession. Egypt J Occup Med 23: 161174. Google Scholar
El-Olemy A  Amin H  (2003) Occupational mercury exposure among dental assistants. Egypt J Occup Med 27: 229242. Google Scholar
Holán V  Krulová M  Zajícová A  Pindjáková J  (2002) Nitric oxide as a regulatory and effector molecule in the immune system. Mol Immunol 38: 989995. Google Scholar Medline
Karahalil B  Rahravi H  Ertas N  (2005) Examination of urinary mercury levels in dentists in Turkey. Hum Exp Toxicol 24: 383388. Google Scholar Medline
Kim S  Johnson V  Sharma R  (2002) Mercury inhibits nitric oxide production but activates proinflammatory cytokine expression in murine macrophage: differential modulation of NF-B and p38 MAPK signaling pathways. Nitric Oxide 7: 6774. Google Scholar Medline
Kim S  Johnson V  Sharma R  (2003) Oral exposure to inorganic mercury alters T lymphocyte phenotypes and cytokine expression in BALB/c mice. Arch Toxicol 77: 613620. Google Scholar Medline
Kim S  Sharma RP  (2003) Cytotoxicity of inorganic mercury in murine T and B lymphoma cell lines: involvement of reactive oxygen species, Ca2+ homeostasis and cytokine gene expression. Toxicol In Vitro 17: 385395. Google Scholar Medline
Langworthl S  S'allsten G  Barreg L  Cynkier I  Lind M-L  Soderman E  (1997) Exposure to mercury vapor and impact on health in the dental profession in Sweden. J Dent Res 76: 13971404. Google Scholar Medline
Mocchegiani E  Muzzioli M  Giacconi R  (2000) Zinc, metallothionins, immune responses, survival and aging. Biogerontology 1: 133143. Google Scholar Medline
Morton J  Mason HJ  Ritchie KA  White M  (2004) Comparison of hair, nails and urine for biological monitoring of low level inorganic mercury exposure in dental workers. Biomarkers 9: 4755. Google Scholar Medline
Moszczyński P  Rutowski J  Słowiński S  Bem S  (1998) Immunological effects of occupational exposure to metallic mercury in the population of T-cells and NK-cells. Analyst 123: 99103. Google Scholar Medline
Noureddin BN  Al-Haddad CE  Bashshur Z  Safieh-Garabedian B  (2006) Plasma thymulin and nerve growth factor levels in patients with primary open angle glaucoma and elevated intraocular pressure. Arch Clin Exp Ophthalmol 244: 750752. Google Scholar Medline
Pinto C  Lima L  Marques M  (2003) Sequential injection analysis of nitrites and nitrates in human serum using nitrate reductase. Clin Chim Acta 337: 6976. Google Scholar Medline
Ritchie K  Burke FJ  Gilmour WH  Macdonald EB  Dale IM  Hamilton RM  (2004) Mercury vapour levels in dental practices and body mercury levels of dentists and controls. Br Dent J 197: 625632. Google Scholar Medline
Ritchie K  Gilmour WH  Macdonald EB  Burke FJ  McGowan DA  Dale IM  (2002) Health and neuropsychological functioning of dentists exposed to mercury. Occup Environ Med 59: 287293. Google Scholar Medline
Ritchie K  Macdonald E  Hammersley R  O'Neil J  McGowan D  Dale I  (1995) A pilot study of the effect of low level exposure to mercury on the health of dental surgeons. Occup Environ Med 52: 813817. Google Scholar Medline
Rojas M  Guevara H  Rin R  Rodrguez M  Olivet C  (2000) Occupational exposure and health effects of metallic mercury among dentists and dental assistants: a preliminary study. Valencia, Venezuela; 1998. Acta Cient Venez 51: 3238. Google Scholar Medline
Roy S  Roy G  Mishara S  Prakash V  (2000) Role of nitric oxide in central regulation of humoral immune response in rats. Indian J Pharmacol 32: 318320. Google Scholar
Santarelli L  Bracci M  Mocchegiani E  (2006) In vitro and in vivo effects of mercuric chloride on thymic endocrine activity, NK and NKT cell cytotoxicity, cytokine profiles (IL-2, IFN-gamma, IL-6): role of the nitric oxide-L-arginine pathway. Int Immunopharmacol 6: 376389. Google Scholar Medline
Santarelli L  Di Lorenzo L  Valentino M  Bracci M  Rapisarda V  Cassano F  (2005) Reduced thymulin production during occupational exposure to lead. G Ital Med Lav Ergon 27 (Suppl. 1): 6872. Google Scholar Medline
Santarelli L  Valentino M  Bracci M  Rapisarda V  Soleo L  Mocchegiani E  (2004) Reversibility of thymulin production impairment by L-arginine supplementation in mice exposed to inorganic mercury. Int J Immunopathol Pharmacol 17 (2 Suppl): 123128. Google Scholar Medline
Savino W  Darbenne M  (2000) Neuroendocrine control of thymus physiology. Endocr Rev 21: 412443. Google Scholar Medline
Silbergeld E  Silva I  Nyland J  (2005) Mercury and autoimmunity: implications for occupational and environmental health. Toxicol Appl Pharmacol 207 (2 Suppl): 282292. Google Scholar Medline
Tezel H  Ertas S  Ozata F  Erakin C  Kayali A  (2001) Blood mercury levels of dental students and dentists at a dental school. Br Dent J 191: 449452. Google Scholar Medline
Tian L  Lawrence DA  (1996) Metal-induced modulation of nitric oxide production in vitro by murine macrophages: lead, nickel, and cobalt utilize different mechanisms. Toxicol Appl Pharmacol 141: 540547. Google Scholar Medline
Tripathi PT  Tripathi PT  Kashyap LK  Vinod S  (2007) The role of nitric oxide in inflammatory reactions. FEMS Immunol Med Microbiol 51: 443452. Google Scholar Medline
Valentino M  Santarelli L  Pieragostini E  Soleo L  Mocchegiani E  (2001) In vitro inhibition of thymulin production in mercury-exposed thymus of young mice. Sci Total Environ 270: 109112. Google Scholar Medline
Zimmer H  Ludwig H  Bader M  Bailer J  Eickholz P  Staehle HJ  (2002) Determination of mercury in blood, urine and saliva for the biological monitoring of an exposure from amalgam fillings in a group with self reported adverse health effects. Int J Hyg Environ Health 205: 205211. Google Scholar Medline

Vol 25, Issue 3, 2009

Recommended Citation

Effect of occupational exposure to elemental mercury in the amalgam on thymulin hormone production among dental staff

SA FarahatDepartment of Occupational Diseases and Industrial Medicine, Faculty of Medicine, Cairo University, Giza, EgyptLA RashedDepartment of Biochemistry, Faculty of Medicine, Cairo University, Giza, EgyptNH ZawillaDepartment of Occupational Diseases and Industrial Medicine, Faculty of Medicine, Cairo University, Giza, Egypt nerhamdy71@hotmail.comSM FaroukDepartment of Occupational Diseases, National Research Center, Cairo, Egypt

Toxicology and Industrial Health

Vol 25, Issue 3, pp. 159 - 167

First published date: May-29-2009

If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click on download.

For more information or tips please see 'Downloading to a citation manager' in the Help menu.


Download article citation data for:
SA FarahatLA RashedNH ZawillaSM Farouk
Toxicology and Industrial Health 2009 25:3, 159-167

Request Permissions

View permissions information for this article