John Wiley & Sons, Ltd.

Lead toxicity to Lemna minor predicted using a metal speciation chemistry approach

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In the present study, predictive measures for Pb toxicity and L. minor were developed from bioassays with 7 surface waters having varied chemistries (i.e., 0.5 to 12.5 mg/L dissolved organic carbon (DOC), pH 5.4 to 8.3 and water hardness 8 to 266 mg/L CaCO3). As expected based on water quality, 10, 20 and 50% inhibitory concentration (IC) values expressed as percent net root elongation (%NRE) varied widely (e.g., IC20s ranging from 306 to > 6,920 nM total dissolved Pb ([Pb]T_Diss)), with unbounded values limited by Pb solubility. In considering chemical speciation, %NRE variability was better explained when both Pb‐hydroxides and the free lead ion were defined as bioavailable (i.e., f{OH}), and colloidal Fe(III)(OH)3 precipitates were permitted to form and sorb metals (using FeOx as the binding phase)). Although cause‐and‐effect could not be established due to covariance with alkalinity (p = 0.08), water hardness correlated strongly (r2 = 0.998 p < 0.0001) with the concentration of total Pb in true solution ([Pb]T_True Solution). Using these correlations as the basis for predictions (i.e., [Pb]T_True Solution vs. water hardness and %NRE vs. f{OH}), IC20, and IC50 values produced were within a factor of 2.9 and 2.2x of those measured, respectively. The results provide much‐needed effect data for L. minor and highlight the importance of chemical speciation in Pb‐based risk assessments for aquatic macrophytes. Environ Toxicol Chem © 2014 SETAC

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