Microbiologically it was demonstrated that amino acids, e.g. cysteine (CySH), and othercompounds, e.g. sodium thioglycollate, containing thiol groups neutralized the activity of silvernitrate against Pseudomonas aeruginosa PAOl. Amino acids with disulphide bonds wereinactive, with the exception of l‐cystine dimethyl ester, as were all amino acids with nosulphur groups. Iodoacetamide reacted with CySH to produce a CyS–acetamide complex thatwas unable to quench the activity of Ag+. Chemical analyses using cyclic voltammetrydemonstrated that high coordination numbers (3·1) were obtained with thiol‐containingamino acids and low numbers (0·28–0·4) with other amino acids. Bothmicrobiologically and chemically, the results imply that interaction of Ag+ with thiolgroups plays an essential role in bacterial inactivation.

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The UK Department of the Environment (DOE) is developing an independent capability to assess proposals made by the nuclear industry for the underground disposal of low and intermediate level radioactive waste. Modelling chemical processes forms an integral part of the underlying DOE research programme which includes the development of probabilistic risk assessment codes, more detailed deterministic models and supporting field and laboratory studies, in a co-ordinated, hierarchical approach. This paper summarises the results of a survey on the current status of this and related research, with emphasis on the assessment of a safety case for shallow land disposal of low level waste in about two years time. Shortcomings in existing work are identified, and a structured programme for future research described.

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