Nanomagnetites affect cadmium bioavailability in soil biota: A lettuce-snail-earthworm system

Soil contamination by cadmium (Cd) is a major problem and a crucial issue to address. Due to their physico-chemical properties and nanometric size, iron nanoparticles are receiving increasing attention for soil remediation. This study investigates the dual impact of Fe₃O₄-NPs on Cd accumulation and toxicity in lettuce (Lactuca sativa), along with their trophic transfer potential in soil biota (including earthworms (Allolobophora caliginosa) and snails (Helix aspersa). Thus, nanomagnetites were applied (1.15 g kg^-1 soil) to Cd spiked soil (20 mg kg^-1 soil). The results showed a statistically significant reduction in leaf biomass of around 50 % for each treatment alone and over 70 % for the Cd+Fe₃O₄-NPs treatment. A significant reduction in photosynthetic yield and in carotenoid content was only observed for Cd+Fe₃O₄-NPs treatment, which seems to be linked to accumulated Cd levels. However, an increase in SOD activity induced by all treatments was measured indicating plant response to oxidative stress. Our results showed that nanomagnetites put lettuce at the level of Cd hyperaccumulator species (> 100 µg g^-1). Cd content in lettuce was twice as high in modalities treated with Fe₃O₄-NPs, without increasing soil Cd availability. Our study demonstrated Fe₃O₄-NPs penetration into plants and earthworms, but not in snails, but at very low levels (maximum BAF of 0.16). Finally, Cd bioaccumulation from most to least was earthworms > plants > snails (BAF between 0.005 and 10.9). This study shows encouraging results for improving Cd accumulation in lettuce using Fe₃O₄-NPs, but further studies are still needed to ensure their environmental compatibility.