Evaluation of Low Cost Chairside Filters as Amalgam Separators

Objective:  This study evaluated the ability of low-cost, chairside filtration systems to remove particulate-based mercury (Hg) from dental-unit wastewater.  Methods: Four dental chairs were used and 123 samples of effluent from one operator working for one day were collected.  Samples were filtered at 0.45 microns, and Hg levels, on the filters, were determined using modified USEPA method 7471.  Prior to collection, the effluents had been filtered by either 10-inch polypropylene filter cartridges with nominal pore sizes of either 100μ, 1μ, or 0.5μ, or a 10-inch 1μ bag filter, or by no filter (baseline).  Baseline and post filter vacuum levels were measured at the chair with a RAMVAC™ Flowcheck™ vacuum gauge calibrated in standard cubic ft/min of air flow.  Dentists were also queried as to the vacuum quality when filter units were installed on their chairs.  Results:  Mean Hg and standard deviations for baseline, 100μ, 1μ, or 0.5μ filters, and the 1μ bag filter were 968.12 (712), 536.60 (1231), 262.08 (158), 2.54 (3), and 40.51 (109), respectively (P<0.001, one-way ANOVA).   Homogenous subsets (Tukey, P≤0.05) are shown in the Table.  Chairside vacuum levels were not substantially affected by any of the filters. Conclusions:  Simple low-cost chairside filters are effective in removing Hg from dental-unit wastewater without sacrificing the quality of chairside suction.  A 0.5μ cartridge will remove an estimated 99.7% ([968.12-2.54]/968.12) of particulate-based Hg without important vacuum degradation after 37 days of use.  This study was supported by the U.S. Navy Bureau of Medicine and Surgery, and the U.S. Environmental Protection Agency, Great Lakes National Program Office.