Presence of High-Density Polyethylene Nanoplastics (HDPE-NPs) in Soil Can Influence the Growth Parameters of Tomato Plants ( Solanum lycopersicum L.) at Various Stages of Development

Contamination of aquatic and terrestrial ecosystems with microplastics (MPs) and nanoplastics (NPs) has raised significant global concerns. While most studies have focused on aquatic contamination, knowledge concerning the effect of MPs and NPs in biosolids on agricultural field crops remains limited, as is the range of polymer types tested. In this study, polyethylene nanoplastics (HDPE-NPs, <500 nm diameter) were produced in the lab, and their effect on tomato plants ( Solanum lycopersicum L.) was studied at different growth stages. Physical and chemical characterizations of the HDPE-NPs were performed. Compared to the control group, the presence of 2.8 mg/kg HDPE-NPs in soil increased tomato leaf greenness ( p < 0.05), while the presence of 0.5 mg/kg HDPE-NPs in the soil lowered water use efficiency (WUE, p < 0.05) of the plants in the early vegetative stage. Soil CO 2 emissions were significantly lower under both the 0.5 mg/kg ( p < 0.05) and 2.8 mg/kg HDPE-NPs treatments ( p < 0.05). At the early germination stage, HDPE-NPs in the soil resulted in stunted seedlings ( p < 0.001). Moreover, the average fruit weight and number of fruits borne by mature plants were adversely affected, possibly because of potential alterations in soil nitrogen content and associated plant uptake pathways. A pattern of hormetic dose response was observed for some measured parameters, including leaf greenness, plant WUE, and soil CO 2 emissions, although the underlying mechanisms remain unclear. Overall, the range between 1 and 5 mg/kg concentration of HDPE-NPs in soil was found to have the greatest impact on tomato plants, while other factors may contribute to the observed effects.