........ published in NEWSLETTER # 62
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........ published in NEWSLETTER # 62
BIODEGRADABILITY PREDICTION
by Dr. W.J.G.M. Peijnenburg, National Institute of Public Health and the Environment, Bilthoven (The Netherlands), and Dr. J. Damborsky, Dept. of Microbiology/Fac.of Sciences, Masaryk University, Brno (Czech Republic)
This book (NATO ASI SERIES 2-23) presents the proceedings of the NATO Advanced Research Workshop "QSAR Biodegradation II: QSARs for Biotransformation and Biodegradation", which was held in Luhacovice (Czech Republic) in May 1996. One of the ideas behind the Workshop was to bring together experts working on biodegradation problems and those working on the development and analysis of Quantitative Structure-Biodegradability Relationships (QSBRs), and initiate a public discussion on 'bringing the knowledge on biological aspects of biodegradation into QSBR models'.
In these proceedings we report on the present state-of-the-art with regard to QSRBs and on the main findings of the deliberations. The contributions may be classified into three distinct categories:
(I) The main characteristics and foundations of biodegradation. This section includes overviews of the microbial aspects of biodegradation, as well as the methods that are available for testing the biodegradability of chemical substances.
(II) Trends and methods in biodegradation modelling. In this section, several computerised systems for the prediction of the biodegradability of chemicals deposited in the environment are highlighted.
(III) The application of predictive methods for biodegradation. The application and validation of some newly developed predictive models for biodegradation of organic compounds in both the aquatic and the terrestrial compartment are highlighted in this section.
Although one of the main conclusions was that there is still insufficient knowledge of the basic processes that take place during biodegradation, a broad range of molecular descriptors is available with high potency to be the relevant parameters for description of the structural features connected with the ability of a compound to be converted by the action of living organisms. Also, highly sophisticated statistical and computational methods (multivariate statistics, neural networks, genetic algorithms) are available to explore and find structure-activity relationships. It was revealed that it is the biodegradation data entering into the analysis and probably also the whole philosophy used for biodegradation modelling which cannot be considered satisfactory at present.
Topics for future activities that were identified include: - Gathering and broadening of the knowledge of the biochemical transformation pathways that chemicals may undergo in the field, including formation of so-called 'dead-end' intermediates and more toxic compounds. - Identification of structural fragments that enhance biodegradation (biophores, or molecular fragments that are recognised by microbes and subsequently transformed) and fragments that retard the process. - Since knowledge about biochemical transformation pathways can be achieved only by means of a multi-disciplinary approach, it was recommended that closer co-operation be initiated between scientists in several distinct fields, e.g. biochemistry, quantum chemistry, microbiology, analytical chemistry, statistics, etc. As a follow-up to the NATO Advanced Research Workshop, further co- operation between the participants was initiated aimed at dealing with some of the major drawbacks that were identified. One of the major problems, which is the lack of uniformly measured biodegradation data, will be dealt with by means of exchange of databases available among the participants. The data will be processed according to the procedures presented during the workshop. Subsequently the results obtained (new QSBR-models) will be validated, exchanged and compared. This is expected to lead to additional recommendations on the use and applications of QSBRs.
Reference books: 1-11, 2-23, E186