Time-dependent movement and distribution of chlorothalonil and chlorpyrifos in tomatoes

The spatial distribution and migration of three typical fungicides in postharvest satsuma mandarin (Citrus unshiu Marc.) fruit

Fungicides are often used to extend the storage time of postharvest satsuma mandarin fruit. In recent years, fungicide residue has become an issue of food safety. This study aimed to investigate the distribution and migration of three typical fungicides (imazalil, prochloraz, thiophanate-methyl) in postharvest satsuma mandarins using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Three fungicides could quickly penetrate satsuma mandarins and their gradient concentrations of residues in the fruit were: carpopodium > mesocarp > epicarp > pulp. However, the residues of three fungicides in the edible pulp were obviously lower than the maximum residue limit (MRL = 5.0 mg kg^-1 in China). Residues of the three fungicides decreased in epicarp and carpopodium but increased in mesocarp and pulp during storage. Fungicides could quickly penetrate the fruit, settling primarily in the carpopodium but little in the pulp. Both epicarp and carpopodium were the breakthrough pathways for the fungicides entering the fruit, while epicarp was the main route for the penetration of fungicides. These findings shed new information on the behavior of fungicides and the safety issue of satsuma mandarins.

Degradation of Carbendazim by Molecular Hydrogen on Leaf Models

Although molecular hydrogen can alleviate herbicide paraquat and Fusarium mycotoxins toxicity in plants and animals, whether or how molecular hydrogen influences pesticide residues in plants is not clear. Here, pot experiments in greenhouse revealed that degradation of carbendazim (a benzimidazole pesticide) in leaves could be positively stimulated by molecular hydrogen, either exogenously applied or with genetic manipulation. Pharmacological and genetic increased hydrogen gas could increase glutathione metabolism and thereafter carbendazim degradation, both of which were abolished by the removal of endogenous glutathione with its synthetic inhibitor, in both tomato and in transgenic Arabidopsis when overexpressing the hydrogenase 1 gene from Chlamydomonas reinhardtii. Importantly, the antifungal effect of carbendazim in tomato plants was not obviously altered regardless of molecular hydrogen addition. The contribution of glutathione-related detoxification mechanism achieved by molecular hydrogen was confirmed. Our results might not only illustrate a previously undescribed function of molecular hydrogen in plants, but also provide an environmental-friendly approach for the effective elimination or reduction of pesticides residues in crops when grown in pesticides-overused environmental conditions.

Exogenous 24-epibrassinolide activates detoxification enzymes to promote degradation of boscalid in cherry tomatoes

BACKGROUND

Boscalid is often used to extend the storage time of postharvest cherry tomato. Pesticide residue has become an issue of food safety. This study sought to investigate the spatial distribution of boscalid residue in cherry tomato fruits and to determine the effect of 24-epibrassinolide (EBR) in promoting boscalid degradation.

RESULTS

Boscalid could quickly penetrate into cherry tomatoes, but mainly remained in the peel. The migration of boscalid from the peel into the core was a time-consuming and complex process during storage. After 72 h, boscalid residues in the pulp and the core began to accumulate gradually. The exogenous application of EBR activated peroxidase, glutathione reductase and glutathione S-transferase, and effectively promoted the degradation of boscalid by a maximum decrease of 44.8% in peel, 54.0% in pulp and 71.2% in core.

CONCLUSION

As one of the common pesticides, boscalid had a strong ability to enter the cherry tomato and thus become a potential risk for public consumption. Therefore, rational use of pesticides is recommended. The results of this study indicate that the possible risk of boscalid residue could be alleviated by EBR pretreatment through activating detoxification enzymes. © 2020 Society of Chemical Industry.

Screening for suitable chemical acaricides against two-spotted spider mites, Tetranychus urticae, on greenhouse strawberries in China

Effective and safe acaricides based on scientific data are needed for that no chemical acaricides has been registered for the control of two-spotted spider mite in strawberry crops in China. To identify suitable acaricides, the efficacy, persistence, and toxicity of eight acaricides (hexythiazox, fenpyroximate, chlorfenapyr, propargite, etoxazole, bifenazate, spirodiclofen, and pyridaben) on greenhouse strawberries were tested. The eight acaricides were ranked, from highest average efficacy at the recommended dosage to lowest, as follows: etoxazole > bifenazate > fenpyroximate > propargite > spirodiclofen > pyridaben > hexythiazox> chlorfenapyr. The average recoveries of the eight acaricides at the spiking levels of 0.05 and 0.5 mg/L ranged from 72.4% to 108.1% (relative standard deviation, 1.3-8.8%). The concentrations of hexythiazox, fenpyroximate, etoxazole, bifenazate, spirodiclofen, and pyridaben at 5 days after application were lower than the maximum residue limits (MRLs) specified by China, the European Union (EU), the Codex Alimentarius Commission, and Japan, but those of chlorfenapyr and propargite residues were 8.8 and 1.9 times higher than the MRLs in the EU. Only propargite posed a high chronic dietary risk to humans. Pyridaben and chlorfenapyr showed unacceptable ecotoxicology risks for honeybees (hazard quotient values of > 50). The recommended acaricides to control spider mites in greenhouse-grown strawberry crops are etoxazole, bifenazate, fenpyroximate, spirodiclofen, and hexythiazox based on the efficacy, persistence and toxicity.

Distribution of chlorpyrifos in rice paddy environment and its potential dietary risk

Chlorpyrifos is one of the most extensively used insecticides in China. The distribution and residues of chlorpyrifos in a paddy environment were characterized under field and laboratory conditions. The half-lives of chlorpyrifos in the two conditions were 0.9-3.8days (field) and 2.8-10.3days (laboratory), respectively. The initial distribution of chlorpyrifos followed the increasing order of water<straw<soil, and soil was characterized as the major absorber. The ultimate residues in rice grain were below the maximum residue limit (MRL) with a harvest interval of 14days. The chronic exposure for chlorpyrifos was rather low compared to the acceptable daily intake (ADI=0.01mg/kg bw) due to rice consumption. The chronic exposure risk from chlorpyrifos in rice grain was 5.90% and 1.30% ADI from field and laboratory results respectively. Concerning the acute dietary exposure, intake estimated for the highest chlorpyrifos level did not exceed the acute reference dose (ARfD=0.1mg/kg bw). The estimated short-term intakes (ESTIs) were 0.78% and 0.25% of the ARfD for chlorpyrifos. The results showed that the use of chlorpyrifos in rice paddies was fairly safe for consumption of rice grain by consumers.

Time-dependent movement and distribution of chlorpyrifos and its metabolism in bamboo forest under soil surface mulching

The dissipation and distribution of chlorpyrifos (CHP) granule formulation in bamboo forest under soil surface mulching conditions (CP) and noncovered cultivation conditions (NCP) from soil to product were investigated. In the CP treatment, the CHP granule with slow-release effect leached from the topsoil to the subsoil. Conversely, the CHP was fixed in the topsoil (0-5 cm layer) in the NCP treatment, and no obvious leaching effect could be observed. The residue of CHP could be found in bamboo shoots from CP treatment, mainly at the bottom part (5 cm length). CHP could be degraded into 3,5,6-trichloro-2-pyridinol (TCP) in the soil and bamboo shoots. In addition, the straw used as the mulching material with higher OM and pH had some regulatory role in changing the pH and OM characteristics of the soil. Thus the straw could indirectly affect the adsorption and degradation behavior of CHP and TCP in the soil.