Dental Clinics Employment of Amalgam Separators, Best Management Practices

Transcription

1 Goethe Institut Friday 25 May 2007, 9:50 AM. Dental Clinics Employment of Amalgam Separators, Best Management Practices Public Dental Health Service, County of Uppsala Dental Sector as a Source of Mercury Contamination Lars D. Hylander, Anders Lindvall, Lars Gahnberg Uppsala University, Department of Earth Sciences Air, Water and Landscape Science

2 Carl von Linné, professor at Uppsala University, celebrated 300 year anniversary yesterday. He introduced mercury for medical treatment in Sweden it took three centuries to phase out the use!

3 False beauty. Photo: ALEXANDER LINDER Ala Lombolo, a lake in Sweden, which must be restaurated because of 200 kg mercury emitted from a dental clinic and a laboratory.

4 Five options regarding toxic, heavy metals (Hg, Ag) in wastewater from dental clinics I. Open end of pipe nothing done to combat pollution II. Chair side trap/mesh/best Management Practice? (ADA) Fan. Pollution Prevention using Best Management Practices for Dental Amalgam Waste. ICMGP Aug III. Amalgam separator (Types: sedimentory/centrifugal/filter/combinations IV. LEX or bark filter with chelator for ion exchange/capere V. No amalgam No heavy metal pollution I. is sufficient OBS that much more Hg is emitted at removal of old amalgam fillings than at inserting new ones

5 Preventive measures: From 1985, agreement about amalgam separators at all Swedish dental clinics. Marketed as having 99% recovery of mercury from clinic wastewater. In reality?

6 Material and methods Study I (Hg emissions from 12 clinics): 12 dental clinics in operation, belonging to the Public Dental Health Service in the County of Uppsala, Sweden. All equipped with amalgam separators (SRAB 99 TM ) for sedimentation, preceded by a mesh (0.7 mm) at each chair in wet suction systems. Drawing: Eva Lindh, Kronobergs län

7 SRAB 99 TM Inlet Outlet SRAB 99 TM

8 Two test periods I. Ordinary conditions, which included regular changing of amalgam separators. II. After a thorough revision of each system, including high pressure cleaning of the waste water system to clean and collect sediment deposited outside the separators, such as in pipes and buffer tanks.

9 Study II (comparing 4 separators): Three amalgam separators (sedimentation type) available on the market with a claimed efficiency of 99% according to Danish and ISO/SEN protocols. Also, an investigational prototype of an improved separator. Study in situ at two dental clinics in regular operation.

10 Rasch 890 Inlet Outlet

11 Mercury Master II Filter Inlet Filter Outlet

12 Low emission experimental separator, LEX

13 Sampling (both studies) All waste water leaving the clinics was collected for several days and analyzed for the content of Hg. Background values were established by sampling without amalgam separator. Mercury content in sediment cleared at revision of the systems was also determined. The amount and type of dental work with amalgam was registered daily.

14 Analytical method Hg determined in three fractions: fraction 1: particulate material precipitating within 12 hours. fraction 2: colloids precipitated by addition of aluminium sulphate at ph fraction 3: dissolved Hg in the remaining water. Digestion with 3 ml acid (conc. H 2 SO 4 +HNO 3, 2: 1) in sealed glass tubes with Teflon lids in stainless steel bombs in a heating block at 200 o C for 2 h. Mercury determined with atomic absorption cold vapor technique (SnCl2 as reduction agent). Further information in: Hylander, L. D., Lindvall, A., & Gahnberg, L High mercury emissions from dental clinics despite amalgam separators. Sci. Total Environ. 362: Hylander, L. D., Lindvall, A., Uhrberg, R., Gahnberg, L., & Lindh, U Mercury recovery in situ of four different dental amalgam separators. Sci. Total Environ. 366:

15 Schematic design of amalgam separator connected to a wet* suction system in a dental clinic. Vacuum bypass pipe Ø25mm From the clinic Ø 50mm To vacuum pump Ø 50mm Separation tank Indicates back suction Buffer tank Ø25mm Electrically maneuvered on-off valve Amalgam separators Non-return valve Drain to community waste water system * Called a dry system in the USA

16 Incorrectly connected amalgam separator Separator tank Buffer tank Pre and main amalgam separators

17 Results from Study I, 12 clinics Insertion of new amalgam fillings: From none at Clinic E 90 a week at Clinic I (9 dentists), and 15 at Clinic K (one dentist). Removal of old amalgam fillings was done at all clinics: From 7 a week at Clinic F (4.5 dentists) 200 at Clinic I (9 dentists) and 30 at Clinic K (one dentist).

18 Water flow and mercury emissions from 11 dental clinics before and after revision of the waste water systems Water flow Fraction 1 Fraction 2 Hg discharge Active chairs l/ day mg Hg/ l mg Hg/ l g/chair and y Before After Before After Before After Before After Before After Average SD N

19 Effect of cleaning and revision The reduction of Hg emissions after cleaning and revision was more than 500 grams of Hg per year from the eleven clinics with 45 active chairs (units). In the twelth clinic, settled Hg was resuspended at the cleaning, resulting in that Hg in waste water increased after cleaning. (Values not included in the average values.)

20 Sustainability criteria not met Waste water leaving the clinics always contained more than 0.07 mg l -1. This does not meet the limit concentration of mg l -1, a value based on the permitted level in sludge used for agricultural production in a sustainable society (Lunds kommun, 2002).

21 Study II. Mercury concentration in untreated wastewater and after four amalgam separators (average and 95 % confidence interval) Logarithmic scale. Numbers indicate N (sampled days). Hg in waste water (mg l -1 ) Without separator Brand A 15 Brand B Brand C LEX Gottsunda Dental clinic Wallingatan

22 Conclusions from Study I Other technics, which can reduce Hg levels to levels needed should be compulsory and the costs be incorporated into the fee patients are paying for inserting amalgam fillings. Most Hg entering the waste water system originated from the removal of old amalgam fillings. Professional installation and regular maintenance of amalgam separators is of great importance. The presently used amalgam separators cannot reduce the Hg content to levels needed for combatting pollution in a society based on criteria of sustainability. Physical laws hinders this type of amalgam separators to perform better when fed waste water at dental clinics, which contain a larger portion of finer particles than used in the laboratory tests.

23 Conclusions from Study II The obtained efficiency of the three commercial amalgam separators dominating the market is far below what is stated by the manufacturer and by authorities assumed to be the efficiency in clinical conditions. Abolishing the use of dental amalgam and cleaning the tubing systems is the most efficient long-term solution to reduce Hg emissions from dental clinics.

24 Conclusions III Physical restrictions prohibit sedimentary type separators to recover the Hg fractions causing the largest damages in wastewater treatment plants. This fraction is not considered in the ISO protocol for testing amalgam separators -- revision needed.

25 Conclusions IV Hg emissions originating from placing, polishing or removing existing amalgam fillings, should be counteracted by complementing amalgam separators with the use of low-emission separators/filters e.g. Capere dental filter apere_dentalfilter

26 Conclusions V Hg emissions due to abrasion from everyday chewing (one third of total Hg emissions in Sweden) cannot be recovered by any amalgam separator. Thanks for your attention!