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

• Published in: Environmental science and pollution research international 2017-03, Vol.24 (9), p.8363-8374
• Main Authors: Constantino, C., Comber, S. D. W., Scrimshaw, M. D.
• Format: Article
• Language: English
• Subjects: Acetic acid; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Benzopyrans - chemistry; Bioavailability; Complexation; Compliance; Copper; Copper - chemistry; Criteria; Dissolved organic carbon; Earth and Environmental Science; Ecotoxicology; Effluents; Environment; Environmental Chemistry; Environmental Health; Environmental science; Ethylenediaminetetraacetic acids; Fulvic acids; Heavy metals; Ligands; Marine environment; Receiving waters; Research Article; Rivers; Sewage; Sewage - chemistry; Sewage treatment; Waste Water - chemistry; Waste Water Technology; Wastewater; Wastewater treatment plants; Water Management; Water Pollution Control; Water Purification; Zinc; Zinc - chemistry
• ISSN: 0944-1344; 1614-7499
• DOI: 10.1007/s11356-016-8332-3

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.