PARENT SESSION

2P Modelling ecotoxic effects
Poster Hall
8:30 AM - Monday, 28 April 2003

(MOP/157) Toxicity studies with lanthanides and Vibrio fischeri - importance of the free ion and QSAR development.

Weltje, Lennart^{1, 2}, de Goeij, Jeroen¹, ¹ Interfaculty Reactor Institute (IRI), Delft, The Netherlands² International Graduate School (IHI), Zittau, Germany

ABSTRACT- The toxicity of lanthanides, the largest group of the rare-earth elements (REE), was assessed in a bioassay with the luminescent micro-organism Vibrio fischeri. Adverse effects were measured as a decrease in the amount of emitted light, which is proportional to the metabolic activity of the bacteria. The exposure medium consisted of a purely inorganic NaNO3 solution of pH 5.5. Speciation of the lanthanides was calculated with the chemical equilibrium program CHEAQS, whose database was extended with all relevant stability constants. Special care was taken not to exceed the low solubility products of lanthanide-hydroxides or -carbonates. Experiments were performed with six different organic ligands and lutetium, the heaviest lanthanide, to determine which species governs the observed toxicity. It appeared that the free-ion concentration (or activity) was a good indicator for the observed effects. However, other inorganic species, which are proportional to the free ion, correlated equally well with the observed toxicity. Overall, it is concluded that all inorganic species may be bioavailable. Of the fourteen naturally occurring lanthanides, eleven were tested, as well as scandium, another REE. A smooth pattern in toxicity of the lanthanides was found, with heavier lanthanides being more toxic than the lighter ones (maximum difference is two orders of magnitude). Lanthanide toxicity to V. fischeri is comparable to that of the well-known heavy metals Cd, Cu, Pb and Zn. Of the chemical characteristics related to toxicity, the first hydrolysis constant appears to be the best descriptor and is therefore proposed as a QSAR for this group of metals.

Key words: Vibrio fischeri, speciation, lanthanides, free-ion activity model