Dispersion and persistence of synthetic detergents in ground water, San Bernardino and Riverside Counties : [a report to the State Water Quality Control Board, September 1964.

  • California. Department of Water Resources.
Date:
1965
Catalogue details

Licence: Public Domain Mark

Credit: Dispersion and persistence of synthetic detergents in ground water, San Bernardino and Riverside Counties : [a report to the State Water Quality Control Board, September 1964. Source: Wellcome Collection.

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    To attain these objectives the following determina- tions were made: the areal extent of ABS concentra- tion in the Colton Narrows area and the changes occurring during the period of investigation, the con- centrations of ABS reaching the ground water by percolation through the unsaturated zone, dispersion of synthetic detergents in the ground water body, ex- tent of vertical mixing of ABS in the ground water body, and persistence of synthetic detergents in ground water. Definitions and Properties of ABS By definition, a detergent is anything that cleanses, including ordinary soap and the new ‘‘syntheties.’’ The most widely used household synthetic detergents contain the anionic surfactant ABS. A surfactant is an organic compound that is ‘‘sur- face active,’’ which means it has the ability to act as a link between the water and dirt particles. Thus, dirt particles are ‘‘tied’’ to the water by the surfactant so that mechanical agitation in the washing process can pull the dirt from the soiled material and keep it in the wash water. Every molecule of ABS does not have exactly the same structural arrangement, as the carbon chain may be branched or may be a single straight chain. Also, the molecule may contain from 9 to 15 carbon atoms. Biological degradability (breakdown of complex or- ganic compounds to simple forms by biological action) is determined by the molecular weight and arrange- ment of the side chain. Straight chains are more sus- ceptible to bacterial and biological degradation than are those with side branching. The predominant arrangement of the ABS molecule consists of the ‘‘alkyl’’ (noneyelic) side chain con- taining 12 carbon atoms in a branched arrangement. and a eyclic-sulfonate benzene ring. Figure 1 shows such a molecular structure and contrasts it with the proposed new linear alkylate sulfonate known as LAS. LAS is biologically degradable under nor- mal sewage treatment and is popularly termed a ‘‘soft type,’’ as opposed to the ‘‘hard tvpe’’ ABS. In addition to the surfactant ABS, household syn- thetic detergents contain many other ingredients that act as wetting, dispersing, bleaching, stabilizing, and TABLE 1 Typical Synthetic Detergent Formulation Proportion by weight, Ingredient in percent Function Surface activeagent 20 Reduces surface tension Phosphate 35 Buffer—assists suspension, dis- persion, and emulsification of soil Sodium sulfate 20 Provides additional electrolyte to aid wetting and dispersion Sodium silicate 10 Prevents metal corrosion Methyl cellulose 1 Prevents redeposition of soil Fatty acids 4 Stabilize foam Sodium perborate 10 Acts as bleaching agent Perfumes, antioxi- dants, fluorescent dyes, and impurities 1 Enhance appearance and aroma of product emulsifying agents. Table 1 gives the formation of a typical synthetie detergent and the function of each ingredient. ABS in even low concentrations causes sudsing or foaming in waters because of the lowering of surface tension at the air-water interface. Foaming occurs particularly during pumping or agitation of the water. This foaming property is what first attracted the pub- he’s attention to the presence of ABS in rivers, sew- age effluents, and water supplies. In other words, aesthetic considerations have been responsible for the public reaction against ABS. The real problem, however, lies in the ability of ABS to pollute ground waters. This is becoming in- creasingly undesirable because of the growing prac- tice of reclaiming waste waters by recharge to ground water basins through spreading or injection. As little as 0.5 mg/l of ABS may cause foaming when the water is drawn from the household tap, particularly if the faucet has a sereening device to agitate the water. Thus, ABS is the main ‘‘Villain’’ that stands in the way of successfully reclaiming waste waters, because the other organic contaminants are largely adsorbed or degraded as they pass through a suffi- cient amount of soil.®)* ABS has not proved to be toxie to man even in con- centrations far in excess of 1 to 3 mg/l, such as those found in ground waters in the study area. However, copious foaming is noted at these concentrations dur- ing pumping of wells. The United States Public Health Service has set a recommended upper limit of 0.5 mg/l for ABS in drinking water supplies based on aesthetic consideration (foaming). Because ABS is reported to be degradable only from 50 to 60 percent by conventional aerobic and biological treatment, a need for the development of a more degradable type of ABS molecule is urgent. The soap and detergent industry has spent millions of dollars in research to develop a more biodegradable detergent. Largely through these efforts, the industry has established a timetable for full-scale distribu- tion of biodegradabie LAS by the middle of 1965. Impact of LAS on Detergent Problem The physica] properties and characteristics of LAS are essentially the same as those of ABS, with the major difference that this material is reported, by laboratory investigators, to be almost entirely biode- gradable by conventional aerobic sewage treatment. It is anticipated that this additional biodegrad- ability will be sufficient to reduce the LAS econcen- trations in the waste waters to a level that will pre- vent foaming. This biodegradability is attributed to the presence of only straight chain hydrocarbons in the molecule. The soap and detergent industry anticipated that by the end of 1963, engineering and cost estimates and full-seale pilot plants would be completed, and sam- ples made available for tests of biodegradability and for washing ability of the new LAS. By mid-1964, the industry expected to start full-scale production * Numbers refer to list of Selected References in Appendix A.