Abstract
In aquatic systems, dissolved organic matter (DOM) constitutes a key component of the carbon cycle controlling the transport, speciation, bioavailability and toxicity of trace metals. In this work, we study the spatio-temporal variability of the MO in terms of both quality and quantity from upstream to downstream the Parisian conurbation. Urban discharges which are the main source of allochthonous organic matter into the Seine at low water periods were also investigated. The DOM collected was fractionated according to polarity criteria into five fractions: hydrophobic, transphilic, hydrophilic acid, hydrophilic basic and hydrophilic neutral. Due to urban discharges a strong enrichment in the hydrophilic (HPI) fraction was observed for downstream sites. This hydrophilic fraction presented stronger binding capacities for copper than hydrophobic fraction from less urbanized site (upstream from Paris) and than Suwannee river fulvic acid (SRFA). Furthermore, biotests highlighted a significant copper bioavailability decrease in presence of hydrophilic DOM.
Highlights
In aquatic systems, trace metals are present in different chemical forms
It has been considered that binding capabilities of the hydrophilic fraction could be neglected whenever metal speciation is computed in most natural aquatic systems
The dissolved organic matter (DOM) collected from urban discharges (CS0s and WWTP effluents) display strong hydrophilic characteristics, low humic substance contents (Fig 1), low SUVA and high contents of protein compounds
Summary
Trace metals are present in different chemical forms. These forms determine the residence time in the different compartments of the environment, and the bioavailability or toxicity of the metal towards living organisms (Town and Filella, 1999). Humic substances (hydrophobic acids), are natural complex organic macromolecules composed of aromatic cycles connected by aliphatic chains and functional groups of acidic nature. This hydrophobic fraction of DOM, is isolated at acidic pH on DAX-8 resin (Thurman and Malcolm, 1981). It is often considered as the major part of DOC (Dissolved Organic Carbon) in most natural aquatic systems, while the hydrophilic fraction of organic matter, not absorbed on DAX-8 and XAD-4 resins, is generally a minor part (Croue, 2004). It has been considered that binding capabilities of the hydrophilic fraction could be neglected whenever metal speciation is computed in most natural aquatic systems
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