Limited effects of different real groundwaters from three coastal cities in China on the transport of low-concentration nanoplastics in quartz sand

Nanoplastics (NPs) have been widely detected in soil-groundwater systems. However, to date, the effect of real groundwater on the fate and transport of NPs has been poorly understood. In this study, the transport and retention behaviors of both polystyrene and poly(lactic-co-glycolic acid) NPs (PS NPs and PLGA NPs) in different real groundwaters from three coastal cities in China were explored using column experiments. PS (0.51 and 1.1 mu m) and PLGA (1 mu m) NPs with a low concentration of 2 mg L-1 were employed. Close observation showed that the transport of PS NPs was much higher than PLGA NPs in different groundwaters, with an average breakthrough curve plateau (C/Co) of similar to 0.81 for PS NPs and similar to 0.19 for PLGA NPs, respectively. As observed for PLGA, the plastic shape- and size-induced straining may be the reason for the minimal transport. Interestingly, we found that although the physicochemical characteristics of different real groundwaters varied significantly, the transport of certain NPs in real groundwater was similar with negligible differences. Closer inspection indicated that similar pHs of different groundwaters may be the reason contributing to these findings. Further investigation revealed that the transport behaviors of PS and PLGA NPs in real groundwater did not follow the classical DLVO theory. These findings suggest that the fate and transport of NPs in real soil-groundwater systems are much more comprehensive than the prediction based on DLVO theory and need intensive investigation. Nanoplastics (NPs) have been widely detected in soil-groundwater systems.

Automated summary

This study investigated the transport and retention behaviors of polystyrene and poly(lactic-co-glycolic acid) nanoparticles (PS NPs and PLGA NPs) in real groundwaters from three coastal cities in China. The results showed that PS NPs had higher transport rates compared to PLGA NPs in different groundwaters. The pH of the groundwaters was found to be a contributing factor to the transport behavior of the nanoparticles.