The suitability of gallium as a substitute for aluminum in tracing experiments

Abstract

Aluminum is a toxic metal whose complex aquatic chemistry, mechanisms of toxicity and trophic transfer are not fully understood. The only isotope of Al suitable for tracing experiments in organisms-(26)Al-is a rare, costly radioisotope with a low emission energy, making its use difficult. Gallium shares a similar chemistry with Al and was therefore investigated as a potential substitute for Al for use in aquatic organisms. The freshwater snail, Lymnaea stagnalis was exposed to either Al or Ga (0.0135 mM) under identical conditions for up to 40 days. Behavioural toxicity, metal accumulation in the tissues, and sub-cellular partitioning of the metals were determined. Al was more toxic than Ga and accumulated to significantly higher levels in the soft tissues (P < 0.05). The proportion of Al in the digestive gland (DG; detoxificatory organ) relative to other tissues was significantly lower than that of Ga (P < 0.05) from day 14 onwards. There were also differences in the proportions of Al and Ga associated with heat stable proteins (HSPs) in the digestive gland, with significantly more HSP present in the DGs of snails exposed to Al, but significantly less Al than Ga associated with the HSP per unit mass protein present. From this evidence, we conclude that Ga may be of limited use as a tracer for Al in animal systems.

The Biotic Ligand Model Can Successfully Predict the Uptake of a Trivalent Ion by a Unicellular Alga Below pH 6.50 but not Above: Possible Role of Hydroxo-Species

“…Aluminum is without doubt the trivalent metal for which toxic effects are the best documented , due to acidification of natural waters which usually leads to an increase in total and free aluminum . However, for the reasons mentioned above, the study of its uptake mechanisms is a technical challenge and several workers have suggested using other trivalent metals as surrogates for Al 3+ . , Scandium (Sc) was selected for this study for two reasons. First, Sc 3+ and Al 3+ share many chemical similarities in addition to their (+III) oxidation state: they have an inert gas electronic configuration, they have a lack of redox capacities in biological systems, the solubilities of their ternary hydroxo-complexes are very similar and they are both class A metals that show preferential and similar affinities for hydroxide, fluoride, sulfate and phosphate .…”

A novel tripodal tris-hydroxypyrimidinone sequestering agent for trivalent hard metal ions: synthesis, complexation and in vivo studies

“…In spite of the fact that the suitability of Ga as a substitute for Al in biological systems seems to be controversial, since some authors agree 38 while others indicate different behaviours, 39,40 the 67 Ga radionuclide appears to be quite convenient for the bioassays it is herein expected to give some clue about the in vivo efficacy of the ligand to mobilize those metals.…”

“…were determined by fitting analysis of the potentiometric data with the HYPERQUAD 2008 program. 27 Al 3+ and Ga 3+ hydroxide species [40][41][42] were included in the equilibrium complexation model and the species distribution curves were obtained with the HYSS program. 27…”

Metallothionein is up-regulated in molluscan responses to cadmium, but not aluminum, exposure

“…Whilst aluminum did not associate with MTs isolated from rat tissue (Vandervoet et al, 1992), there is some evidence of an association in the marine mussel, Mytilus galloprovincialis (Santiago-Rivas et al, 2007). Similarly, in the freshwater snail Lymnaea stagnalis, Al associates with heat stable proteins (the group to which MTs belong) to a greater extent than another hard metal Gallium (Walton et al, 2010). There is, however, no published evidence showing that Al itself increases the levels of expression of MTs or MTLPs in aquatic invertebrates.…”