High-density polyethylene microplastics in agricultural soil: Impact on microbes, enzymes, and carbon-nitrogen ratio.

Microplastics (MPs), recognized as emerging pollutants, pose a significant threat to diverse organisms and have adverse effects on agricultural soil. High-density polyethylene (HDPE) holds a prominent position among prevalent forms of MPs. In the current investigations, the impact of HDPE was assessed at four different concentrations (0.25%, 0.5%, 0.75%, and 1.0%) on agricultural soil, microbial population, exoenzymes activities including amylase, cellulase, and invertase, and alteration in carbon-to-nitrogen (C/N) ratio. Both bacterial and fungal populations exhibited a non-concentration-dependent response to different concentrations of HDPE over time. In this study, we refer to the concentrations of 0.25%, 0.5%, 0.75%, and 1.0% as HT1, HT2, HT3, and HT4, respectively. Initial MP application significantly reduced bacterial colony counts for HT1, HT2, and HT4, while HT3 showed no significant change. On the 60th day, HT1 and HT3 exhibited a higher bacterial colony count compared to the control. On the other hand, fungal populations increased to maximum on day 1 but displayed no distinct time-dependent trend from days 15 to 60. Furthermore, enzyme activities decreased with increasing concentrations of MPs over an extended period. Molecular docking studies suggest that HDPE can hinder enzyme activity by forming hydrogen bonds with enzymes. The C/N ratio was found to be significantly higher in MP-treated soils on the 60th day relative to control, suggesting relatively slower degradation of carbon compounds in the MP-treated soils.

Polyvinylchloride and polypropylene as adsorbents of the pesticide monocrotophos enhance oxidative stress in Eudrillus eugeniae (Kinberg).

The use of plastics has increased significantly with consequent rise in the generation of wastes. Microplastics (MPs) with particle size <5 mm are produced in natural terrestrial habitats by weathering of the discarded plastic debris and therefore are likely to impact soil biota. Earthworms are the dominant soil fauna which play vital role in soil formation and decomposition of organics. Since these animals are soil feeders, MP particles contaminating soil are likely to enter in to the gut of these animals affecting their physiology. MPs have been shown to be potent adsorbents of various other pollutants such as heavy metals and agrochemicals. This study reports the effects of two MPs, polyvinyl chloride (PVC) and polypropylene (PP) alone and in combination with the pesticide monocrotophos in soil on tissue protein, lipid peroxidation (LPX), activities of lactate dehydrogenase (LDH) and catalase (CAT) of an epigeic earthworm Eudrillus eugeniae over an exposure period of 48h. Results from molecular docking and laboratory experiment confirmed that both the MPs are potent adsorbents of the pesticide and enhanced oxidative stress on the animal with significant reduction in protein, increased LPX level and enzyme activities. PP indicated significantly higher pesticide adsorption relative to PVC.