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

Abstract

In the present study, predictive measures for Pb toxicity and Lemna minor were developed from bioassays with 7 surface waters having varied chemistries (0.5-12.5 mg/L dissolved organic carbon, pH of 5.4-8.3, and water hardness of 8-266 mg/L CaCO3 ). As expected based on water quality, 10%, 20%, and 50% inhibitory concentration (IC10, IC20, and IC50, respectively) values expressed as percent net root elongation (%NRE) varied widely (e.g., IC20s ranging from 306 nM to >6920 nM total dissolved Pb), 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 because of covariance with alkalinity (p = 0.08), water hardness correlated strongly (r(2) = 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 times and 2.2 times 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.

The derivation of effects threshold concentrations of lead for European freshwater ecosystems

“…Therefore, it was decided not to include the toxicity data originating from the studies that use Aldrich humic acid (used as a surrogate for DOC) in the test media. In summary, new chronic toxicity data were added for L. minor , P. subcapitata , Chlorella kesslerii , Chlamydomonas reinhardtii , C. dubia , Diaphanosoma birgei , Alona rectangula , L. stagnalis , P. rapida , C. riparius , Baetis tricaudatus , B. calyciflorus , P. promelas , Acipenser sinensis , and Oncorhynchus mykiss . Compared with the Pb EU Voluntary Risk Assessment Report , which included 69 individual high‐quality NOEC data for 17 different freshwater species, chronic toxicity data for an additional 8 species were added: L. minor (higher plant), C. reinhardtii (unicellular alga), D. birgei (cladoceran), P. rapida (rotifer), A. rectangular (cladoceran), C. riparius (insect), B. tricaudatus (insect), and A. sinensis (fish).…”

Cadmium Bioavailability, Uptake, Toxicity and Detoxification in Soil-Plant System

“…When actual measurements are not feasible, computer speciation models (capable of performing complex calculations) offer a cost-effective alternative (Shahid et al 2012b(Shahid et al , 2014b, although site-specific validation is required to confirm the accuracy of the model's output. The most widely used speciation models include: the Windermere Humic Aqueous Model VI (WHAM VI), CHESS, CHEAQS, PHREEQC and VISUAL MINTEQ (Tipping et al 1998;Parkhurst and Appelo 1999;Gustafsson, 2008;Antunes and Kreager 2014;Shahid et al 2014d). These models offer the advantage of desk-top computing and are appropriate for both small and large scale applications.…”

Recent developments in surface complexation modeling

“…Research into the relationships between speciation, bioavailability, and toxicity continues to develop. The final study in this section, by Antunes and Kreager , shows how chemical speciation modeling can aid the description of dose‐response relations for biota under laboratory conditions.…”