4.7 Article

Leaching of herbicides mixtures from pre-exposed agricultural plastics severely impact microalgae

Journal

CHEMOSPHERE
Volume 326, Issue -, Pages -

Publisher

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.chemosphere.2023.138475

Keywords

Agricultural plastics; Bifenox; Oxyfluorfen; Microalgae; Mixture toxicity; Pollutant vectors

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Farmlands act as sources of both aged plastics and pesticides, which can impact the surrounding environment. This study examined the potential role of agricultural plastics in carrying a mixture of herbicides and their effects on freshwater microalgae. The results revealed that aged plastics had an increased capacity to retain and release herbicides, leading to adverse effects on the microalgae including oxidative stress and metabolic dysfunction. The toxicological interactions of the herbicide mixture varied depending on the effect level, showing both antagonistic and synergistic effects. This study confirms that aging enhances the vector behavior of agricultural plastics for toxic chemicals to biota.
Farmlands represent a source of aged plastics and pesticides to the surrounding environments. It has been shown that chemicals can be sorbed and desorbed from plastics, but the interaction between plastic and mixtures of pesticides and their effects on freshwater biota has not been assessed yet. The aim of the work was to assess the potential role of agricultural plastics as vectors for a mixture of two herbicides and the impact of the herbicide mixture lixiviated from them towards the freshwater microalga Chlamydomonas reinhardtii. Pristine and aged polyethylene plastics collected from agricultural areas were exposed to the herbicides, bifenox, oxyfluorfen and their mixtures. The microalgae were exposed for 72 h to the leachates desorbed from plastics and the effect was quantified in terms of total chlorophyll content and several physiological parameters assessed by flow cytometry. Our results showed that changes in physicochemical properties (hydroxyl and carbonyl index, hydrophobicity, texture) in aged plastics increased their capacity to retain and to desorb the herbicides. Microalgae exposed to leachates containing bifenox, oxyfluorfen, or their mixture showed reactive oxygen species overproduction, lipid peroxidation, membrane potential hyperpolar-ization, intracellular pH acidification, and a loss of metabolic activity. The toxicological interactions of the leachate mixture were assessed using the Combination Index (CI)-isobologram method showing antagonism at low effect levels turning to synergism when the effect increased. In this work, we proved the hypothesis that ageing increases the capacity of agricultural plastics to behave as vector for toxic chemicals to the biota.

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