Ecological behavior of cationic surfactants from fabric softeners in the aquatic environment

The use of cationic surfactants in fabric softeners has reached considerable proportions in the Western industrialized nations during the last 10 years. In the Federal Republic of Germany alone, some 22,000 ton of cationic surfactants were marketed in 1981 for this specific purpose. The considerable share (12%) of total consumption which this class of surfactants accounts for is equivalent to a theoretical wastewater concentration of ca. 5 mg/L. Consequently, it raises questions concerning environmental behavior of this class of substances. The following factors are of substantial importance in this regard: acute and chronic toxicity in the aquatic environment; biodegradability under aerobic and anaerobic conditions; and the possibility of bioaccumulation in the aquatic organisms, particularly in fish. Basically, the ecological behavior of cationic surfactants, like that of distearyl dimethyl ammonium chloride (DSDMAC) and dialkyl imidazolinium salts (DAIC) which are mostly used, is determined markedly by their physicochemical properties, above all their strong adsorption on surfaces, e.g., on clay minerals or on activated sludge, thus leading to their elimination in water treatment plants and water courses. Of far‐reaching consequence from the toxicological aspect is the fact that they form neutral salts with the anionic surfactants present in excess in domestic wastewater, thus leading to a considerable decrease in toxicity. Although adsorption and ion‐exchange processes are primarily effective in climination of cationic surfactants of the DSDMAC and DAIC types in wastewater treatment, there are significant indications on the basis of experiments that these substances are subject to extensive aerobic biochemical degradation. However, it appears that anaerobic degradation does not take place. Tests conducted so far on the bioaccumulation behavior, particularly on a laboratory scale, indicate that these substances practically do not accumulate in the edible parts of fish and thus no risks are being discerned at present as regards the residue situation.