There
is growing concern of microplastics (MPs) contamination in
farmlands and freshwater systems. This research investigated the impact
of polyethylene (PE)-MPs (22–48 μm) on Romaine lettuce
under a 30-day exposure at 50, 250, and 1000 (mg/kg or mg/L) in soil
or hydroponic conditions. Growth parameters (plant height, root length,
and fresh weight of shoots and roots) of hydroponic lettuce were lower
with two lower doses of PE-MP treatments, but not affected by the
highest dose. The growth parameters of soil-grown lettuce decreased
by all PE-MP treatments. Moisture content was decreased by PE-MPs
in hydroponic lettuce but increased in soil-grown lettuce. Ash followed
an opposite trend to moisture. Ascorbic acid was lower in both groups
of lettuce. Chlorophylls, total phenolics, and antioxidant capacity
were increased in hydroponic lettuce but decreased in soil-grown lettuce.
Lettuce firmness increased in both groups, which positively correlated
to the increased lignin in plant cell walls. All PE-MP-treated lettuce
experienced greater weight loss and accelerated color change during
the 30-day storage at 4 °C, suggesting a shortened shelf life.
Findings indicate that plant growth and quality were affected by the
MP dose, growth systems, and their interactions, which should raise
awareness of the risks of MPs in different agroecosystems.