Silver chloride

Endpoint summary

Additional information

In line with the risk assessment/classification approach adopted for other metals and inorganic metal compounds (ECHA 2012), terrestrial toxicity information requirements are “read across” from the properties of the soluble silver salts. Almost exclusively these are studies that used silver nitrate (AgNO₃) as the test substance. Silver nitrate is considered to be the form of silver with the greatest toxicity. Where applicable, further justification of the validity of this read-across approach is made in endpoint summaries.

It is noted that the scope of the terrestrial effects assessment under REACH is restricted to soil organisms in a narrow sense, i.e., non-vertebrate organisms living the majority of their lifetime within the soil and being exposed via the soil pathway. Reliable chronic toxicity data are available for the long-term effect of silver on 11 terrestrial species or microbial endpoints covering the 3 trophic levels (4 terrestrial plants, 4 invertebrates and 3 microbial endpoints) (Table 1). A total of 135 reliable EC10 and NOEC values, ranging between 0.3 and 488 mg Ag/kg dry weight (dw), were selected for derivation of a PNEC value. All results were obtained with the soluble silver salt AgNO3. Nitrate is not hazardous to soil organisms. It is a major fertilizer constituent and applied in large amounts on soils without impact on soil organisms. Therefore, it can be safely concluded that all effects observed are caused by the silver ion.

The bioavailability and toxicity of silver to soil organisms was significantly affected by the equilibration time and the properties of the soils tested. Toxicity to soil organisms decreased with longer equilibration time, showing lower toxicity in field conditions compared to standard laboratory settings. Toxicity to terrestrial plants decreased with higher organic carbon content and higher pH of the soil. Toxicity to terrestrial invertebrates and microbial endpoints decreased with higher cation exchange capacity of the soil. Toxicity data were only considered reliable and useful for derivation of a PNEC value when information was available on the relevant soil properties of the test soil, allowing normalization of the EC10 and NOEC. Geometric mean values were derived for the most sensitive endpoint per species or microbial process in case multiple data were available for one species or process. Species or process geometric mean values for the most sensitive endpoint without correction for bioavailability vary between 1.4 mg Ag/kg for microbial ammonium oxidation and 301.7 mg Ag/kg for root growth of Sorghum bicolor (Table 1). After correction for differences between lab and field conditions and normalization to the same soil properties of an example reference soil with pH 6, 2% organic carbon, 10% clay and an eCEC of 10 cmolc/kg, species or process mean values vary between 2.6 mg Ag/kg for biomass of the earthworm Allolobophora chlorotica and 224.1 mg Ag/kg for root growth of Sorghum bicolor.

Table 1. Overview of the chronic soil toxicity values selected for the PNEC derivation for toxicity of silver to terrestrial organisms (based on total Ag concentrations).

Test organism	Taxonomic group	Endpoint*	Original NOEC or EC10values, not corrected for bioavailability (mg Ag/kg dw)		NOEC or EC10values corrected for differences between laboratory and field conditions and normalized to the same soil properties** (mg Ag/kg dw)
			Range (and amount)	Species or process mean	Range (and amount)	Species or process mean
Plants
Hordeum vulgare	Poaceae(monocotyledon)	root elongation	13.0 – 249.0 (n=15)	55.6	34.0 – 201.2 (n=15)	75.6
		shoot elongation	45.0 – 422.0 (n=14)	132.3	37.9 – 486.7 (n=14)	166.0
Lycopersicon esculentum	Solanaceae(eudicotyledon)	shoot biomass	5.3 – 108.0 (n=4)	35.0	19.3 – 98.9 (n=4)	49.3
		shoot biomass (aged)	60.0 – 253.0 (n=2)	123.2	52.7 – 115.8 (n=2)	78.1
		Shoot height	5.2 – 62.0 (n=10)	29.6	18.9 – 94.8 (n=10)	51.6
		Shoot height (aged)	110.0 – 180.0 (n=4)	129.1	41.6 – 210.9 (n=4)	86.8
Phaseolus radiatus	Fabaceae(eudicotyledon)	root length	186.6 (n=1)	186.6	205.5 (n=1)	205.5
		shoot length	298.5 (n=1)	298.5	328.8 (n=1)	328.8
Sorghum bicolor	Poaceae(monocotyledon)	root length	301.7 (n=1)	301.7	224.1 (n=1)	224.1
		shoot length	400.0 (n=1)	400.0	297.2 (n=1)	297.2
Invertebrates
Allolobophora chlorotica	Lumbricidae(annelida)	mortality	35.3 (n=1)	35.3	13.0 (n=1)	13.0
		biomass	7.2 (n=1)	7.2	2.6 (n=1)	2.6
Eisenia fetida	Lumbricidae(annelida)	reproduction	5.5 – 108.0 (n=13)	23.2	2.6 – 114.6 (n=13)	18.4
		growth	6.8 – 221.0 (n=14)	55.5	14.1 – 213.3 (n=14)	52.0
		mortality	5.3 –211.0 (n=19)	70.2	6.6 –381.6 (n=19)	79.4
Enchytraeus crypticus	Enchytraeidae(annelida)	reproduction	11.7 – 38.0 (n=3)	20.1	9.9 – 76.0 (n=3)	30.2
		mortality	52.0 (n=1)	52.0	104.0 (n=1)	104.0
Porcellionides pruinosus	Porcellionidae(arthropoda)	biomass	176.6 (n=1)	176.6	353.1 (n=1)	353.1
		mortality	40.6 (n=1)	40.6	81.1 (n=1)	81.1
Microorganisms
Natural soil microbial communities	nitrogen transformation	potential nitrification rate	1.2 –488.0(n=11)	29.8	6.0 – 57.1 (n=11)	15.7
		substrate induced nitrification	0.3 – 371.0 (n=13)	35.6	0.5 – 91.5 (n=13)	19.0
		potential ammonium oxidation	1.4 (n=1)	1.4	27.7 (n=1)	27.7
	carbon transformation	glucose induced respiration	6.0 – 42.0 (n=2)	15.9	2.0 – 9.8 (n=2)	4.4
		biomass	2.5 (n=1)	2.5	49.5 (n=1)	49.5

* The most sensitive endpoints selected are marked in bold.

** pH 6, 2% organic carbon, 10% clay, eCEC 10 cmol_c/kg.

Since the available ecotoxicity database for the effects of Ag to soil organisms is large, the use of the statistical extrapolation method is preferred for PNEC derivation. Based on an uncertainty analysis, the application of an Assessment Factor of 3 is proposed on theHC_5,50%derived with the statistical extrapolation methodfor the derivation of a robust and ecological relevant PNEC to be retained for the risk characterization.

The reasonable worst-case PNEC_soil, based on the10^thpercentile of the distribution of normalized HC_5,50%values for an extensive, representative dataset of 4116 European soils,is 1.05 mg Ag/kg dry weight.If information on specific soil type and soil conditions is available, a soil-specific PNEC_soilcan be calculated, by applying the bioavailability corrections depending on soil properties.

For full details of the calculated PNEC and the identification and selection of the data see the PNEC summary document attached in IUCLID Section 13.