Aluminum toxicity is usually attributed to dissolved species in general and the Al3+ hexa-aquo ions in particular. Indeed, the "free" ions are the main concern whereas complexed Al is less toxic. Regarding non dissolved, there appears to be a general consensus that Al in solid phases does not pose any toxicity problems. However, these claims are based on the study of "large" objects (i.e., µm sized or larger), but very little is known about the toxicity of nano-sized Al phases. We examined the toxicity of two Al nanophases, viz. nano-boehmite and the Al13 tridecamer, a nano-sized Al polymer. Boehmite is a common Al oxyhydroxide; it is considered as non toxic. In a first approximation, nano-boehmite is also considered as harmless, by analogy with the larger sized counterpart. There are only isolated reports of the occurence of Al13 in natural environments. It is a hydrolysis product of Al3+ and is frequently used in water treatment processes, and may thus enter ecosystems using this route. As a matter of fact, typical Al concentration used in drinking water plants were also used here. The Al13 species is knwon to exhibit severe toxic effects towards crops. Nano-boehmite as well as Al13 exhibit toxic effects toward P. Brassicacearum and E. Coli. Oxidative stress is a likely mechanisms. Indeed, the E Coli sodAsodB double mutant showed increased sensitivity to Al stress compared to the wild strain. A remarkable point is the amplitude of the responses which differs greatly whether AlOOH or Al13 is present in the medium. With P. Brassicacearum, the toxic effects in terms of survival rate observed with nano-boehmite occur also in the presence of Al13 at concentrations lower by 2 orders of magnitude. With E. Coli, the same trend was observed. In this case, the increased sensitivity of the superoxide dismutase deficient strains was evident from the lowest tested concentrations (0.1 mM). The evolution of the Al speciation occurred on a timescale incompatible with NMR analyses. Ferron based determinations showed however that the Al13 nanophase becomes undetectable in the growth medium within 90 minutes. Proton NMR based metabolomics suggest that distinct metabolic routes are affected by nano-boehmite and Al13.

Ecotoxicity of manufactured Al nanophases

253rd National Meeting (2017)

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