Behavior of dental composite materials in sterilized and non-sterilized landfill leachate

Treatment of used and unused dental resin based composites resulting from the activities of dental industries and clinics is challenging. Disposal to landfill site is commonly utilized to manage this waste. We investigated the release of monomers from dental composites in landfill leachate and the chemical changes of sterilized and non-sterilized leachate in the existence of dental composites. Solid phase micro-extraction (SPME) coupled with high performance liquid chromatography (HPLC) was used to extract and quantify the released monomers. Chemical characterization of leachate was carried out using pH meter, gas chromatography (GC), ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS). The HPLC results, revealed that Bis-GMA, TEGDMA, UDMA, HEMA and BPA monomers were released from dental composites. According to the results of pH, GC, IC and ICP-MS, the presence of dental composites has no significant effect in the chemistry of leachate except increasing the production of CH4 and CO_2. However, autoclaving increased pH values and decreased calcium concentration in sterilized samples. Furthermore, Mn^concentration increased and Fe^ concentration decreased in non-sterilized samples due to microbial activities

Simultaneous detection of monomers associated with resin-based dental composites using SPME and HPLC

As resin-based composites (RBC) replace dental amalgam for environmental reasons, there is a requirement to understand the environmental impact of this alternative dental restorative material. In this study we standardize the simultaneous detection of five monomeric components associated with RBCs using high performance liquid chromatography (HPLC) coupled with solid-phase microextraction (SPME). Factors affecting method performance (detection wavelength, calibration conditions, method sensitivity/accuracy/precision, extraction time/efficiency) are evaluated using standard solutions containing the mixture of TEGDMA, UDMA, Bis-GMA, BPA and HEMA. Detection sensitivity and analytical efficiency of the method is optimized for these compounds using 200 nm detection wavelength, PDMS/DVB fiber and extraction time of 90 min. Analytical accuracy of the HPLC is >95% for all monomers, with precision of 2.3–5.1%. Detection limits under the conditions described are 25 µg/L for HEMA, BPA, UDMA, Bis-GMA, and 100 µg/L for TEGDMA. The extraction time is governed by the largest molecular weight compounds

Enhancement of in situ biodegradation of organic compounds in groundwater by targeted pump and treat intervention

This study demonstrates the value of targeted pump and treatment (PAT) to enhance the in situ biodegradation of organic contaminants in groundwater for improved restoration. The approach is illustrated for a plume of phenolic compounds in a sandstone aquifer, where PAT is used for hydraulic containment and removal of dissolved phase contaminants from specific depth intervals. Time-series analysis of the plume hydrochemistry and stable isotope composition of dissolved species (δ34S-SO4, δ13C-CH4, δ13C-TDIC (TDIC=Total Dissolved Inorganic Carbon)) in groundwater samples from high-resolution multilevel samplers were used to deduce changes in the relative significance of biodegradation processes and microbial activity in the plume, induced by the PAT system over 3years. The PAT system has reduced the maximum contaminant concentrations (up to 6800mgL-1 total phenols) in the plume by 50% to ~70% at different locations. This intervention has (i) stimulated in situ biodegradation in general, with an approximate doubling of contaminant turnover based on TDIC concentration, which has increased from 350mgL-1, (ii) enhanced the activity of SO4-reducing microorganisms (marked by a declining SO4 concentration with corresponding increase in SO4-δ34S to values >7-14‰V-CDT relative to background values of 1.9-6.5‰V-CDT), and (iii) where the TDIC increase is greatest, has changed TDIC-δ13C from values of -10 to -15‰V-PDB to ~-20‰V-PDB. This indicates an increase in the relative importance of respiration processes (including denitrification and anaerobic methane oxidation, AMO) that yield 13C-depleted TDIC over fermentation and acetoclastic methanogenesis that yield 13C-enriched TDIC in the plume, leading to higher contaminant turnover. The plume fringe was found to be a zone of enhanced biodegradation by SO4-reduction and methanogenesis. Isotopically heavy methane compositions (up to -47.8‰V-PDB) and trends between δ13C-TDIC and δ13C-CH4 suggest that AMO occurs at the plume fringe where the contaminant concentrations have been reduced by the PAT system. Mass and isotope balances for inorganic carbon in the plume confirm the shift in spatial dominance of different biodegradation processes and significant increase in contribution of anaerobic respiration for contaminant biodegradation in zones targeted by the PAT system. The enhanced in situ biodegradation results from a reduction in organic contaminant concentrations in the plume to levels below those that formerly suppressed microbial activity, combined with increased supply of soluble electron acceptors (e.g. nitrate) into the plume by dispersion. An interruption of the PAT system and recovery of the dissolved organic contaminant concentrations towards former values highlights the dynamic nature of this enhancement on restoration and relatively rapid response of the aquifer microorganisms to changing conditions induced by the PAT system. In situ restoration using this combined engineered and passive approach has the potential to manage plumes of biodegradable contaminants over shorter timescales than would be possible using these methods independently. The application of PAT in this way strongly depends on the ability to ensure an adequate flux of dissolved electron acceptors into the plume by advection and dispersion, particularly in heterogeneous aquifers