Freshwaters: which NOM matters?

One of the difficulties encountered in the study of natural organic matter (NOM) in aquatic environments concerns terminology: a large number of different names and acronyms are used. In fact, this diversity merely reflects the variety of approaches applied to the study of NOM, leading to the definition and measurement of different operationally-defined fractions. As a result, the choice of the ‘best' method to use and of the ‘best' fraction to work on in a particular case is far from straightforward. This has as a consequence that often very simple methods for NOM characterisation are used in applied environmental studies and surveys. This study includes, first, a review of the most widely applied terminology, as described in over 500 articles, and, second, a first attempt at assessing how the panoply of methods available is really used in applied environmental studie

Trace element complexation by humic substances: issues related to quality assurance

Despite the amount of data available and the effort that has been put into studying the binding of trace elements by humic substances, there is still a significant amount of uncertainty surrounding the validity and applicability of the existing values in solving particular problems in the environmental, toxicity and industrial fields. This paper discusses the problems associated with the characterisation of humic binding and proposes a general approach for quality assessing trace element-humic substances complexation data, which includes the normalisation of raw experimental data prior to any data treatment (modelling

Processos geoquímics en abocadors d'escombraries

In a densily populated industrialized country, waste disposal must be compatible with the requirements of the environment. This is one of the indispensable requirements to guarantee an effective protection of the environment. While in the past, waste disposal performance was more or less evaluated in terms of short-term costs, there is at present a reorientation in the direction of a science-based waste disposal industry. These new tendencies are taking into account ecological factors as well as the long-term consequences of waste disposal methods. This field confronts science with an urgent challenge and calls for close collaboration between many different specialized disciplines. In this light, an overview of the geochemical processes taking place in landfills is presented in this paper

A simple method for quantifying the humic content of commercial products

A method based on an analytical technique, initially developed for quantifying aquatic refractory organic matter (often called humics), has been applied to commercial samples claiming to contain humic-type substances. At present, no method exists for quantifying the humic content on this type of sample. The analytical method is based on measuring the peak current obtained by adsorptive stripping voltammetry of the complex formed by refractory organic matter in the presence of trace amounts of Mo(VI). The quantification procedure requires the response obtained for the unknown sample to be compared with the response obtained with International Humic Substance Society (IHSS) reference humic substances. A very simple procedure that enables the humic content of any sample to be expressed as IHSS standard equivalents is described in detail. The method is highly selective, reproducible and suitable for routine analysi

Chemical modelling of multicomponent mixtures: quality assurance is more than just equilibrium data quality assessment

Despite the large amount of data available, the great effort put into searches for the ‘best' parameters and many comparative modelling studies, considerable uncertainties continue to plague chemical thermodynamics. An important factor in this ongoing failure has been the notion that the problem can be solved by better assessment of data quality on a case-by-case basis. This approach has proved strikingly unsuccessful. A different methodology must therefore be found to meet the general requirements of thermodynamic modelling in aquatic chemistry. This paper discusses current practices in quality assessment of thermodynamic data and the problems associated with them. It outlines a general approach which might address the above problem based on two concepts: (i) using large databases to store as much of the available data as possible in the form that it appears in the literature along with an assessed ‘score' or ‘measure of information content' and (ii) then using automatic mechanisms informed by this score to produce the thermodynamically consistent datasets needed for modelling calculation

The fate of inorganic colloidal particles in Lake Brienz

Abstract.: The fate of colloidal particles in Lake Brienz and its two main tributaries, the Aare and Lütschine Rivers, was studied over a period of more than a year. Lake colloid loads from the unmodified Lütschine fluctuated significantly across seasons. The highest loads are in summer due to glacier melting. Colloid loads from the Aare reflected the seasonal water use by upstream hydropower plants. A significant number of mineral particles, even outside the theoretical non-settling range, remain in suspension in the epilimnion of Lake Brienz in summer because of the mineralogical nature and shape of the particles and the high input loads. Only 1730 of the 16,800 tons of colloidal particles that entered the lake during the period from 1 June 2004 - 31 July 2005 were exported through the lake outlet. The remainder was presumably lost in the lake through coagulation-sedimentation processes. Coagulation properties of non-fractionated colloid samples in quiescent conditions were studied in the laboratory both in the absence and presence of different organic compounds representative of natural organic matter. Lake Brienz colloids coagulate slowly, as expected from particles (mainly phyllosilicates) bearing a net negative surface charge. Slightly higher coagulation rates were recorded in March and April during the spring algal bloom, which suggests that colloid coagulation is enhanced by carbohydrates. This effect was confirmed in laboratory experiments. However, the concentration of natural organic matter in Lake Brienz is so low that it is not having any significant effect on the fate of inorganic colloid

Quantification of refractory organic substances in freshwaters: further insight into the response of the voltammetric method

A recently published method for quantifying refractory organic matter (often referred to as humic substances) in freshwaters was applied to a wide range of International Humic Substance Society (IHSS) humic compounds in order to (i) gain a better understanding of the mechanism of the voltammetric response which is the basis of the analytical method and (ii) provide guidance on choosing the optimal standard to be used. At the same time, the sensitivity of the technique has been increased by switching from the pulse mode initially proposed to the square-wave mode. The results obtained show that (i) differences in adsorption onto the electrode rather than differences in complexation strength are responsible for the differences in the intensity of the signal obtained for the different humic compounds, (ii) carboxylate, N- and S-containing groups do not play a role in the voltammetric signa

Estimation of WHAM7 constants for GaIII, InIII, SbIII and BiIII from linear free energy relationships, and speciation calculations for natural waters

We compiled the equilibrium constants for the interactions of the technology-critical elements (TCEs) GaIII, InIII, SbIII and BiIII with ammonia, fluoride, hydroxyl and ligands with oxygen atoms. We then combined them with predictive equations to estimate parameters for Humic Ion-Binding Model VII, which permits the calculation of metal binding by natural organic matter (fulvic acid, FA, and humic acid, HA). Derived values of the Model VII parameter quantifying the interaction of metal ions with carboxyl-type groups (log KMA) were among the highest estimated so far, as were the values for the parameter (ΔLK2) that quantifies the tendency of the metal ion to interact with softer ligand atoms (N and S). The Windermere Humic Aqueous Model, version 7 (WHAM7), which incorporates Model VII, was then used to estimate the chemical speciation of each TCE element

Biophysical Environmental Chemistry: A New Frontier for Chemistry

The paper discusses the position and role of environmental chemistry among the other environmental disciplines. It discusses the various aspects of environmental chemistry and emphasizes the need for developing fundamental studies in biophysical environmental chemistry in order to better understand the functioning of environmental systems. These systems include a large number of various structures in the nanometer to meter range which play key roles on compound fluxes and consequently on the homeostasis of ecosystems and on their disturbance by anthropogenic activities. Both structures and fluxes are presently ill-known and new concepts and methods must be developed in this field. For chemistry, this is a challenging area where supramolecular structures and processes play dominant roles. It is also a challenging field for the development of environmental sciences since detailed and sound physico-chemical processes are needed in macroscopic modeling of compound circulation in ecosystems. In addition, teaching this discipline to chemistry students would allow them to confront complex, structured real systems. This paper also discusses the relationship between biophysical environmental chemistry and the other environmental disciplines within integrated multidisciplinary studies. The structure used at the Faculty of Sciences of the University of Geneva to favour a flexible but efficient integration is briefly described

Desenvolupament d'un sistema expert per a l'estudi de l'especiació química

És generalment acceptat que 1'especiació química consisteix en la determinació de les diferents formes físico-químiques d'un element, el conjunt de les quals ens dóna la concentració total d'aquest en un sistema particular. L'especiació química pot ésser estudiada mitjançant càlculs basats en els equilibris existents en el sistema. Han estat elaborats molts programes, amb llurs pròpies bases de dades, capaços de dur a terme aquests càlculs, encara que, en general, són d'aplicació més aviat restringida. La finalitat del present projecte es la de desenvolupar un sistema expert per a 1'estudi de 1'especiació química (Joint Expert Speciation System, JESS), és a dir, un conjunt de programes de càlcul que inclourà una base de dades i un ajut «expert» que ha de guiar sempre l'usuari.Speciation is now accepted as meaning the different physico-chemical forms of an element that make up its total concentration in a particular environment. One way of determining speciation is to perform equilibrium calculations. Many programs exist that do such calculations, each with their own databases and most with rather restricted applications. The aim of the project is to develop a joint Expert Speciation System (JESS), a general equilibrium calculation and database package that will include an «expert» facility which will guide the user at all times