Quantifying ‘humics’ in freshwaters: purpose and methods

Abstract

Natural organic matter (NOM) plays an important role in many environmentally relevant processes. NOM includes many different types of compounds, not all of which behave similarly. Much effort has gone into characterising some fractions of NOM (e.g. humic substances) in the different environmental compartments, in finding tracers to ascertain their origin, etc. However, few methods exist for quantifying the different types of NOM and, as a result, field studies have limited themselves to measuring only total or dissolved organic carbon. In this article, the few existing methods for humic substance quantification are reviewed, and the implications of the current lack of simple measurement methods are discussed in relation to two fields of high environmental relevance: trace element speciation modelling and natural colloid and engineered nanoparticle fate.

HPLC Fingerprints of Porewater Organic Compounds as Markers for Environmental Conditions

“…Absorbance spectroscopy with a single detection wavelength has been verified as a suitable detection method after HPLC separation (Lepane, 2010a). The UV absorbance at 250-280 nm has been widely used to provide an estimation of aromatic compounds (Filella, 2010). In the present study, multi-wavelength HPLC analysis has been carried out to detect changes in pwDOM composition and molecular mass profiles down the cores.…”

Environmental chemistry: a discipline standing on two shoulders

“…[33] necessarily their proximity to truth' [27] and that this consistency is often reached through extensive (hidden) parameter fitting, it is clear that there is an urgent need to acknowledge the (hidden) degree of empiricism associated to the current use of apparently mechanistic-based modelling in many fields such as, for instance, ecotoxicicity assessment. [28] This, of course, opens the question of the extent to which considering environmental chemistry a strictly deductive science might be an illusion.…”

A simple method for quantifying the humic content of commercial products

“…[1], any analytical method measures a property of an analyte (or its reaction product), but the operationally defined nature of 'humics', together with the concomitant elusive and non-constant composition and structure of these substances, makes it difficult to find such an intrinsic property for them. Recently, an electroanalytical method based on cathodic stripping preceded by the adsorptive collection of Mo(VI)-humic or fulvic acid complexes has been proposed for natural samples [3,4].…”

“…Moreover, none of the methods occasionally used in research and in environmental monitoring is without drawbacks (see Ref. [1] for a recent review), not least the fact that most of the methods 'see' only a certain fraction of humics [1], the proportion of which does not remain constant from system to system. It is important to point out that this situation is exclusively due to the uncommon nature of these substances: fulvics and humics are operationally defined fractions of natural organic matter and not compounds with reproducible structures and composition.…”