Wang, X.Ma, Y.Hua, L.McLaughlin, M.2010-04-062010-04-062009Environmental Toxicology and Chemistry, 2009; 28(3):662-6670730-72681552-8618http://hdl.handle.net/2440/57340The effect of pH on the acute toxicity of Cu to barley (Hordeum vulgare) root elongation was investigated in solution culture. The results showed that the median effective concentrations (EC50s; i.e., the concentration that reduced root elongation by 50% based on free Cu²⁺ activity) were not significantly different in the low-pH range from 4.5 to 6.5, but in the high-pH range from 7.0 to 8.0, a significant effect of pH on EC50s was found. The nonlinear relationship between EC50 and H⁺ activity in the present study indicated that the increased toxicity with increasing pH in solution may not be caused by decreasing H⁺ competition. When we take account of CuOH⁺ activities, a good linear relationship (r²> 0.97) between the ratio of CuOH⁺ activity to free Cu²⁺ activity and acute Cu toxicity to barley root elongation was achieved, which indicated that the observed toxicity in the highpH range may be caused by CuOH⁺ plus free Cu²⁺ in solution. Linear-regression analysis suggested CuOH⁺ had a greater binding affinity than Cu²⁺ at the biotic ligand sites. The logistic dose–response curve showed that expressing the Cu dose as Cu²⁺ +2.92 ·CuOH⁺ improved the data fit significantly compared to consideration of the free Cu²⁺ activity only. Thus, our results suggest CuOH⁺ was highly toxic to barley root elongation. The enhanced toxicity of CuOH⁺ therefore needs to be considered when modeling the effect of pH on Cu toxicity to barley for exposures having pH greater than 6.5.enCopperHydroxyl copperpHBiotic ligand modelJournal article002009016410.1897/07-641.10002632037000252-s2.0-6664911724539318McLaughlin, M. [0000-0001-6796-4144]