Effects of soil amendments on cadmium transfer along the lettuce-snail food chain: Influence of chemical speciation.

Cadmium (Cd) trophic transfer along the soil-lettuce-snail food chain was investigated using the root bags-based pot experiments. Two amendments (corn straw biochar and micro-hydroxyapatite (μHAP)) were investigated on Cd (0, 2.5, and 5 mg/kg soil) availability in soils, chemical distribution in plant cells and accumulation in snails. After 60 days, both the CaCl2 extractable Cd in rhizosphere soil (CdCaCl2,rhizo) and Cd accumulation in lettuce decreased with amendments addition. Biochar had a great capacity to reduce both Cd contents and toxicity-sensitive associated Cd (CdFi+Fii) percentages in lettuce roots at 2.5 mg/kg Cd contaminated soil; while μHAP generates a higher reduction in both Cd contents and chain transfer associated Cd (CdFi+Fii+Fiii) percentages in lettuce shoots at 5 mg/kg Cd contaminated soil. Linear regression showed that both contents of root CdFi+Fii and shoot CdFi+Fii+Fiii are better correlated with the CdCaCl2,rhizo (R2 > 0.70, p < 0.01). After 15 days feeding, almost 90% content of Cd accumulated in snail viscera. μHAP had a higher reduction in snail soft tissues Cd accumulation than biochar. Distributions of Cd in snail tissues are significantly correlated with CdFi+Fii+Fiii in shoots (viscera R2 = 0.835; soft tissue R2 = 0.771). Established quantitative relationships could be used to predict the bioavailability and transfer of Cd in terrestrial food chain in the presence of amendments.