Vertical distribution of microplastics in urban farmland soils. A case of Mabibo Bonde la Mchicha farm, Dar es Salaam, Tanzania

Abstract

The rise of microplastics (MPs) is a global concern jeopardizing environmental safety. Initial studies have extensively concentrated on aquatic ecosystems, leaving their presence in terrestrial environments unknown. Thus, this study was carried out to investigate the vertical distribution of MPs in farmland soils of Mabibo Bonde la Mchicha Farm (MBMF), Dar es Salaam. 39 soil samples collected from MBMF were investigated using a Stereomicroscope and QATR-S FTIR. Results herein showed that MPs were found in all soil samples in different depths up to 15 cm deep, ranging from 4.8 to 82.2 items g-1 dry weight (DW). There was a statistically significant difference in MP abundance in depths between 0–5, 5–10 and 10–15 cm layers (P = 0.033) at ὰ = 0.05. The observations were revealed by the observed colors, in which white (36.5 %) was the most frequently observed, followed by blue (21.4 %), brown (20.2 %), black (12.8 %) and red (9 %). Fibers (49.7 %), fragments (32.9 %) and films (17.3 %) were the dominant shapes. Polyethylene (PE) and polypropylene (PP) were the dominant polymers observed constituting 33 % each, polyethylene terephthalate (PET) 11 %, high-density polyethylene (HDPE) 8 %, polyester (PES) 7 %, polyamide (PA) 7 % and polyvinyl chloride (PVC) 1 %. It can be inferred that PE and PP exhibited greater vertical mobility. However, PA and PVC were only observed in the topsoil layer. This study reveals MPs' occurrence and vertical transfer in urban farmland soils of MBMF in Dar es Salaam.