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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Reference
Endpoint:
bioaccumulation in aquatic species: fish
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study carried out according to official guidelines and GLP.
Qualifier:
according to
Guideline:
OECD Guideline 305 E (Bioaccumulation: Flow-through Fish Test)
Principles of method if other than guideline:
"Bioconcentration Test of Chemical Substance on Fish" provided in "Test method on new chemical subsatnce" (Kan-Ho-Gyo No. 5, Yaku-Hatu No. 615, 49 Ki-Kyoku No. 392, July 13, 1974, revised October 8, 1998) and "Bioconcentration: Flow-through Fish Test (Guideline 305, June 14, 1996" provided in "OECD Guidelines for Testing of Chemicals".
GLP compliance:
yes
Radiolabelling:
yes
Vehicle:
yes
Test organisms (species):
Cyprinus carpio
Details on test organisms:
Size 5.8-7.4cm
Route of exposure:
aqueous
Test type:
flow-through
Water / sediment media type:
natural water: freshwater
Total exposure / uptake duration:
28 d
Test temperature:
Concentration Level 1: 25.0 - 25.2 degrees C
Concentration Level 2: 25.0 - 25.2 degrees C
Control: 25.0 - 25.5 degrees C
pH:
Concentration Level 1: 7.2 - 7.5
Concentration Level 2: 7.2 - 7.4
Control: 7.2 - 7.4
Dissolved oxygen:
Concentration Level 1: 7.4 - 7.6 mg/l
Concentration Level 2: 7.2 - 7.6 mg/l
Control: 7.3 - 7.9 mg/l
Details on test conditions:
Water media type: Tap water of Tokyo laboratory treated through activated carbon filtration. The water was analysed and quality shown to meet the standards required for the toxicity test (full details supplied).

The master solution was delivered to the test vessel (at a rate of 0.04ml/min) simultaneously with test water (delivered at 400ml/min). This gave a total of 576 L/day delivered to the test vessel (capacity 50L).
Nominal and measured concentrations:
nominal concentration level 1: 0.8 microgram/l
nominal concentration level 2: 0.08 microgram/l
Lipid content:
4.52 %
Time point:
end of exposure
Type:
BCF
Value:
92
Calculation basis:
steady state
Remarks on result:
other: Conc.in environment / dose:0.8 micrograms/l
Type:
BCF
Value:
200
Calculation basis:
steady state
Remarks on result:
other: Conc.in environment / dose:0.08 micrograms/l
Details on results:
Test concentration level 1 0.8 microgram/l
BCF: 92

Test concentration level 2 0.08 microgram/l
BCF: 200

Results indicate low potential for bioaccumulation however it should be noted that liquid scintillation counting was the method of analysis for all water and fish samples and no analysis of 4,4'-MDI itself was carried out during the course of the study.

Conclusions:
MDI is virtually unavailable in aqueous solution, and in consequence no bioaccumulation of the substance is expected. The bioconcentration of 4,4’-MDI has been evaluated in this study, using flow-through exposures of 0.8 and 0.08 ug/L MDI. Whereas the analytics (liquid scintillation counting) for this study are suspect due to the expected reactivity of MDI in water and fish tissues, steady state bioconcentration factors (BCFss) of 92 and 200 are reported for these respective MDI exposure concentrations. Using a similar test procedure with (Cyprinius carpio), no measureable bioconcentration of the 4,4'-MDA substance, present at only low concentrations from reaction of MDI with water, was observed. Based on the exposure concentration (0.2 and 0.02 mg/L) and analytical detection limits for water and fish tissues, BCF values of 3-14 and <3-15 (respectively) were reported for these MDA exposures. (EU Risk Assessment Report 4,4’-methylenedianiline).

Description of key information

Due to the high reactivity of the substances of the MDI category with water, bioaccumulation tests can in principle not be performed with these substances.

However, one bioaccumulation test (OECD 305E) with 4,4-MDI and a mesocosm study with PMDI with an indication of bioaccumulation potential have been performed. As no analytical measurements were done, it cannot be determined if the values are truly related to MDI. However, based on the available information and the reactivity of MDI substances of the category approach, no new bioaccumulation study is deemed necessary.

Key value for chemical safety assessment

BCF (aquatic species):
200 dimensionless

Additional information

The test substance is covered by the category approach of methylenediphenyl diisocyanates (MDI). Hence, data of the category substances can be used to cover this endpoint. The read-across category justification document is attached in IUCLID section 13. It is important to note that the MDI category approach for read-across of environmental and human hazards between the MDI substances belonging to the MDI category is work in progress under REACH. Therefore the document should be considered a draft.

It is recognised that there is a measured log Pow value of 4.51 for monomeric MDI. This log Pow value is only of theoretical interest as MDI is very unstable in aqueous media (hydrolysis half-life T1/2 = 20h), see Section 5.1.2: Hydrolysis). The determination was by an HPLC method and comparison to reference chemicals.

A BCF study (CERI, 2002) carried out according to guideline principles with [14C] radiolabelled 4,4’-MDI and Cyprinus carpio, derives BCF values of 92 and 200 for concentrations of 0.8 and 0.08 µg MDI/L. The reported BCF values are highly questionable given the known rapid hydrolysis of MDI under these conditions. Liquid scintillation counting was the method of analysis for all water and fish samples and no analyses of 4,4’-MDI itself were carried out during the course of the study. A BCF value of 200 indicates low potential for bioaccumulation, but it must be recognised that this value probably reflects the bioconcentration of water soluble hydrolysis products which most likely include 4,4’-MDA and low molecular weight ureas. So it can be concluded that degradation products of MDI do not bioaccumulate.

MDI reacts with water to form predominantly high molecular weight, inert polyureas and trace amounts of 4,4’-methylenedianiline (MDA). This MDA is considered as the only degradation product of significance, and it has a log Pow value of 1.55. Its measured BCF is < 14 (at 0.2 mg/L) in Cyprinus carpio (EU Risk Assessment Report: 4,4’-methylenedianiline, 2001). So, it is concluded that degradation products of MDI do not bioaccumulate.

There is a mesocosm study on PMDI (Heimbach 1993, PMDI dossier 6.1.2a) study, carried out over 112 days, at a loading of 10,000 mg PMDI/L. MDI was detected neither in the water (detection limit 0.005 mg/L) nor in fish (detection limit 0.51 mg/kg). A numeric BCF can not be calculated from these non-detects, but clearly these results show in a practical way that MDI does not accumulate in fish.

Lastly, a BCF value of 439 for 4,4’-MDI may be estimated using the BCFBAFTM (v 3.00) model, a part of the Estimation Program Interface Suite (v.4.00, 2009) of QSAR tools. An estimated BCF value of 439 for 4,4’-MDI suggests a low potential for bioaccumulation. This is in line with the low bioaccumulation value found in the bioaccumulation study and in the mesocosm study.

To summarise, a new bioaccumulation study is not deemed necessary due to rapid hydrolysis (resulting in unlikely exposure) of substance of the MDI category. Supporting data including a mesocosm study, modelling and assessment of degradation products, all indicate no potential for significant bioaccumulation in the aquatic environment.