Many studies have investigated the toxic effects of microplastics (MPs) ingested by aquatic animals, but the effects of MPs that adhere to the roots of macrophytes require further exploration. Thus, the present study investigated the dose-dependent toxic effects of adding 10-500 mg/kg of polycaprolactam microplastics (PCM) on allelopathic cyanobacterial inhibition by a wetland macrophyte due to the influence on rhizosphere bacteria in a pot trial. First, comparisons of sterilized and unsterilized Iris pseudacorus rhizosphere soil showed that the unsterilized soil could enhance the root activity and allelopathic inhibition of Microcystis aeruginosa cyanobacteria. Furthermore, adding 50-100 mg/kg PCM to the unsterilized soil significantly altered the abundances of many types of bacteria, and decreased the root activity and bacterial biodiversity in the rhizosphere. Importantly, PCM changed the secondary metabolites profile in the roots, as well as decreasing production of the allelochemical palmitic acid and the allelopathic potential of I. pseudacorus. Moreover, a dominant strain of functional bacterium AAP51 was identified as an allelopathic promoter, isolated, and successfully inoculated into the sterilized soil. The decomposition of PCM produced the toxic monomer caprolactam in the rhizosphere soil at an average rate of 0.067 mg/kgd under treatment with 50 mg/kg PCM. Toxicological testing showed that 5 mg/kg caprolactam inhibited the activities of the dominant bacteria and expression of the allelopathic gene FAD2 to weaken the allelopathic effect of I. pseudacorus. Thus, the findings obtained in this study indicate that PCM inhibited the allelopathic potential of the macrophyte due to the release of toxic caprolactam damaging bacteria in the rhizosphere. Consequently, it is necessary to remove MP pollutants from aquatic ecosystems in order to maintain the strong allelopathic potential of macrophytes and efficiently control cyanobacterial blooms.

Neonicotinoids represent 25% of the insecticidal market and are essential for crop production, yet traditional neonicotinoids are toxic to most pollinators, which are also essential for food production. This issue may be addressed by the use of some chiral neonicotinoid isomers, which are much less toxic. Here, we review the chiral neonicotinoids dinotefuran, sulfoxaflor, cycloxaprid, and paichongding, with focus on their chiral characteristics, configuration stability, biological activity, ecological toxicology, and environmental fate. Isomeric separation of chiral neonicotinoids can be achieved by chromatography. The dinotefuran R isomer is less toxic than the S isomer to honeybees and earthworms by a factor of 2.7-145.9, with similar control efficiency of common agricultural pests. The insecticidal activity of (5R,7S)-paichongding are up to 20.1 times higher than that of other isomers, and it is absorbed fastest by crop roots and tends to be preferentially degraded and mineralized in soils. Therefore, formulations containing R-dinotefuran or (5R,7S)-paichongding could decrease ecological damage without compromising food production. On the other hand, it has not been possible to synthesize chiral isomers of sulfoxaflor and cycloxaprid, owing to the instability of their monomers in polar solvents.