Journal of Pharmacy And Bioallied Sciences

ORIGINAL ARTICLE
Year
: 2017  |  Volume : 9  |  Issue : 5  |  Page : 79--81

Recovery of mercury from dental amalgam scrap-Indian perspective


Kadandale Sadasiva1, Sreeram Rayar1, Unnikrishnan Manu1, Kumarappan Senthilkumar1, Srinivasan Daya2, Nagarajan Anushaa3,  
1 Department of Conservative Dentistry and Endodontics, Chettinad Dental College and Research Institute, Kanchipuram, Tamil Nadu, India
2 Department of Pedodontics, Chettinad Dental College and Research Institute, Kanchipuram, Tamil Nadu, India
3 Department of Dental Surgeon, Chennai, Tamil Nadu, India

Correspondence Address:
Kadandale Sadasiva
Department of Conservative Dentistry and Endodontics, Chettinad Dental College, Kanchipuram  -  603  103, Tamil Nadu
India

Abstract

Aim: The aim is to recycle mercury from dental amalgam scrap using the vacuum distillation method. Materials and Methods: A total of 150 g of dental amalgam scrap was taken in a round bottom flask and was subjected to vacuum distillation at 398°C. The vapor of mercury was collected in another round bottom flask. Observation: The procedure is carried out for mercury recovery using vacuum distillation apparatus, and mercury vapor are collected in a round bottom flask, and the silver is recovered using sucrose as reducing agent. Using 150 g of dental amalgam scrap 50%–80% of silver are recovered, and silver has a purity of 70%–80%. However, the total time required in the reduction process ranged between 303 and 600 min. Conclusion: Mercury could be recycled from dental amalgam scrap through vacuum distillation method at 398°C and its implication of dental amalgam scrap in an Indian perspective.



How to cite this article:
Sadasiva K, Rayar S, Manu U, Senthilkumar K, Daya S, Anushaa N. Recovery of mercury from dental amalgam scrap-Indian perspective.J Pharm Bioall Sci 2017;9:79-81


How to cite this URL:
Sadasiva K, Rayar S, Manu U, Senthilkumar K, Daya S, Anushaa N. Recovery of mercury from dental amalgam scrap-Indian perspective. J Pharm Bioall Sci [serial online] 2017 [cited 2022 Aug 19 ];9:79-81
Available from: https://www.jpbsonline.org/text.asp?2017/9/5/79/219305


Full Text



 Introduction



Dental amalgam is one of the most commonly used permanent filling materials in restorative dentistry. In 1997, WHO held a consultation to emphasize the need for research on alternatives to amalgam.[1]

Its physical and mechanical properties, stability, ease of use, and relatively low cost have made amalgam the preferred choice in many clinical situations when compared with other direct restorative materials such as composites and glass ionomers.[2] However, one of its major components is mercury which is of particular concern due to its potential adverse effects on humans and the environment.[2]

There are four possible harmful effects of dental amalgam– oral galvanism, toxicity, allergenicity, and ecological grievances.[3]

Hence, our focus was to extract mercury from dental amalgam scrap to limit ecological grievances.

Aim

The aim of this study was to recycle mercury from dental amalgam scrap using the vacuum distillation method [Figure 1].{Figure 1}

 Materials and Methods



Dental amalgam scrap was collected from the preclinical conservative laboratory, at Chettinad Dental College and Research Institute; Kelambakkam; Tamil Nadu; India. The collected scrap was sent to the Laboratory of Chemical Residues, VIT University, Chennai, India.

Ethical committee clearance was obtained from Chettinad Academy of Research and Education ref no. IHEC/02/2014/DESPNO.359-28.02.2014.

The proposal of the study was sent to ICMR and approved for funding. ref. ICMR-2014000558, F-no-21/1/2014BMS-STS.

150 grams of dental amalgam scrap was taken in a round bottom flask and was subjected to vacuum distillation at 398°C. The vapor of mercury was collected in another round bottom flask as shown in [Figure 2].{Figure 2}

Separation of other metals: Other metals that would be still left are silver, tin, copper in the form of residue and it will be initially diluted with nitric oxide 32.5% (25 ml) and this resulted in the formation of AgNo3 (CuNo3).[2] The solution is centrifuged, and residue with tin is stored for metal recovery. The AgNo3 (CuNo3)[2] was then mixed with sodium chloride20% (10 ml), and Ag precipitated as Agcl2. The solution is again centrifuged. The precipitate containing copper nitrate was then stored for metal recovery. The Agcl2 solid was mixed with 100:1 (deionized water: nitric acid) until supernatant become colorless. This process resulted in the isolation of the metallic silver. This was further purified by constant heating and agitation with sodium hydroxide and sucrose, as reducing agent. This procedure will reduce the metallic silver a relatively less toxic form. Alternatively, ascorbic acid will be used as a reducing agent in place of sucrose.

 Observation and Results



The procedure is done for mercury recovery using vacuum distillation apparatus, and mercury vapor is collected in a round bottom flask and the silver is recovered using sucrose as reducing agent. By using 150 g of dental amalgam scrap 50%–80% of silver are recovered, and silver has a purity of 70%–80%. However, the total time required in the reduction process ranged between 303 and 600 min.

 Discussion



Dental amalgam particles are one of the sources of mercury, which pollutes the environment in various ways. It is known to be neuro toxic and nephrotoxic.[4] According to a recent German report, approximately 46% of the freshly triturated amalgam is inserted as new amalgam restorations, and 54% approximately disposed of through sewage systems.[5]

Richards in his study-Amalgam, risk, benefits, and the precautionary principle 2008 calculated that “the environmental impact of mercury from 800 000 dental offices worldwide would represent between 0.04% and 0.20% of the total worldwide environmental mercury pollution from all sources.”[6]

Muhamedagic et al. in 2009 concluded that the quantity of hazardous wastes in dental solid wastes is a small proportion, there is still cross infection risk and potential danger for environment associated with mismanaged wastes.[7] For this reason, knowledge of waste composition and development of proper management alternatives are needed.[7]

The release of amalgam particles into the dental office waste water or on solid waste is of major concern as once mercury enters the water or soil, bacteria convert it into methyl mercury, which is a potent neurotoxin which causes brain, kidney, and lung damage.[8]

Mercury commonly occurs in nature as sulfides and in a number of minerals.[2] From these deposits, mercury is circulated naturally in the biosphere, primarily by degassing from the earth's crust and oceans.[2] Natural emission of mercury amounts to around 150,000 tons a year.[2] Globally, approximately 10,000 tons of mercury are mined each year, with an estimated 3%–4% is used in dentistry.[2]

In the present scenario, the role of dental amalgam exercise in dental curriculum plays a vital role in the training of dental students for its manipulation and placement of restoration which is considered as standard and basic.

In India, there are about 309 dental colleges, which use dental amalgam for preclinical exercises and restorations in clinical outpatient departments.[9]

During these exercises lot of dental amalgam, scrap is produced and deserves proper disposal. Based on an average calculation made about 77 kg of dental amalgam scrap is produced from these colleges, which requires proper destination so that it will not affect the eco system. The possible toxic effects of mercury are strongly dependent on its chemical form.[2] In dentistry, only the metallic form is used while inorganic and organic compounds are also present in the environment. The metallic form is mainly absorbed in the human body through the skin while mercury vapor absorption is through the lungs.[2] However, in our research, we chose vacuum distillation; hence, there will not be any occupational hazards involved. Valenzuela (1985) proposed a method for recycling the mercury present in amalgam residues originated from dental offices. The method consisted in heating the residues at 650°C, causing evaporation of mercury and condensation in another refrigerated container. This mercury presented high levels of impurity and organic elements which would be further removed with washes in 1% nitric acid solution and in 1% potassium cyanide and sodium peroxide solutions diluted in distilled water. Thereafter, the material was dried and distilled, resulting in a 99% pure mercury.[10]

In the current study, the amalgam scrap was heated at 398°C[11] hence making the procedure simpler and less technique sensitive obtaining mercury.

Adding the process of vacuum distillation to mercury recovery, thus eliminating the use of toxic reagents as cyanide and avoiding production of more residues.[10]

The environmental impact of dental mercury is mainly due to the poor management of dental amalgam waste. We should consider the various possibilities that can satisfy both the application of dental amalgam as a restorative material as well as minimizing the environmental effects. Tackling this problem by the use of this method of mercury waste handling will reduce the environmental concerns of dental waste and this methodology does not require sophisticated equipment or specialized personnel, and is a cost-effective alternative.

 Conclusion



This research was a testimony to the fact that mercury could be recycled from dental amalgam scrap through vacuum distillation method and the obtained mercury can be effectively used especially in preclinical exercises where the quality of mercury does not play a major role. Although pros and cons exist regarding mercury toxicity, still the usage of dental amalgam in dentistry plays a major role in terms of permanency, economical, and its ease of placement in the cavity. Hence, proper care should be executed in collection and disposal of mercury containing amalgam scrap and final destiny to mercury meticulously planned to avoid contamination of the environment from dentistry. Further studies are also needed to form stringent protocols for proper disposal and waste management of mercury.

Financial support and sponsorship

Indian council of medical research (ICMR).

Conflicts of interest

There are no conflicts of interest.

References

1Ballal S. Ready Reckoner Series in Dental Science: Dental Materials. Vol. 14. New Delhi, India: CBS Publication; 2013. p. 217-8.
2Chin G, Chong J, Kluczewska A, Lau A, Gorjy S, Tennant M, et al. The environmental effects of dental amalgam. Aust Dent J 2000;45:4.
3Mercury BM. Handbook on the Toxicology of Metals. Amsterdam: Elsevier Science Publishers; 1986. p. 387-445.
4Agarwal B, Singh SV, Bhansali S, Agarwal S. Waste management in dental office. Indian J Community Med 2012;37:201-2.
5Chin G, Chong J, Kluczewska A, Lau A, Gorjy S, Tennant M, et al. The environmental effects of dental amalgam. Aust Dent J 2000;45:246-9.
6Richards D. Amalgam, risk, benefits and the precautionary principle. Evid Based Dent 2008;9:2.
7Muhamedagic B, Muhamedagic L, Masic I. Dental office waste - Public health and ecological risk. Mater Sociomed 2009;21:35-8.
8Berglund A. Estimation by a 24-hour study of the daily dose of intra-oral mercury vapor inhaled after release from dental amalgam. J Dent Res 1990;69:1646-51.
9Available from: http://www.dciindia.org.in/CollegeSearch.aspx?ColName=&CourseId=1&SplId=0&StateId=&Hospital=&Type=0&Status=-Select. [Last accessed on 2017 May 22, 15:24].
10Iano FG, Santos Sobrinho OD, Silva TL, Pereira MA, Figueiredo PJ, Alberguini LB, et al. Optimizing the procedure for mercury recovery from dental amalgam. Braz Oral Res 2008;22:119-24.
11Pereira HA, Iano FG, da Silva TL, de Oliveira RC, de Menezes ML, Buzalaf MA, et al. Recovery of silver residues from dental amalgam. J Appl Oral Sci 2010;18:121-6.