Monitoring of Nitrophenols and Insecticides in the Daecheong Lake, Served as Resources of Drinking Water

Abstract

Objectives:This study aimed to investigate distributions of three nitrophenols (4-nitrophenol, 2,4-dinitrophenol, 2-methyl-4,6-dinitrophenol) and five insecticides (acetamiprid, dinotefuran, thiacloprid, triflumuron, chlorfluazuron) in the Daecheong lake that is primary water resources for the central area in Korea including Daejeon. Furthermore, the effect of land use type and monthly precipitation on the concentration trends of nitrophenols and insecticides were assessed.Methods:River water samples were obtained for once in a month for five months (June to October in 2016) in seven sites of the Daecheong lake. All residues were analyzed by LC-ESI/MSMS after extraction using solid phase extraction cartridge. Method detection limit (MDL) of nitrophenols and insecticides were 0.4-1.2 ng/L and 0.2-5.0 ng/L, respectively. Average recoveries were 93.1% for nitrophenols (2,4,6-Tribromophenol), 68.7% and 41.3% for insecticides (Acetamiprid-d3, Thiacloprid-d4, respectively).Results and Discussion:Detection frequencies (DF) and total concentrations of three nitrophenols were 71.4 to 100%, and not detected (ND) to 487 ng/L, respectively. Among insecticides, DF of neonicotinoids (acetamiprid, dinotefuran, thiacloprid) and benzoylureas (triflumuron, chlorfluazuron) ranged 28.6 to 100%, and 0 to 28.6%. Total concentrations of insecticides were ND to 253 ng/L. Total concentrations of all target compounds showed a significant difference between upstream and downstream, and adjacent lake by Mann-whitney U test. According to raising precipitation, an increasing pattern of three nitrophenols was revealed in tributaries and lakes but not observed three neonicotinoids in three lake sites. In June, dinotefuran was not detected at the Juwon upstream site with a forest land coverage, however the concentrations rapidly increased from July to August, followed by a sharp decrease in September. For the other four sites (Daecheong dam, Munui, Chudong, and Pumgok streams), dinotefuran concentrations increased by over 20 times between July and October.Conclusions:In the Daecheong lake, which is used as a water supply source for over 3,470,000 personnel, three nitrophenol levels indicated 1,000 times lower than US EPA water quality criteria (WQC) unless high detection frequency (up to 70%). Similarly, there is only WQC among insecticides, acetamiprid showed under 1% of those of guideline. These results are acceptable as a drinking water supply source. To assess the correlation between characteristics of potential origin sources by land coverage and pollutant distributions, and relative monthly precipitation, it is indicated to be increased levels along with upstream surrounding with shrubland to downstream and adjacent lake covered with mixed land coverage (i.g. shrub, and human activities such as rice paddy, farm, transportation, and living). Besides, precipitation was higher as much as increasing concentration. It might be assumed that nitrophenols and insecticides spilled as non-target contamination sources with rainfall. Dinotefuran concentrations in Juwon upstream and three-site of lakes were massively increased in summer and autumn season considered as a pesticide spraying season for bug control such as Japanese pine sawyer, fruit moth, lace bug, and mites. These results implicated the possibility of using insecticides in a sanctuary where use of pesticides is prohibited.