Microplastics in soils with contrasting texture, organic carbon and mineralogy: changes in cadmium adsorption forms and their mobility in soil columns.

Environmental contamination with high-density polyethylene microplastics (MPs) can alter the dynamics of Cd adsorption in soil. The objective of the present study was to identify changes induced by MPs in the Cd adsorption on soils with contrasting texture, organic matter, and clay mineralogy. Leaching columns (three sections of 0.05 × 0.15 m) were filled with disturbed samples (< 2 mm) of the A and Bi horizons of Udic Inceptisol (UI), and Humic Inceptisol (HI) and A, E and Bh of Orthod Spodosol (OS). The first layer of soil (0-0.05 m) was mixed with 2% (w/w) of MPs (two sizes: 150 µm and 40-48 µm). The soil columns were incubated for 90 days, with 10 periodic Cd applications (1 L each) (92, 185, 231, 527, 1186 mg L) in column surface. The pseudo-total, water-soluble, exchangeable (outer sphere), and inner sphere Cd fractions were extracted by selective and sequential treatments and determined by ICP-OES. MPs did not result in impacts on pseudo-total Cd in soils layers. The pseudo-total Cd for the sandy soil (OS) (clay < 100 g kg) accumulated in the first layer due to its higher organic carbon (18.2 g kg). A negative effect was observed for the smaller MPs on the outer sphere adsorption of Cd in the most electronegative first layer (A horizon) of HI and OS. There was difference among soil class on total Cd collected in leaching solution collected in the column base (mg column): OS-695.1 > UI-367.8 > HI-214.1. In practical case of double environmental contamination, the addition of < 2% (w/w) of MPs did not interfere in the cationic heavy metal dynamics, independent of the texture, organic matter content and mineralogy of the clay fraction of the used soils.