Mechanistic insights into polystyrene micro/nanoplastics-facilitated cadmium trophic transfer and aggravated toxicity along a lettuce-snail terrestrial food chain

The co-occurrence of micro/nanoplastics (MNPs) and cadmium (Cd) in terrestrial ecosystems threatens food safety, yet their combined trophic transfer and toxicity remain unclear. This study investigated how polystyrene MNPs (PS-MNPs) modulate Cd dynamics in a lettuce-snail food chain. Results from the diffusive gradients in thin-films (DGT) technique revealed that PS-MNPs significantly increased soil Cd availability from 19.2 μg L in the control to 27.1 and 25.9 μg L in the HN (0.1% 100 nm PS-NPs) and HM (0.1% 1 μm PS-MPs) treatments (p < 0.05). This increase was attributed to decreased pH (0.50 and 0.15 units), increased organic matter (5.4% and 8.7%), and elevated cation exchange capacity (8.1% and 15.5%) under the HN and HM treatments, respectively, which in turn significantly reduced soil Cd adsorption capacity by 22.8% and 13.3% (p < 0.05). Consequently, Cd accumulation in lettuce leaves was significantly increased by 73.3% and 61.2% in the HN and HM treatments, along with a 10.4%-15.1% increase in bioavailable Cd forms. Notably, PS-MNPs facilitated Cd biomagnification, with visceral trophic transfer factors reaching 2.7 (HN) and 2.2 (HM), respectively. Confocal imaging further confirmed the uptake of PS-MNPs by lettuce and their accumulation in the snail intestines. Moreover, co-exposure induced dose-dependent and aggravated toxicity in snails, characterized by more significant oxidative stress, severe intestinal damage, gut barrier dysfunction, and disruption of pantothenate/CoA biosynthesis and energy metabolism. This study demonstrates that PS-MNPs amplify Cd trophic transfer and toxicity along the terrestrial food chain, highlighting the necessity for improving agricultural plastic management.