The potential for unanticipated biodegradation during EIS analysis of polymer-coated metallic substrates

During a recent long-term electrochemical test in aqueous NaCl produced from deionized water, microscopic inspection revealed that the surface of the polymer was heavily colonized by micro-organisms, which had developed naturally. The deionized water was considered as a possible source and, to establish the extent of contamination, samples were procured from universities in Italy, the U.S.A. and England. In all cases, when aliquots were cultured to test for the presence of biological contaminants, both bacterial and fungal growth ensued, thus reflecting the widespread contamination of deionized water systems. Many electrochemical experiments currently employ electrolytes produced from deionized water, and there is a body of evidence suggesting both that biodegradation may be partially responsible for early failure of inoculated samples and that the technique of EIS is sensitive enough to reveal such failures when they occur. There is, however, no conclusive evidence showing that EIS is capable of distinguishing between classical and biologically induced degradation. Thus, unanticipated biological contamination of long-term electrochemical tests may seriously affect the integrity of an experiment and subsequent interpretation of results. However, even if a source of non-contaminated water is available, a problem may still exist due to the ubiquitous nature of contaminants. Thus, assuming the absence of extraordinary measures to destroy biological contaminants, samples associated with longer term electrochemical experiments may suffer from inadvertent inoculation and subsequent growth. In addition, it seems likely that where this is followed by undetected and unanticipated biodegradation of a coating, a metal or the combined system, subsequent EIS analysis may produce spurious data. © 1997 Elsevier Science Ltd. All rights reserved.