Sulfones and thiones, such as bistrichloromethylsulfone and tetrahydro-3, 5-di-methyl-2H-l,3,5-thiadiazine-2-thione, are noncompetitive organosulfur microbiocides. In water, they decompose to form solutions similar to microbial metabolites, but which are actually metabolite analogues and consequently cause cell death. As with all organosulfurs, they are pH sensitive, with the former most reactive in industrial water at a range of 6.5-7.5 and the latter in the pH range of 7.0-8.0.

Sodium dimethyldithiocarbamate and disodium ethylene bisdithiocarbamate are organosulfur compounds which possess excellent microbiocidal capabilities. They are readily soluble in water and function best at pH 7 and above.

The carbamates are competitive microbial inhibitors and function much like methylene bisthiocyanate. They are composed of basically two chemical structures as shown in Figure 5-38, the monoalkyl and dialkyl groups.

The dialkyl molecule appears to function as the more potent microbiocide. An inverse relationship exists between alkyl chain length and toxicity; the shorter the alkyl chain, the greater its toxicity.

These have long been used as algicides and bactericides; molds and fungi, however, are generally resistant. Environmental concern over heavy metals has limited their use in recent years. Generally, they have been effective as industrial water microbiocides when used in the range of 1-2 ppm copper sulfate. Cupric salts are usually not recommended for use in industrial water systems, however, because cupric ions plate on steel, become cathodic and cause the surrounding steel to corrode.

These are effective algicides at low concentrations. The high molecular weight salts are often combined with quaternary ammonium compounds for better dispersion.

Beta amines and beta diamines are effective surfactants which can kill microorganisms. When combined with phenolics, they can act synergistically.

Organo-tin compounds are known for their toxicity to algae, molds and wood-rotting organisms. They are characterized by at least one tin-carbon bond per molecule.

Organo-tin compounds function best in the alkaline pH ranges and are often combined with quaternary ammonium compounds or complex amines to improve their dispersant abilities. Formulations of this type provide synergistic activity, with the total microbial efficacy exceeding that expected of any individual ingredient.