Trophic transfer of cadmium from duckweed (Lemna Minor L.) to Tilapia (Oreochromis mossambicus)

Abstract

The transfer of the toxic heavy metal Cd from duckweed (Lemna minor L.) to the freshwater fish tilapia (Oreochromis mossambicus) was investigated. Concentrations of Cd in different chemical forms in duckweed and in different tissues (gut, edible muscle, and remnants) of tilapia, i.e., ethanol-extractable (FE ), HCl-extractable (FHCl ), and residual fractions (FR ) were quantified, and the bioaccumulation factors (BAF) of Cd in the tilapia body were calculated. Simple linear regression analysis was used to unravel the correlation and accumulation mechanisms of Cd along the short food chain. Our results show that with increasing exposure concentrations of Cd (0-50 µM for duckweed and 0-10 µM for tilapia), the total, FE (Fe,d ), FHCl (Fh,d ), and FR (Fr,d )-Cd concentrations in duckweed and different tissues of tilapia increased progressively. The Cd sources (aqueous or dietary) influenced the BAF for Cd accumulation in the whole body of tilapia. Furthermore, regression analyses yielded significant positive correlations (R2 > 0.96) between the Cd concentration in duckweed and in both the three parts and the whole body of tilapia. This finding suggests that Cd transfer from duckweed to tilapia can be quantitatively evaluated when tilapia is exposed only to duckweed. In addition, the linear regression between Cd accumulation in whole tilapia and Fe,d , Fh,d and Fr ,d -Cd showed that particularly the correlation with Fe,d -Cd is statistically significant (p < 0.001). The accumulated Cd concentrations and chemical forms in tilapia tissues also positively correlated with Cd sources (solution or duckweed). Compared to waterborne exposure only, duckweed especially increased the accumulation of Cd in the gut of tilapia. Taken together, our findings suggest a strong dependence of Cd accumulation and transfer from duckweed to tilapia on its chemical forms, especially on Fe,d -Cd. This knowledge may expedite more accurate risk assessment of heavy metals through aquatic food chain ecosystems. This article is protected by copyright. All rights reserved.