Monitoring of cholinesterase-inhibiting activity in water from the Tone canal, Japan, as a biomarker of ecotoxicity

Modelling pesticide concentrations in Japanese paddy fields using the RICEWQ model

Increasing concerns about plant protection products in surface waters have highlighted the importance of pesticide monitoring and modelling, both nowadays integral components of the pesticide registration process. The Rice Water Quality (RICEWQ) model predicts the fate and transport of pesticides under various paddy environmental conditions. The model has been used widely for regulatory purpose in the U.S., while its use in Europe has been limited to regulatory submissions, despite multiple recommendations to adopt RICEWQ as a high tier assessment model for regulatory purposes. The applicability of the RICEWQ model under Japanese agricultural conditions remains unexplored. This study leverages field experimental data to evaluate the RICEWQ model's capability to simulate daily concentrations of two herbicides, mefenacet and pretilachlor, in paddy water and paddy soil in Japan. The RICEWQ model provided a reasonable level of performance for predicting the fate and transport of the two herbicides by ensuring that the simulated daily water balance corresponded with field observations and with minor pesticide-specific calibration. To further improve the performance of the simulations, we implemented a straightforward calibration framework. Calibrating the RICEWQ model improved the accuracy of all simulations; for both herbicides and in both paddy water and paddy soil compartments, the lowest Nash-Sutcliffe efficiency achieved was 0.725, demonstrating excellent performance. However, the RICEWQ model consistently underestimated the peak concentrations of herbicides in paddy water within the first three days of simulation. Simulation results suggested that approximately 50 % of the total applied herbicide was lost from the paddy system. Increasing the duration of the water holding period after pesticide application or increasing the storage capacity of the rice field via excess water storage depth management has the potential to reduce greatly herbicide loss to below 10 % of the total applied herbicide.

Enhancement of anti-cholinesterase activity of aqueous samples by hypochlorite oxidation for monitoring traces of organophosphorus pesticides in water

A reproducible method for monitoring traces of cholinesterase (ChE) inhibitors in aqueous samples is described: the method is based on chemical oxidation and a ChE inhibition assay. Chlorine was tested as an oxidizing reagent for conversion of various thiophosphorus pesticides (P=S compounds) into their P=O analogs, which have higher ChE-inhibiting activity. After treating buffered pesticide solutions (pH 6.0) with chlorine (final concentration less than 10 mg/l) of at 25°C for 15 min, the ChE-inhibiting activities and detection limits for each pesticide were determined. Greater ChE-inhibiting activities, leading to lower detection limits (ppb levels), were observed for the chlorine-treated solutions fortified azinphos methyl, diazinon, isoxathion and ronnel etc. No changes in the ChE-inhibiting activities were observed for carbamate pesticide solutions tested before and after chlorination, but an additive effect showed against ChE when these compounds were mixed with paraoxon in water. This combination of oxidative derivatization and ChE inhibition assay was applied successfully to the detection and determination of ChE inhibitors in natural and drinking water samples.

[Formation mechanism and chemical safety of nonintentional chemical substances present in chlorinated drinking water and wastewater]

This paper reviews the formation mechanism and chemical safety of nonintentional chemical substances (NICS) present in chlorine-treated water containing organic contaminants. Undesirable compounds, i.e., NICS, may be formed under certain conditions when chlorine reacts with organic matter. The rate and extent of chlorine consumption with organics are strongly dependent on their chemical structures, particularly whether double bonds or sulfur and nitrogen atoms occur in the molecules. Organothiophosphorus pesticides (P=S type) are easily oxidized to their phosphorus compounds (P=O type) in chlorinated water containing HOCl as little as 0.5 mg/l, resulting in an increase in cholinesterase-inhibitory activity. Chlorination of phenols in water also produces a series of highly chlorinated compounds, including chlorophenols, chloroquinones, chlorinated carboxylic acids, and polychlorinated phenoxyphenols (PCPPs). In some of these chloroquinones, 2,6-dichloroalkylsemiquinones exhibit a strong mutagenic response as do positive controls used in the Ames test. 2-phenoxyphenols in these PCPPs are particularly interesting, as they are present in the chlorine-treated phenol solution and they are also precursors (predioxins) of the highly toxic chlorinated dioxins. Polynuclear aromatic hydrocarbons (PAHs) were found to undergo chemical changes due to hypochlorite reactions to give chloro-substituted PAHs, oxygenated (quinones) and hydroxylated (phenols) compounds, but they exhibit a lower mutagenic response. In addition, field work was performed in river water and drinking water to obtain information on chemical distribution and their safety, and the results are compared with those obtained in the model chlorination experiments.

In vitro cyclooxygenase inhibition assay for evaluating ecotoxicity of the surface water and domestic wastewater in the Tone Canal, Japan

Cyclooxygenase (COX) plays an important role in eicosanoid metabolism. Nonsteroidal anti-inflammatory drugs (NSAIDs) function as COX inhibitors and are frequently detected in the aquatic environment. Here, we measured the in vitro COX-inhibiting activity of the surface water and domestic wastewater in the Tone Canal, Japan. The concentrations of several NSAIDs in the some samples were also determined using gas chromatography-tandem mass spectrometry for confirming the validity of the assay. The target compounds were extracted from the samples using a solid-phase extraction cartridge. A dose-response relationship between the inhibiting activity and sample volume were observed in the wastewater sample. The higher COX-inhibiting activities were observed in the wastewater sample, as compared with the samples of the surface water in the canal. These inhibiting activities reflected the trends of NSAIDs distribution in the canal. However, the inhibiting activities of the water samples could not be entirely explained by the NSAIDs that were selected for instrumental analysis in this study. Other compounds that were not measured by instrumental analysis in this study might contribute to the inhibiting activities. Therefore, the COX-inhibiting assay would be effective for evaluating inclusive ecotoxicity in the aquatic environment.