BOOK REVIEWS

1Sylvie DENEUX-MUSTIN; Sylvie ROUSSEL-DEBET; Christian MUSTIN; Pascale HENNER; Colette MUNIERLAMY; Claude COLLE; Jacques BERTHELIN; Jacqueline GARNIER-LAPLACE & Corinne LEYVAL, 2003; Mobilité et transfert racinaire des éléments en traces: influence des micro-organismes du sol. Editions TEC & DOC, Paris. 304 p., 15,5x24 cm. ISBN 2-7430-0539-9. Price 60 €

2This book is an elaborate literature study, which aims to gather all the information currently available regarding the influence of micro-organisms on the mobility and root transfer of trace elements and thus contribute to a better understanding of these processes. To this effect, the book consists of two main parts. The first part gives a general overview of the processes involved in the mobility and root transfer of trace elements in soils, aiming to introduce the subject and to allow people who are not specialized in the area to understand the remainder of the book. In the latter part, a number of elements are discussed in more detail, and fiches are made containing a lot of element-specific information.

3The first, general part is divided into three chapters. The first chapter focuses on the physicochemical processes relating to the mobility of elements in soils, and starts by defining the various chemical forms under which trace elements can be present in the soil (free ions, soluble complexes, soluble methylised forms). Next, the physicochemical processes involved in dissolving or precipitating the elements, dependent on pH and Eh, are discussed. Additionally, the processes of mobilization and immobilization that play a major role in the solution chemistry of soils are described, such as adsorption, precipitation and aggregation. And finally the partition coefficient Kd that quantifies the distribution of the trace element between the soil solution and the solid phase is discussed and the influence of physicochemical parameters such as pH and Eh on this coefficient is dealt with.

4This first chapter is, in my opinion, mainly aimed at people who already have some knowledge about these processes and concepts, and is meant to freshen up things that are already known by the reader, since the explanation is generally too brief to offer a complete understanding, and is also confusing at times. More specifically, one key figure (figure 1: Potentiel ionique des éléments) is not explained thoroughly and seems to lack some information regarding the trend lines that are indicated.

5The second chapter then deals with the microbiological processes that interfere with the mobility of elements in soils and their transfer to plants. Before these processes are discussed, however, the principal groups of micro-organisms are brieflypresented, the division being made according to their source of energy and nutrition, with specialattention being given to the symbiotic organisms. As a next point, the different processes in which microorganisms influence the mobility of trace elements are considered, divided into solubilising, precipitating and element-specific processes. Processes resulting in the solubilisation of trace elements (that are discussed in this book) include the production of acids and other chelating agents, the reduction of Fe and Mn (resulting in the dissolution of oxides and hydroxides) and the oxidation of sulphides. Precipitation can be induced by the biodegradation of organometal complexes (resulting in the formation of insoluble Fe and Mn oxides and hydroxides), the reduction of sulphate and the following neoformation of sulphur minerals, and finally biosorption and bioaccumulation. Some processes are specific for certain elements, such as oxydoreduction and biomethylation, and these are also given attention. Additionally, the role of micro-organisms regarding the kinetics of these mobilisation/immobilisation processes is considered. Finally, the behaviour and destiny of elements in the plant-soil system is discussed. To this effect, the transfer factor is introduced, a factor that quantifies the enrichment of trace elements in the plant tissue by comparing the concentration of the element in the plant tissue to that in the soil. Also, the absorption of trace elements by the root system is briefly described, as well as the translocation of these elements to the upper parts of the plant. As a last point, the influence of micro-organisms on this soil-plant transfer is discussed, distinguishing between symbiotic and non-symbiotic organisms.

6The third and last introductory chapter deals with the toxicity of elements and the acquisition of tolerance in the soil-plant system. The first part of the chapter is concerned with the toxicity of trace elements and the effect that this has on micro-organisms and plants. The difference between essential and non-essential trace elements is explained, and attention is given to the fact that certain parameters can influence the toxicity of trace elements. It is also pointed out that toxic effects on micro-organisms can be divided in those relating to the nature and density of microbial populations, and those that are linked to the microbial activity. For plants, visual effects should be regarded as well as the possible effect on the metabolism. The second part then explains how micro-organisms and plants shield themselves from these toxic elements and lists the methods with which they achieve tolerance. Some emphasis is also put on the fact that, even though micro-organisms can achieve tolerance, the toxicity often does induce a change in density or variety of the microbial population, therefore disturbing the environment nonetheless.

7In the second part of the book element-specific information is gathered and a fiche (a few pages long) is made for each element in which the following points are considered: general characteristics (such as symbol, mass, radio-isotopes, presence in the environment), the influence of physicochemical parameters and principal soil constituents on the mobility of the element and the influence of micro-organisms on the mobility of the element in soils and the transfer to plants. The elements that are considered are Americium (Am), Antimony (Sb), Arsenic (As), Beryllium (Be), Boron (B), Cadmium (Cd), Caesium (Cs), Chromium (Cr), Tin (Sn), Iodine (I), Nickel (Ni), Niobium (Nb), Protactinium (Pa), Lead (Pb), Plutonium (Pu), Radium (Ra), Selenium (Se), Technetium (Tc), Thorium (Th) and Uranium (U). These fiches offer a concise overview of all the information available on these elements, and can certainly be very useful as a base knowledge to start from.

8These elements were chosen because of “their possible presence, their uses, the lack of knowledge concerning their behaviour, the possible, direct or indirect, influence of micro-organisms on their behaviour, as well as the fact that some of these elements are of interest both as an oligo-element and as a potentially toxic element

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