Microbiocides

The threat of accidental misuse of quaternary ammonium compounds coupled with potential harmful effects to sensitive species of fish and invertebrates has prompted some concern. Industry has responded with an effort to replace the questionable compounds with those of a more environmentally friendly nature. Newer classes of quaternaries, eg, esters (206) and betaine esters (207), have been developed. These materials are more readily biodegraded. The mechanisms of antimicrobial activity and hydrolysis of these compounds have been studied (207). AppHcations as surface disinfectants, antimicrobials, and in vitro microbiocidals have also been reported. Examples of ester-type quaternaries are shown in Figure 1. 

The activity of the sorbates at a higher pH is one distinct advantage over the two other most commonly used food preservatives, benzoic and propionic acids, because the upper pH limits for activity of these compounds are approximately pH 4.5 and 5.5, respectively. Although the effect of sorbates can be microbiocidal under certain conditions, activity is most often manifested as a microbial growth retardant. 

A combination of the two dioxaborinanes, (2) and (3), is marketed as a fuel microbiocide by Hammonds Euel Additives, Inc., Houston, Texas, under the trademark BIOBORJE. Annual U.S. production and consumption is estimated at 140—230 metric tons (28). 

Malachite green (0.0...2.0) uracil derivatives, triazine herbicides [163] polar lipids [246, 247] phospholipids [248, 249] fatty acids, fatty aldehydes, phospholipids and glycolipids [250] microbiocidal isothiazolones [251]... 

Quinoline derivatives of formula 115 are outstandingly active as microbiocides and can be preferentially used as agricultural fungicides and bactericides for the control of undesired plant pathogens (96EUP703234). 

MIcrobiocldes. There are several microbiocides available commercially that can perform an effective function in controlling microbial activity. Some of these chemicals are inorganic, such as chlorine, sodium hypochlorite, calcium hypochlorite, hydrogen peroxide, chromates and compounds of mercury and silver. However, the organic chemicals find the highest use as microbiocides. Some examples of these organic compounds are peracetic acid, paraformaldehyde, polychlorophenols and quaternary ammonium derivatives, to name a few [208]. 

Microbiocides may be toxic to humans therefore, care must be taken when used. When selecting the microbiocide, the field engineer can obtain pertinent information on chemicals from the service company providing the chemicals. The microbiocide selected must be compatible with the system in which it is being used. Some chemicals such as quaternary amines have dual functions one as microbiocides and the other as film-forming corrosion inhibitors. Insufficient concentrations of this type of chemical may not be enough to coat the whole surface of metal and can cause pitting corrosion. The selection must also depend on chemicals that can produce the desired control in minimum time limits and... 

Mlcrobiocidal Treatment. Once the microbial activity reaches a high enough level to cause problems, physical and chemical methods may be used to control the problem. In drilling operations, the most effective method is chemical treatment—the use of microbiocides [184,208]. 

To select a microbiocide one should consider its compatibility with the system. Some chemicals may affect the performance of the drilling fluids and lead to other problems. For example, quats, amines, and chlorinated phenols may cause clay flocculation of the drilling fluid if present in sufficient quantities. Therefore, the effect of the microbiocide on the drilling fluid properties must be thoroughly tested and understood before the chemical is used. 

Once the microbiocide is selected, a method of application should be considered. The chemical can be introduced to the system by either batch treatment, continuous treatment or by a combination of both. For batch treatment, NACE provides an equation given below. This equation can be used to determine the concentration of chemical at any time during the eight hour period. The equation is... 

This is one of the most important factors in alleviating microbial problems. A decrease in microbial activity after treatment indicates a positive response to the microbiocidal treatment. Continuous monitoring is imperative for effective control. 

Microbiocides. For a general guideline about 100 mg/L of the microbiocide with at least 50 wt% active ingredient should be added to the drilling fluid. Exact dosage and treatment frequency has to be estimated based on the severity of the problem. 

Calculation of system volume to ensure adequate nitrite reserve and, for lower temperature systems, the use of a microbiocide. 

It is not usual for unopened drums of nitrite-based chemical to degrade, and the product should remain in good condition for several years. However, it is possible for tannin-based corrosion inhibitors to degrade, even in unopened drums. Under warm conditions (such as storage in a boil-erhouse) and in the absence of a small amount of suitable microbiocide in the formulation, plastic drums containing tannin products may swell considerably because of microbiological degradation and gas formation. Care is needed to avoid accidents. 

Apart from physically cleaning tanks periodically, dispersants that promote homogeneity are employed. These often take the form of dispersant packages, which are polymer blends containing asphaltene and wax dispersants and other problem-specific additives. In addition, low-priced general-purpose dispersants, microbiocides, and antioxidants form part of the package. 

It would be diflBcult to estimate the quantity of TGDD which enters the environment each year. In addition to the common pesticides listed in Table I, other chlorophenols nd their derivatives are used widely. For example, large amounts of the disinfectant, hexachlorophene (2,2 -methylenebis(3,4,6-trichlorophenol)), are used in homes, hospitals, and industry, and the Dowcides 2 and B (2,4,5-trichlorophenol and its sodium salt) are industrial microbiocides. More than 50,000,000 lbs of trichloro-phenol are made in the United States each year (24), and much of it eventually must be dispersed in the environment. The dioxin content seems to be variable but is generally below 0.5 ppm (25). 

Isonicotinic acid hydrazide reagent 318 Isoprenaiine 395,396 Isoprenoid compounds 44 Isopulegol 59 Isoquercitrin 279, 280, 323 Isoquinoline alkaloids 46, 66, 262 Isorhamnetin 323 Isothiazolones, microbiocidal 45 Isothiocyanates 75 Isotopes, j8-radiation-emitting 41 -, detection limits 41 Itaconic acid 61... 

Isoihamnetin la 323 Isothiazolone, microbiocidal la 45 Isothiocyanates la 75 lb 312 Isothiocyanate anions lb 307 Isotopes, detection limits la 41 Itaconic acid, reduction la 61 lodazide reaction lb 301,303... 

Lactide/glycolide polymers have been investigated for delivery of agents in applications outside the pharmaceutical field. For example, the microbiocidal properties of chlorine dioxide disinfectants have been improved by formulating a long-acting chlorine dioxide system based on lactide/glycolide copolymers. Blends of microspheres based on 50 50 and 87 13 copolymers were developed to afford the release of chlorine dioxide over several months (114). 

There are around 250 chemical entities that have been identified as active components of microbiocidal products in the European Union. The aim ofthis chapter is to introduce the range of chemicals in common use and to indicate their activities and applications. 

At low pH the existence of HOCl is favoured over OCl" (hypochlorite ion). The relative microbiocidal effectiveness of these forms is of the order of 100 1. By lowering the pH of hypochlorite solutions the antimicrobial activity increases to an optimum at about pH 5 however, this is concurrent with a decrease in stability of the solutions. This problem may be alleviated by addition of NaOH (see above equation) in order to maintain a high pH during storage for stability. The absence ofbuffer allows the pH to be lowered sufficiently for activity on dilution to use-strength. It is preferable to prepare use-dilutions of hypochlorite on a daily basis. 

A product to be labelled sterile must be flee of viable microoiganisms. To achieve this, the product, or its ingredients, must undergo a sterilization process of sufficient microbiocidal capacity to ensure a minimum level of sterihty assurance (Chapter 20). It is essential that the required conditions for sterihzation be achieved and maintained through every operation of the sterilizer. 

There are two main scopes for the use of microbiocides in PVC and other polymers. The classical approach is the protection of susceptible plastic material whereas a more recent approach is the achievement of biocidal surfaces. 

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