Microplastics (MPs) defined as 0.1 – 5 mm size of plastics have received attraction due to their widespread distribution and negative potential impacts. As discernable size of MPs has been detected from lakes to the marine habitats all over the world, number of studies have exponentially increased exploring on the occurrence and fate of MPs in the ocean and surface water. Recently, the occurrence of MPs in groundwater has been reported in literature, however, information on the fate and transport of MPs in groundwater is lacking. Especially, studies on their vertical mobility in unsaturated soil are very limited. Therefore, this study investigated how various factors impact the vertical mobility of MPs in unsaturated soil systems using a lab-scale column. To gain an insight into the characteristics of MPs detected in groundwater, the groundwater collected was analyzed. Also, unsaturated soil systems were simulated by employing rainfall scenario using a sand-filled column. Two categorized factors were considered as influencing factors on transport of MPs: (1) environmental factors: soil grain size & rainfall intensity, and (2) the MP chacteristics: polymer type & their morphology. To evaluate the vertical mobility of MPs, the number of MPs moved at different soil depth and in effluent was counted. Lastly, the ranking of the factors impacting their transport was determined using the entropy weighting technique. Mostly, fiber-form of MPs was observed in the groundwater samples with 22.9 ± 6.3 MPs/L which is above the MPs detected in the wastewater effluent (10.0 ± 2.6 MPs/L). As soil grain size is smaller, more MPs was remaining in the upper soil. And the heavy rainfall makes the MPs mobility faster to the effluent. The fiber-form of MPs showed higher mobility than the fragment-form. Lastly, the light MPs showed lower vertical mobility than the dense MPs. The ranking of factors assessed is under way.

Evaluation of various factors impacting the transport of Microplastics in unsaturated soil systems

ACS Fall 2021

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