title: 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.
authors.affiliation: School of Geography, Earth and Ocean Sciences, Plymouth University, Drake Circus, Plymouth PL4 8AA, UK.
authors.forename: Leyla
authors.initials: L
authors.lastname: Shams
authors.affiliation: School of Geography, Earth and Ocean Sciences, Plymouth University, Drake Circus, Plymouth PL4 8AA, UK. Electronic address: aturner@plymouth.ac.uk.
authors.forename: Andrew
authors.initials: A
authors.lastname: Turner
authors.affiliation: Marine Institute, Plymouth University, Drake Circus, Plymouth PL4 8AA, UK.
authors.forename: Geoffrey E
authors.initials: GE
authors.lastname: Millward
authors.affiliation: School of Marine Science and Engineering, Plymouth University, Drake Circus, Plymouth PL4 8AA, UK.
authors.forename: Murray T
authors.initials: MT
authors.lastname: Brown
mesh_terms: D000327:Adsorption; D059001:Aquatic Organisms / Q000254:growth & development / Q000378:metabolism*; D002708:Chlorella / Q000254:growth & development / Q000378:metabolism*; D004784:Environmental Monitoring; D005110:Extracellular Space / Q000737:chemistry*; D006207:Half-Life; D042541:Intracellular Space / Q000737:chemistry*; D007700:Kinetics; D058086:Microalgae / Q000254:growth & development / Q000378:metabolism*; D010984:Platinum / Q000378:metabolism*; D013696:Temperature
chemical_list: D010984:Platinum
keywords: Accumulation; Adsorption; Chlorella stigmatophora; Marine microalgae; Platinum group metals; Speciation