Contaminated Soils, 3rd International Conference on the Biogeochemistry of Trace Elements held in Paris (France), May 15-191 1995, R. Prost (Editor), lNRA editions, 147, rue de l Universite-75388 Paris Cedex 07 with Full Proceedings on CDROM
In the Preface the Editor mentions about the objective of the Third International Conference on the Biogeochemistry of Trace Elements which was to establish the state of knowlwdge concerning the biogeochemistry of trace elements and to discuss the risks to human health and biodiversity posed by toxic elements in soils and sediments. Altogether there were 300 papers presented, 158 were presented orally and 142 were presented as posters. The proceedings are published in a book including a CD-ROM. This book includes introductive speeches, invited papers and some others chosen in order to have an overview of themes and symposia.
A.M. Bernard in Effects of heavy metals in the environment on human health comments that the exposure of the general popuiation to heavy metals has reached levels sufficiently high to cause some effects among sensitive groups of the general population. The review summarises the current state of our knowledge about the possible health consequences of the environmental pollution by lead, cadmium and mercury and also addresses the issues that complicate the interpretation of epidemological data ancl their translation into public health risks. Fortunately, we are presently witnessing a substantial reduction of the atmospheric emissions of lead and apparently also of cadmium which is mirrored in the blood concentrations of these metals in the general population. However, he cautions, one should not loose sight as the fact that heavy metals which have been massively discharged in the environment, will persist in the biosphere for centuries. They represent potential sources of exposure for future generations especially in case their acumulation by plants or aquatic food chains would be enhanced as a result of some environmental changes as acidification or global warming.
S.P. McGrath in Behaviour of trece elements in terrestrial ecosystems reviews recent studies on behaviour of trace elements, focussing on those related to soils. The situation of meatal aacumulation in soils is typified by slow accumulation but very long residence times. The soils have not attined steady-state where the where the input of many metals is greater than the losses and hence they are accumulating. This situation ,he predicts is likely to continue in the foreseeable future, and so soil pollution with trace elements is a truly long-term problem. He observed one important gap is that studies on biological effects in soils have rarely been related to measurements of the bioavailable fraction of trace elemnts in soils, especially when organisms other than plants are studied. This aspect has been emphasised by Davison, W. Zhang,H and Miller,S. in In situ procedures for measuring chemical speciation and availability of trace metals in soils and sediments . To obtain a true representation of the distribution of chemical techniques are required. They have devised and demonstrated new methods for in situ measurements such as DGT ( diffusive gradients in thin films) and DET ( diffusion equillibrium in thin films). This paper examines the procedures available for measuring the speciation of trace metals in situ.Although addressed to both soils and sediments, it focusses on the latter. The saturated nature of sediments simplifies in situ measurements and has led to the development and application of a range of techniques. There are two broad categories of measurements. Those that try to measure equillibrium and those that provide an assessment of available or labile metal by actively removing components from solution. This available fraction, which may include a component which is readily released from the soild phase, can be useful surrogate for bioavailability.
Sheppard, M.I. and Stephenson,M. in Critical evaluation of selective extraction methods for soils and sediments have urged the requirements for environmental quality assessment and management have necessiated the development of selective chemical extraction procedures to evaluate trace metal mobility in soils and sediments and uptake by biota. This article reviews the major extraction techniques in use and considers criticisms and suitability of these methods in light of recent research findings. They discussed the problems associated with coring and sectioning of samples, failure to obtain pore water samples, to maintain sediments under inert atmosphere during processings etc. and suggested three alternatives to these problems
1) the broarder use of sediment and soil contaminant pore water concentrations as an additional or complementary tool to chemical extarction schemes, 2) the use of thermodyanim calculations and pathways analysis along with sequential extractions to cross check the results and 3) the use of direct surface analysis, such as Enhanced Xray Absorption Fine Structure EXAFS, spectroscopy. They conclude the review with recommendations for further developments to improve the validity of extarction techniques and understanding of the important biogeochemical phases and processes in soils and sediments. In the next article, Manceau, A. and others demonstrate the direct determination of heavy metals speciation in soils by EXAFS spectroscopy. Berti,W.R. and others discuss sequential chemical extarction of trace elements with an outlook on the development and use in remedaiating contaminated soils. The book has several interesting articles on mobility of trace metals through soils and sediments (Charlatchka,R. and others), plant uptake of metals (Rule and Adriano, Joner and Leyvai).
Destouni,G. discussed modelling sub-surface element fiuxes and concentrations exemplified by the Lagrangian transport formulation. The exemplification is made for transport through unsaturated soil, in terms of the expected soil water concentration profile for sorptive solute and the expected field-integrated discharge of solute mobilised by mineral dissoulution. In the sub -chapter on Impacts and pathways of exposure, Dickinson and Lepp describe metals resistance traits in trees with particuiar attention to the relative importance of genetic variation versus phenotypically plastic responses to toxic metals. The toxic effects of elevated metals in soils can be readily observed in tree seedlings, but once established, trees appear to be particularly resistant to metal stree. Patterns of metal uptake in trees vary and elevated concentrations of metals in foliage, abrk, roots and woody issues may not be synonymous with symptoms of toxicity. Knowledge of this variation in resistance and uptake patterns ofmetals provides a potentiai opportunity to use trees for biotreatment of contaminated soils. In situations where soil metal levels are elevated by agricultural and industrial activities, the use of short-rotation coppice in bioremediation programmes may allow uptake, harvest and removal of metals. This would be particularly beneficial to future disposal of organic wastes to land, in which metal removal from woodland ecosystems could keep pace with metal inputs. A few papers discuss on the factors controlling heavy metais concentrations in small lakes (Steinnes,E.), Biogeochemical cycling of trace elements ( Taillefert,M and others) and few are described in French language which can not be deciphered here. Overall, the book along with the CD-ROM should be an exceilent possesion for researchers on biogeochemistry, soil sciences, environmental sciences etc.
Dr. G.J. Chakrapani
Department of Earth Sciences
University of Roorkee
Roorkee - 247667
Uttar Pradesh, India