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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

No reliable studies (Klimisch score 1 or 2) are available for thiourea. However, a new reliable bioaccumulation in aquatic species study does not need to be conducted, as in accordance with column 2 of REACH Annex IX the substance has a low potential for bioaccumulation (log octanol water partition coefficient less than 3). 
This is further supported by two studies (both with reliability score 3) conducted by Geyer et al. (1984) and Freitag et al. (1985) examining bioconcentration in algae (Chlorella) and fish (Leuciscus idus melanotus) after 1 and 3 days, respectively. The BCF (1 d) for the alga Chlorella was determined to be 54. The BCF (3 d) of thiourea for the fish Leuciscus idus melanotus is reported to be < 10.
In addition, the study available in the context of the existing chemicals survey program in CSCL, Japan (NITE) demonstrates a BCF for Cyprinus carpio in the range of < 0.2 to < 2.
Therefore, it can be concluded that thiourea does not have a significant potential for bioaccumulation.

Key value for chemical safety assessment

BCF (aquatic species):
54 dimensionless

Additional information

Studies with a reliability score of 1 or 2 (Klimisch) that might be used in the assessment of thiourea are not available. Nonetheless, a new reliable bioaccumulation study in aquatic species does not need to be conducted, as in accordance with column 2 of REACH Annex IX the substance has a low potential for bioaccumulation (the substance has a log octanol-water partition coefficient less than 3).

However, two studies with a reliability score fo 3 conducted by Geyer et al. (1984) and Freitag et al. (1985), as well as one study rated "4" (NITE) are available that support the waiving argument:

Geyer et al. (1985) exposed algae (Chlorella) with dry weights of 20 mg/200 ml to 14C-labelled thiourea (50 µg/L) in 500 ml Erlenmeyer flasks with glass stoppers in nutrient solution for at least 24 h at room temperature (20-25 °C). The samples were illuminated (16 hours per day) and agitated. After 24 hours the algae suspension was centrifuged (4000 rpm). Algae were removed and a hydroluma scintillation cocktail was used for counting radioactivity in the water sample. The 14C activity in the algae was determined by LSC after combustion (Packard Tri Carb liquid scintillation counter model 3385).

The bioaccumulation factor was calculated as follows:

BCF (1 d) = (c(thiourea) in algae wet weight) / (final chemical concentration in water) [(µg/g algae) / (µg/g water)].

The BCF (1 d) for the alga Chlorella was determined to be 54.

Freitag et al. (1985) determined the bioconcentration of thiourea in the fish Leuciscus idus melanotus via the average constant exposure to the chemical dissolved in water (exclusive uptake through water). The BCF was determined after 3 days of exposure using the following equation:

BCF (3 d) = (concentration of chemical in fish wet weight [µg/g]) / (medium concentration of chemical in water [µg/g])

The BCF of thiourea for the fish Leuciscus idus melanotus is reported to be < 10.

In the context of the "Existing chemicals survey program" in CSCL, Japan (NITE) one study is available where thiourea was tested for its bioaccumulation potential in Cyprinus carpio according to a guideline similar to OECD 305C. The substance was tested at initial concentrations of 0.3 ppm and 3 ppm for six weeks under flow-through conditions.

After six weeks the following results were obtained:

- Initial concentration 0.3 ppm: BCF ≤ 2

- Initial concentration 3 ppm: BCF ≤ 0.2

Due to the information and results presented above, it can be concluded that thiourea does not have a significant potential for bioaccumulation. The highest value of BCF = 54 is used as key value in the risk assessment, following a worst case approach.