title: A resin-buffered nutrient solution for controlling metal speciation in the algal bottle assay.
abstract: Metal speciation in solution is uncontrolled during algal growth in the traditional algal bottle assay. A resin-buffered nutrient solution was developed to overcome this problem and this was applied to test the effect of chloride (Cl⁻) on cadmium (Cd) uptake. Standard nutrient solution was enriched with 40 mM of either NaNO₃ or NaCl, and was prepared to contain equal Cd²⁺ but varying dissolved Cd due to the presence of CdCl(n)(2-n) complexes. Both solutions were subsequently used in an algal assay in 100 mL beakers that contained only the solution (designated "-R") or contained the solution together with a cation exchange sulfonate resin (2 g L⁻¹, designated "+R") as a deposit on the bottom of the beaker. Pseudokirchneriella subcapitata was grown for 72 h (1.4 × 10⁵-1.4 × 10⁶ cells mL⁻¹) in stagnant solution and shaken three times a day. Growth was unaffected by the presence of the resin (p>0.05). The Cd concentrations in solution of the -R devices decreased with 50-58% of initial values due to Cd uptake. No such changes were found in the +R devices or in abiotic controls. Cd uptake was unaffected by either NaNO₃ or NaCl treatment in the +R device, confirming that Cd²⁺ is the preferred Cd species in line with the general concept of metal bioavailability. In contrast, Cd uptake in the -R devices was two-fold larger in the NaCl treatment than in the NaNO₃ treatment (p<0.001), suggesting that CdCl(n)(2-n) complexes are bioavailable in this traditional set-up. However this bioavailability is partially, but not completely, an apparent one, because of the considerable depletion of solution ¹⁰⁹Cd in this set-up. Resin-buffered solutions are advocated in the algal bottle assay to control trace metal supply and to better identify the role of metal complexes on bioavailability.
authors.affiliation: Division of Soil and Water Management, Department of Earth and Environmental Sciences, K.U.Leuven, Kasteelpark Arenberg 20-Box 2459, 3001 Heverlee, Belgium. liesbeth.verheyen@ees.kuleuven.be
authors.forename: L
authors.initials: L
authors.lastname: Verheyen
authors.forename: R
authors.initials: R
authors.lastname: Merckx
authors.forename: E
authors.initials: E
authors.lastname: Smolders
mesh_terms: D001681:Biological Assay / Q000379:methods; D002021:Buffers; D002104:Cadmium / Q000378:metabolism*; D002712:Chlorides / Q000494:pharmacology*; D000460:Chlorophyta / Q000378:metabolism*; D003470:Culture Media / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D012117:Resins, Synthetic / Q000737:chemistry*; D013997:Time Factors
chemical_list: D002021:Buffers; D002712:Chlorides; D003470:Culture Media; D008670:Metals; D012117:Resins, Synthetic; D002104:Cadmium; C046797:amberlite