7-1917-Cor Heavy Metal Wastewater

Concentrations of Heavy Metals in Wastewater of One of the Largest Dentistry Schools in Iran

1Department of Community Oral Health, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran

Correspondence to
Hadi Ghasemi, DDS, PhD, Department of Community Oral Health, School of Dentistry, Shahid Beheshti University of Medical Sciences, Daneshjou Blvd, Evin, Tehran 1983963113, Iran

Tel/Fax: +98-21-2242-1813

E-mail: ha.ghasemi@sbmu.ac.ir

Received: Feb 2, 2020

Accepted: Feb 15, 2020

Wastewater of dental units, due to the use of amalgam, chemical solutions for radiographic film processing, prosthetic appliances, etc, contains various heavy metals including mercury, silver, nickel, lead, copper, chromium, and cadmium. All these heavy metals are hazardous to health and regulatory limits have been set to control them.1

In a study for evaluating the waste stream of dental offices in Seattle, USA, the authors reported concentrations of nickel <400 µg/L, cadmium <14 µg/L, copper 19 000 µg/L, mercury 150 µg/L, and lead <300 µg/L, and concluded that most of the samples have mercury and copper above the local discharge limits.2 Shraim, et al, studying wastewater of three public dental clinics in Madinah, Saudi Arabia in 2009, found the concentrations of copper 10 000 µg/L, mercury 5300 µg/L, and lead 600 µg/L, to be much higher than the local permissible limits.3

Schools of dentistry, due to the high workload of clinical dental activities with a large number of dental units, have a substantial contribution to waste production. We therefore conducted this cross-sectional study to evaluate the concentrations of heavy metals in wastewater of the Dentistry School of Shahid Beheshti University of Medical Sciences, Tehran, Iran.

In this dentistry school, wastewater of 253 dental units arrives into two buffer tanks and then discharges to an absorption well. All dental units are equipped with filters that prevent big particles from entering the wastewater pipes. The buffer tanks have also amalgam separators. The process of data collection included convenient sampling of 16 samples taken from the wastewater of the outlet of the buffer tanks once every two weeks during four months, from April to July 2018, plus one sample taken from the inlet water to the dental units of the school.

The samples were collected in a 500-mL plastic container and immediately transferred to the laboratory. At the first stage, 2.5 mL of nitric acid was added to the 500 mL of the wastewater sample; 100 mL of this solution was then subjected to 5 mL of hydrochloric acid and kept in a steam bath for 15 min. Concentrations of mercury, lead, cadmium, nickel, and copper were measured using direct air-acetylene flame atomic absorption spectrometry by a Hach® DR5000 spectrophotometer.

The Ethics Committee of Shahid Beheshti School of Dentistry approved this study. Due to the budget restriction, sampling of mercury was performed only one time through the four months.

The difference between the metal concentrations in the inlet water and wastewater reflected an approximate added metal to the environment due to dental practices. The concentration difference for lead was 107.75 µg/L; copper, 587; cadmium, 52.8; nickel, 86.2; and mercury 8.9. The concentrations of the metals, but mercury, were below the maximum permissible values (Table 1).

Table 1: Mean (SD) concentrations of five heavy metals measured in the inlet water and wastewater of the dental school studied, along with the maximum permissible limits for the metals set by the US Environmental Protection Agency (EPA)4 and Iran Department of Environment (DOE). The unit of measurement is μg/L.

Heavy Metal

Inlet water

Wastewater

US EPA

Iran DOE

Lead

2.9

110.6 (16.5)

2000

1000

Copper

76.5

663.5 (469.1)

6000

1000

Cadmium

0.45

53.3 (6.1)

1500

100

Nickel

5.1

91.1 (28.1)

4000

2000

Mercury

0.1

9

2.6

<1

We found that although practice of dentistry in this school adds some heavy metals to the environment, the amount is still below the permissible levels for lead, copper, cadmium, nickel; however, we need to have more control on the safe disposal of mercury.

Acknowledgments

The financial support of the Shahid Beheshti School of Dentistry, Deputy of Research for this study is appreciated.

Conflicts of Interest: None declared.

References

  1. Martin S, Griswold W. Human health effects of heavy metals. Environmental Science and Technology Briefs for Citizens 2009;15:1-6.
  2. Welland C. Dental office waste stream characterization study: Metro 1991. Available from https://p2infohouse.org/ref/03/02193.pdf (Accessed February 8, 2020).
  3. Shraim A, Alsuhaimi A, Al-Thakafy JT. Dental clinics: a point pollution source, not only of mercury but also of other amalgam constituents. Chemosphere 2011;84,1133-9.
  4. Milwaukee Metropolitan Sewerage District. Discharge regulations and enforcement procedures MMSD rules, Chapter 11. Available from www.mmsd.com/application/files/9614/8211/4535/Discharge_Regulations_and_Enforcement_Procedures.pdf (Accessed February 8, 2020).

Cite this article as: Ghasemi H, Masoudirad A. Concentrations of heavy metals in wastewater of one of the largest dentistry schools in Iran. Int J Occup Environ Med 2020;11:113-114. doi: 10.34172/ijoem.2020.1917




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 eISSN: 2008-6814

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