Effect of iodine on mercury concentrations in dental-unit wastewater.

OBJECTIVE: This study was undertaken to determine whether iodine used to control bacteria in dental unit waterlines could increase mercury concentrations in dental wastewater. METHODS: The study was conducted in four parts. Part 1. Solutions containing iodine in concentrations ranging from zero (control) to 20 mg/L were mixed with ground and sieved dental amalgam and then allowed to equilibrate by settling. Cold vapor atomic absorption spectrometry was used to determine mercury levels in the settled supernatants at 24 h and at 7 days. Part 2. Deionized water was pumped through an iodine-releasing water-treatment cartridge, collected, and mixed with ground and sieved dental amalgam. Mercury levels in settled supernatants were measured at 24 h and at 7 days. Part 3. Iodine in water from two commercial iodine-releasing cartridges was measured using Inductively Couple Plasma Mass Spectrometry. Part 4. Baseline mercury levels in settled supernatants from wastewater collected from two dental chairs were compared to samples taken from chairs equipped with iodine-releasing cartridges. RESULTS: Part 1. A linear correlation between iodine and mercury concentration (r2=0.9167 and 0.9459, respectively, both P<0.001) was seen at both 24 h and 7 days. Part 2. Mean mercury levels in 24h samples were 3.0 times higher than the controls (0.2864 mg/L compared with 0.0939mg/L for the 24 h controls). Mean mercury levels in the 7-day samples were 5.9 times higher than the 7-day controls (0.2048 mg/L compared with 0.0348 mg/L for the 7-day controls). Part 3. The effluent from two iodine-releasing cartridges showed iodine concentrations averaging 3.2 mg/L (n=10, SD=0.8, range=2.5-4.6). Part 4. Data from the clinical study showed a statistically significant 2.5-fold increase in mercury levels with iodine-containing samples compared to baseline (0.0853 mg/L, n=18, SD=0.0441 and 0.0345 mg/L, n=18, SD=0.0145, respectively; P<0.001). SIGNIFICANCE: Data suggest that iodine can increase concentrations of dissolved mercury in dental unit wastewater.

Disinfectants' effect on mercury release from amalgam.

BACKGROUND: Mercury environmental discharge is under increased scrutiny by the U.S. Environmental Protection Agency (EPA). Dental amalgam should be processed properly to prevent an additional environmental burden. Some processing agencies require that submitted amalgam be noninfectious. Investigations have demonstrated that oxidizing disinfectants mobilize mercury from amalgam into solution and add mercury to the environmental burden if it is disposed of improperly. The authors conducted a study to evaluate the effect of representative disinfectants on amalgam mercury release. METHODS: The authors sized a high-copper spherical amalgam alloy to match that typically found in dental unit suction traps. They exposed 20 grams of the alloy to several disinfectant solutions and evaluated the filtered supernatant solution for mercury content. RESULTS: Chlorine disinfectant materials discharged the most mercury ions, followed by bromide, iodophor, peroxide/peracetic acid and phenolic disinfectants. The quaternary ammonium compound did not discharge mercury ions above the detection limit (0.2 parts per billion) into solution. CONCLUSIONS: A quaternary ammonium compound did not mobilize mercury ions into solution when used as a disinfectant agent for amalgam. Chlorine disinfectants mobilized mercury ions the most, followed by bromide, iodophor, peroxide/peracetic acid and phenolic disinfectants. CLINICAL IMPLICATIONS: Dentists are obligated to be good environmental stewards and should follow practices that reduce environmental mercury release. Dental personnel should be aware that oxidizing disinfectants mobilize mercury ions into solution, which will be added to the environment if they are processed improperly. If required by processing, dental personnel should consider the different oxidizing effects of commonly used disinfectants.