Development of the terrestrial biotic ligand model for predicting nickel toxicity to barley (Hordeum vulgare): ion effects at low pH.
The focus of the present study was to investigate the potential for Al3+, Mg2+, and H+ to influence Ni2+ toxicity for barley seedlings grown in acidic aqueous solutions and to assess the capacity of a two-site terrestrial biotic ligand model (tBLM) to accurately predict 50% effect activities (EA50s). To accomplish these objectives, 48-h EA50Ni2+ values were obtained for three sets of exposures in which the pH and activity of Al3+ and Mg2+ were varied. Exposures contained both Al alone and in combination with Mg so that compound ion effects could be investigated. A tBLM was then constructed to predict EA50Ni2+ values from the exposure solution chemistry. The results show a slight protective effect of H+ against Ni2+ toxicity and a strong protective effect of Mg2+, as indicated by a 4.6- and 8.0-fold increase in the measured EA50Ni2+ values corresponding to changes in pH from 6.0 to 4.5 and {Mg2+} from 0 to 1.40 mM, respectively. Increasing solution {Al3+} from 0 to 0.5 microM had no effect on Ni2+ toxicity, although Al itself negatively affected root elongation. Comparison of EA50 values calculated as both Ni2+ and measured concentration of total Ni in the root ([Root-Ni]T) showed [Root-Ni]T to be a more normalized measure of Ni bioavailability. The strong correlation between root growth inhibition and tBLM-predicted root-Ni accumulation suggests that toxicity was influenced by Ni2+ binding to low-affinity ligands within the cell wall, in addition to Ni2+ uptake through Mg2+ transporters. Predicted EA50Ni2+ values generated with the model were all within a factor of +/-1.5 from measured values--a result that emphasizes the advantage of using the tBLM for risk assessment.
Antunes
Paula M C
PM
AquaTox Testing and Consulting, 11B Nicholas Beaver Road RR3, Guelph, Ontario N1H 6H9, Canada. pcypas@gmail.com
Kreager
Nancy J
NJ
D000535:Aluminum / Q000737:chemistry; D001467:Hordeum / Q000187:drug effects* / Q000254:growth & development; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000737:chemistry; D008954:Models, Biological; D009532:Nickel / Q000633:toxicity*; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D011522:Protons; D012989:Soil Pollutants / Q000737:chemistry / Q000633:toxicity*
D011522:Protons; D012989:Soil Pollutants; D009532:Nickel; D000535:Aluminum; D008274:Magnesium