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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
Both the target substance Ferbam and the source substance Ziram quickly hydrolyse forming dimethyldithiocabamates. The analogue hypothesis is that both substances dissociate in acidic and neutral aqueous solutions to the common breakdown product dimethyldithiocarbamate, which determines the (eco-)toxicological properties. Therefore, the basis for this analogue approach is the “(Bio)transformation to common compound(s)” (scenario 1). This scenario covers the analogue approach for which the read-across hypothesis is based on (bio) transformation to common compound(s). For the REACH information requirement under consideration, the effects obtained in a study conducted with one source substance are used to predict the effects that would be observed in a study with the target substance if it were to be conducted. The same type of effect(s) or absence of effect is predicted. The predicted strength of the effects may be similar or based on a worst-case approach (Read-Across Assessment Framework, RAAF, ECHA, 2017).

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
The source substance is Ziram (IUPAC name: zinc bis(dimethyldithiocarbamate , CAS no. 137-30-4; EC no. 205-288-3). Ziram is an organometallic mono-constituent substance with a typical purity of ca. 99% (w/w), ranging from > 98% to 100%. In general, impurities are known and are likely to vary depending on the manufacturing process, but are considered not relevant for classification or labelling of the substance.
The target substance is Ferbam (IUPAC name: N,N-dimethylcarbamodithioate;iron(3+), CAS no. 14484-64-1; EC no. 238-484-2). Also Ferbam is an organometallic mono-constituent substance, with a typical purity of ca. 99% (w/w), ranging from > 98% to 100%. In general, impurities are known and are likely to vary depending on the manufacturing process, but are considered not relevant for classification or labelling of the substance.
The substance identities and all REACH Annex VII and VIII information on physicochemical properties, environmental fate, ecotoxicity and toxicity are summarised in the read-across statement attached under section 13 of this IUCLID file. Both substances are dimethyldithiocarbamates with a central metal. The high structural similarity is also reflected in very similar physicochemical properties. Both substances are primarily used fungicides.

3. ANALOGUE APPROACH JUSTIFICATION
The biodegradation of Ziram in water has been investigated in two screening studies. In a closed bottle test according to OECD TG 301D the biodegradation over 27 days was 3.1%, as determined by oxygen consumption (Monego, 2007), while partial, but acceptable inhibitory effects on the microorganisms were observed. In a CO2 evolution test according to OECD TG 301B Ziram showed inhibitory effects on the microorganisms. The maximum degradation of 7.7% was observed on day 4. Summarising the results, it is concluded that Ziram is not readily biodegradable in water. Due to the similar hydrolysis, the read-across of the studies and their results is justified, as substances are applied in dilution to water. For further information on the justification of the analogue approach please refer to the read-across statement attached under section 13 of this IUCLID file.

4. DATA MATRIX
Please refer to the data matrix in the read-across statement attached under section 13 of this IUCLID file.
Reason / purpose:
read-across source
Oxygen conditions:
aerobic
Inoculum or test system:
natural water
Key result
Parameter:
% degradation (O2 consumption)
Value:
3.1
Sampling time:
27 d
Remarks on result:
other: maximum value

Theoretical oxygen demand (ThOD)

Theoretical oxygen demand is the total amount of oxygen required to oxidize a chemical completely. It is calculated from the molecular formula and is also expressed as mg oxygen required per mg test compound.

The ThOD is calculated if the elemental composition is determined or known (Compound: CcHhClclNnNanaOoPpSs). The following equations are used to calculate the ThOD:

- without nitrification: ThOD = ((16 x (2c + 0.5 (h - cl - 3n) + 3s + 2.5p + 0.5na - o)) / MW

- with nitrification: ThOD = ((16 x (2c + 0.5 (h - cl) + 2.5 + 3s + 2.5p + 0.5na - o)) / MW

where: MW is the molecular weight

Biodegradability

The biochemical oxygen demand (BOD) is calculated after each time period by subtracting the oxygen depletion of the inoculum blank from that exhibited by the test substance. This corrected depletion is divide by the concentration of the test substance to obtain the specific BOD as mg oxygen per mg test substance.

The percentage of biodégradation is calculated dividing the specific BOD by the specific theoretical oxygen demand (ThOD).

BOD (mg O2 / mg test substance) = ((mg O2/L) uptake by test substance - (mg O2/L) uptake by blank) / (test substance amount (mg))

% degradation = ((Specific production (mg O2 / mg test substance) / (ThOD (mg O2 / mg test substance))) x 100

The nitrite and nitrate analysis were performed and the results were lower than the limit of detection (LD = 0.1 mg/L) and lower than the limit of quantitation (LQ = 0.2 mg/L), respectively. In this case, the degradation of the test substance was calculated using the ThOD with nitrification.

Table 1: Dissolved oxygen measurement during exposure of the test.

Dissolved oxygen (mg O2/L)
Test flask Replicate 0 7 14 21 27
Inoculum blank A 8,28 8,23 8,15 8,00 8,06
B 8,26 8,23 7,93 8,02 8,11
Mean 8,27 8,23 8,04 8,01 8,09
Procedure control A 8,29 8,72 6,00 6,17 6,24
B 8,29 8,74 6,41 6,10 6,31
Mean 8,29 8,73 6,21 6,14 6,28
Test suspension A 8,26 8,80 8,06 8,20 8,02
B 8,26 8,80 8,06 8,22 8,01
Mean 8,26 8,80 8,06 8,21 8,02
Toxicity control A 8,27 8,04 5,92 4,75 4,75

Table 2: Specific BOD obtained during the exposure period of the test.

Specific BOD (mg O2 / mg test substance)*
Test flask 0 7 14 21 27
Procedure control 0,00 1,52 1,86 1,90 1,83
Test suspension 0,00 0,00 0,00 0,00 0,00
Toxicity control 0,00 0,19 2,12 3,26 3,34
* The amount of O2 were corrected for the inoculum blank amount.

Table 3: Percentage of degradation during exposure period of the test.

Percentage of degradation**

Test flask

0

7

14

21

27

Procedure control

0,00

51,90

63,40

64,70

62,50

Test suspension

0,00

0,00

0,00

0,00

0,00

Toxicity control

0,00

3,00

33,20

51,00

52,2

** The amount of 02 were corrected for the inoculum blank amount.
Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
It can be observed that when the test substance and the reference substance are in the same flask (toxicity control), Ziram presents firstly some inhibitory effects on the microorganisms but the total degradation of test and reference substance reaches the pass level of 25% degradation based on ThOD at day fourteen, indicating only partial inhibition. The degradation of test substance was 3.1% in the end of the test.
Executive summary:

A 27 days laboratory biodegradability study was conducted to determine the ready biodégradation of Ziram under aerobic condition in water. This study was conducted according the OECD Guidelines for the testing of Chemicals Method 301D "Closed Bottle Test" (1992). A suspension of the test substance in a mineral medium was inoculated and incubated in the dark for 27 days. A reference compound (potassium hydrogen phtalate) and a control of the endogenous activity of the inoculum (inoculum blank) was run parallel to check the operation of the procedures. Also, the possible inhibitory effect of the test substance was checked by adding both test substance and reference substance (toxicity control). The degradation was followed by the determination of dissolved oxygen at several time intervals.

The results from the reference substance and toxicity control reached the maximum degradation values of 64.7% in 21 days and 52.2% in 27 days of the test.

These results showed the activity of the inoculum. Some initial inhibition of the inoculum by the test substance has occured but not in such an extent to prevent degradation of the reference substance.

Description of key information

A 27 days laboratory biodegradability study was conducted to determine the ready biodegradation of Ziram under aerobic condition in water. This study was conducted according GLP and the OECD Guidelines for the testing of Chemicals Method 301D "Closed Bottle Test" (1992).

It can be observed that when the test substance and the reference substance are in the same flask (toxicity control), Ziram presents firstly some inhibitory effects on the microorganisms but the total degradation of test and reference substance reaches the pass level of 25% degradation based on ThOD at day fourteen, indicating only partial inhibition. The degradation of test substance was 3.1% in the end of the test.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

RA-source_Key: Monego, 2008

A 27 days laboratory biodegradability study was conducted to determine the ready biodegradation of Ziram under aerobic condition in water. This study was conducted according the OECD Guidelines for the testing of Chemicals Method 301D "Closed Bottle Test" (1992). A suspension of the test substance in a mineral medium was inoculated and incubated in the dark for 27 days. A reference compound (potassium hydrogen phtalate) and a control of the endogenous activity of the inoculum (inoculum blank) was run parallel to check the operation of the procedures. Also, the possible inhibitory effect of the test substance was checked by adding both test substance and reference substance (toxicity control). The degradation was followed by the determination of dissolved oxygen at several time intervals.

The results from the reference substance and toxicity control reached the maximum degradation values of 64.7% in 21 days and 52.2% in 27 days of the test.

These results showed the activity of the inoculum. Some initial inhibition of the inoculum by the test substance has occured but not in such an extent to prevent degradation of the reference substance.

RA-source_Supporting information: Monego, 2007:

A 28 days laboratory biodegradability study was conducted to determine the ready biodegradability of the test substance Ziram under aerobic condition in water.

This study was conducted according the OECD Guidelines for the testing of Chemicals Method 301B "Ready Biodegradability - C02 Evolution Test" (1992). A suspension of the test substance in a mineral medium was inoculated and incubated in the dark for 28 days. A reference compound (potassium hydrogen phtalate) and a control of the endogenous activity of the inoculum (inoculum blank) was run parallel to check the operation of the procedures. Also, the possible inhibitory effect of the test substance was checked by adding both test substance and reference substance (toxicity control). The degradation was followed by the determination of the C02 evolved at several time intervals. The results from reference substance and toxicity control reached the maximum degradation values of, respectively, 85.9% in 10 days and 37.7% in 4 days of the test. These results shown the activity of the inoculum and that the test substance had inhibitory effects on the microorganisms. For the test substance, the degradation reached the maximum value of 7.7% in 4 days of the test. The test substance Ziram can be classified as a compound not readily biodegradable.