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Sediment toxicity

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sediment toxicity: long-term
Type of information:
experimental study
Adequacy of study:
weight of evidence
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: test was carried out in conformity with the draft OECD document , May 1998 "Chironomid testing using spiked sediment" and OECD principles of GLP

Data source

Reference Type:
study report

Materials and methods

Test guideline
according to
other: OECD draft document, may 1998
the deviations are assumed not to have effected the results of the study.
Principles of method if other than guideline:
egg masses were not obtained from an own TNO culture.
The peat used was autoclaved before preparing the artificial sediment to better enable wetting.
extra nitrite and ammonia determinations were carried out a t=0.14 and 28days to confirm that these parameters did not disturb the results of the tests.
conditioning of the sediment, after mixing of the constituents, lasted 8d and not 7d as stated in Annex A of the protocol
an amendment to the protocol with respect tot the boron analyses was not prepared
according to the guideline the TOC of the artificial sediment should be 2 +/- 0.5% and not 2%
the TOC value in the artificial sediment was 2.73% instead of 2 +/- 0.5%
the pH KCl value of the artificial sediment (being 7.8) was above the intended value of 7.0 +/- 0.5
GLP compliance:
yes (incl. certificate)

Test material

Details on test material:
- Name of test material (as cited in study report): Boric Acid, manufacturing grade
- Purity test date: +/- 99,9%
- physical appearance: white powder
- solubility in water: 4.7% at 20°C

Sampling and analysis

Analytical monitoring:
Details on sampling:
- quantity: 1000 gram
- received from sponsor
- date of receipt in delft: 18 june 1999
- packing: one litre square polyethylene bottle
- Sample storage conditions before analysis: stored at room temperature, no protection from light

Test substrate


Test organisms

Test organisms (species):
Chironomus riparius
Details on test organisms:
- Common name: non biting midge
- Source: egg masses were obtained form RIZA in lelystad, the netherlands
- Date of collection: Feb, 16 2000
- the hatched first instar larvae (larvae without hemoglobin) were used for the test

- Acclimation period: Feb 16 --> Feb 19
- Equilibration period = 2 days
- Acclimation conditions : eggs were stored in a refrigerator, at that time they were placed in DSWL-E water for further development.
- Test started on Feb 25, 2000
- Feeding: larvae were fed daily with a dried fish food suspension (Aquariaan, 20g suspended in 100ml ultrapure water).
amount: 100 µl per test vessel, except at t=3,4,5,6,7,8 and 9 days (50 µl was given). The animals were not fed on Sundays, the double amount of food was given on Saturdays.
- The test vessels were covered with pieces of cloth from the 12th days to prevent escaping of emerged midges.

Study design

Study type:
laboratory study
Test type:
Water media type:
Type of sediment:
artificial sediment
Limit test:
Exposure duration
28 d
Exposure phase:
total exposure duration
=time needed for emergence of the adults in the control

Test conditions

Test temperature:
20.2 - 20.5 °C
artificial sediment: 7.8
overlying water: 7.1-8.1
Dissolved oxygen:
> 5.9 mg/l
Nominal and measured concentrations:
- Test substance concentrations: 18, 32, 56, 100, 180 and 320 mg B/kg dry weight of sediment d.w. 4 replicates were used.
- Control group: 32, 100 and 320mg/kg exposure concentrations
Details on test conditions:
- Test container (material, size): vessel=600mL beakers with diameter ca. 8cm
- Sediment volume: 1.5cm spiked sediment or control sediment/replicate container
- No. of organisms per container (treatment): 5 larvae per test vessel
- No. of replicates per substance concentration: 20 instar larvae
- Test vessels were covered by watch glasses during the test
- Equilibration period: 2 days

- Composition (artificial substrate):
* 5-10% sphagnum peat, finely ground, no visible plant remains (66.4% of dry weight)
* 20% kaolin clay (99% of dry weight)
* 70-75% fine sand (100% of dry weight)
- Dry weight of artificial sediment: 59.6%
- The sediment/water systems were not replaced during the test

- artificial sediment:
pH-KCl = 7.8
TOC content = 2.73g C/100g dry weight
- overlying water:
pH = 7.1-8.1
lowest measured oxygen concentration: 5.9 mg/l
temperatur: 20.2-20.5°C
ammonia and nitrite concentrations were below the critical value for Chironomus riparius

- Pretreatment of artificial and spiked sediment and of sediment/water exposure systems: prepared from an artificial sediment and the TNO standard water DSWL-E.
- Artificial sediment:dry weight 59.6%
- 4 replicate batches were prepared by mixing portions of 600f of clay, 2175g of sand and 225g of sphagnum peat. The peat was wetted the day before by addition of 1.5L of DSWL-E, followed by autoclaving for 20 minutes at 121°C. The clay and sand part were added together wit 0.5L of DSWL-E and 19g of CaCO3. The mixtures in the jars were homogenised by rolling them for 1 days on a roller bank, the content of the jars were added together, 1L of DSWL-E was added followed by aeration. The sediment was mixed and the dry weight of a sample was determined several times.
- After 8 days the sediment was mixed to obtain a homogenous distribution, before being placed in the exposure vessels and the overlying water was added.
- Sediments were spiked in the test beakers based on the dry sediment weight. For each exposure concentration a number of four replicate containers were separately filled with a layer of ca 1.5cm spiked sediment or controled sediment. For chemical analystical purposes 2 extra vessels were prepared for the control: 32, 100 and 320mg/kg exposure concentration. DSWL-E water was added to obtain a ratio between sediment layer and water column in the range of 1:4. this sediment/water system was allowed to settle for ca. 48h before the test animals were added. the overlying water of the sediment/water systems was slightly aerated during the test, without disturbing the sediment layer.

Results and discussion

Effect concentrationsopen allclose all
28 d
Dose descriptor:
Effect conc.:
180 mg/kg sediment dw
Nominal / measured:
Conc. based on:
Basis for effect:
28 d
Dose descriptor:
Effect conc.:
180 mg/kg sediment dw
Nominal / measured:
Conc. based on:
Basis for effect:
emergence rate
Details on results:
- Some turbidity from suspended solids was observed during the test. De turbidity decreased during the test.
- From day 14 some solids were present on the walls of the test vessel; this pfenomenon increased during the remaining period of the test.

- at the end of the test the boron concentrations in pore water and overlying water are similar; equilibrium between overlying water and pore water has been reached.
- at the start of the test the concentrations in pore water are higher than in the overlying water.

the 28d LC50 is 278 mg B/k dw (nominal), the 28d LOEC for mortality and emergence is 320 mg B/kg dw and the 28d NOEC for mortality and emergence is 180 mg B/kg dw.
Reported statistics and error estimates:
LC50 values and their interval were calculated by means of a parametric model (Kooiman, 1981).
Emergence data are arcsin transformed and the Dunnett test (sign level 99%) was used to detect significant differences with the control.

Any other information on results incl. tables

28d LOEC: 320 mg/kg (mortality & emergence)

28d LC50: 278 mg/kg

nominal conc. of mg B/kg sediment dw emerged larvae at the end of the testmale female total %0 34 42 76 95 18 34 44 78 98 32 36 37 73 91 56 35 43 78 98 100 34 44 78 98 180 42 37 79 99 320 1 1 2 2.5

Applicant's summary and conclusion

Validity criteria fulfilled:
The test was carried out in conformity with the draft OECD document and OECD principles of GLP.
The test is well described.