A Comparison of Copper Speciation Measurements with the Toxic Responses of Three Sensitive Freshwater Organisms

Abstract

Environmental Context.A rapid Chelex resin method is shown to be a valuable speciation screening tool for use in a tiered risk assessment of copper toxicity in fresh waters. It is a more conservative measure than toxicity testing with sensitive biota, but a better indicator of toxicity than a dissolved copper measurement. Abstract.Twelve natural fresh waters with similar pH and hardness, but varying dissolved organic carbon (DOC) and copper concentrations, were assessed for (a) toxicity to an alga (Chlorella sp. 12), a cladoceran (Ceriodaphnia cf. dubia) and a bacterium (Erwinnia sp.), and (b) copper speciation using a rapid Chelex extraction method, diffusive gradients in thin films (DGT) and anodic stripping voltammetry (ASV). In synthetic fresh water with no added DOC, at pH 7.0 and low hardness, the toxic responses (EC/IC50) of all three organisms to copper were similar. However, in the toxicity of copper added to natural water samples exhibited a negative linear relationship to DOC (r2 = 0.82–0.83), with respective slopes for algae, cladocerans and bacteria decreasing in the ratio 7.4 : 3.5 : 1. The marked difference in responses in the presence of natural dissolved organic matter indicated that not all of the organisms conformed to the free ion activity model (FIAM). This was confirmed by copper ion selective electrode measurement of copper ion activity. Copper toxicity to algae in the presence of DOC was overestimated by free ion activity possibly due to surface binding of DOC. Copper toxicity to the bacteria was greater than predicted and was shown to be a result of bioavailability of some copper complexes formed with organic matter. Cladocerans appear to more closely follow FIAM predictions. These findings have important implications for attempts to extend predictive models of metal toxicity beyond fish to more sensitive freshwater species. The measured labile copper concentrations of copper-spiked natural waters varied from 0 to 70% of total copper concentrations. There was no clear relationship between the three measurement techniques. Good correlations were obtained between both algal and bacterial growth inhibitions measured on copper-spiked natural waters and the corresponding Chelex-labile copper concentrations. A single natural water sample was manipulated to different pH and hardness values, spiked with copper, and tested using the above three organisms with the Chelex method. Toxicity test results generally agreed with studies performed in synthetic fresh waters, showing that the relationships between toxicity, pH and hardness were organism-specific. Chelex-labile copper was always over-predictive of toxicity but significantly better (P ≤ 0.05) than dissolved copper concentrations, as it only detects the fraction of total copper that is reactive over biologically-relevant timescales. Colloidally-bound copper and copper associated with strong ligands are not detected. The Chelex method is therefore useful as a measure where speciation is accepted in water quality regulations.

The Effect of Composition of Different Ecotoxicological Test Media on Free and Bioavailable Copper from CuSO4 and CuO Nanoparticles: Comparative Evidence from a Cu-Selective Electrode and a Cu-Biosensor

“…Thus, in case of CuSO 4 , the free ion concentration may be considered as relatively suitable parameter for toxicity prediction, as also earlier demonstrated by Apte et al . [44]. To our surprise, a good agreement between the EC 50 values and free Cu content was observed in our experiments, even though they were conducted with different organisms of substantially different biological complexity (ranging from bacteria to algae and crustaceans).…”

Bioavailability of Cd in 110 polluted topsoils to recombinant bioluminescent sensor bacteria: effect of soil particulate matter

“…Soil-water suspensions were chosen for analysis due to our previous results showing that bioavailability of heavy metals in direct contact with soil particles may increase bioavailability of metals compared to that is leached to soil aqueous fraction (Ivask et al 2004;Apte et al 2005;Kahru et al 2005;Brandt et al 2006;Bondarenko et al 2008). Our results showed that 4.5% of the total Cd in soil T REF and 0.9% of the total Cd in the soil Mg10 were bioavailable to Cd sensor bacteria in a contact assay.…”

Determination of Free Nickel Ion Concentrations Using the Ion Exchange Technique: Application to Aqueous Mining and Municipal Effluents

“…Over the past two decades, many papers have been published on metal speciation in aquatic systems. These publications have mainly focused on the measurement of labile metals (free plus rapidly dissociating complexes) using methods such as Diffusive Gradients in Thin Films Technique (DGT) (Zhang and Davison 2000;Unsworth et al 2005;Unsworth et al 2006;Sigg et al 2006) and competing ligand exchange methods using ion exchange or electrochemical techniques (Mandal et al 2002;Fasfous et al 2004;Apte et al 2005;Chakraborty et al 2006); the exception to this statement is the Donnan membrane technique which is also gaining promise in measuring free metal ion concentration (Temminghoff et al 2000). Although labile metal species may be indicators of metal bioavailability (Batley et al 2004;Apte et al 2005), the free metal ion concentration is believed to be a better predictor of bioavailability (Morel 1983).…”