The use of biocides

The key essential properties of biocides for use in polymer dispersions were listed by the author (Gillatt, 1990) and are given in Table 13. 

Published work (above) and experience has shown that a very wide range of microorganisms can cause contamination of polymer dispersions. Thus a biocide to be used in such products must be able to control all such organisms - bacteria, moulds and yeasts, at a cost effective concentration. 

The pH range of polymer dispersions is from 2 to 10, although the majority are in the range 4 to 9.5. Thus a biocide must not only be stable but must be active over that range. 

Mean air temperature Polymer dispersion temperature after 10 days 

Since most storage tanks are insulated, the effect will be even greater in many instances. It should also be remembered that dispersion is often constantly being pumped into the storage tank and removed from it. Therefore the product temperature may often be almost permanently elevated. 

---

Offshore oil production is one area in which environmental pollution has been highlighted as an issue, particularly in the use of biocides in production waters. Tetrakis-hydroxymethyl phosphonium salts exhibit acceptable environmental profiles [1120], and they are regarded as the preferred products for bacterial control within the oil production industry. 

Good plant hygiene procedures are critical to maintaining an effective production, however due to the nature of the process, this will not be wholly effective and the use of biocides is critical to maintain a low microbiological population to prevent paper failure. The table below (Table 4) illustrates the types of biocides that are commonly encountered within the paper processing. 

Although there are many biocide alternatives available on the market, for example enzyme technology or bio-dispersants, there appears to be a continued requirement for the use of biocides in order to reduce the levels of microbiological contamination entering the paper making process. The increased awareness of environmental and safety aspects will continue to play an important role on the selection of biocides for paper making processes. The use of legislation to select biocides must be done in parallel with each plants internal risk assessment. No one biocide active will meet all the criteria set out by different European countries and hence the use of these actives must be carefully assessed on a plant by plant basis. 

Biocides are by their nature intrinsically toxic, in this respect any adventitious release to the environment requires an assessment of the relative risk posed. The 5th Environmental Action Plan of the EU is committed to a substantial reduction in the use of biocides. In particular, the Biocidal Products Directive (98/08/EC) is concerned with controlling biocidal products in the market place. Compliance with this directive is required from all member states by 14th May 2000. In this context, a strategy to control the release of biocides is timely, if continued protection is to be afforded to industry and consumer alike. One approach to controlling the release of biocide is to encapsulate in an inert inorganic framework, prior to incorporation in the coating.1... 

Numerous applications for biocides have been found in fields as diverse as ethical pharmaceuticals and cat litter products. The aim of this Cl book is two-fold to provide a comprehensive guide to the use of biocides across a range of applications and to aid in the selection of a biocide that is "fit for purpose". It covers a Cl cross-section of traditional measures, novel ideas and innovative developments, as well as addressing the biocides market, the political outlook and future trends of biocide use. 

The use of biocides is in Europe controlled and regulated by the EU Biocidal Products Directive [15]. Registration of a biocide is expensive and only a few active biocide substances will in the future be available for the leather industry in the EU. The directive will include a list of active substances that are permitted to use by the leather industry (a so-called positive list). Many eco-labels and RSL does already today include restrictions of the use of some biocides. 

The use of biocides is spread across the whole polymer range, e.g., paints, ropes, textiles, fibres, etc. Many are copper, silver or arsenic compounds and also various heterocyclic compounds, e.g., isothiazolines (which have some structural resemblance to penicillin). 

The term biocide will be used in the discussion, although in many cases organisms may only be inhibited rather than destroyed (B-76MI11500). One important consideration in the use of biocides is that they are toxic materials, exhibiting varying degrees of hazard to both man and the environment. In most countries, therefore, these materials are subject to controls. 

Health, Safety, Responsible Care, and Environmental Legal Problems Related to the Use of Biocides... 

In the United States, the European Union, and many other countries, as has been mentioned earlier, there are regulations that control the use of biocides and other types of chemicals in industrial situations. Successful efforts to clean up rivers, improve working environments, and remove pollutants from being discharged cannot just be ignored or overridden. The cooling system operator often has a duty to review all water treatment chemicals, including biocides, prior to their potential use on-site. The owner may have rules in place over what biocides are or are not acceptable in the workplace. 

The problem of bioactivity can be reduced or eliminated by the use of biocides. There are different types of biocides and one must be aware of the toxicity level of these to decide the most suitable biocide for that application. Already affected systems can be treated with biocides but it is very difficult to release the biofilm once it is formed. In that case a biocide treatment... 

The use of biocides in plastics is commonplace. They are added to protect the plastic itself from degradation by microbes or alternatively to provide an external antimicrobial hygienic surface. The choice of suitable test method and the appropriate biocide can be difficult, as the different ways in which biocides work will affect how they perform under certain test protocols. 

Legislation on the use of biocides in plastics varies by eountry and application. 

Under this directive, the use of biocides in plasties and rubber application falls under one of several seetions. Each product type will be examined over the next few years until all application areas are covered. These areas include ... 

The use of biocides in coatings is discussed with reference to reasons for using combinations of biocides, effects of global regulations, biocide selection, and advances in combination technology (combination biocides for in-can preservation and for diy-film protection). 

ENVIRONMENTALLY ACCEPTABLE PAINT PRODUCTION. A CHALLENGE ALSO FOR OPTIMISING THE USE OF BIOCIDES... 

The importance of these findings to the petroleum industry relies on the underestimation about the use of biocides in continental platforms, oil storage tanks, and pipelines. Those environments are constantly subjected to anaerobic microbial activity, which are usually controlled through the addition of biocides in the absence of surfactants. 

Bott, T.R., 1992, The use of biocides in industry, in Melo, L.F. et al eds. Biofilms - Science and Technology, Kluwer Academic Publishers, Dordrecht. 

In Chapter 14 the use of additives to combat potential fouling was discussed. In the use of chemical treatment for cooling water there has to be an emphasis on effective and rapid dispersion since the concentration of the additives employed must be low, i.e. a few mg/l where possible, to minimise cost and to reduce potential pollution problems. In general the additive formulation will be based on the need to limit corrosion (i.e. the use of corrosion inhibitors), scale formation (i.e. the use of crystal modifiers, dispersants or threshold chemicals or a combination) and biofouling (i.e. the use of biocides and dispersants). In many installations additives are injected on the suction side of the main pump so that turbulence within the pump will provide rapid mixing. In very large cooling systems multiple injection nozzles will be required to enhance distribution. 

Quite a number of publications giving concentrations of biocides in household dust are available, but most of them lack any description of the use of biocides (e.g. Butte and Walker, 1994 Lahl and Neisel, 1989 Pdhner et al., 1997 Roinestad et al., 1993 Stolz and Krooss, 1993 Stolz et al., 1996 Walker et al. 1994). Results for dust samples obtained after certain incidents are compiled in Table 3.5-4A. Furthermore, concentrations for biocides in the dust of households from Germany obtained from representative... 

Wood preservatives and agents against insects and fleas are used by more than two-thirds of the population thus their residues can be found in nearly every home. Only in two households (< 1 %) could no biocide or synergist be observed. On the other hand chlorpyriphos, propoxur and lindane were present in more than 10 %, PBO in more than 50 %, DDT, permethrin and methoxychlor in more than two-thirds and PCP in nearly every sample. Results regarding concentrations of biocides in household dust were confirmed by those obtained in Schleswig-Holstein (LANU, 1997), but information about the use of biocides indoors was not obtained for the latter study. 

The list will be decreased as a result of the implementation of new directives, such as the European Biocide Directive that will be fuUy implemented by 2010. The use of biocides in paper production is often further limited by national health authorities, e.g. FDA (USA) and BfR (Europe) for food packaging paper, as well as green label lists such as White Swan. A list of substances used to control microbiological growth on a paper machine is given below ... 

Since various industrial products have known spoilage problems as mentioned above, the use of Biocides is essential. Industrial preservation has revolved around the use of isothiazolone (IT) and formaldehyde donor (FD) biocides. 

With so much regulatory pressure on the use of biocides for the future, the challenge will be to take the favourable active ingredients and produce blends that offer as much value as possible. As such, the next few years are going to be very interesting indeed ... 

Sterilization of the system by gamma or UV irradiation for disinfection of materials and environments may be useful to mitigate biocorrosion (51). Sterilization by chemical methods such as the use of biocides to control biofilm formation in closed systems such as heat exchangers, cooling towers, and storage tanks will mitigate biocorrosion (51, 52). 

---