TR 053 – DHTDMAC: Aquatic and Terrestrial Hazard Assessment (CAS No. 61789-80-8)
TR 053 : DHTDMAC: Aquatic and Terrestrial Hazard Assessment (CAS No. 61789-80-8) | February 1993
Dihydrogenatedtallow dimethyl ammonium chloride (DHTDMAC) is almost exclusively used as a fabric softener in the household laundry rinsing process. Consequently the chemical is widely dispersed and may reach the aquatic and terrestrial environment following sewage treatment. This report refers to data related to the time period when the highest quantities (approx. 50,000T/year) of DHTDMAC were consumed in Europe. Since 1990 changes in the fabric softener formulations on the European market have resulted in a 80-90% decrease of consumption.
Due to its physical and chemical properties DHTDMAC adsorbs strongly onto surfaces and easily forms complexes with anionics such as alkylsuphonates or natural humic acids.
In standard laboratory tests, DHTDMAC is not readily biodegradable but in the presence of adapted biomass it shows total mineralization in up to 200 days.
In sewage treatment an average of 95% of DHTDMAC is removed from waste water. A large part of this removal is due to adsorption on sludge solids. Mass balance studies suggest that primary biodegradation in the biological step of sewage treatment may be significant.
In river water systems 70% of primary biodegradation was observed after 40 days. This result is consistent with mineralization studies performed without and with sediments showing respectively 10 and up to 65% conversion of 14C a-alkylcarbon into 14CO2.
Studies performed in soil indicated that 50-60% mineralization occurs in 120-430 days.
The highest environmental concentrations were found in waste water. The mean concentrations are normally around 1mg/l; exceptionally they may reach 4mg/l. Concentrations in effluents are generally in the order of 0.05mg/l.
The concentrations measured in rivers in different countries vary between 0.002 and 0.04mg/l depending on the sites, river size etc. In some low velocity systems e.g. canals and polders substantially polluted by other chemicals, concentrations of DHTDMAC up to 0.1 mg/l have been measured.
The laboratory results on aquatic toxicity of DHTDMAC are highly dependent on the test conditions, sample preparation and presence of impurities.
The chemical appears to be very toxic especially to algae when tested only in laboratory water, whereas in natural waters, effects may be observed only at concentration 2-3 orders of magnitude higher. The lowest NOEC in laboratory water was observed with Selenastrum capricornutum (0.006mg/l). In treated sewage effluent diluted in river water it was 20.3mg/l. In the same effluent diluted river water the NOEC for the most sensitive species Ceriodaphnia dubia was 4.53mg/l.
Hazard assessment of chemicals of this type presents particular difficulties because of their physico-chemical properties (insolubility/adsorption/complexation) which determine their bioavailability and thus the toxic effects. Hence methods have to be adopted which take proper account of the factors applying in practical situations. For DHTDMAC such approaches lead to PNEC/PEC ratios in the range of 8-450 using conservative approaches.
Terrestrial organisms, higher plants and earthworms exposed to DHTDMAC in sludge amended soil, even at levels grossly in excess of those expected during normal practice, do not exhibit adverse effects in toxicity tests. There was no evidence of bioaccumulation in toxicity tests to earthworms or of impairment of the general metabolism of soil as a result of contamination with DHTDMAC.
Based on the above considerations, it can be concluded that the environmental concentration of DHTDMAC discussed do not pose a hazard to aquatic and terrestrial systems.