PARTICLE SIZE AND DOSE DEPENDENT INTERACTION OF POLYSTYRENE MICROPLASTICS IN MAIZE (Zea mays L.)

Abstract

Microplastics (MPs) are an emerging class of noxious substances that needs to be taken into consideration as an important category of environmental pollutants of rising distress. This anthropogenic material can engender undesirable environmental variations in the soil matrix and is capable of causing potential effects to plant growth. Despite of unfavorable prospects, a limited amount of data has been reported pertinent to this category of contaminants. Current study is the first of its kind to investigate and elucidate the impacts of variable sizes of polystyrene microplastics (PSMPs) at different concentration levels on the growth of Maize (Zea mays L.) as well as on soil properties in soil-plant ecosystem. In an effort to bridge this gap, a pot experiment was conducted for 60 days, PSMPs were used, with three variable particle sizes (500- 250µm), (250-150µm) and (150 > 75µm) at three different application rates 0.1,1 and 3% w/w percent in dry soil. Shoot length and biomass of the maize plant was reduced when exposed to small particle size (150 > 75µm) of PSMPs at 3% concentration level. Root length and biomass was reduced when soil was exposed to PSMPs for all the treatments at high concentrations. Soluble sugar and chlorophyll content in the leaf of maize was reduced when exposed to (150 > 75µm) of PSMPs. An increased in proline content was recorded when the stress was increased and the size of the PSMPs was decreased. It was also identified that hydrogen peroxide (H2O2) and Malondialdehyde (MDA) content increased in maize leaves when exposed to high concentrations of PSMPs. Additionally, the activities of antioxidants (SOD and POD) were also increased as the degree of severity of the stress increased. Due to addition of PSMPs in soil an increase in soil pH was observed meanwhile decrease in soil available micronutrients concentrations including soluble potassium, nitrate nitrogen and phosphorus was recoded when exposed to high concentration of PSMPs. PSMPs addition in soil raised the water holding capacity of the soil for variable plastic sizes. Small particle size (150>75µm) of PSMPs at high concentrations significantly enhanced the soil ureases activities while for catalase activity was reduced. Different numbers of soil bacterial count were observed in various treatments however PSMPs addition in soil changed the bacterial structure depending upon variable size and dose of plastic. PSMPs addition in soil with high percentage and small size (150 >75µm) significantly reduced the soil bacterial count. The results of the present study indicate that addition of PSMPs in soil can affect Maize (Zea mays L.) by altering physiological responses, soil properties and soil biodiversity. Therefore, there is dire a need to conduct further research on MP polymers for a holistic assessment of ecological risk posed by them on agroecosystem.