Removals of pesticides and pesticide transformation products during drinking water treatment processes and their impact on mutagen formation potential after chlorination

Abstract

Removal efficiencies of 28 pesticide transformation products (TPs) and 15 parent pesticides during steps in drinking water treatment (coagulation-sedimentation, activated carbon adsorption, and ozonation) were estimated via laboratory-scale batch experiments, and the mechanisms underlying the removal at each step were elucidated via regression analyses. The removal via powdered activated carbon (PAC) treatment was correlated positively with the log K at pH 7. The adjusted coefficient of determination (r) increased when the energy level of the highest occupied molecular orbital (HOMO) was added as an explanatory variable, the suggestion being that adsorption onto PAC particles was largely governed by hydrophobic interactions. The residual error could be partly explained by π-π electron donor-acceptor interactions between the graphene surface of the PAC particles and the adsorbates. The removal via ozonation correlated positively with the energy level of the HOMO, probably because compounds with relatively high energy level HOMOs could more easily transfer an electron to the lowest unoccupied molecular orbital of ozone. Overall, the TPs tended to be more difficult to remove via PAC adsorption and ozonation than their parent pesticides. However, the TPs that were difficult to remove via PAC adsorption did not induce strong mutagenicity after chlorination, and the TPs that were associated with strong mutagenicity after chlorination could be removed via PAC adsorption. Therefore, PAC adsorption is hypothesized to be an effective method of treating drinking water to reduce the possibility of post-chlorination mutagenicity associated with both TPs and their parent pesticides.

Hybrid Process of Adsorption/Coagulation/Ceramic MF for Removing Pesticides in Drinking Water Treatment—Inline vs. Contact Tank PAC Dosing

“…Microfiltration, either alone or combined with coagulation, did not result in effective removal of pesticides (MF in Figure 3a; Alum/MF in Figure 4a). These results were expected as pesticides are too small to be retained by the 0.1 µm pore size membrane, and removal of microcontaminants by coagulation has been shown to be relevant only for very highly hydrophobic compounds (Log Kow > 6) and waters with high turbidity/NOM [7,43,44], which is not the case in the present study. With no PAC addition, removals below 10% were observed for all pesticides in the second trial (Alum/MF, Figure 4a), whereas a variation between 8% and 61% was observed in the first trial (MF, Figure 3a), the upper value for tebuconazole.…”

“…On one hand, pesticides' removal by coagulation depends on their adsorption onto colloids or NOM, a phenomenon apparently relevant only for very highly hydrophobic compounds (Log Kow > 6) and waters with high turbidity/high molar mass NOM [7,43,44], which are not the conditions studied. In fact, our previous work with PAC/coagulation/ flocculation/sedimentation [11] corroborated coagulation inefficacy for removing the pesticides herein targeted from waters similar to W2.…”

“…Powdered activated carbon (PAC) based solutions are amongst the best available technologies for controlling organic microcontaminants in conventional water treatment plants (WTPs) due to PAC high adsorption ability for a wide range of microcontaminants [7][8][9][10], high flexibility and easy implementation, simultaneously avoiding the potential formation of undesired by-products with unknown toxicity (sometimes more toxic than the parent compounds). A reliable downstream filtration is nevertheless required to retain PAC fines, particularly in challenging conditions for coagulation to occur, such as low turbidity/low organic matter/low alkalinity waters [11].…”

Evaluation of azamethiphos and dimethoate degradation using chlorine dioxide during water treatment

“…Anthropogenic activities, e.g., industrial and agricultural activities, mining, and climate change induced by these activities, can influence and change groundwater flows and also influence water quality by introducing contaminants (Milojković et al 2018;Azizian et al 2017;Şener et al 2017). Water quality is clearly important for both human and aquatic life (Adityosulindroa et al 2018;Matsushita et al 2018;Alvarez-Zaldívar et al 2018).…”

A Demonstration of Mass-spectrometric Exploration of Organic Ecotoxicants from Simulated Sewage-treatment-plant Effluents

“…Hogenboom et al [21] evaluated the toxicity of the leachates from polluted landfill soils with a zebrafish embryo toxicity test, and identified two causative ecotoxicants by a non-targeted mass spectrometric analysis with a LC-ESI-Orbitrap MS. In other reports [22][23][24][25][26][27][28][29][30][31], these inventions help us explore, elucidate or identify unknowns in water samples. Unfortunately, a large number of components are generally detected in STP effluents when analyses are conducted by a non-targeted mass spectrometric analysis by the nature of a precursor ion analysis (so-called a full scan).…”