Quaternary ammonium compounds, bis(C16-18 and C18-unsatd. alkyl)dimethyl, chlorides

Endpoint summary

Additional information

Read across for DTDMAC from structurally similar Quats DHTDMAC/DODMAC can be applied and the corresponding effect data form DHTDMAC/DODMAC used for DTDMAC as well.

Tests concerning the toxicity of DODMAC/DHTDMAC for aquatic organisms are listed in the table below. For DHTDMAC only those are chosen which are relevant for the risk assessment but many more are cited in ECETOC, 1993. As an example for marine organisms only the most sensitive species is mentioned in the table as there are no great differences in the range of toxi­city between marine/estuarine and limnic species.

Toxicity of DODMAC/DHTDMAC to aquatic organisms

Species	Endpoint	Effect Conc.	Substance	Water quality	Reference
Lepomis macrochirus	96h LC50	1.04 mg/l 0.62-3.0 mg/l 10.1 - >24 mg/l 9.4 mg/l 186 mg/l nominal conc.	DODMAC DHTDMAC DHTDMAC DHTDMAC/C12LAS 2:1 DHTDMAC/C12LAS 1:2	well water laboratory w. river water laboratory w. laboratory w.	Lewis & Wee, 1983
Pimephales promelas	96h LC50	3.55 mg/l 6.3 - 13.8 mg/l 21.3/36.2 mg/l nominal conc.	DODMAC DODMAC DODMAC	well water well water + humic acids river water	Versteeg & Shorter, 1992
Pimephales promelas	96h LC50	0.29-0.558 mg/l nominal conc.	DHTDMAC	laboratory water	Versteeg, 1989, cited in ECETOC, 1993
Pimephales promelas	34d NOEC 33d NOEC	0.053 mg/l 0.23 mg/l measured conc.	DHTDMAC DHTDMAC	well water river water	EG & G Bionomics, 1982
Pimephales promelas	7d NOEC	> 12.7 mg/l measured conc.	DODMAC	river water	Versteeg & Shorter, 1993
Gasterosteus aculeatus	96h LC50 28d NOEC abnormal behaviour of larvae	3.5 mg/l 0.58 mg/l nominal conc.	DHTDMAC with 1.7% MTTMAC	lake water 1-4 mg/l suspended solids	Roghair et al., 1992
Daphnia magna	48h LC50 48h LC50	3.1 mg/l 0.16 mg/l measured conc.	DODMAC DODMAC	river water laboratory w.	Lewis & Wee, 1983
Daphnia magna	48h LC50 48h LC50	0.19/0.48 mg/l 1.06 mg/l nominal conc.	DHTDMAC DHTDMAC	laboratory w. well water	Lewis & Wee, 1983
Daphnia magna	21d NOEC	0.38 mg/l measured conc.	DODMAC	river water	Lewis & Wee, 1983
Daphnia magna	21d NOEC	0.18 mg/l nominal conc.	DHTDMAC	ground water	Akzo, 1991a
Daphnia magna	21d NOEC	0.18 mg/l 0.32 mg/l 0.32 mg/l 0.18 mg/l nominal conc.	DHTDMAC + 0%MTTMAC 1%MTTMAC 2%MTTMAC 3%MTTMAC	laborat. water	Akzo, 1991b, cited in ECETOC 1993
Ceriodaphnia dubia	7d EC20 7d EC50	0.26 mg/l 0.70 mg/l measured conc.	DODMAC DODMAC	river water river water	Versteeg & Shorter, 1993
Ceriodaphnia dubia	7d EC20 7d EC50	0.20 mg/l 0.78 mg/l measured conc	DHTDMAC DHTDMAC	river water river water	Taylor, 1984,cited in ECETOC, 1993
Ceriodaphnia dubia	7d MATC	0.1-3.75 mg/l measured conc	DHTDMAC	river water + wwtp effluent	Versteeg 1987
Mysidopsis bahia	96h LC50 28d NOEC life cycle, parent mortality	0.22/0.42 mg/l nominal conc. 0.075 mg/l measured conc.	DHTDMAC DHTDMAC	filtered nat. sea water filtered nat. sea water	EG & G Bionomics, 1981a EG & G Bionomics, 1983
Selenastrum capricornutum Microcystis aeruginosa	96h EC50 96h EC50	0.06 mg/l 0.05 mg/l nominal conc.	DODMAC DODMAC	laboratory water laboratory water	Lewis & Hamm 1986
Selenastrum capricornutum	96h EC50 96h EC100	1.12 mg/l > 16.4 mg/l measured conc.	DODMAC DODMAC	river water river water	Versteeg & Shorter, 1993
Selenastrum capricornutum	96h EC50 96h NOEC 96h EC50 96h NOEC	1.17 mg/l 0.6 mg/l 0.46 mg/l 0.16 mg/l nominal	DODMAC   DODMAC	river water   laboratory water	Akzo, 1990a,b, cited in ECETOC, 1993
Selenastrum capricornutum	96h EbC50 96h NOEC 96h EC50	0.026 mg/l 0.006 mg/l 0.074 mg/l nominal conc.	DHTDMAC " "	laboratory water " "	Akzo, 1991c
Selenastrum capricornutum	96h EC50 96h EC50 96h EC50 96h EC50	0.014 mg/l 0.021 mg/l 0.017 mg/l 0.026 mg/l nominal conc.	DHTDMAC + 0%MTTMAC 1%MTTMAC 2%MTTMAC 4%MTTMAC	laboratory water	Akzo, 1990a,b, cited in ECETOC 1993
Selenastrum capricornutum	5d NOEC 5d EC100 5d NOEC 5d EC100	0.078 mg/l 0.228 mg/l 0.062 mg/l 0.708 mg/l nominal conc.	DHTDMAC " DHTDMAC "	laboratory water " river water "	EG & G Bionomics, 1981 b,c,d
Selenastrum capricornutum	5d NOEC 5d EC100	0.075 mg/l 0.13 mg/l nominal conc.	DHTDMAC, 4.6% MTTMAC	laboratory water "	Procter & Gamble, 1974 - 1986, cited in ECETOC 1993
Selenastrum capricornutum	5d EC100	2.58/35.7 mg/l nominal conc.	DHTDMAC	river water	EG & G Bionomics, 1981 b,c,d
Microcystis aeruginosa	5d NOEC 5d EC100 5d NOEC 5d EC100	0.13 mg/l 0.32 mg/l 0.078 mg/l 0.21mg/l nominal conc.	DHTDMAC   DHTDMAC	laboratory water   river water	EG & G Bionomics, 1981 b,c,d
Microcystis aeruginosa	5d NOEC 5d EC100	0.075 mg/l 0.12 mg/l nominal conc.	DHTDMAC, 4.6% MTTMAC	laboratory water	Procter & Gamble, 1974 - 1986, cited in ECETOC 1993

 

Fish:

The acute toxicity of DODMAC for fish was investigated in a study by Lewis & Wee, 1983. A static 96 h US EPA test was used with well water andLepomis macrochirus(pH = 7.1 - 7.9, total hardness = 315 - 348 mg/l CaCO3). A LC50 of 1.04 mg/l was derived (nominal concen­tration of active ingredient). When the same test method was used for DHTDMAC and recon­stituted laboratory waters the LC50-values ranged from 0.62 to 3.0 mg/l. In these cases it is not known whether different water qualities might have been used or which other test para­meters were varied. These results demonstrate similar toxicities for DODMAC and DHTDMAC forLepomis macrochirus.

Compared with the results described above the toxicity of DHTDMAC forLepomis macro­chiruswas reduced in natural surface water which received municipal waste water effluent (Town River, Massachusetts: pH = 6.4 - 7.7, total hardness = 14 -38 mg/l CaCO3, 2-84 mg/l suspended solids, 0.04 - 0.59 mg/l methylene blue active substances - MBAS, 10-15 µg/l disul­fine blue active substances - DBAS). 96h LC50-values of 10.1 to > 24.0 mg/l were derived (Lewis & Wee, 1983). A combination with C12LAS reduced the adverse effects of DHTDMAC in laboratory water tests. The 96h LC50-values at molar ratios of DHTDMAC/ C12LAS ranging from 2:1 to 1:2 varied from 9.4 to 186 mg/l (nominal concentrations of active ingredient). In these tests of Lewis & Wee, 1983, no information is given on the purity of the test substance but isopropanol or methanol were added as carrier solvent.

In ECETOC, 1993, for different molar ratios of DHTDMAC/C12LAS the following 96h LC50-values forLepomis macrochirusare cited: 7.1 mg/l at 2:1; 17.6 mg/l at 1:2; 7.9-171 mg/l at 1:1 (no more details on test procedure, Procter & Gamble, 1974 - 1986).

The acute toxicity of DODMAC (97% purity, containing no MTTMAC) forPimephales promelaswas also investigated in different filtered natural river waters and well water enriched with different contents of humic acids (Versteeg & Shorter, 1992). Fish were exposed for 96 hours under static renewal conditions. In well water alone a LC50 of 3.55 mg/l (nominal) was derived (< 1 mg/l total organic carbon). In well water to which different amounts of dissolved humic acids extracted from natural rivers were added (1.6 - 2.2 mg/l total organic carbon) the corresponding LC50-values were 6.3 to 13.8 mg/l. In river water with a total organic carbon content of 4.6 mg/l (Dry Fork Creek,Ohio; pH = 8.4 - 8.6, hardness = 173 mg/l CaCO3) the LC50 was 21.3 mg/l. In another river with a total organic carbon content of 6.2 mg/l the LC50 was 36.2 mg/l (Little Miami River, Ohio; pH = 7.5 - 8.5, hardness = 175 mg/l CaCO3). In these tests the toxicity of DODMAC was positively correlated with the humic acid concentration and the total organic carbon content.

To assess the long-term toxicity of DHTDMAC (71.4% active ingredient, 8% MTTMAC) embryo larval tests were conducted withPimephales promelasin filtered well water and natu­ral river water (EG & G Bionomics, 1982; Lewis & Wee, 1983). Exposure was initiated within 48 hours after fertilization and continued through 30 days post hatch in a flow-through system. In well water the most sensitive parameters were mean percent survival, length and weight of larvae. The NOEC was 0.053 mg/l (measured concentration) after 34 days test duration. In river water the NOEC for the most sensitive parameters hatchability and mean weight of larvae was 0.23 mg/l after 33 days test duration. The river water (TownRiver) had the following characteristics: pH = 6.4 - 6.9, total hardness = 62 mg/l CaCO3, 9.4 mg/l suspended solids, 0.59 mg/l MBAS and triethyleneglycol was used as carrier solvent. The well water had a hard­ness of 28 -31 mg/l CaCO3, pH = 6.8-7.6 and isopropanol was used as carrier solvent. In well water the measured concentrations were equal to the nominal concentrations whereas in river water measured concentrations averaged 45-67% of the nominal concentrations.

In a study with natural water from Little Miami River, Ohio, newly hatched larvae ofPime­phales promelaswere exposed to DODMAC for 7 days (Versteeg & Shorter 1993). Measured concentrations up to 12.7 mg/l did not cause toxicity. However, the carrier solvent acidic methanol reduced the dry weight of the larval fish in a dose-dependent manner relative to con­trol fish so that the authors concluded that it would be better to test the substance in the absence of a carrier solvent. (river water quality, filtered: 5.4 mg/l total organic carbon, pH = 8.1 - 8.4, hardness = 171 mg/l CaCO3.) That this NOEC is higher than that derived by EG & G Bionomics possibly is caused by exposure in different periods in the life cycle and does not necessarily show that DHTDMAC is more toxic than DODMAC. (DODMAC was synthesized by a special route which ensures no MTTMAC.)

 

Invertebrates:

The influence of the test medium on the acute toxicity of DODMAC toDaphnia magnawas investigated by Lewis & Wee, 1983. Surface water was collected from a North American river which received municipal wastewater effluent (White River,Indiana). The quality of the river water was: pH = 8.4 - 8.6, total hardness = 345 - 363 mg/l CaCO3, 3-5 mg/l suspended solids, < 25 µg/l MBAS, 2 µg/l DBAS. As reference laboratory reconstituted water was used: pH = 6.6 - 7.9, total hardness = 131 -163 mg/l CaCO3, no suspended solids, < 25 µg/l MBAS, < 1 µg/l DBAS. In semistatic tests the LC50-values were 3.1 mg/l in river water and 0.16 mg/l in laboratory water after 48 hours (measured conc.).

Daphnia magnawas also tested in a 21d-static renewal test with the same river water as quali­fied above (Lewis & Wee, 1983). Referring to the reproduction rate and mean length of the daphnids a NOEC of 0.38 mg/l DODMAC was derived (measured conc.). Parent mortality was not significantly affected up to 0.76 mg/l.

The acute toxicity of DHTDMAC (no information on purity) toDaphnia magnawas assessed for different reconstituted waters and well water with the same US EPA test method as above (Lewis & Wee, 1983). After 48 hours LC50-values of 0.19 and 0.48 mg/l were derived for the reconstituted waters and the LC50 for well water was 1.06 mg/l (nominal levels of the active ingredient). From the available reference it is not possible to relate the LC50-values to the different qualities of the reconstituted waters, which were given as follows. One water had a pH of 6.5 to 7.3 and a total hardness of 131 - 163 mg/l CaCO3. The other water had a pH of 7.0 to 7.6 and a total hardness of 34 - 40 mg/l CaCO3. (Well water: pH = 7.1 - 7.9, total hard­ness = 315 - 348 mg/l CaCO3.) All waters contained no solids and the surfactants concen­trations were below the detection limit.

In a semistatic 21d-study (OECD 202) withDaphnia magnaDHTDMAC (76.6% active ingre­dient) was emulsified in reconstituted groundwater by treatment for 30 minutes in an ultrasonic vibration bath (Akzo, 1991a). All test vessels were conditioned with the test solutions 24 hours before the start of the test. The most sensitive endpoint was the reproduction rate with a NOEC of 0.18 mg/l (nominal concentration of active ingredient). The NOEC for adult morta­lity was 0.56 mg/l. Test substance was analyzed at the end of the test only for concentrations of 0.56 mg/l and higher showing that they had not decreased in the course of the test. Analytical determination of all test concentrations at the start of the test revealed higher measured concentrations than nominal concentrations in tests up to 0.10 mg/l.

The toxicity of DODMAC toCeriodaphnia dubiawas investigated in a 7 day static renewal test (Versteeg & Shorter, 1993). As test medium filtered water from the Little Miami River, Ohio, was used (5.4 mg/l total organic carbon, pH = 8.1 - 8.4, hardness = 171 mg/l CaCO3). Based on reproduction the EC20 was 0.26 mg/l and the EC50 was 0.70 mg/l (measured con­centrations). Survival was affected from 0.41 mg/l upwards. These results have to be treated with care as the reproduction was decreased by exposure to the carrier solvent acidic methanol alone. Results fromTaylor, 1984 (cited in ECETOC, 1993) were similar for DHTDMAC tested inOhio Riverwater. A 7 d EC50 of 0.78 mg/l and an EC20 for reproduction of 0.20 mg/l were reported (nominal conc.). (DODMAC was synthesized by a special route which ensures no MTTMAC.)

In tests reported by Versteeg (1987) DODMAC (this is assumed to be DHTDMAC) concen­trations were produced by treatment of surfactant containing influents of two municipal wwtps in a laboratory scale continuous activated sludge system (CAS). The influent was supple­mented with different amounts of 0, 1 and 3% untreated industrial plant wastewater. This resulted in different DODMAC concentrations in the effluent matrix which were diluted with Little Miami River water. (The system was preacclimatized for 32 days.) Toxicity toCeriodaphnia dubiawas measured in a 7 d reproduction test with the effluents diluted with river water. MATC-values were lowest in theCASeffluents where no industrial waste water was added additionally with 99 and 267 µg/l DODMAC, which is simi­lar to studies with river water. In theCASeffluents where industrial wastewater was added toxicity was reduced to between 1.0 and 3.75 mg/l, demonstrating the high influence of the effluent matrix. The con­centrations of total suspended solids in the first case were 3.8 and 6.6 mg/l and in the second case 13 to 33 mg/l which might be one possibility of explanation for the different toxicities. The concentration of MTTMAC increased with decreasing toxicity.

The acute data forDaphnia magnashow that the toxicity of DODMAC is very similar to that of DHTDMAC. This conclusion can be supported by the long-term data forCeriodaphnia dubia.

Algae:

The toxicity of DODMAC forSelenastrum capricornutumandMicrocystis aeruginosain laboratory water was investigated according to anASTMmethod (Lewis & Hamm, 1986). For growth reduction after 96h the EC50 was 0.06 mg/l forSelenastrum capricornutumand 0.05 mg/l forMicrocystis aeruginosa(nominal concentrations; pH = 6.8 - 7.2, hardness = 131 - 146 mg/l CaCO3).

An algae study with DODMAC in filtered natural water of the Little Miami River, OH (5.4 mg/l total organic carbon, pH = 8.1 - 8.4, hardness = 171 mg/l CaCO3) was conducted by Versteeg & Shorter, 1993. ForSelenastrum capricornutuma 96h EC50 of 1.12 mg/l was derived for growth reduction (measured concentration) and the algistatic concentration was above 16.4 mg/l. In this study acidic methanol was used as carrier solvent, which had a growth stimulating effect on the algae. (DODMAC was synthesized by a special route which ensures no MTTMAC.)

Another study with DODMAC is cited in ECETOC, 1993, but no test protocol is available (Akzo, 1990a).Selenastrum capricornutumwas tested in laboratory and river water but water qualities are not characterized. In laboratory water the EC50 was 1.17 mg/l, in river water an EC50 of 0.46 mg/l was measured after 96 hours (nominal conc.).

Selenastrum capricornutumwas also tested with DHTDMAC (no information on purity) in laboratory water according to OECD guideline 201 (Akzo, 1991c). Although the study was initiated by the same sponsor as above it is not clear whether the same test method was used with DODMAC. DHTDMAC was emulsified in the stock solution by a 60 minutes ultrasonic treatment. The test flasks were conditioned by incubation with the test solutions prior to the test. For biomass reduction a 96h NOEC of 0.006 mg/l, an EC10 of 0.013 mg/l and an EC50 of 0.026 mg/l were derived. For effects on the growth rate an EC50 of 0.074 mg/l resulted. The effect values were based on nominal concentrations of the active ingredient although in a preliminary range finding test DHTDMAC concentrations had decrea­sed below the detection limit of 20 µg/l in flasks which were not incubated with algae. A shorter sonication of<10 minutes resulted in a higher 96h EC50- and NOEC-value of 0.21 mg/l and 0.12 mg/l (no details on test conditions; Akzo, 1991d, cited in ECETOC, 1993).

The influence of different test media on the sensitivity ofSelenastrum capricornutumtowards DHTDMAC (71.4% active ingredient) was investigated by EG & G Bionomics, 1981 b,c,d. Laboratory water with a hardness of 20 mg/l CaCO3 (no further characterization) and algae nutrient enriched White River water (Indiana) of the following quality prior to autoclaving were used: pH = 7.3, total hardness = 299 mg/l CaCO3, 68 mg/l suspended solids, 0.2 µg/l MBAS) In laboratory water a NOEC of 0.078 mg/l and an algistatic concentration of 0.228 mg/l were derived for the reduction of cell number after 5 days (nominal concentrations of active ingredient). The corresponding values for the river water were: NOEC = 0.062 mg/l and algistatic concentration = 0.708 mg/l. The table above shows that results forMicrocystis aeruginosaare similar (EG & G Bionomics, 1981 b,c,d).

In ECETOC, 1993, also the toxicity of DHTDMAC containing 4.6% MTTMAC toSelenast­rum capricornutumandMicrocystis aeruginosain laboratory water is cited (no details on test conditions, Procter & Gamble, 1974 - 1986). The 5 d EC50-values were 0.13 and 0.12 mg/l and the NOECs for both species were 0.075 mg/l, which are a factor of 2-3 lower than the effect values for DHTDMAC containing 8% MTTMAC derived in EG & G Bionomics, 1981 b,c,d.

In tests with two other river waters, for which the water quality was not characterized in the test protocol, the 5 day algistatic concentrations were 2.58 mg/l and 35.7 mg/l (nominal con­centrations of active ingredient, EG & G Bionomics, 1981 b,c). From the reference Lewis and Wee, 1983, it could be concluded possibly that it might be autoclaved Rapid Creek water in one case and in the other the same water enriched after filtration with 131 mg/l sediment. (Rapid Creek,South Dakota: pH = 6.6 - 7.3, total hardness = 388 - 442 mg/l CaCO3, 131 mg/l suspended solids, < 20 µg/l DBAS). In the tests EG & G Bionomics, 1981 b,c,d isopropanol was used as carrier solvent and DHTDMAC contained 8% MTTMAC.

The toxicity of DODMAC (this is assumed to be DHTDMAC) incorporated in wwtp effluent toSelenastrum capricornutumwas reported by Versteeg (1987). Test solutions were prepared from laboratory scaleCAS-units as described above forCeriodaphnia dubia.After 96 hours the EC20-values for growth reduction were in the range of 0.047 and 2.91 mg/l. The toxicity decreased with increasing amounts of added industrial wastewater. In a comparable study from Versteeg & Woltering (1990) DODMAC concentrations inCAS-unit effluents up to 20.3 mg/l had no effect onSelenastrum capricornutum. The test concentrations were produced by treat­ment of surfactant containing influents of two municipal wwtps in a laboratory scale continuous activated sludge system (CAS). The influent was supplemented with different concentrations of untreated industrial plant waste water. This resulted in different DODMAC concentrations in the effluent matrix. The system was preacclimatized for 32 days. Toxicity to Ceriodaphnia dubia was measured in a 7 d reproduction test with the effluents diluted with river water. MATC-values were lowest in theCASeffluents where no industrial waste water was added additionally with 99 and 267 µg/l DODMAC, which is similar to studies with river water. In theCASeffluents where industrial wastewater was added toxicity was reduced to between 1.0 and 3.75 mg/l, demonstrating the high influence of the effluent matrix. The concentrations of total suspended solids in the first case were 19 and 21 mg/l and in the second case 38 to 111 mg/l might be one possibility of explanation for the different toxicities. The concentration of MTTMAC increased with decreasing toxicity.

Micro-organisms

There are several tests concerning toxicity of DHTDMAC to bacteria which can be used for the derivation of a PNECWWTP, but no test was conducted with DODMAC. In each case labo­ratory water was used.

Table 3.2.1b:toxicity of DHTDMAC to bacteria:

Inoculum	Endpoint	Effect Conc.	Substance	Reference
Pseudomonas putida	18h EC50	48 / 58 mg/l	DHTDMAC	UBA, 1992
secondary effluent	5d EC50	2.0 / 6.5 mg/l	DHTDMAC	UBA, 1992
activated sludge	3h EC50	520 mg/l	DHTDMAC	UBA, 1992
nitrifying bacteria	>119h IC50	2.1 mg/l	DHTDMAC	Wagner & Kayser, 1990
Aerobic bacteria	3h EC20 3h EC50 3h EC80	131 mg/l 278 mg/l 590 mg/l	DHTDMAC	Hoechst, 1993
Anaerobic bacteria	28d NOEC	200 mg/L	DTDMAC	Akzo, 1990

 

The toxicity of DHTDMAC toPseudomonas putidawas investigated in a growth inhibition test according to a GermanDIN-guideline (Bringmann & Kühn method; UBA, 1992). In two tests EC50-values of 48 and 58 mg/l were derived after 18 hours (nominal values, graphically extrapolated).

Secondary effluent of a domestic waste water treatment plant was used as inoculum in a closed-bottle inhibition test (OECD 301D, UBA, 1992). The graphically extra­polated EC50-values of two tests were 2.0 and 6.5 mg/l (nominal concentrations) after a test duration of 5 days.

In an activated sludge respiration inhibition test (OECD 209) inoculum from a predominantly domestic waste water treatment plant was used (UBA, 1992). A 3h EC50 of 520 mg/l was derived graphically from the dose response curve. The corresponding statistically derived value was 267 mg/l (nominal concentrations).

The toxicity of DHTDMAC to nitrifying bacteria enriched in a laboratory waste water treat­ment plant (domestic sludge originally) was investigated in a manometric respirometer test (Wagner & Kayser, 1990). The test duration in the reference was referred to between 119 and 254 hours for different substances and was stopped when the nitrification of the controls was completed. The IC50 for inhibition of respiration was 2.1 mg/l active ingredient of DHTDMAC (a carrier solvent was used).

Aerobic bacteria from a domestic waste water treatment plant were exposed to DHTDMAC in an OECD 209 test (Hoechst, 1993). The inhibition of respiration was measured after 3 hours and the EC20 was 131 mg/l, the EC50 = 278 mg/l.

Using different safety factors according to the sensitivities of the test systems and the mean effect values the lowest PNEC-values are as follows:

 

Pseudomonas putida     EC50 = 53 mg/l, SF = 100              PNEC = 0.53 mg/l

nitrifying bacteria          EC50= 2.1 mg/l, SF = 10                 PNEC = 0.21 mg/l

secondary effluent          EC50= 4.3 mg/l, SF = 100               PNEC = 0.043 mg/l

 

With all these PNECs it has to be considered that the microorganism toxicity derived in labora­tory water tests has to be handled with care as a high influence of the composition of the waste water (e.g. suspended particles, complexing agents) can be assumed, which is the same phenomenon as in surface water tests. Moreover the lowest PNECmicro-organisms of 0.043 mg/l seems to be unrealistic as it is reported that waste water treatment plants operate at DHTDMAC concentrations of 3 to 8 mg/l (chap. 3.1.2.1). However, it is not documented whether the treatment process would be more effective without this DHTDMAC load in the influent and how less adapted plants might react. Nitrifying bacteria were found to be the most sensitive micro-organisms with the lowest EC50 of 2.1 mg/l on which the risk assessment should be based (PNECmicroorganism = 0.21 mg/l) to ensure that the most sensitive treat­ment process can take place.