Bio-accumulation of lanthanum from lanthanum modified bentonite treatments in lake restoration.

Lanthanum (La) modified bentonite (LMB) is one of the available mitigating agents used for the reduction of the phosphorus (P) recycling in eutrophic lakes. The potential toxicity of the La from LMB to aquatic organisms is a matter of concern. In this study the accumulation of La was investigated in the macrophyte Elodea nuttallii, in chironomid larvae and in several fish species during periods up to five years following in situ LMB applications. The application of LMB increased the La concentration of exposed plants and animals. During the first growing season following LMB applications, the La content of E. nuttallii increased 78 fold (3.98-310.68 μg La g-1 DW) to 127 fold (2.46-311.44 μg La g-1). During the second growing season following application, the La content decreased but was still raised compared to plants that had not been exposed. The La content of chironomids was doubled in the two years following LMB application, although the increase was not significant. Raised La concentrations in fish liver, bone, muscle and skin were observed two and five years following to LMB application. Liver tissues showed the highest La increase, ranging from 6 fold (0.046-0.285 μg La g-1 DW) to ∼20 fold (0.080-1.886 μg La g-1, and 0.122-2.109 μg La g-1) two years following application and from 6 fold (0.046-0.262 μg La g-1) to 13 fold (0.013-0.167 μg La g-1) after five years in pelagic and littoral fish. The La content of the liver from Anguilla anguilla (eel) had increased 94 fold (0.034-3.176 μg La g-1) two years and 133 fold (0.034-4.538 μg La g-1) five years following LMB application. No acute and chronic effects of La accumulation were observed and human health risks are considered negligible. We advocate the long-term study of effects of La accumulation following future LMB applications.