Investigation of concentrations of paddy herbicides and their transformation products in the Sakura River, Japan, and toxicity of the compounds to a diatom and a green alga

Ligand-Enabled Gold-Catalyzed C(sp2)-S Cross-Coupling Reactions

Herein we report C(sp²)-S cross-coupling reactions of aryl iodides and arylsulfonyl hydrazides under ligand-enabled, Au(I)/Au(III) redox catalysis. This strategy operates under mild reaction conditions, requires no prefunctionalized aryl coupling partner, and works across several aryl iodides. The utility of this protocol is highlighted through the synthesis of various medicinally relevant biaryl sulfones. The reaction mechanism is supported with control experiments, mass spectrometry, and NMR studies.

Sensitivity differences among seven algal species to 12 herbicides with various modes of action

Seven algal species were used to conduct toxicity assays with 12 herbicides to determine differences in species sensitivity. A fluorescence microplate toxicity assay was used as an efficient and economical high-throughput assay. The obtained toxicity data were standardized based on the species sensitivity distribution concept. The most-sensitive individual species differed among herbicides: Desmodesmus subspicatus was most sensitive to chloronitrofen and pendimethalin; Achnanthidium minutissimum was most sensitive to chlorpropham; Nitzschia palea was most sensitive to diquat, glyphosate, and dichlobenil; Navicula pelliculosa was most sensitive to trifluralin; and Pseudanabaena foetida was most sensitive to glufosinate, asulam, and 2,4-D. Surprisingly, Raphidocelis (formerly Pseudokirchneriella) subcapitata, a standard green alga, was not the most sensitive to any of the herbicides. The results clearly showed that a single algal species cannot represent the algal assemblage in terms of sensitivity. Therefore, multispecies algal toxicity data sets are essential for assessing the ecological effect of herbicides.

Studies on the behavior and ecotoxicity of pesticides and their transformation products in a river

To clarify the properties of pesticide transformation products (TPs) for which the risk to aquatic organisms should be evaluated, I monitored the concentrations of paddy pesticides and their TPs in the Sakura River, Japan, during the rice-growing season in 2007-2010. I also conducted algal growth inhibition tests of herbicides and their TPs using a diatom and a green alga and acute toxicity tests of insecticides and their TPs using a caddisfly and a daphnid. Moreover, on the basis of the results of pesticide monitoring and toxicity tests, I attempted to evaluate the risk of these compounds to the riverine organisms as well as the risk of mixtures of insecticides and their TPs for caddisflies and cladocerans. The TPs were detected in the river water depending on the half-lives of the parent compounds and of the TPs in water and soil. The toxicities of the parent compound and its TPs may be related to their hydrophobicities and chemical structures. Some toxic and persistent TPs that formed rapidly in water and soil posed a risk to the organisms over a long period. The physicochemical properties and chemical structures of a parent compound and its TPs can be key factors in evaluating the pesticide TP risk to aquatic organisms in rivers.

Determining the suitability of a polar organic chemical integrated sampler (POCIS) for the detection of pesticide residue in the Ishikawa River and its tributary in Osaka, Japan

The monitoring of pesticide concentrations in Japanese rivers was conducted via a grab sampling method and a passive sampling method using the polar organic chemical integrated sampler (POCIS). The results showed that cumulative detections were 84 with grab sampling and 98 with the POCIS. All of the pesticides detected by grab sampling could be quantified with a POCIS except for one (although its traces were detected). In addition, 15 detections quantified by POCIS were undetected by grab sampling. The average concentrations of pesticides detected by both the POCIS and grab sampling during the investigation period were compared. A good correlation was observed between the two methods with a slope of 1.00 and a coefficient of correlation (r) of 0.897 (n=79). Although high temporal variability was observed in the pesticide concentrations by grab sampling, the average pesticide concentrations obtained by the two methods showed similar values during the investigation period.

Simulating the fate and transport of nursery-box-applied pesticide in rice paddy fields

BACKGROUND

The Pesticide Concentration in a Paddy Field model (PCPF-1) was modified by adding a root zone compartment to simulate nursery-box-applied (NB-applied) pesticide. The PCPF-NB model was validated for predicting the concentrations of NB-applied fipronil and imidacloprid in rice paddy fields using two treatment methods: before transplanting (BT) and at sowing (AS). Uncertainty and sensitivity analyses were used to evaluate the robustness of the concentrations predicted by the model.

RESULTS

The hourly predicted concentrations of imidacloprid and fipronil were accurate in both paddy water and 1 cm deep paddy soil. The coefficient of determination and Nash-Sutcliffe model efficiency were greater than 0.87 and 0.60 respectively. The 95th percentiles of the predicted concentrations of fipronil and imidacloprid indicated that the influence of input uncertainty was minor in paddy water but important in paddy soil. The pesticide deposition rate and the desorption rate from the root zone were identified to be the major contributors to the variation in the predicted concentrations in paddy water and soil.

CONCLUSION

The PCPF-NB model was validated for predicting the fate and transport of NB-applied fipronil and imidacloprid using the BT and AS treatment methods. © 2015 Society of Chemical Industry.