Ecotoxicity and Risk to Zooplankton of a Novel Insecticide Used in Rice Paddies in a Simulated Ecosystem.

Diamide insecticides are widely used in rice paddies and pose a potential threat to aquatic organisms. However, the risk research related to their application in major rice-producing areas is very limited, especially mesocosm research to simulate the impact on aquatic ecosystems of long-term exposure, as well as exposure analysis based on local models and local scenarios. To assess potential risks from a novel diamide insecticide (tetrachlorantraniliprole) to aquatic nontarget organisms in the field over long-term exposure, an outdoor mesocosm study was performed, and the environmental concentrations were predicted by the multimedia paddy-pond model (TOPRICE). The mesocosm experiment showed that tetrachlorantraniliprole mainly stayed in the aqueous phase after entering the water body. Although the chemical dissipated quickly in the aqueous phase (half-life of 0.79-1.5 days), it showed toxic effects on zooplankton communities. Cladocerans, represented by Simocephalus vetulus, were most sensitive to tetrachlorantraniliprole stress. Significant short-term toxicity to cladocerans occurred in all treatment groups, but all recovered within 8 weeks except for the highest concentration group (30.0 µg /L). Based on the ecological recovery results, 7.74 µg tetrachlorantraniliprole/L (nominal concentration, 10.0 µg /L) is suggested to be the no-observed-ecological-adverse-effect concentration (NOEAEC) for the zooplankton community. When this NOEAEC was compared with predicted environmental concentrations (PECs; the PECs in natural ponds simulated by the TOPRICE model for 148 application scheme combinations in major rice-producing areas), a relatively high risk of applying tetrachlorantraniliprole during the rice tillering stage was found. The present study makes a positive contribution to the hypothesis that the current Tier 1 approaches for global acute risk assessment have a sufficient protective effect for assessing the risk of tetrachlorantraniliprole to aquatic organisms. Also, the present results should help us to gain a fuller understanding of the ecological risk of diamide insecticides in aquatic ecosystems and their rational application schemes. Environ Toxicol Chem 2024;43:429-439. © 2023 SETAC.

Non-target-site resistance to ALS-inhibiting herbicides in a Sagittaria trifolia L. population.

Sagittaria trifolia L. is one of the most competitive weeds in rice fields in northeastern China. The continuous use of acetolactate synthase (ALS)-inhibitors has led to the evolution of herbicide resistant S. trifolia. A subpopulation BC1, which was derived from the L1 population, was analyzed using DNA sequencing and ALS enzyme activity assays and levels of resistance to five ALS-inhibiting herbicides was determined. DNA sequencing and ALS enzyme assays revealed no amino acid substitutions and no significant differences in enzyme sensitivity between susceptible and resistant populations. Whole-plant dose-response experiments showed that the BC1 population exhibited different levels of resistance (resistance ratios ranging from 2.14 to 51.53) to five ALS herbicides, and the addition of malathion (P450 inhibitor) to bensulfuron-methyl, penoxsulam and bispyribac-sodium strongly reduced the dry weight accumulation of the BC1 population compared with the effects of the three herbicides alone. The results of the present study demonstrated that the BC1 population has evolved non-target-site resistance to ALS-inhibiting herbicides.

Simultaneous determination of pyrametostrobin and its two metabolites in cucumber and soil using a quick, easy, cheap, effective, rugged, and safe method with HPLC-MS/MS.

An easy, effective and sensitive analytical method for the simultaneous determination of a novel fungicide pyrametostrobin and its two metabolites pyrametostrobin-M1 and pyrametostrobin-M2 in cucumber and soil was developed using a quick, easy, cheap, effective, rugged, and safe method with high-performance liquid chromatography and tandem mass spectrometry. The extraction solvent was acetonitrile, and cleanup sorbents were primary secondary amine and graphitized carbon black for cucumber samples and primary secondary amine for soil samples. The three target compounds were successfully separated between 3.2 and 3.9 min using a Waters CORTECS™ C18 column connected to an electrospray ionization source. All the matrix-matched samples at three fortified levels (10, 100 and 1000  µg/kg) provided satisfactory recoveries in the range of 78.8-93.8% with relative standard deviations below 6.9%. The limits of quantitation for the three compounds were below 0.183 µg/kg. The proposed method was validated by analyzing real samples.

Aquatic risk assessment of a novel strobilurin fungicide: A microcosm study compared with the species sensitivity distribution approach.

The ecotoxicological effects of pyraoxystrobin, a novel strobilurin fungicide, were studied using outdoor freshwater microcosms and the species sensitivity distribution approach. The microcosms were treated with pyraoxystrobin at concentrations of 0, 1.0, 3.0, 10, 30 and 100µg/L. Species sensitivity distribution (SSD) curves were constructed by means of acute toxicity data using the BurrliOZ model for fourteen representatives of sensitive invertebrates, algae and fish and eleven taxa of invertebrates and algae, respectively. The responses of zooplankton, phytoplankton and physical and chemical endpoints in microcosms were studied. Zooplankton, especially Sinodiaptomus sarsi was the most sensitive to pyraoxystrobin exposure in the microcosms. Short-term toxic effects (<8 weeks) on zooplankton occurred in 1µg/L treatment group. The duration of toxic effects on S. sarsi could not be evaluated within the initial 56 days. Significant long-term toxic effects were observed at 10, 30 and 100µg/L (>281 days) for S. sarsi and the zooplankton community. Based on the results obtained from the organisms in the microcosm system, 1µg/L was recommended as the NOEAEC (no observed ecologically adverse effect concentration). Also, 0.33µg/L was derived as the Regulatory Acceptable Concentration based on the ecological recovery option (ERO-RAC) of pyraoxystrobin. For all fourteen tested species, the median HC5 (hazardous concentration affecting 5% of species) was 0.86µg/L, and the lower limit HC5 (LL-HC5) was 0.39µg/L. For the eleven taxa of invertebrates and algae tested, the median HC5 was 1.1µg/L, and the LL-HC5 was 0.26µg/L. The present study positively contributes to the suggestion of adequately using acute L(E)C50-based HC5/ LL-HC5 for deriving protective concentrations for strobilurin fungicides, and it should be valuable for full comprehension of the potential toxicity of pyraoxystrobin in aquatic ecosystems.