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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 4  |  Issue : 1  |  Page : 4-8

Managing amalgam phase down: An evaluation of mercury vapor levels in a dental center in Lagos, Nigeria


1 Department of Restorative Dentistry, Lagos State University College of Medicine, Lagos, Nigeria
2 Department of Preventive Dentistry, Lagos State University College of Medicine, Lagos, Nigeria
3 Department of Restorative Dentistry, Lagos State University Teaching Hospital, Lagos, Nigeria

Date of Web Publication3-Jul-2017

Correspondence Address:
Afolabi Oyapero
Department of Preventive Dentistry, Lagos State University College of Medicine, Ikeja, Lagos
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jdrr.jdrr_20_17

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  Abstract 

Background: Occupational exposure to elemental mercury vapor in a dental setting is mainly through inhalation exposure during preparation, insertion, polishing, and removal of amalgam fillings including storage of amalgam waste before disposal. This study aims to determine the indoor air levels of elemental mercury vapor in the dental operatories and ancillary sites at the Lagos State University Teaching Hospital (LASUTH). Materials and Methods: Samples of the ambient air were taken at seven locations the Dental Center of LASUTH by a trained technician between 9:00 and 11:00 a.m. This was done at a predetermined height (41/2feet) above the floor for mercury vapor concentration using Lumex 915 light data logger mercury vapor analyzer manufactured by Ohio Lumex Company Incorporation, USA®. Results: The highest level of 1434 ng/m3 of mercury vapor in the air was found in the restorative clinic while the lowest of 23 ng Hg/m3 was found in the ambient air at the entrance of the dental Center. The Oral Surgery clinic had mercury vapor level of 318 ng/m3 which was slightly higher than Environmental Protection Agency recommended value of 0.3 μg/m3. Conclusion: An unacceptably high level of mercury vapor was detected, especially in the restorative clinic. Every dental clinic should have its ambient air evaluated for mercury vapor level for the purpose of forming a baseline data for monitoring purposes during the period of phase down of amalgam use. Best practices should also be instituted to reduce the level of exposure of patients and dental care workers to mercury vapor.

Keywords: Amalgam, ambient air, dental clinics, mercury, phase down


How to cite this article:
Loto AO, Oyapero A, Awotile AO, Adenuga-Taiwo A O, Enone LL, Menakaya IN. Managing amalgam phase down: An evaluation of mercury vapor levels in a dental center in Lagos, Nigeria. J Dent Res Rev 2017;4:4-8

How to cite this URL:
Loto AO, Oyapero A, Awotile AO, Adenuga-Taiwo A O, Enone LL, Menakaya IN. Managing amalgam phase down: An evaluation of mercury vapor levels in a dental center in Lagos, Nigeria. J Dent Res Rev [serial online] 2017 [cited 2017 Aug 23];4:4-8. Available from: http://www.jdrr.org/text.asp?2017/4/1/4/209358


  Introduction Top


Mercury is a naturally occurring heavy metal with a silvery appearance and dense liquid at room temperature. It occurs as cinnabar (Hg s) in rocks, soil, and sediments; and trace amounts are also found in coal. Mercury occurs in three forms – elemental or metallic form (Hg°), inorganic compounds, and organic compounds. It can be released naturally into the environment through weathering and erosion process involving rocks, soil and sediments, volcanic eruptions, and forest fires; and through human activities, such as chlorine factories, coal mining and burning, gas-powered plants, oil powered plants, artisanal and small scale gold mining,[1] cement production, nonferrous metal production,[2] municipal and hazardous waste disposal, pig-iron and steel production, mercury production mainly for batteries, and dental amalgam production and use.

All forms of mercury are highly toxic to the brain and kidney with varying degrees of neurological and renal consequences.[3],[4] Chronic exposure to mercury vapor in the range of 0.7–42 μg Hg/m 3 can lead to sleep disturbance tremors and impaired cognitive skills.[3] Acute exposure to high level of mercury vapor can also lead to psychotic reactions such as delirium, hallucination, suicidal tendency, erethism, irritability, fatigue, insomnia, tremor, loss of memory, depression, and vivid dreams.[5] Children and fetuses are more vulnerable to mercury exposure because their brains, and kidneys are at the initial stage of growth and development. The U.S. Environmental Protection Agency (EPA), World Health Organization, and the Agency for Toxic substances and Disease Registry treat mercury as an occupational hazard and have established specific occupational exposure limits.[6],[7],[8]

Occupational exposure to elemental mercury vapor in a dental setting is primarily through inhalation during the preparation, insertion, polishing, and removal of amalgam fillings including storage of amalgam waste before disposal.[9] Up to 88% of inhaled mercury is absorbed through the lungs and readily crosses to the blood–brain barrier. Metallic mercury is slowly volatized at the rate of 7-μg Hg/cm 2/h at 20°C and its elemental gaseous form can remain in the atmosphere for up to a year, transporting globally because of its high mobility.[10] A number of studies at dental sites in many countries have been carried out and reported with declarations of high levels of mercury vapor in the air of operatories, in which amalgam fillings were carried out;[11] and many of these levels did exceed the permissible limit recommended for safe physical and mental health.[12],[13] It is a well-established fact that dental health workers as well as patients are ultimately exposed to mercury pollutant.[14],[15] The mean urine mercury levels in dental personnel have been variously reported to range from 3 to 22 μg/L, compared to 1–5 μg/L as the normal range for nonoccupational groups.[16] The increased body burden can be attributed to mixing, placing, and removal of amalgam restorations, and this urinary mercury levels can be over 4 times that of control subjects.[17]

The realization of this fact as well as the general concern for the negative impacts of mercury on people's health did help international community to renew efforts to eliminate mercury use by adopting and signing of the Minamata Treaty in Japan in 2013.[18] The treaty mandated every signatory to phase down and control use of mercury with a moratorium timeline of about 10 years, and the use of alternative materials such as composite resins, glass ionomer cements, ceramics and gold alloys, is increasing, due to their esthetic properties and apparent health concerns related to the use of dental amalgam. Unlike in other nations,[19] Nigeria has little or no quantitative studies in the area of elemental mercury vapor evaluation in dental operatories. Therefore, aim of this study was to determine the indoor air levels of elemental mercury vapor in the dental operatories and ancillary sites in the Dental Centre at the Lagos State University Teaching Hospital (LASUTH) with a view to establishing a base line data for monitoring purposes so as to keep in line with permissible levels of mercury vapor in a clinical setting and in the spirit of amalgam phase down and mercury-free dentistry.


  Materials and Methods Top


This study was carried out by the dental Centre, LASUTH. Permission was obtained from the coordinator of the dental center as well as the management of LASUTH. Capsulated amalgam is sometimes used for restorations at the Restorative clinic.

The following sampling areas or sites were selected for evaluation:

  1. The entrance to the dental center
  2. The patient waiting room
  3. The dental laboratory
  4. The X-ray room
  5. Oral surgery clinic (four operatories)
  6. Oral diagnosis clinic (eight operatories); and
  7. Restorative clinic (eight operatories).


All the operating clinics, X-ray room, dental laboratory, and patients' waiting room were air-conditioned with split air conditioners. Ambient air in each of the identified areas was measured, at a predetermined height (4½ feet) above the floor for mercury vapor concentration using Lumex 915 light data logger mercury vapor analyzer manufactured by Ohio Lumex Company Incorporation, USA ®. This machine is an atomic absorption, spectrometer designed to measure mercury vapor indoor, and outdoor in real time; and the sensitivity range is 0.1 μg Hg/m 3 – 200 μg/Hg/m 3.

Samples of the ambient air were taken at seven different locations or sites in the dental center of LASUTH. The measurements were taken after a proper calibration of the mercury analyzer by a technician who had been trained in the use of the machine. The measurements were carried out between 9:00 and 11:00 h in the morning. The ambient air speed was also measured using an air meter. Real-time readings from the machine were taken after 10–15 min of operating the Lumex machine. Temperature of the operatories and ancillary sites were measured using the air conditioners' temperature indicators.


  Results Top


The mercury vapor concentrations of the tested areas are presented in [Table 1].
Table 1: Mercury vapor concentrations at the various tested sites in the dental center

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Number of amalgam restorations performed over 4 years in the LASUTH restorative Dentistry clinic is presented in [Table 2].
Table 2: Number of amalgam fillings performed over a 4 years period

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  Discussion Top


Dentistry is a profession dedicated to promoting and enhancing oral health and well-being. To accomplish these goals, dentists use a variety of materials and equipment. Unfortunately, some of the materials that are currently in use – including heavy metals and biomedical waste – present potential challenges to the environment.[20] Dental amalgam has been used for over 150 years for the treatment of dental cavities and is still used in large cavities because it is a long-lasting, cost-effective, and resilient restorative material. It however contains silver, mercury, copper, tin and zinc, with mercury constituting up to 50% by weight of dental amalgam, while dentists contribute between 3% and 70% of the entire mercury load entering wastewater treatment facilities.[21] The negative impact of mercury pollution on humans and the environment is well recognized nationally and internationally by various researchers.[7],[22],[23],[24] This recognition has led to the establishment of different occupational exposure standards (OES) to control exposure of workers and environment to mercury pollution in specific fields of human activities.[6],[7],[8] The EPA OES for mercury vapor is 3 μg/m 3.

A number of earlier studies, at dental centers, in many countries reported high levels of mercury vapor in the air of operatories where amalgam restorations were carried out.[9] Majority of these levels of mercury vapor reported at the research sites exceeded the permissible limit recommended for safe physical and mental health. In the LASUTH restorative Dentistry clinic, 9205 amalgam fillings or an average of 2400 amalgam fillings were performed annually. The capsulated amalgam form is usually used. The highest level of 1434 ng/m 3 of mercury vapor in the air was found in the restorative clinic; and it was approximately 5 times higher than the recommended value of exposure by U.S. EPA. This is conflicting to recent studies which showed reductions in mercury vapor levels in dental clinics in developed countries owing to reduction in the use of amalgam, best in-house hygiene practices during amalgam preparation, insertion, removal, polishing, storage of amalgam waste, mercury spillage, and disposal of amalgam waste. The level of mercury vapor in the air in the restorative clinic, in this study, could be higher if the samples were taken on the floor at the base of the dental chair, on the table where amalgam is prepared, at the storage site of amalgam waste and other potential sites of deposition of mercury and particles of amalgam. Studies have shown that the mercury vapor in the air samples taken at the floor and other potential sites of mercury deposition are generally higher than air-bone mercury vapor measured at breathing zone. However, in this study, the air samples were taken at a predetermined height of 4.5 feet above the floor which is equivalent to the breathing zone of dentists.

The lowest mercury vapor level of 23 ng Hg/m 3 was found in the ambient air at the entrance of the dental center, and it was below EPA value. It was also within the range of values generally found in “nonhotspots” for mercury emissions. The levels of mercury vapor in the other clinics and other tested sites were considerably less than that of restorative clinic as well as being below EPA recommended value. However, oral surgery had mercury vapor level of 318 ng/m 3; and it was slightly higher than EPA recommended value of 0.3 μg/m 3. It must be noted that the oral surgery clinic is closely situated to restorative clinic and any increase in the level of mercury vapor in the restorative clinic would definitely lead to an increase in the level of mercury vapor in oral surgery clinic because of high mobility of mercury in air. The high level might also be due to crushing of amalgam during the extraction of amalgam-filled teeth and poor storage of such teeth before disposal.

The mercury vapor levels are mainly influenced by in-house environmental practices for occupational health and safety, the types of dental procedures or activities being performed, the working routines, duration of practice, quantity level of ventilation, temperature, speed of indoor air, quantity of restoration done per day, the method of amalgam preparation and insertion; and the method of air and particles evacuation during removal and polishing of amalgam. The aforementioned factors could be responsible for the variations in the levels of mercury vapor at the different tested sites in this study. Herber et al.[25] showed that mercury exposure was directly related to the hygienic measures taken in the dental clinic; and many other studies have indicated that good hygiene is essential in reducing exposure to mercury vapor. Metallic mercury is slowly vaporized at room temperature and about 80% of the vapor entering the lungs can be absorbed. It is likely that the environmental values of mercury vapor will fluctuate throughout the day in a dental surgery as found by Nixon et al. In 2009, Farahat et al. reported on the effect of occupational exposure to elemental Hg in the amalgam on thymulin hormone production among dental staff, especially among dental nurses.[26] However, best in-house environmental practices for occupational health and safety would reduce possible adverse effects of mercury exposure in dentistry. The clinical significance of this study is to determine a baseline data for the purpose of monitoring mercury vapor levels in dental clinics during the phase down of amalgam. Therefore, it is essential that every dental clinic should determine baseline information on mercury vapor levels at specified time lines which will serve as controls during the period of phase down of amalgam use.


  Conclusion Top


It is concluded that the mercury vapor levels varied among the various clinics and the ancillary areas tested. The variations could be attributed to the types of activities being performed in each clinic as well as other factors such a level of ventilation, temperature, speed of air, and in-house hygienic practices for occupational health and safety.

Therefore, it is recommended that every dental surgery should have its ambient air evaluated for mercury vapor level for the purpose of forming a baseline data for monitoring purposes during the period of phase down of amalgam use. It is also appropriate that there should be periodic evaluations of mercury vapor levels in and around dental clinics as well as the levels of mercury in the blood of dentists to control and reduce the level of exposure of patients and dental care workers to mercury vapor.

Finally, the signing of Minamata Convention or Treaty on Mercury by Nigeria has made it imperative that mercury vapor levels at dental sites all over Nigeria should be evaluated to form a baseline data for monitoring purposes during the amalgam phase down strategic plan.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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25.
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26.
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    Tables

  [Table 1], [Table 2]



 

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