The occurrence and behaviour of ditallow-dimethyl-ammoniumchloride (DTDMAC) during drinking water production

Cationic quaternary ammonium compounds are used as fabric softeners. DTDMAC, a technical product with an ecotoxicological risk for aquatic organisms, is the most well known. Ecotoxicological risk values have been determined, followed by an agreement to ban the product from fabric softeners. The quaternary ammonium compounds are highly adsorptive for anionic surfactants, particles and sediments in watersystems. This report describes research on occurrence and behaviour of DTDMAC during drinking water production and gives possible risks for public health. DTDMAC occurs in raw surface water (maximum 30 mug/l), in bankfiltrate (maximum 5 mug/l) and in finished drinking water (maximum 4.3 mug/l ; median 1.7 mug/l). The measured concentrations in drinking water do not give risks for public health. The maximum acceptable value, calculated on the basis of literature data is 0.8 mg/kg food or water. On every sampling point only two measurements were carried out, and therefore effects due to the purification processes can only be interpreted qualitatively. In general, a relatively high concentration of DTDMAC can be decreased easily (bottom passage, conventional purification steps) to a few mug's, but the compound cannot be removed completely even by ozone or activated carbon filtration. In surface water the concentrations are much higher than the negligible risk value (0.5 mug/l) for aquatic ecosystems. The actual concentration given in this report give no reason to continue the research into the meaning of DTDMAC for drinking water supplies.DGM/DWB-