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Sediment toxicity

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Reference
Endpoint:
sediment toxicity: short-term
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
Study conducted according to a modified OECD guideline, no mention of GLP, no analytical monitoring and lack of water quality measurements.
Qualifier:
equivalent or similar to
Guideline:
EPA OPPTS 850.1735 (Whole Sediment Acute Toxicity of Invertebrates, freshwater)
Deviations:
yes
Remarks:
the media used was soil and water
GLP compliance:
not specified
Analytical monitoring:
no
Vehicle:
yes
Details on sediment and application:
PREPARATION OF SPIKED SEDIMENT

- Pooling or mixing of different substrates: soil and water

- Method of mixing: not reported

- Details of spiking: sand spike, using 10% of the total dry weight of soil. This involved adding an appropriate amount of compound to analar grade acetone to form a stock solution for the 1000 mg/kg dose. Aliquots of the stock solution were then diluted with acetone to prepare lower doses. Acetone solutions were added to silica sand in 500 ml amber glass jars. Mixtures were mixed thoroughly with a stainless steel spatula. The acetone was left to evaporate in a fume cupboard, leaving the test item coated onto the sand. Appropriate amount of moist soil was added to each of the glass jars. The dosed or undosed sand was incorporated into the bulk of the soil using a paletted knife. Jars were then sealed with screw top lids containing aluminium foil inserts and tumbled overnight (ca. 16 h) on a rotary soil tumbler 50 rpm.

- Equilibration time: not reported

- Controls: One aliquot of sand was dosed with acetone only to serve as solvent control. A jar with an aliquot of sand only served as untreated control - both with the appropriate amount of moist soil added thereafter.

- Chemical name of vehicle (organic solvent, emulsifier or dispersant):

- Concentration of vehicle in test medium (stock solution and final test solution): acetone solutions was added between 1-7 ml to 5-35g of silica sand. The sand was left to evaporate the acetone completely before initial exposure, so that the concentration of vehicle would be negligible.

- Evaporation of vehicle before use: yes


PREPARATION OF SPIKED WATER

- Details of spiking: not spiked
Test organisms (species):
other: Heterocypris incongruens
Details on test organisms:
TEST ORGANISM

- Common name: ostracods

- Justification for species other than prescribed by test guideline: testing new method

- Source: obtained as dormant cysts in test kits (Ostracodtoxkit F. Chronic "direct contact" Toxicity Test for Freshwater Sediments, MicroBio Tests Inc. Deinze, Belgium).

- Breeding conditions: as test kit instructed. Organism were hatched in standard hard water in a covered petri dish for 52 h at 25 degC before introduction to the prepared soil.

- Age of animals at beginning of exposure: a few hours old

- Feeding during test

- Food type: algae powder (Spirulina sp, provided with the toxkit)

- Amount: one tube

- Frequency: once, four hours before the test began



ACCLIMATION

- Acclimation period: none
Study type:
laboratory study
Test type:
static
Water media type:
freshwater
Limit test:
no
Duration:
6 d
Exposure phase:
total exposure duration
Test temperature:
25 +/- 2 degC
pH:
not reported
Dissolved oxygen:
not reported
Nominal and measured concentrations:
Nominal concentrations: 0, 300, 1000 mg/kg dw soil
Details on test conditions:
TEST SYSTEM

- Test container (material, size): polystyerene, multi well plates, supplied with the Ostracodtoxkit F.

- Amount of soil or substrate: 300ul og either reference sediment (supplied with the kit) or treated soil

- No. of organisms per container (treatment): 10

- No. of replicates per treatment group: 3

- No. of replicates per control: 3

- No. of replicates per vehicle control: 3



SOURCE AND PROPERTIES OF SUBSTRATE

- Geographic location: Heath Farm, Leicester Lane, LandLook (Midlands), Leamington Spa, from Dr Graham Beard. OS map reference 32896926.

- Pesticide use history at the collection site: assumed to be pesticide free, as the field the soil was taken from land that had been set aside for 3-4 years.

- Collection procedures: the soil was sieved to 2 mm.

- Sampling depth (cm): 5-20cm to avoid surface root mat

- Soil texture

- % sand: 63.8%-64.8%

- Soil classification: sandy loam soil. The soil is described as soil series, Bomsgrove, standard soil number 33, variant.

- Organic carbon (%): 1.3%

- Maximum water holding capacity: ca. 40%

- Pretreatment of soil: the soil was treated with gamma radiation (27 KGy) in order to kill the indigenous nematodes and potential predators. However observation from extracted fresh soil indicated that interference from the indigenous population was likely to be insignificant. Consequently, the definitive test were carried out using unsterilised soil.

- Storage: stored in closed black plastic bags at 4 degC until required.


OTHER TEST CONDITIONS

- Photoperiod: plates were incubated in the dark

-Other: animals were fed with 3x10^7 algal cells


EFFECT PARAMETERS MEASURED: Growth was determined by measuring the length of ostracods at the beginning (on a sub-sample) and end of the exposure period (surviving individuals). Measured once the ostracods were fixed in Lugols solution and via a calibrated graticule under a binocular microscope. Mortality (immobilisation) was measured at the end of the test.


VEHICLE CONTROL PERFORMED: yes


TEST CONCENTRATIONS

- Spacing factor for test concentrations: 3

- Range finding study: no
Reference substance (positive control):
yes
Remarks:
dimethoate
Duration:
6 d
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/kg sediment dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: reproduction and survival
Details on results:
- Mortality at end of exposure period: 0%
Results with reference substance (positive control):
- Results with reference substance valid? yes

- Relevant effect levels: 160 mg/kg dw soil
Reported statistics and error estimates:
Probit analysis (Finney 1971) was used to determine EC50 values and their corresponding 95% intervals in definitive tests.

Table 1. Summary of findings.

 Concentration (mg/kg dw soil Mortality (%) 
Control
10 
10 
Acetone control       
 0
 0
 30 0
 0
 0
 100  0
 0
10
 300  20
   10
   10
 1000  40
   0
   0
Validity criteria fulfilled:
yes
Remarks:
on the data provided, however not enough data on water quality
Conclusions:
A 6 d EC50 value of >1000 mg/kg dw soil has been determined for the effects of the test substance on population numbers of the ostracod H. incongruens.

Description of key information

Long term: In accordance with section of REACH Annex XI the long term toxicity to sediment organisms study does not need to be conducted because it is technically not possible. Short term: (6 d) EC50 >1000 mg/kg dw soil H. incongruens.

Key value for chemical safety assessment

Additional information

Short-term toxicity

A 6 d EC50 value of >1000 mg/kg dw soil (1.3% organic carbon) has been determined for the effects of the test substance on population numbers of the ostracod Heterocypris incongruens (Shell, 2004). This study was conducted using a mixture of water and soil as a substrate.

The study reflects the only value that is available for this endpoint.

Long-term toxicity

Testing for sediment toxicity is not considered necessary because:

In accordance with Annex XI, section 2, the long-term toxicity effects studies to sediment dwelling organisms (required in Section 9.5.1) do not need to be conducted as the study is technically not possible. This is due to the very short sediment half-life once desorbed (see the discussion of Biodegradation in water and sediment for further details), preventing maintenance of exposure concentrations for the duration of either a standard short-term or long-term test. Therefore, sediment hazard assessment is based on the EQPM PNECs derived from the aquatic data.

PNECsediment has been calculated from PNECfreshwater on the basis of the equilibrium partitioning method.