Extra- and intra-cellular accumulation of platinum group elements by the marine microalga, Chlorella stigmatophora

Abstract

To better understand the marine biogeochemistry of the platinum group elements (PGE), Rh(III), Pd(II) and Pt(IV) were added in combination and at ppb concentrations to cultures of the marine microalga, Chlorella stigmatophora, maintained in sea water at 15 °C and under 60 μmol m(-2) s(-1) PAR. The accumulation of PGE was established in short-term (24-h) exposures, and under varying conditions of algal biomass and PGE concentration, and in a longer-term exposure (156-h) by ICP-MS analysis of sea water and nitric acid digests and EDTA washes of the alga. In short-term exposures, and under all conditions, the extent of accumulation by C. stigmatophora was in the order: Rh > Pd >> Pt; and Pd was internalised (or resistant to EDTA extraction) to a considerably greater extent than Rh and Pt. Accumulation isotherms were quasi-linear up to added PGE concentrations of 30 μg L(-1) and all metals displayed a significant reduction in accumulation on a weight-normalised basis with increasing density (biomass) of C. stigmatophora, an effect attributed to the production of exudates able to stabilise metals in sea water through complexation. In the longer-term exposure, kinetic constraints on the reactivities of Rh and, in particular, Pt, resulted in final degrees of accumulation and internalisation by C. stigmatophora that were greatest for Rh and similar between Pd and Pt. Among the PGE, therefore, Rh is predicted to participate in biological removal and transport processes in the marine environment to the greatest extent while decoupling in the biogeochemistries of Pd and Pt is predicted in shorter-term or more transient processes.

Precise determination of dissolved platinum in seawater of the Japan Sea, Sea of Okhotsk and western North Pacific Ocean

“…Cd and Ag strongly interact with marine biota (Martin and Knauer, 1973;Fisher and Wente, 1993;Ratte, 1998;Lane and Morel, 2000;Ho et al, 2003), which induces low concentrations of both elements in surface waters. Conversely, Pt exists as PtCl 4 2− and PtCl 5 OH 2− in seawater (Cosden and Byrne, 2003;Cobelo-García et al, 2013) as previously described, but there is little research concerning the relationship between Pt and organisms (Ravindra et al, 2004;Mulholland and Turner, 2011;Shams et al, 2014). The conservativetype vertical profile implies that there are relatively few interactions between Pt and biota.…”

The English Channel: Contamination status of its transitional and coastal waters

“…Rhodium also exhibited this behaviour but to a lesser extent, and was also more particle reactive with K d s in the range 10 3 -10 4 (Cobelo- Garcia et al, 2008). Rhodium also showed the greatest sorption to, and uptake into, the marine unicellular alga Chlorella stigmatophora (Shams et al, 2014). Kinetic constraints on the partitioning of Pt suggested that sorption of the dissolved metal to particles would be favoured in longer residence time coastal waters (Cobelo-Garcia et al, 2008).…”

Behavior and fluxes of Pt in the macrotidal Gironde Estuary (SW France)

“…Secondly, reactions involving Pt are kinetically controlled because of the slow rearrangements of the coordination spheres of Pt(II) and Pt(IV) and this effect is known to constrain the rates of both the complexation and adsorption of aqueous Pt (Turner et al, 2006;Shams et al, 2014). Thirdly, Pt P in catalytic form is relatively unreactive and unlikely to undergo mobilisation readily, and fourthly, we have not considered the potential for benthic fluxes of the metal from tidally disturbed sediment and pore waters.…”