Thiophanate-methyl

Sediment toxicity

Link to relevant study record(s)

Reference

Endpoint:

sediment toxicity: long-term

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2001-11-15 to 2002-04-08

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 219 (Sediment-Water Chironomid Toxicity Test Using Spiked Water)

Version / remarks:

Draft Document February 2001

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

WATER / SEDIMENT / PORE WATER
Water, pore water and sediment samples from the test systems were taken on Day 0 (approximately one hour after the test item application), on Day 7 and at the test termination on Day 28. The test systems of the middle and the highest test concentration (nominal 0.5 and 2 mg/L) and the control were sampled (control on Days 0 and 28 only).

Vehicle:

no

Details on sediment and application:

PREPARATION OF SEDIMENT
An artificial sediment was used according to the test guideline. The artificial sediment was prepared on the basis of dry weights as follows:
% distribution
Sphagnum peat: 4%
(air dried, very finely ground to ≤1 mm)
Kaolin clay (content of Al203: 36.3%): 20%
Sand (Sihelco 36): 76%
Size analysis
0.25 mm 1.0%
0.18 mm 6.0%
0.125 mm 80.0%
0.09 mm 12.0%
<0.09mm 1.0%
Calcium carbonate (CaCO3): 0.26%
The total organic carbon (TOC) in this artificial sediment was 2.0% (based on dry weight).

All dry constituents were weighed to the correct portions. The finely ground peat was moistened with purified water by intense mixing by an ultra-turrax and gentle stirring for four days at room temperature in the dark. The pH of the peat suspension was 5.0 at start of moistening. CaCO3 was added for pH adjustment, and after the moisture procedure the pH was 5.5. Then all constituents were thoroughly blended in a HOBART laboratory mixer to receive a homogeneous wet sediment. Purified water was added to obtain a sufficient moisture of the final mixture of 46 %.
A sediment sample of about 10 g was shaken with 25 mL of a 0.1 mol KCI solution for 30 minutes and then the pH was measured in this suspension. The pH of the final mixture of sediment was 6.6. This wet sediment was filled into the test beakers.

PREPARATION OF SPIKED WATER
The test water used in this study was reconstituted water ("M7-medium") with an initial pH of 7.9 ± 0.3. In purified water analytical grade salts and additives were added to obtain the following nominal concentrations:
MAIN COMPOUNDS:
CaCl2 2H2O - 293.80 mg/L
MgSO4-7H2O - 123.30 mg/L
KCl - 5.80 mg/L
NaHCO3 - 64.80 mg/L
Na2SiO39H2O - 10.00 mg/L
NaNO3 - 0.27 mg/L
KH2PO4 - 0.14 mg/L
K2HPO4 - 0.18 mg/L

TRACE ELEMENTS
B - (H3BO3) - 125.0 µg/L
Fe – (FeS04-7H2O) - 50.0 µg/L
Mn - (MnCI2-4H2O) - 25.0 µg/L
Li - (LiCI) - 12.5 - µg/L
Rb - (RbCI) - 12.5 µg/L
Sr - (SrCI2-6H2O) - 12.5 µg/L
Br - (NaBr) - 3.1 µg/L
Mo – (Na2MoO4-2H2O) - 6.3 µg/L
Cu – (CuCl-2H2O) – 1.6 µg/L
Zn – (ZnCl) – 6.3 µg/L
Co – (CoCl.6H2O) – 2.5 µg/L
J – (KJ) – 2.5 µg/L
Se – (NaSeO) – 1.0 µg/L
V – (NH4VO3) – 0.3 µg/L
EDTA – (Na EDTA 2H2O) – 625 µg/L

VITAMINS
Thiamine HCl - 75.0 µg/L
Cyanocobalamine (B12) 1.0 µg/L
Biotin (Be) - 0.75 µg/L

Test organisms (species):

Chironomus riparius

Details on test organisms:

TEST ORGANISM
- Common name: midge
- Source: Novartis Crop Protection AG, CH-4002 Basel, Switzerland
- Breeding conditions: under similar temperature and light conditions as in the test, and in the same kind of test water as used in the test
- Age of animals at beginning of exposure: the larvae were 3 days old (first-instar larvae)
- Feeding during test: yes
- Food type: Tetra Min® fish food
- Amount: 0.467 – 0.934 mL/vessel

Study type:

laboratory study

Test type:

static

Water media type:

freshwater

Type of sediment:

artificial sediment

Limit test:

no

Duration:

28 d

Exposure phase:

total exposure duration

Remarks:

full maturation of the larvae to adult midges

Hardness:

200 mg/L as CaCO3

Test temperature:

20.0 - 21.8 °C

pH:

6 - 9

Dissolved oxygen:

6.5 mg/L (= 75 % oxygen saturation)

Nominal and measured concentrations:

Nominal: 0.125, 0.25, 0.5, 1 and 2 mg/L
Measured: 0 - 2 % of the nominal initial test concentrations after 28 days

Details on test conditions:

TEST SYSTEM
- Test container used for each generation (material, size, volume): Glass beakers (600 mL, approximately 8 cm in diameter)
- Weight of wet sediment with and without pore water: 130 g wet weight
- Overlying water volume: 250 mL
- Aeration: yes
- Aeration frequency and intensity: During the whole study, gently.

EXPOSURE REGIME
- No. of organisms per container (treatment): 4
- No. of replicates per treatment group: 5
- No. of replicates per control / vehicle control: 1
- Type and preparation of food: Tetra Min® fish food (mixture of fresh green algae Scenedesmus subspicatus from a laboratory culture and a Tetra Min® fish food suspension). The fish food flakes were finely ground and suspended in test water.
- Amount of food: 0.467 – 0.934 mL/vessel

OVERLYING WATER CHARACTERISTICS
- Type of water: Elendt medium acc. to OECD TG 219

CHARACTERIZATION OF ARTIFICIAL SEDIMENT
- % dry weight of sphagnum moss peat: 4 %
- Particle size distribution
- % sand: 76 %
- % Kaolin clay: 20 %
- Method of preparation: All dry constituents were weighed to the correct portions. The finely ground peat was moistened with purified water by intense mixing by an ultra-turrax and gentle stirring for four days at room temperature in the dark.
- Maturation of artificial substrate: yes
- Moisture: 46 %
- pH dry matter and/or whole sediment: 5.5
- Total organic carbon (%): 2.0 %

OTHER TEST CONDITIONS
- Photoperiod: 16-h light to 8-h darkness photoperiod (30 minutes transition period)
- Light intensity: 560 - 680 Lux
- Aeration of overlying water: yes

EFFECT PARAMETERS MEASURED:
- Emergence: the number of fully emerged midges per test vessel at each inspection day are analysed
- Visual assessment: symptoms of toxicity at larvae, pupae and emerged midges were assessed

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 2
- Range finding study: yes
- Test concentrations: 0.004 mg/L: 0.02 mg/L: 0.1 mg/L: 0.5 mg/L: 2 mg/L: 0 %.
- Results used to determine the conditions for the definitive study: yes

Reference substance (positive control):

not specified

Duration:

28 d

Dose descriptor:

other: EC15

Effect conc.:

> 1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

development rate

Duration:

28 d

Dose descriptor:

other: EC15

Effect conc.:

0.952 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

emergence rate

Key result

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

development rate

Key result

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

0.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

emergence rate

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

development rate

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

1.227 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

emergence rate

Details on results:

No symptoms of toxicity were observed for the larvae, pupae and emerged midges during the study.

Results with reference substance (positive control):

no information

Table 1: Emergence ratio (male and female midges pooled)

Emergence rati	Nominal initial test item concentration (mg/L)
	control	0.125	0.25	0.5	1.0	2.0
Sum of inserted larvae per treatment	80	80	80	80	80	80
Sum of emerged midges per treatment	75	76	76	78	65	0
% of emerged midges per treatment (mean)	94	95	95	98	81	0
Emergence ratio ERarc: mean	1.359	1.415	1.410	1.458	1.139	0.000
SD	0.1631	0.1932	0.1858	0.1302	0.1571	0.0000
min	1.173	1.173	1.249	1.345	0.991	0.000
max	1.571	1.571	1.571	1.571	1.345	0.000
n	4	4	4	4	4	4
% of control	100	104	104	107	84	0
STAT	--	n.s.	n.s.	n.s.	s.	s.

ERarc: arcsin-transformed emergence ratio

STAT: results of a Williams-test (α = 0.05, one-sided smaller)

n.s.: mean ERarc not significantly lower than in the control

s.: mean ERarc significantly lower than in the control

 

Table 2: Development rate

Development rate of males
	Nominal initial test item concentration (mg/L)
Development rate per treatment (d^-1)	control	0.125	0.250	0.5	1.0	2.0
Mean	0.066	0.064	0.063	0.065	0.063	n.a.
SD	0.0017	0.0035	0.0019	0.0039	0.0003	n.a.
min	0.064	0.060	0.061	0.061	0.062	n.a.
max	0.068	0.068	0.065	0.069	0.063	n.a.
n	4	4	4	4	4	4
% of control	100	97	96	99	96	n.a.
STAT	--	n.s.	n.s.	n.s.	n.s.	n.a.

 

Development rate of females
Development rate per treatment (d^-1)	Nominal initial test item concentration (mg/L)
	control	0. 125	0.25	0.5	1.0	2.0
Mean	0.062	0.058	0.059	0.061	0.057	n.a.
SD	0.0027	0.0024	0.0017	0.0006	0.0085	n.a.
min	0.058	0.056	0.057	0.060	0.052	n.a.
max	0.065	0.062	0.060	0.062	0.069	n.a.
n	4	4	4	4	4	4
% of control	100	94	95	98	92	n.a.
STAT	—	n.s.	n.s.	n.s.	n.s.	n.a.

STAT: results of a Williams-test (α = 0.05, one-sided smaller)

n.s.: mean development rate not significantly lower than in the control

s.: mean development rate significantly lower than in the control

n.a.: not applicable (no midge emerged)

 

Table 3: Balance of applied radioactive residue of the samples treated at a nominal concentration of 0.5 mg/L after extraction of the sediment.

Nominal Initial water concentration 500 µg/L corresponding to (125 µg per sample)	Incubation Time
	Day 0				Day 7				Day 28
	µg	volume* weight*	µg/L µg/kg	%	µg	volume* weight*	µg/L µg/kg	%	µg	volume* weight*	µg/L µg/kg	%
water phase water	111.18	250.0	444.7	88.9	63.58	250.0	254.3	50.9	17.32	250.0	69.3	13.9
pore water	0.05	4.5	11.3	0.0	3.93	8.20	479.4	3.1	5.56	10.8	514.4	4.4
Sediment extraction ** at Room temperature	3.35	124.7	26.9	2.7	47.58	117.5	405.0	38.1	43.77	121.5	360.4	35.0
Non extradantes	1.80	124.7	14.4	1.4	13.40	117.5	114.1	10.7	58.64	121.45	482.8	46.9
Total in sediment	5.15	124.7	41.3	4.1	60.99	117.5	519.1	48.8	102.40	121.5	843.2	81.9
Total	116.4		-	93.1	128.5		-	102.8	125.3		-	100.2

* in µg/L water or µg/kg wet sediment without pore water

** Acetonitrile/water (8:2; v/v); day 0 (once), days 7 and 28 (three times).

Note: The concentration in the water phase was calculated based on the initial volume 250 mL to be able to compare all intervals.

The calculations were performed by means of a commercially available computer program (Excel 4.0). The results given in the tables are rounded. Thus, hand calculations may differ slightly from those presented due to rounding.

 

Table 4: Balance of applied radioactive residue of the samples treated at a nominal concentration of 2 mg/L after extraction of the sediment.

Nominal Initial water concentration 500 µg/L corresponding to (125 µg per sample)	Incubation Time
	Day 0				Day 7				Day 28
	µg	volume* weight*	µg/L µg/kg	%	µg	volume* weight*	µg/L µg/kg	%	µg	volume* weight*	µg/L µg/kg	%
water phase water	450.54	250.0	1802.1	90.1	253.41	250.0	1013.6	50.7	71.42	250.0	285.7	14.3
pore water	0.51	6.0	84.4	0.1	19.63	8.0	2454.2	3.9	44.07	14.3	3081.9	8.8
Sediment extraction ** at Room temperature	17.97	124.8	144.0	3.6	158.34	121.7	1300.7	31.7	169.68	119.0	1426.1	53.9
Non extradantes	9.30	124.8	74.5	1.9	36.90	121.7	303.1	7.4	197.62	119.0	1660.9	39.5
Total in sediment	27.28	124.8	218.5	5.5	195.24	121.7	1603.8	39.0	387.3	119.0	3087.1	73.5
Total	478.32		-	95.7	458.28		-	93.7	482.79		-	96.6

* In µg/L water or µg/kg wet sediment without pore water

** Acetonitrile/water (8:2; v/v); day 0 (once), days 7 and 28 (three times).

Note: The concentration in the water phase was calculated based on the initial volume 250 mL to be able to compare all intervals.

The calculations were performed by means of a commercially available computer program (Excel 4.0). The results given in the tables are rounded. Thus, hand calculations may differ slightly from those presented due to rounding.

 

ANALYTICAL RESULTS

The measured concentrations of the test item in the test media one hour after the test item application corresponded to 87-89% of the nominal initial test concentrations.

The test item was not stable in the water of the water-sediment systems during the test period. Seven days after the test item application the concentrations of the test item in the water columns had strongly decreased to 6 - 17 %, at the study termination after 28 days to 0 - 2 % of the nominal initial test concentrations.

In contrast, in the sediment the concentrations of the test item slightly but continuously increased until Day 28. At the test concentration of nominal 0.5 mg/L the concentration was in maximum 0.049 mg/kg dry sediment, at nominal 2 mg/L in maximum 0.188 mg/kg. In the pore water the concentrations of the test item were always below the detection limit during the study period.

Only the degradation products Carbendazim (CF-27) and 2-Aminobenzimidazole (2-AB) were found in significant concentrations in the water phase and in the sediment, but not in the pore water. The highest concentrations of Carbendazim were found on Day 7. On Day 28 the concentrations of Carbendazim had already decreased. For detailed analytical results of the test item and its metabolites see the attached analytical report.

Since the measured test item concentrations in the application solutions and in the test media one hour after application corresponded with the theoretical values, all reported biological results are related to the nominal initial concentrations of the test item in the water column.

 

Table 5: Amounts of ¹⁴C-Thiophanate-methyl and its degradates in the samples treated at concentrations of 0.5 mg/L and 2 mg/L during the incubation period. Values are given in mg parent equivalents per litre water or per kg dry sediment.

Radioactive Fractions	Concentration	Incubation time in days
		0.5 mg/L Concentration			2 mg/L Concentration
	Sample	0	7	28	0	7	28
Parent Thiophanate-methyl	A	435.8	31.0	-	1773.3	343.6	30.0
	B	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
	C	n.a.	24.7	49.4	n.a.	189.9	188.2
CF-27	A	-	223.3	30.0	-	496.7	147.6
	B	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
	C	n.a.	380.3	284.2	n.a.	854.6	895.6
2-AB	A	-	-	39.3	-	150.0	108.3
	B	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
	C	n.a.	-	13.3	n.a.	115.8	238.2
M2 Unknown	A	-	-	-	-	-	-
	B	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
	C	n.a.	-	-	n.a.	26.0	38.5
IMPURITY	A	8.9	-	-	28.8	23.3	-
	B	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
	C	n.a.	-	13.3	n.a.	88.4	65.6
Non-Extractables	-	14.4	114.1	482.8	74.5	303.1	1660.9

n.a.: not analysed

*: not detected

A: water phase

B: sediment pore water

C: sediment extract

 

Table 5: Amounts of ¹⁴C-Thiophanate-methyl and its degradates in the samples treated at concentrations of 0.5 mg/L and 2 mg/L during the incubation period. Values are given in percent of initial applied radioactivity.

Radioactive Fractions	Concentration	Incubation time in days
		0.5 mg/L Concentration			2 mg/L Concentration
	Sample	0	7	28	0	7	28
Parent Thiophanate-methyl	A	87.2	6.2	-	88.7	17.2	1.5
	B	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
	C	n.a.	2.3	4.8	n.a.	4.6	4.5
	Total	87.2	8.5	4.8	88.7	21.8	6.0
CF-27	A	-	44.7	6.0	-	24.8	7.4
	B	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
	C	n.a.	35.7	27.6	n.a.	20.8	21.3
	Total	-	80.4	33.6	-	45.6	28.7
2-AB	A	-	-	7.9	-	7.5	5.4
	B	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
	C	n.a.	-	1.3	n.a.	2.8	5.7
	Total	-	-	9.2	-	10.3	11.1
M2 Unknown	A	1.8	-	-	-	-	-
	B	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
	C	n.a.	-	1.3	n.a.	0.6	0.9
	Total	1.8	-	1.3	-	0.6	0.9
IMPURITY	A	1.8	-	-	1.4	1.2	-
	B	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
	C	n.a.	-	1.3	n.a.	2.2	1.6
	Total	1.8		1.3	1.4	3.3	1.6
Non-Extractables	-	1.4	10.7	46.9	1.9	7.4	39.5

n.a.: not analysed

*: not detected

A: water phase

B: sediment pore water

C: sediment extract

Validity criteria fulfilled:

yes

Conclusions:

The mean development rates of both males and female midges were up to and including the test concentration of nominal initial 1.0 mg/L not significantly lower than in the control. At the next higher test concentration of 2.0 mg/L (equivalent to 0.188 mg/kg sediment dw) no midges emerged. The 28-day EC15 or EC50 for the development rate could therefore not be calculated, but were both higher than 1.0 mg/L.

Thus, taking into account the emergence ratios and the development rates of Chironomus riparius and any toxicity symptoms, the 28-day NOEC (highest tested concentration without toxic effects) of the test item in this water-sediment study was 0.5 mg/L (equivalent to 0.049 mg/kg sediment dw). The 28-day LOEC (lowest concentration tested with toxic effects) was 1.0 mg/L due to the reduced emergence ratio of the midges. The NOEC and LOEC are based on the initial test item concentration in the water phase.

Executive summary:

Toxic effects of the test item on the development of sediment-dwelling larvae of the midge Chironomus riparius in water-sediment systems were investigated following the OECD Guidelines for Testing of Chemicals, Proposal for a new Guideline 219, Draft Document: "Chironomid Toxicity Test Using Spiked Water" (2001).

For this purpose, first-instar larvae of Chironomus riparius were exposed for a period of 28 days until full maturation of the larvae to adult midges. The test parameters of the study were the development time/rate of the midges and the emergence ratio as the number of fully emerged male and female midges. The test item was applied to the water column in static water-sediment systems. The nominal initial test item concentrations in the overlaying water columns were 0.125, 0.250, 0.5, 1.0 and 2.0 mg/L. A control (water-sediment systems without test item application) was tested in parallel.

Radiolabelled test item was used for the analysis of the actual concentrations of ¹⁴C-labelled test item, and its metabolites in the overlaying water column, the pore water and the sediment during the exposure period. The measured concentrations of the test item in the test media one hour after the test item application corresponded to 87 - 89 % of the nominal initial test concentrations. Seven days after the test item application the concentrations of the test item in the water columns had strongly decreased to 6 - 17 %, at the study termination after 28 days to 0 - 2 % of the nominal initial test concentrations. In contrast, in the sediment the concentrations of the test item slightly but continuously increased until Day 28. At the test concentration of nominal 0.5 mg/L, the concentration was in maximum 0.049 mg/kg sediment dw, at nominal 2.0 mg/L in maximum 0.188 mg/kg sediment dw. In the pore water, the concentrations of the test item were always below the detection limit during the study period.

Only the degradation products Carbendazim and 2-Aminobenzimidazole were found in significant concentrations in the water phase and in the sediment, but not in the pore water. The highest concentrations of Carbendazim were found on Day 7. On Day 28 the concentrations of Carbendazim had already decreased.

Since the measured test item concentrations in the application solutions and in the test media one hour after application corresponded with the theoretical values, all reported biological results are related to the nominal initial concentrations of the test item in the water column.

Up to and including the test concentration of nominal initial 0.5 mg/L, the mean emergence ratio of the midges was not significantly reduced. The emergence ratio was reduced first at the test concentration of nominal initial 1.0 mg/L. The 28-day EC₁₅ for the emergence ratio was calculated to be 0.952 mg/L, the 28-day EC₅₀ for this parameter was 1.227 mg/L. The 95 % confidence limits for the EC₁₅ and EC₅₀ could not be calculated on the present database.

The mean development rates of both males and female midges were up to and including the test concentration of nominal initial 1.0 mg/L not significantly lower than in the control. At the next higher test concentration of 2.0 mg/L no midges emerged. The 28-day EC₁₅ or EC₅₀ for the development rate could therefore not be calculated, but were both higher than 1.0 mg/L.

Thus, taking into account the emergence ratios and the development rates of Chironomus riparius and any toxicity symptoms, the 28-day NOEC (highest tested concentration without toxic effects) of the test item in this water-sediment study was 0.5 mg/L. The 28-day LOEC (lowest concentration tested with toxic effects) was 1.0 mg/L due to the reduced emergence ratio of the midges. The NOEC and LOEC are based on the initial test item concentration in the water phase.

Description of key information

The mean development rates of both males and female midges were up to and including the test concentration of nominal initial 1.0 mg/L not significantly lower than in the control. At the next higher test concentration of 2.0 mg/L (equivalent to 0.188 mg/kg sediment dw) no midges emerged. The 28-day EC₁₅ or EC₅₀ for the development rate could therefore not be calculated, but were both higher than 1.0 mg/L.

Thus, taking into account the emergence ratios and the development rates of Chironomus riparius and any toxicity symptoms, the 28-day NOEC (highest tested concentration without toxic effects) of the test item in this water-sediment study was 0.5 mg/L (equivalent to 0.049 mg/kg sediment dw). The 28-day LOEC (lowest concentration tested with toxic effects) was 1.0 mg/L due to the reduced emergence ratio of the midges. The NOEC and LOEC are based on the initial test item concentration in the water phase.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater sediment:

0.049 mg/kg sediment dw

Additional information

Toxic effects of the test item on the development of sediment-dwelling larvae of the midge Chironomus riparius in water-sediment systems were investigated following the OECD Guidelines for Testing of Chemicals, Proposal for a new Guideline 219, Draft Document: "Chironomid Toxicity Test Using Spiked Water" (2001).

For this purpose, first-instar larvae of Chironomus riparius were exposed for a period of 28 days until full maturation of the larvae to adult midges. The test parameters of the study were the development time/rate of the midges and the emergence ratio as the number of fully emerged male and female midges. The test item was applied to the water column in static water-sediment systems. The nominal initial test item concentrations in the overlaying water columns were 0.125, 0.250, 0.5, 1.0 and 2.0 mg/L. A control (water-sediment systems without test item application) was tested in parallel.

Radiolabelled test item was used for the analysis of the actual concentrations of ¹⁴C-labelled test item, and its metabolites in the overlaying water column, the pore water and the sediment during the exposure period. The measured concentrations of the test item in the test media one hour after the test item application corresponded to 87 - 89 % of the nominal initial test concentrations. Seven days after the test item application the concentrations of the test item in the water columns had strongly decreased to 6 - 17 %, at the study termination after 28 days to 0 - 2 % of the nominal initial test concentrations. In contrast, in the sediment the concentrations of the test item slightly but continuously increased until Day 28. At the test concentration of nominal 0.5 mg/L, the concentration was in maximum 0.049 mg/kg sediment dw, at nominal 2.0 mg/L in maximum 0.188 mg/kg sediment dw. In the pore water, the concentrations of the test item were always below the detection limit during the study period.

Only the degradation products Carbendazim and 2-Aminobenzimidazole were found in significant concentrations in the water phase and in the sediment, but not in the pore water. The highest concentrations of Carbendazim were found on Day 7. On Day 28 the concentrations of Carbendazim had already decreased.

Since the measured test item concentrations in the application solutions and in the test media one hour after application corresponded with the theoretical values, all reported biological results are related to the nominal initial concentrations of the test item in the water column.

Up to and including the test concentration of nominal initial 0.5 mg/L, the mean emergence ratio of the midges was not significantly reduced. The emergence ratio was reduced first at the test concentration of nominal initial 1.0 mg/L. The 28-day EC₁₅ for the emergence ratio was calculated to be 0.952 mg/L, the 28-day EC₅₀ for this parameter was 1.227 mg/L. The 95 % confidence limits for the EC₁₅ and EC₅₀ could not be calculated on the present database.

The mean development rates of both males and female midges were up to and including the test concentration of nominal initial 1.0 mg/L not significantly lower than in the control. At the next higher test concentration of 2.0 mg/L no midges emerged. The 28-day EC₁₅ or EC₅₀ for the development rate could therefore not be calculated, but were both higher than 1.0 mg/L.

Thus, taking into account the emergence ratios and the development rates of Chironomus riparius and any toxicity symptoms, the 28-day NOEC (highest tested concentration without toxic effects) of the test item in this water-sediment study was 0.5 mg/L. The 28-day LOEC (lowest concentration tested with toxic effects) was 1.0 mg/L due to the reduced emergence ratio of the midges. The NOEC and LOEC are based on the initial test item concentration in the water phase.