Quaternary ammonium compounds, di-C16-18-alkyldimethyl, chlorides

Biodegradation in water and sediment: simulation tests

Key value for chemical safety assessment

Half-life in freshwater sediment:

500 d

Additional information

Degradation in water

Ultimate and primary biodegradation of Quaternary ammonium compounds, di-C16-18 (even numbered) -alkyldimethyl, chlorides were assessed in the frame of an OECD 303A test.

At least 95% of Quaternary ammonium compounds, di-C16-18 (even numbered) -alkyldimethyl, chlorides are eliminated from waste waters after passing the treatment unit. The fraction of the substance in the sludge decreases continuously. Primary biodegradation is high.

This percentage demonstrates that Quaternary ammonium compounds, di-C16-18 (even numbered) -alkyldimethyl, chlorides is

almost completely removed by biodegradation from the wastewater by biodegradation in conventional biological wastewater treatment plants. In the European risk assessment reference is also made to Hoechst study (Zahn-Wellens-test, OECD 302B with industrial activated sewage sludge), in which DHTDMAC was eliminated to more than 70% after 3 hours. Elimination reached 92 % after 15 days, measured as DOC reduction. A rate of biological degradation could not be determined (Hoechst AG, 1993a). An OECD-confirmatory test was conducted with DHTDMAC and activated sludge from a domestic wastewater treatment plant (Hoechst AG, 1989b). The system was dosed with increasing concentrations of 0.5 -5 mg/L. Based on the concentration of disulfineblue active substance in the effluent of the test system the elimination was higher than 95% after 10 days. Most of the data referring to the elimination in wastewater treatment plants do not distinguish between biodegradation and adsorption. Therefore no degradation constant can be derived but an elimination of 95% is used in the following calculations based on the monitoring data. It can be estimated that about 55% of the elimination are attributable to adsorption.

Degradation in sediment

For degradation in sediments, simulation tests are lacking. One test on degradation in river water spiked with sediment was performed (Larson & Vashon, 1983). In river water alone (50 mg/L suspended solids, < 25 mg/L sediment), degradation was low (8% of 0.05 mg/L and 19% of 0.5 mg/L in 28 days). After 63 days the degradation results are not much higher (11% and 22% respectively), and the degradation curve ends in a plateau, suggesting that degradation will not continue. However, in the presence of higher amount of sediment (5g/L), degradation was significantly higher (43% of 0.05 mg/L after 28 days and 65% after 63 days).

The available monitoring data reveal that biodegradation in environmental sediments is lower. Hellmann (1995) found an increase of the DHTDMAC concentration at high river flows. As the causes whirling of sediments and rinsing of agricultural soil during strong rainfalls are stated. These results indicate that DHTDMAC adsorbed onto sediments is not or very slowly degraded. A degradation rate cannot be derived from the monitoring data. Therefore, analogously to the degradation in soil, a half-life of 500 d (k = 1.4 . 10-3 d-1) for the aerobic sediment layer is used in the exposure assessment.

There is no hint that Quaternary ammonium compounds, di-C16-18 (even numbered) -alkyldimethyl, chlorides can be degraded under anaerobic conditions.