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

## TL;DR

This study shows that polystyrene microplastics harm bean plant growth, while biodegradable ones do not.

## Contribution

The first study to compare the effects of synthetic and biodegradable microplastics on Phaseolus vulgaris L. growth.

## Key findings

- Polystyrene microplastics reduced leaf and root biomass and disrupted chlorophyll production.
- Polystyrene microplastics decreased microbial counts in soil, indicating negative effects on plant microbiota.
- Biodegradable microplastics did not significantly affect plant growth compared to control soil.

## Abstract

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.