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An exhaustive review of biodegradation (biotic and abiotic) potential for Quaternary ammonium compounds, di-C16-18 (even numbered) -alkyldimethyl, chlorides

(indicated as DHTDMAC) has been done in the frame of the European Risk Assessment carried out by German Authorities and published in 2002. The conclusions of this review for the different compartments are summarized hereafter.

Degradation in Wastewater treatment plant (WWTP) and surface water

A modified closed bottle test was used to compare the biodegradability of DODMAC and DHTDMAC by a mixture of preadapted soil bacteria (Clancy & Tanner, 1991). The degradation of DODMAC was approx. 36% and that of DHTDMAC was approx. 19% of the theoretical BOD after 20 days (1 mg/L test substance, 15 mg/L O2-content). When the inoculum was not adapted degradation was only 8% at 1 mg/l DHTDMAC and 35% at 0.4 mg/L.

In a SCAS test (OECD 303A) with domestic sludge, DHTDMAC was eliminated to more than 95% after 45 days, measured as DOC reduction (Boutonnet, 1990). In a Zahn-Wellens-test (OECD 302B) with industrial activated sewage sludge, 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, 1993a).

An OECD-confirmatory test was conducted with DHTDMAC and activated sludge from a domestic wastewater treatment plant (Hoechst, 1989d). 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.

The results of a continuous activated sludge test and a SCAS test are reported in ECETOC (1993). In the SCAS test 80 to 98% of 0.5 mg/L DSDMAC and DHTDMAC were adsorbed to the sludge after 7 days (Hopping, 1975). Production of 14CO2 could not be observed. In the CAS test 71.2% of 0.01 mg/l DSDMAC were adsorbed after 5 days (Shimp, 1992). Production of CO2 was not monitored.

Results for DODMAC and DHTDMAC degradation in batch activated sludge tests measuring 14CO2 production are cited in ECETOC 1993 (Brown, 1975). Degradation of DHTDMAC was better than DODMAC under the respective comparable conditions in every case (up to 89.8%, non-adapted, without LAS). Adaptation had no influence and increasing LAS concentrations had a slightly decreasing tendency.

In another river water die-away test primary degradation of DHTDMAC was assessed (Schneider & Levson, 1987). With an initial concentration of 8.25 mg/L 70% degradation were observed after 40 and 70 days. With a substance concentration of 0.5 mg/L primary degradation was almost the same with 75% after 40 and 55 days. Degradation started after 15 resp. 20 days. Therefore DHTDMAC is biodegradable.

It is shown in several tests that DHTDMAC is not readily biodegradable.

Adaptation seems to be necessary for significant degradation but even then mineralisation is very slow. In river water tests with adapted inocula degradation is occurring with a half-life in the range of several weeks.

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.

In 1991, van Ginkel assessed the biodegradation potential of DHTDMAC in the frame of a 301D test. This report has been identified as the key report. Secondary activated sludge was obtained from a plant treating predominately domestic wastewater. The sludge was pre-conditioned to reduce the endogenous respiration rates. To precondition, the sludge (200 mg Dry Weight (DW)/Litre) was aerated for a period of one week. The sludge was diluted to a concentration in the BOD bottles of 2 mg DW/Litre. Ammonium chloride was omitted from the medium to prevent nitrification. Due to omission the pH of the medium decreased slightly. DHTDMAC was not biodegraded in the closed bottle test after 28 days (3%). However, in the prolonged closed bottle test DHTDMAC is biodegraded 68 % at Day 287.The pH of the medium at day 28 was 6.9.

Degradation in soil

Biodegradation studies performed in soil indicated that 18-60% mineralisation was observed within 120-430 days. Therefore it can be considered that DHTDMAC is stable in soil.

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). Comparison of biodegradation rates in laboratory screening studies with rates in natural waters suggests degradation half-life's in sediment of 80 days or lower. Some experimental details did presumably not represent regular environmental conditions, e.g. sediments were possibly pre-adapted and the concentration of biodegrading microorganisms is regarded to be increased above the normal level.

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 DHTDMAC can be degraded under anaerobic conditions.

Abiotic degradation

Degradation of DHTDMAC through hydrolysis is not considered as based on its structure which does not contain any hydrolysable covalent bonds DHTDMAC is not expected to be degraded under environmental conditions.

Phototransformation in air/soil/water and sediment are not required under REACH.

Bioaccumulation

Lepomis macrochiruswas exposed to 14C-DHTDMAC for 49 days in a continuous flow-through system in river water and laboratory water with mean concentrations in the test period of 18 μg/L and 16 μg/L respectively (no solvent carrier, Lewis & Wee, 1983). The river water was sampled at Town River, Massachusetts, and contained 2 -84 mg/L suspended solids, 0.04 -0.59 mg/L methylene blue active substances - MBAS and 10-15 mg/l disulfine blue active substances -DBAS (pH = 6.4-7.7, total hardness = 14-38 mg/L CaCO3). In river water BCFs of 13 L/kg in the whole body and 94 in the inedible tissue (viscera) were estimated based on measured concentrations. When laboratory water was used the respective BCFs were 32 and 256 L/kg. In both waters DHTDMAC did not concentrate to a significant degree in edible tissue (BCF of the fillets < 5 L/kg). In a depuration phase in well water 93% of the accumulated radioactivity was eliminated from the inedible tissues after 14 days.

Therefore Quaternary ammonium compounds, di-C16-18 (even numbered) -alkyldimethyl, chlorides is considered to be non bioaccumulative.

Bioaccumulation in terrestrial organisms is not a formal REACH requirement.

Adsorption/desorption

The determination of a Koc from log Kow is not opportune, because the common Koc derivations are not valid for surface active substances like DHTDMAC. DHTDMAC adsorbs onto both the mineral and the organic fraction of soil and sediments. Kappeler (1982) found that on average 27% of the DHTDMAC in river water is adsorbed onto suspended matter (mean 22 mg/L suspended solids). The Kpsusp is calculated to 16,800 L/kg from these values.

This demonstrates that DHTDMAC can be bound very strongly by some minerals, while in others relatively small distribution constants were estimated. Under environmental conditions, the sorption properties of DHTDMAC probably vary in a wide range depending on the nature of the adsorbant.