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Title: Assessment of the temporal variability of surface water quality parameters in setting environmental quality standards for metals
Author: Lathouri, Maria
ISNI:       0000 0004 2716 3942
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2012
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Metals, such as copper, zinc, cadmium, nickel and lead, can vary significantly in concentration over time and across small specified areas at the micro scale (geographic regions), either naturally or also due to human activities, such as urbanization, industrial and agricultural activities. Their chemical forms and distribution control their mobility, bioavailability and subsequent potential for toxicity which, in turn, dictates surface water quality. The physicochemical forms in which a metal ion is present (i.e. its speciation) determine the behaviour of the metal and therefore its bioavailability and toxicity due to biological accessibility in the environment. Bioavailability of a metal is expressed as the fraction of the metal that the organism is proximately exposed to during a given time and under defined conditions. It is generally accepted that the total metal concentrations in surface water are not considered to be very representative of the metal fraction that is taken up by the aquatic organisms, while the free metal ion [M"+] is considered to be the most toxic metal species. The complexation of metals by ligands has an important influence on the speciation of metals in natural waters, reducing the free metal aqueous activity and affecting the metal bioavailability and toxicity. Like all substances, metals can behave as contaminants, when present in excess, posing risks to the environment. As part of water quality management regimes, these risks are managed through the establishment of Environmental Quality Standards (EQS). EQS define concentrations of the metals in the surface water environment that are protective of the aquatic life. Current EQS values are based either on total or dissolved metal concentrations; however, they do not consider whether metals are in potentially bioavailable forms, or seasonal variability that would affect their bioavailability and potential for toxicity over time. Considering these limitations the objectives of the presented research were: to identify the temporal variability of chemical and physical determinands in a variety of aquatic environments and identify any changes that may significantly affect the quality of the aquatic system, to assess the temporal variability of metal speciation and bioavailability/toxicity through the use of chemical equilibrium and toxicity models, to assess the temporal variability in water quality using the present EQS for metals (Cu, Zn, Cd, Ni and Pb), based on total and dissolved concentrations, as well as the chemical equilibrium and toxicity modelling results, to evaluate the performance of the standard and bioavailability/toxicity based EQS setting methods in a variety ofUK surface water systems. The geochemical modelling studies have been carried out using two chemical equilibrium models: the Windermere Humic Ion Binding Model (WHAM) and the PHREEQC model. The Biotic Ligand Model (BLM) was utilised to assess the acute and chronic toxicity and to estimate the effects of Cu, Zn and Cd concentrations for acute; as well of Cu concentration for chronic toxicity for the aquatic organism Daphnia magna.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available