Role of soil organic matter on the retention and mobility of common plastic additives, Di(2-ethylhexyl) phthalate, bisphenol A and benzophenone, in soil

The objectives of this study were to assess the role of soil organic matter on retaining plastic additives, Di(2-ethylhexyl) phthalate (DEHP), Bisphenol A (BPA) and Benzophenone (BP), to postulate the retention mechanisms and mobility in soil. Batch experiments were conducted for red yellow podzolic soil (OM) and soil subjected to high temperature oxidation at 600 °C for 2 h to remove total organic matter (OMR). Pristine soil, which contains organic matter abbreviated as OM (soil with organic matter) whereas total organic matter removed soil is abbreviated as OMR (organic matter removed soil). The pH edge and kinetic experiments were conducted with 20 g/L soil suspension spiked with 10 mg/L of each additive, whereas 1-20 mg/L concentration range was used in isotherm experiments and analyzed using high performance liquid chromatography. DEHP demonstrated the highest retention, 331 and 615.16 mg/kg in OM and OMR soils respectively, at pH 6.6. However, BPA and BP showed highest retentions of 132 and 128 mg/kg, respectively around pH 4.3 in pristine soil. DEHP interaction with soil OM indicated weak physical bonding whereas chemisorption to OMR soil. In the case of BPA, physisorption governed its interaction with both soil organic matter and mineral fraction. Nevertheless, BP demonstrated chemical interactions with OM and minerals. Desorption of DEHP was close to 100% however, BPA and BP were <15%. Overall, DEHP and BPA could be easily released into soil water and possibly be available for plant uptake while, BP is immobilized in soil.