Response of garlic (Allium sativum L.) to the combined toxicity of microplastics and arsenic

The extensive utilization of mulch films in agricultural settings, coupled with the persistence of microplastic remnants in soil following the natural degradation of plastics, has given rise to detrimental microplastic impacts on crops. Arsenic (As) contamination in the environment is known to accumulate in crops through aquatic pathways or soil. Garlic (Allium sativum L.), a globally popular crop and seasoning, contains alliin, a precursor of its flavor compounds with medicinal properties. While alliin exhibits antimicrobial and antioxidant effects in garlic, its response to microplastics and arsenic has not been thoroughly investigated, specifically in terms of microplastic or As uptake. This study aimed to explore the impact of varied stress concentrations of microplastics on the toxicity, migration, and accumulation of As compounds. Results demonstrated that polystyrene (PS) fluorescent microspheres, with an 80 nm diameter, could permeate garlic bulbs through the root system, accumulating within vascular tissues and intercellular layers. Low concentrations of PS (10 and 20 mg L) and As (2 mg L) mitigated the production and accumulation of reactive oxygen species (ROS) and antioxidant enzymes in garlic. Conversely, garlic exhibited reduced root vigor, substance uptake, and translocation when treated with elevated As concentrations (4 mg L) in conjunction with PS concentrations of 40 and 80 mg L. An escalation in PS concentration facilitated As transport into bulbs but led to diminished As accumulation and biomass in the root system. Notably, heightened stress levels weakened garlic's antioxidant defense system, encompassing sulfur allicin and phytochelatin metabolism, crucial for combating the phytotoxicity of PS and As. In summary, PS exerted a detrimental influence on garlic, exacerbating As toxicity. The findings from this study offer insights for subsequent investigations involving Liliaceae plants.