Plastic mulch in agriculture: the case of low density polyethylene and its interactions with pesticides and soil microbiota

Low Density Polyethylene is the most applied plastic mulch in agriculture, for decreasing water evaporation, increasing soil temperature, or preventing weeds. Incomplete removal of polyethylene mulch causes plastic pollution in agricultural soils. In conventional agriculture the use of plastic mulch is combined with the use of pesticides. Little is known about the long term effects on soils of plastic debris accumulations in relation with pesticides residues.

We studied 18 parcels in vegetable farms, under organic or conventional management, where plastic mulch has been used for 5 to 20 years in Cartagena’s country side (SE Spain). We sampled soil at two depths: 0-10 cm and 10-30 cm. We compared the macro and micro plastic debris contents, the pesticides residue levels and the soil physiochemical properties between parcels. The ribosomal 16S and ITS DNA regions were sequenced to study shifts in bacterial and fungal communities, respectively. Soils under conventional management contained on average more than 6 different pesticides residues and soils in both managements contained on average 0.2±0.26 g/kg plastic debris. This study also showed how plastic and pesticides interact in soils and affect the microbial community. We identified the most sensitive groups which can act as bioindicators for plastic and pesticide pollution in soils.