The Search for Biodegradable Detergents
H. LOMAS, Research Scientist
Department of Chemistry
Ontario Research Foundation
Toronto, Canada
INTRODUCTION
Modern detergents are complex mixtures and each ingredient is chosen for its
unique properties.   Most of those on the market today contain the following:
Surfactant: The synthetic organic surface active agent used as the active in
gredient is the one with which we are concerned in the problem of biodegradability.    It is usually a sulphate or a sulphonate with a non-polar hydrocarbon chain,
having wetting, dispersing, and emulsifying properties.
Builder: Inorganic dirt particles are readily dispersed by inorganic salts of the
polyphosphate type. The polyvalent anion also increases the surface activity of
the surfactant, and sequesters insoluble calcium salts.
Anti-redeposition agent: Addition of a polyelectrolyte, usually carboxy-
methylcellulose, enhances the negative charge on the fibres of the fabric being
washed and thus hinders re-deposition of the dirt particles which are similarly
charged.
Foam stabilizer: Accumulation of grease in the wash water acts as an anti-
foaming agent. A compound which increases the emulsifying power of the surfactant is therefore added. The common stabilizer is a fatty acid ethanolamide
which helps to hold the grease in suspension and prevents it from breaking the
foam.
Other additives used in smaller quantities are bleaches, optical bleaches,
anti-tarnish agents, and hydrotropic agents.
The synthesis of syndets with the object of imparting biodegradability is a
recent development, but a large number of those developed and used during the
last thirty years fall into this class. However, by a process of elimination one
syndet has become the most widely used of all types in household detergents,
namely, dodecyl benzene sulphonate or, commonly, ABS. It has long been ac-
cepted that ABS with branched -chain alkyl groups is responsible for the slow bio -
degradability of these detergents (1,2,3,4,5). It is hoped that this paper will
stimulate a wider search for biodegradable syndets so that by another process of
elimination, the most suitable will be found.
PROBLEMS CAUSED BY SYNDETS
The effects of syndets in sewage and effluent systems are by now familiar to
all those concerned with these systems. Foam in aeration tanks (6) interferes with
their operation and even constitutes a pollution hazard when wind-blown. The
presence of syndets has been shown to reduce air-transfer rates in these systems
(7). Foam in rivers and canals is a potential danger to all users of such waterways. Appreciable concentrations of syndets have been found in many rivers (8,
9,10,11,12) and in general they appear to have a half life of 16 days or more.
(13). Re-use of water in other towns downstream results in appreciable concentrations in drinking water. This has been particularly apparent in Germany, where
rivers are a large source of water and towns are close together. Syndets act as
dispersing agents and prevent adequate settling of sludge.   If the build-up of syn-
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