The impact of leachate from waste rubber particles on duckweed: growth, oxidative stress, and cell structure.

Waste rubber particles, especially tire wear particles (TWPs), have become major contributors to microplastic pollution. Through rainwater and road runoff, TWPs can enter the water environment, posing potential threats to aquatic organisms. However, systematic research on the effects of waste rubber particles on duckweed remains limited. Thus, Spirodela polyrhiza was exposed to rubber leachate at 10%, 15%, 20%, and 25% levels, aiming to evaluate the effects of rubber leachates on duckweed at the individual, physiological, and cellular levels. The results showed that rubber leachates significantly inhibited duckweed growth and reproduction. Exposure to the 25% leachate significantly reduced root length, root volume, and root activity of duckweed plants by 74.6%, 63.9%, and 29.7% (p < 0.05), respectively. Leachate exposure also induced the accumulation of osmoprotectants, with significant increases of soluble sugars (170.7%, p < 0.05) and proline content (73.6%, p < 0.05) under the 25% treatment. This was accompanied by reactive oxygen species (ROS) overproduction, reflected in significantly elevated superoxide anion and hydrogen peroxide contents in root tips. Furthermore, the leachates induced oxidative stress in duckweed, as evidenced by increased antioxidant enzyme activities and antioxidant contents. In addition, the leachates compromised the integrity of both cell and mitochondrial membrane, reduced cell wall component contents, and induced apoptosis. Collectively, these findings demonstrate that the toxicity of rubber leachates is mediated through oxidative stress and cellular structural damage.