Zinc selenite

Endpoint summary

Description of key information

In accordance with the EU risk assessment, and in a same approach as for aquatic ecotoxicity, the soluble zinc ion is considered as the toxic entity for zinc substances in this section on soil. Consequently, the analysis below is relevant for all zinc compounds.

It is noted that the scope of the terrestrial effect 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 to substances via the soil pathway. Reliable chronic toxicity data are available for the long-term effect of zinc on 35 terrestrial species or microbial endpoints covering the 3 trophic levels (12 terrestrial plants, 10 invertebrates and 13 microbial endpoints). A total of 220 reliable EC₁₀ and NOEC values, ranging between 31.2 and 8003.5 mg Zn/kg dry weight (dw), were selected for derivation of a PNEC value. All results were derived for soluble zinc substances (Zn(CH₃COO)₂, ZnCl₂, Zn(NO₃)₂ or ZnSO₄, including hydrated forms).

The bioavailability and toxicity of zinc 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 effective cation exchange capacity (eCEC = CEC at pH of the soil) and higher pH of the soil. Toxicity to terrestrial invertebrates decreased with higher eCEC and toxicity to microbial endpoints decreased with higher background Zn concentrations in 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 without correction for bioavailability vary between 37 mg Zn/kg for reproduction of the invertebrate Enchytraeus doerjesi and 1246 mg Zn/kg for microbial dehydrogenase activity. 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, eCEC of 10 cmol_c/kg and 25 mg Zn/kg, species or process mean values vary between 79 mg Zn/kg for reproduction of the invertebrate Enchytraeus doerjesi and 8948 mg Zn/kg for microbial dehydrogenase activity.

 

Table1. Overview of the selected chronic soil toxicity values for zinc selected forthePNEC derivationfor toxicity of inorganic zincto terrestrial organisms (based on total Zn concentrations).

Test organism	Taxonomic group	Endpoint	Original NOEC or EC10values, not corrected for bioavailability (mg Zn/kg dw)		NOEC or EC10values corrected for differences between laboratory and field conditions and normalized to the same soil properties* (mg Zn/kg dw)
			Range (and amount)	Species or process mean	Range (and amount)	Species or process mean
Plants
Allium cepa	Amaryllidaceae(monocotyledon)	Yield	220 (n=1)	220	328 (n=1)	328
Avena sativa	Poaceae(monocotyledon)	Grain yield	238 – 702 (n=4)	374	447 – 1983 (n=4)	1046
Brassica rapa	Brassicaceae(eudicotyledon)	First bloom	546 – 549 (n=2)	547	341 – 594 (n=2)	450
Cucumis sativus	Cucurbitaceae(eudicotyledon)	Shoot yield	179 – 5213 (n=10)	782	326 – 7953 (n=10)	1650
Hordeum vulgare	Poaceae(monocotyledon)	shoot yield	91 (n=1)	91*	201 (n=1)	201
		root elongation	937 – 1900 (n=3)	1453	419 – 818 (n=3)	548
Populus trichocarpa	Salicaceae(eudicotyledon)	root yield	272 (n=1)	272	571 (n=1)	571
		root elongation	105 (n=1)	105*	219 (n=1)	219
Lycopersicon esculentum	Solanaceae(eudicotyledon)	shoot yield	174 (n=1)	174	189 (n=1)	189
		root yield	161 (n=1)	161*	174 (n=1)	174
Trifolium pratense	Fabaceae(eudicotyledon)	shoot yield	40 – 135 (n=6)	65	111 – 335 (n=6)	259
		root yield	40 – 115 (n=6)	58*	111 – 335 (n=6)	227
Trigonella foenum graceum	Fabaceae(eudicotyledon)	yield	150 (n=1)	150	217 (n=1)	217
Triticum aestivum	Poaceae(monocotyledon)	shoot yield	245 – 5925 (n=14)	612	528 – 16769 (n=14)	1950
		grain yield	96 – 4779 (n=11)	574	267 – 3187 (n=11)	556
		biomass yield	56 – 2835 (n=8)	362*	105 – 1099 (n=8)	346
Vicia sativa	Fabaceae(eudicotyledon)	shoot yield	108 (n=1)	108	327 (n=1)	327
		root yield	40 (n=1)	40*	111 (n=1)	111
Zea mays	Poaceae(monocotyledon)	shoot yield	253 – 578 (n=2)	382	887 – 908 (n=2)	898
Invertebrates
Aporrectodea caliginosa	Lumbricidae(annelida)	reproduction	302 – 584 (n=2)	420*	352 – 643 (n=2)	476
		mortality	1425 (n=1)	1425	4034 (n=1)	4034
Eisenia andrei	Lumbricidae(annelida)	reproduction	431 (n=1)	431	947 (n=1)	947
Eisenia fetida	Lumbricidae(annelida)	reproduction	99 – 1341 (n=30)	306*	255 – 1759 (n=30)	719
		growth	439 – 736 (n=3)	561	1078 – 1611 (n=3)	1255
		mortality	752 – 932 (n=3)	808	1570 – 2041 (n=3)	1809
Enchytraeus albidus	Enchytraeidae(annelida)	reproduction	90 – 182 (n=3)	130	137 – 398 (n=3)	252
Enchytraeus doerjesi	Enchytraeidae(annelida)	reproduction	32 – 47 (n=3)	37	69 – 103 (n=3)	79
Lumbricus rubellus	Lumbricidae(annelida)	reproduction	461 (n=1)	461	575 (n=1)	575
Lumbricus terrestris	Lumbricidae(annelida)	reproduction	442 (n=1)	442	533 (n=1)	533
Folsomia candida	Isotomidae(arthropoda)	reproduction	31 – 1261 (n=22)	261	115 – 3055 (n=22)	579
Proisotoma minuta	Isotomidae(arthropoda)	reproduction	217 (n=1)	217	1906 (n=1)	1906
Sinella curviseta	Entomobryidae(arthropoda)	reproduction	217 (n=1)	217	282 (n=1)	282
Microorganisms
Natural soil microbial communities	nitrogen transformation	ammonification	1057 (n=1)	1057	1594 (n=1)	1594
	nitrogen transformation	denitrification	84 (n=1)	84	102 (n=1)	102
	nitrogen transformation	nitrification	77 – 697 (n=19)	179	101 – 955 (n=19)	284
	carbon transformation	acetate mineralization	346 (n=1)	346	628 (n=1)	628
	carbon transformation	glutamic acid induced respiration	53 – 494 (n=5)	126	91 – 585 (n=5)	208
	carbon transformation	glucose induced respiration	41 – 1393 (n=16)	269	182 – 3075 (n=16)	486
	carbon transformation	mineralization of dissolved organic carbon	89 – 198 (n=4)	130	134 – 346 (n=4)	213
	carbon transformation	basal respiration	55 – 313 (n=4)	167	278 – 1179 (n=4)	557
	carbon transformation	maize residue mineralization	56 – 1144 (n=11)	249	64 – 1393 (n=11)	324
	enzyme activity	arylsulphatase	120 – 8004 (n=5)	862	188 – 5798 (n=5)	1177
	enzyme activity	dehydrogenase	1246 (n=1)	1246	8948 (n=1)	8948
	enzyme activity	phosphatase	387 – 2727 (n=3)	1128	130 – 5443 (n=3)	1238
	enzyme activity	urease	84 – 689 (n=2)	241	296 – 352 (n=2)	323

* pH 6, 2% organic carbon, 10% clay, eCEC 10 cmol_c/kg and 25 mg Zn/kg

 

Additional information

A quality-screened database on the toxicity of zinc towards soil organisms has been compiled from the Zn RAR (Munn et al. 2010. European Union Risk Assessment Report - Zinc Metal. EUR 24587 EN. Luxembourg (Luxembourg): Publications Office of the European Union. JRC61245. https://op.europa.eu/en/publication-detail/-/publication/111d589d-8f52-442e-8720-c0ed745d2ed3/language-en) and updated with newly retrieved literature data (search 1995-2019). A total of 220 reliablechronic EC₁₀ and NOEC values, ranging between 31.2 and 8003.5 mg Zn/kg dry weight (dw), were selected for derivation of a PNEC value. Reliable chronic toxicity data are available for the long-term effect of zinc on 35 terrestrial species or microbial endpoints covering the 3 trophic levels (12 terrestrial plants, 10 invertebrates and 13 microbial endpoints). Bioavailability corrections for zinc to soil organisms were derived from comprehensive research projects, where various toxicity assays were performed in a range of soils after various spiking treatments. The bioavailability corrections were discussed, agreed and applied in the EU risk assessment on zinc and 5 zinc compounds (Munn et al 2010).

 

Since the available ecotoxicity database for the effect of Zn to soil organisms is large, the use of the statistical extrapolation method is preferred for PNEC derivation. Based on an uncertainty analysis, and in particular the large toxicity database covering a representative range in plant and invertebrate species, microbial processes and soil conditions, the availability of normalization models, an extensive field validation, and the inherent conservatism resulting from the setting of the HC_5,50%value with reference to realistic worst-case conditions of bioavailability (10^th percentile of normalized HC_5,50% values for 4130 soils representative for Europe), it can be concluded that the available database and models allow for the derivation of an HC_5,50% that is protective for the terrestrial environment. The application of an AF = 1 is therefore proposed on the HC_5,50% for the derivation of a robust and ecological relevant PNEC to be retained for the risk characterization.

 

The reasonable worst-case PNEC_soil, based on the 10^th percentile of the distribution of normalized HC_5,50% values for an extensive, representative dataset of European soils, is 83.1 mg Zn/kg. If information on specific soil type and soil conditions is available, a soil-specific PNEC_soil can be calculated, by applying the bioavailability corrections depending on soil properties. To this end, a tool is available that includes all data and bioavailability corrections for Zn, allowing derivation of site-specific PNEC values taking into account the local soil properties (https://www.arche-consulting.be/tools/threshold-calculator-for-metals-in-soil/).