The effect of wastewater effluent derived ligands on copper and zinc complexation

Abstract

The shift toward bioavailability-based standards for metals such as copper and zinc not only improves the ecological relevance of the standard but also introduces significant complexity into assessing compliance. This study examined differences in the copper and zinc complexation characteristics of effluents from a range of different sewage treatment works and in relation to so-called ‘natural’ samples. This information is essential to determine whether the inclusion of effluent-specific complexation characteristics within the regulatory framework could enhance the environmental relevance of compliance criteria. The data show that for copper, binding affinity was not greater than that measured for materials derived from the receiving water environment, with a mean log K of between 4.4 and 5.15 and mean complexation capacity ranging from 38 to 120 μg/mg dissolved organic carbon (DOC) for effluents compared with a log K of 5.6 and complexation capacity of 37 μg/mg DOC for the Suwannee River fulvic acid. For zinc, however, effluents exhibited a much higher complexation capacity, with effluent means ranging from 3 to 23 μg/mg DOC compared with the Suwannee River fulvic acid, for which the complexation capacity could not be determined. Synthetic ligands in sewage effluent, such as ethylenediaminetetraacetic acid (EDTA), are implicated as contributing to these observed differences. This suggests that the current biotic ligand models for zinc might overstate the risk of harm in effluent-impacted waters. The data also show that the copper and zinc complexation characteristics of effluent samples obtained from the same sewage treatment works were less different from one another than those of effluents from other treatment works and therefore that sewage source has an important influence on complexation characteristics. The findings from this study support the case that the contribution to complexation from effluent-derived ligands could enhance the environmental relevance of bioavailability-based compliance criteria, in particular for zinc, owing to the additional complexation capacity afforded by effluent-derived ligands.

Development of a Sensitive Escherichia coli Bioreporter Without Antibiotic Markers for Detecting Bioavailable Copper in Water Environments

“…Some components, such as EDTA and other "EDTA-like" substances, are known to bind metal ions, which may influence metal bioavailability in an unpredictable manner (Knepper et al, 2005;Peters et al, 2014;Constantino et al, 2017). Recent data from 162 wastewater treatment effluents in the United Kingdom reveal the median EDTA concentration of 128 mg/L (0.44 mM), which is 5.3 and 22.9 times greater than those of dissolved zinc and copper, respectively (Constantino et al, 2017). We also confirmed that EDTA-bound copper affects the bioavailability of copper in aqueous solution (Figures 6C,D).…”

Surface water processes in coping with anthropogenic impact in a coastal Eastern Mediterranean region

“…The different water types (Nitrate-phosphate type for both Kaleb and Ibrahim versus sulfate type for Beirut river course) do not affect the behavior of total Cu in water. It is well known that Cu undergoes a phenomenon of solvation in water to form copper hydrate, which is a stable form in addition to the other forms of copper chemical species at pH 7 due to inorganic complexation (mainly copper carbonate(Byrne and Miller, 1985;Conry, 2005;Constantino et al, 2017; …”