Disilver oxide

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.046 µg/L

Assessment factor:

3

Extrapolation method:

sensitivity distribution

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.86 µg/L

Assessment factor:

10

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

0.025 mg/L

Assessment factor:

1

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

438.13 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

438.13 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

assessment factor

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

1.05 mg/kg soil dw

Assessment factor:

3

Extrapolation method:

sensitivity distribution

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

See CSR Annex 4 - PNEC Summary Report

Conclusion on classification

In the below table, the ERV values, TDp data (where applicable) and derived classifications (incl. M-factors) for silver compounds are summarised. Molecular weight of silver is 107.87.

Table 1: Basis for environmental classification of silver compounds, including reference to relevant figures/tables in CLP guidance (ECHA 2017).

Acute ERV = 0,00022 mg Ag/L

Chronic ERV = 0,0001 mg Ag/L

	Ag2O	AgNO3	AgCl	AgBr	AgI	Ag2SO4	Ag2CO3
MW (g)	231,74	169,87	143,32	187,77	234,77	311,8	275,75
classify as…	insoluble	soluble	soluble	soluble	soluble	soluble	soluble
TDp(7d;1 mg/L) in mg/L	0,053	/	/	/	/	/	/
TDp(28d;1 mg/L) in mg/L	0,062	/	/	/	/	/	/
TDp(28d;0.1 mg/L) in mg/L	0,0062*	/	/	/	/	/	/
Acute ERV (substance basis; mg/L)	0,00047	0,00035	0,00029	0,00038	0,00048	0,00064	0,00056
Chronic ERV (substance basis; mg/L)	0,00021	0,00016	0,00013	0,00017	0,00022	0,00029	0,000256
Acute classification	Acute 1	Acute 1	Acute 1	Acute 1	Acute 1	Acute 1	Acute 1
Chronic classification	Chronic 1	Chronic 1	Chronic 1	Chronic 1	Chronic 1	Chronic 1	Chronic 1
Acute M	100	1000	1000	1000	1000	1000	1000
Chronic M	10	100	100	100	100	100	100
*assuming 10x lower dissolution
Reference in CLP Guidance version 5.0 (July 2017)
Basis for classification - acute	Fig IV.4	Fig IV.4	Fig IV.4	Fig IV.4	Fig IV.4	Fig IV.4	Fig IV.4
Basis for classification - chronic	Fig IV.5	Fig IV.5	Fig IV.5	Fig IV.5	Fig IV.5	Fig IV.5	Fig IV.5
Basis for M acute	ratio TDp(7d;1mg/L) / ERV(acute)	Table IV.1	Table IV.1	Table IV.1	Table IV.1	Table IV.1	Table IV.1
Basis for M chronic	ratio TDp(28d;0.1mg/L) / ERV(chronic)	Table IV.1	Table IV.1	Table IV.1	Table IV.1	Table IV.1	Table IV.1

Acute and chronic ERV values for the silver ion 

Acute and chronic aquatic toxicity data are available for a range of different freshwater and marine species. For silver metal and silver compounds, the acute ecotoxicity reference value (ERV) is 0.22 µg Ag/L and the chronic ERV is 0.1 µg Ag/L.

In line with the risk assessment/classification approach adopted for other metals and inorganic metal compounds (ECHA 2017), ecotoxicity data are reported in terms of the concentration of dissolved silver ions from soluble inorganic silver species. Predominantly, these are studies that used silver nitrate (AgNO₃) as the source of dissolved silver ions. Silver nitrate is considered as the silver substance with the greatest toxicity as it dissociates rapidly and completely in aqueousmedia. Where data for silver nitrate was not available, data derived from other inorganic silver salts (e.g. silver chloride) were used, but only after the exposure conditions were determined to be acceptable (e.g. testing was conducted within the limits of solubility and the Ag+ ion was likely to be the dominant dissolved species).

A complete base set of acute ecotoxicity studies is available for soluble inorganic silver species, comprising numerous studies for fish, invertebrates and algae. The lowest reliable acute value is an EC50 of 0.22 µg Ag/L for the invertebrateDaphnia magna(pH 8.2, total organic carbon <0.1 mg/L; Bianchini et al. 2002).

A complete chronic data set is also available for soluble inorganic silver species, with chronic ecotoxicity data available for various species of fish, invertebrates and algae. The lowest reliable chronic value is an EC10 of 0.1 µg Ag/L for the algaePseudokirchneriella subcapitata(pH 7.2-8.5, DOC 0.38-0.88 mg/L; Fraunhofer 2017). Additional chronic toxicity data of similar sensitivity are also available forIsonychia bicolor(14-day NOEC of 0.16 µg Ag/L; Diamond et al, 1990),Salmo trutta(217-day EC10 of 0.23 µg Ag/L; Davies et al, 1998) andBrachionus calyciflorus(EC10 of 0.31 µg Ag/L; Arijs et al. 2021).

CONCLUSION: for the silver ion, the Acute ERV = 0.22 µg Ag/L and the Chronic ERV = 0.1 µg Ag/L.

Poorly soluble silver compounds: environmental classification

The classification and labelling guidance states that if the solubility of a metal compound is greater than the L(E)C50 then it should be classified for acute and chronic hazard based on the available ecotoxicity data and the standard classification criteria. On 10th March 2011, Commission Regulation (EC) No 1272/2008 [CLP Regulations] was amended for the second time. The acute environmental classification is still based on acute data. However, the chronic environmental classification is now based on a chronic data set, if this is available. A complete chronic data set is available for silver and silver compounds.

The Guidance on the Application of the CLP Criteria describes the method that compares both acute and chronic ecotoxicity data with the results from Transformation / Dissolution tests and details how to calculate acute and chronic M-factors.

For silver and silver compounds, the acute ecotoxicity reference value (ERV) is 0.22 µg Ag/L and the chronic ERV is 0.16 µg Ag/L. The solubility of disilver oxide has been measured in a full Transformation / Dissolution test (CIMM 2009) which gave results of 52.51 µg/L after 7 days (sample loading of 1 mg/L) and 62.03 µg/L after 28 days (sample loading of 1 mg/L). If extrapolated and assuming linear behavior (i.e. 10x lower dissolution), the value after 28 days at a hypothetical sample loading of 0.1 mg/L is calculated as 62.03/10 = 6.2 µg/L.

The solubility of disilver oxide is greater than the ecotoxicity reference values and therefore, the classification for acute and chronic hazard is based on the available ecotoxicity data. As the acute ERV is <1 mg/L, disilver oxide meets the criteria for classification as aquatic acute category 1. As the chronic ERV is <0.1 mg/L, disilver oxide also meets the criteria for aquatic chronic category 1.

Under the CLP Regulations, M-factors must be assigned to substances classified as acute category 1 and/or chronic category 1. The Guidance on the Application of the CLP Criteria (ECHA, 2017) describes how to determine the appropriate M-factor for poorly soluble substances. The results from the Transformation / Dissolution tests at 7 days (at 1 mg/L) and 28 days (at 0.1 mg/L) are compared to the ecotoxicity reference value (ERV) to derive the appropriate M factor.

The M-factors for disilver oxide are derived from the ratio of the soluble metal ions concentrations obtained from Transformation / Dissolution (at respectively 7 days or 28 days) and the corresponding ERV (on a substance basis). For acute effects the ratio is 111 (= 52.5 / 0.472), for chronic effects the ratio is 29 (=6.20/0.22) (rounded values). The corresponding M-values then become M(acute) = 100 and M(chronic) = 10.