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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
Study period:
from 1995-09-22 to 1995-10-02
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study
Qualifier:
according to guideline
Guideline:
other:  Proposed ISO Guideline and PARCOM protocol
Deviations:
yes
Remarks:
see below
Principles of method if other than guideline:
The sediment used in the test is marginally outside the constraints recommended in the 1993 PARCOM ring-test.  This deviation would not have effected the results.  All pH, DO, salinity and temperature measures were found to be acceptable.
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
no
Details on sediment and application:
PREPARATION OF SPIKED SEDIMENT

- Details of spiking: The wet sediment was spiked with a 50 ml aliquot containing the appropriate weight of test material in dilution water, or 50 ml clean dilution water for the controls. Equal volumes of dilution water were then added to each of the treatment bottles in order to liquefy the sediment sufficiently to obtain good mixing. The sediments were homogenised before distribution to the test vessels. 

- Equilibration time: 24 h

- Equilibration conditions: 15 deg C

- Controls: received the same treatment as exposure vessels but did not receive any test compound

Test organisms (species):
other: Corophium volutator
Details on test organisms:
TEST ORGANISM

- Source: The test organisms were collected from the southern shore of the Oosterschelde in The Netherlands. The location is near to the intake point where TNO collects seawater, close to a break in the former sea dike where a trickle of freshwater emerges.

- Age of parental stock (mean and range, SD): 5-8 mm long.

- Feeding during test: not reported


ACCLIMATION

- Acclimation period: no acclimation reported
Study type:
laboratory study
Test type:
static
Water media type:
freshwater
Type of sediment:
natural sediment
Limit test:
no
Duration:
14 d
Exposure phase:
total exposure duration
Test temperature:
The test vessels were held at a temperature of 15 degrees C (+/- 2).
pH:
The pH of all control and test media ranged between 7.8 and 8.2.
Dissolved oxygen:
The lowest value recorded as 6.4 mg/l
Salinity:
from 30.4 to 33.2 parts per thousand
Nominal and measured concentrations:
Nominal test concentrations were 100, 320, 1000, 3200 and 10000 mg/kg dry sediment. 
Details on test conditions:
TEST SYSTEM

- Test container (material, size): Glass beakers with a volume of approximately 250 ml containing 75 ml of sediment and topped up to 225 ml with dilution water

- Aeration: yes

- Aeration frequency and intensity: not reported


EXPOSURE REGIME

- No. of organisms per container (treatment): five organisms per vessel. 

- No. of replicates per treatment group: Four test vessels per concentration 

- No. of replicates per control / vehicle control: Four test vessels

- Feeding regime: feeding not reported


RENEWAL OF OVERLYING WATER

- Details on volume additions: not reported



OVERLYING WATER CHARACTERISTCS

- Type of water (e.g. deionized, ground water, sea water, Elendt medium acc. to OECD 219): Natural seawater passed through a sand filter, a carbon filter and a 5 um membrane filter before use.

- Source of water (if non-standard medium): sea water

- Location: Eastern Scheldt

- Description of sampling site: relatively unpolluted location

- Filtration: filtered through sand. Before testing it is also filtered over a carbon filter and a 5um membrane filter.

- Other: the water is checked for concentrations of volatile organic compounds and mineral oil which were found to be in acceptable concentrations. Each batch of water is also checked for gross pollution in a 4 day crustacean test with Mysidopsis bahia.


SOURCE OF NATURAL SEDIMENT

- Location and description of sampling site: Natural sediment was obtained from the site where the organisms were collected. The sediment was sieved to 0.5 mm.

- Contamination history of site: not reported


HANDLING OF NATURAL SEDIMENT

- Time of collection: the water is pumped directly from the sea

- Core depth: not reported

- Water depth: not reported

- Storage conditions: the water is pumped directly from the sea


CHARACTERIZATION OF NATURAL SEDIMENT

- Particle size distribution: median grain size between 63 and 125 um

- % silt clay: (<63 um) 26.9%

- Moisture: not reported

- Further constituents: not reported

- Sediment sieved: yes

- Proof of absence of chemical contaminants: not reported


OTHER TEST CONDITIONS

- Photoperiod: The vessels were held under 16 hour light-8 hour dark cycle with a 15 minute transition period.


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Mortalities were recorded after 5 (surface observations only) and 10 days (sorting of sediment) exposure. pH and oxygen concentrations were measured in the control and test solutions. 


TEST CONCENTRATIONS

- Spacing factor for test concentrations: 3.2

- Range finding study: not reported
Reference substance (positive control):
no
Duration:
10 d
Dose descriptor:
NOEC
Effect conc.:
>= 2 500 mg/kg sediment dw
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
mortality
Duration:
10 d
Dose descriptor:
LC50
Effect conc.:
> 2 500 mg/kg sediment dw
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
mortality
Details on results:
- Mortality of test animals at end of exposure period: 1 animal was not recovered in the controls. See table 1 for further details
Reported statistics and error estimates:
LC50 values and 95% confidence intervals determined using a parametric model developed by Kooijman. NOEC determined by visual comparison of treatments with controls.

Table 1. Mortalities with the marine sediment Corophorium spp. during a 10 day exposure with DTPMP-7Na

 Day   Nominal concentration (mg/l)               
 0  0  100  320  1000  3200  10 000
 10  19*  18*  18*  18*  20  19

* no mortalities were observed, these animals were not recovered.

Result expressed as nominal concentration. Properties of the test substance and evidence from other studies (where
concentrations were measured) indicate that nominal and measured concentrations are likely to be in good agreement.

Validity criteria fulfilled:
yes
Conclusions:
A reliable 10 day LC50 value of >2500 mg active acid/kg dw sediment has been determined for the effects of DTPMP-7Na on the mortality of the marine sediment ostracod Corophorium spp.

Description of key information

No long-term test data are available for freshwater sediment-dwelling organisms.

(10 d) LC50 >2500 mg active acid/kg dw Corophorium spp.

Key value for chemical safety assessment

Additional information

No test data are available for long term sediment-dwelling organisms.

One short term test with a marine species is available. A reliable 10 day LC50 value of >2500 mg active acid/kg dw and a 10 day NOEC value of ≥ 2500 mg active acid/kg dw sediment have been determined for the effects of DTPMP(5-7Na) on the mortality of the marine sediment ostracod Corophorium spp (TNO, 1997). This study is supported by a second short-term read-across study for DTPMP(1-3Na) reporting a 10 day LC50 value of >4500 mg active acid/kg dw sediment also conducted with the marine sediment ostracod Corophorium spp (Zeneca, 1995). While the data indicate low toxicity to sediment organisms, they do not provide a definite value (being larger than values) and they do not represent long-term toxicity, therefore the risk characterisation is best understood by determining a PNEC with the equilibrium partitioning method.

In the absence of definitive long-term test, a PNECsediment can be calculated from the PNECaquatic by the equilibrium partitioning method. Any requirement for further testing will be determined on the basis of the outcome of the risk characterisation carried out in accordance with Annex I.

In accordance with Column 2 of REACH Annex X, there is no need to further investigate the effects of this substance to sediment dwelling organisms because, as indicated in guidance R.7b (Section R.7.8.14) (ECHA, 2017), the quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio is below 1, therefore the risk is already adequately controlled and further testing is not justifiable.

An additional factor of 10 is applied to the screening assessment when undertaking risk characterisation based on equilibrium partitioning PNEC for sediment for substances which have log Kow >5. This is to account for additional exposure via ingestion of adsorbed substance on particles and it is therefore scientifically appropriate to consider making a similar adjustment for substances which have binding or adsorption properties indicating highly adsorbing behaviour, equivalent to a high log Kow. Phosphonates are highly adsorbing even though the log Kow value is extremely low, as discussed in IUCLID Section 5.4. In view of the tendency to bind irreversibly to the inorganic substrate; the generalised lack of uptake and rapid clearance from the body associated with oral exposure, and low bioaccumulation potential, these are strong arguments against a need to make such an adjustment to RCR values. On this basis, the extra factor of 10 is not applied in this assessment.

The substance is involatile and highly adsorbing and low toxicity was observed in short and long-term aquatic tests, and there is no reason to expect effects in the sediment compartment that were not expressed in the aquatic compartment. The phosphonate ligand binds strongly and irreversibly to various minerals present in sediment and so bioavailability to sediment organisms is extremely limited. The PNEC calculated by Equilibrium Partitioning has been derived for the purpose of conducting a chemical safety assessment, and the risk characterisation ratios are below 1. Furthermore, no effects were observed in a short-term exposure of Corophium spp. up to the highest tested concentration (2500 mg active acid/L), indicating low toxicity to sediment organisms. Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6.0 Ecotoxicological Information and Chapters 9 and 10 of the Chemical Safety Report, respectively.

The acid and salts in the DTPMP category are freely soluble in water and, therefore, the DTPMP anion is fully dissociated from its cations when in solution. Under any given conditions, the degree of ionisation of the DTPMP species is determined by the pH of the solution. At a specific pH, the degree of ionisation is the same regardless of whether the starting material was DTPMP-H, DTPMP (1-3Na), DTPMP (5-7Na), DTPMP (4-8K), DTPMP (xNH4) or another salt of DTPMP.

 

Therefore, when a salt of DTPMP is present in test media or the environment, the following is present (separately):

1. DTPMP is present as DTPMP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the media and not whether DTPMP-H, DTPMP (1-3Na), DTPMP (5-7Na), DTPMP (4-8K), DTPMP (xNH4), or another salt was used for testing.

2. Disassociated ammonium, potassium or sodium cations. The amount of ammonium, potassium or sodium present depends on which salt was added.

3. Divalent and trivalent cations have much higher stability constants for binding with DTPMP than the sodium, potassium or ammonium ions so would preferentially replace them. These ions include calcium (Ca2+), magnesium (Mg2+) and iron (Fe3+). Therefore, the presence of these in the environment or in biological fluids or from dietary sources would result in the formation of DTPMP-dication (e.g. DTPMP-Ca, DTPMP-Mg) and DTPMP-trication (e.g. DTPMP-Fe) complexes in solution, irrespective of the starting substance/test material.

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