Biological Deterioration

By definition, true leathers are resistant to bacterial attack. If, however, rawhide, parchment or pseudo-leathers become wet, putrefaction sets in and they will decay rapidly due to the action of proteolytic enzymes secreted by the bacteria. Even prolonged exposure in very damp atmospheres can render parchment open to bacterial attack. 

From time to time, conservators are asked to repair physical damage caused by vertebrate pests. In the author s experience these include mice, squirrels, cats, dogs, small boys and a parrot. No doubt other conservators can add to this list. 

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The situation with some forms of biological deterioration is somewhat different. Where the agent is macrobiological, as in the case of rodents, insects, and marine borers, the attack is physical in nature, such as by gnawing or boring. The attack is not at the atomic or molecular level. Any breaking of molecular bonds such as in polymer chain shortening is thus accidental. The attack may be said to be at the material s structural level, not the polymer molecule level. 

Any biological deterioration of cellulose acetate membranes is always by "accidental". To prevent this kind of deteriorations, chlorine injection to feed water is common practice. Inadequate control of chlorine injection may result in the enzymic deterioration of cellulose acetate membrane. 

Figure 6. Scanning electron microscopic view of membrane surfaces that were biologically deteriorated. Colonies of the microorganism on the surface were removed.

Figure 7. Cross section of biologically deteriorated membrane...

Table II. Types of Biological Deterioration of Wood and the Organisms Responsible...

Biological deterioration of water quality is primarily caused by toxic substances, products of putrefactive degradation, pathogens and radioactive substances. A schematic illustration of the effect of pollutants on water quality in the recipient is shown in Fig. 3.39. 

Techniques for Suppressing Deterioration. The methods that might be chosen to suppress deterioration depend on the type of deterioration that is taking place. The nature of biological deterioration has been amply covered in previous chapters. 

Dimensionally Stabilized Wood. Wood that has been saturated by immersion in water for long periods of time and subjected to related biological deterioration will often require a dimensional stabilization treatment before drying can be permitted safely. This treatment is usually done with bulking compounds such as polyethylene glycol (PEG). 

CORROSION, BIOLOGICAL - Deterioration of metals as a result of the metabolic action of microorganisms. Also often named fouling. 

The possible impact of nonbacterial species such as algae on the biological deterioration of concrete has been explained in a previous section (see Section 4.5.1.2.1.1) and the related references given there, and it will not be repeated here. However, the impact of microorganisms on MID will be briefly described. 

During harvest (and particularly in cool growing regions), it may not be feasible to deal with stuck fermentations immediately. In these cases, the wine should be stabilized against further biological deterioration by draw-... 

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