The Influence of Polystyrene and Biodegradable Microplastics on Phaseolus vulgaris L. Growth

The presence of microplastics (MPs) in the soil represents a growing threat to food security, affecting plant growth and ecosystem health. In this context, it is essential to investigate the effects of soils contaminated with different types of MPs on plant growth. This study evaluated, for the first time, the influence of two types of MPs (synthetic and biodegradable) on the growth of Phaseolus vulgaris L. Three types of soil were used: control (without MPs), soil loaded with biodegradable MPs, and soil loaded with expanded polystyrene MPs. Twelve seeds were individually buried in each soil sample. The lengths of the leaves and stems were measured on days 7, 14, 21, and 38 after planting. Fresh and dry biomass of leaves, stems, and roots were quantified, as well as the soil pH. The chlorophyll content was analyzed on days 7 and 38 by spectrophotometry. Microbiological analysis was performed at the beginning and at the end of the experiment to estimate the number of bacteria and fungi. The results indicated that soil with PS-MPs reduced the biomass of leaves and roots, showed irregular behavior in chlorophyll production, and lower microbial number, evidencing its negative effects on plant growth. The soil loaded with Bio-MPs did not show relevant changes when compared to the control soil. In general, the results indicated that PS-MPs negatively impact bean development, affecting its morphology and microbiota, leading the plant to stress and senescence.