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Information taken from EU-RAR (2008) and SIAP (2008), Nickel and nickel compounds:

As for the aquatic compartment, bioavailability models were used to normalize ecotoxicity data to sets of standard physicochemical conditions. For the soil compartment, relationships between cation exchange capacity (CEC) and chronic nickel toxicity were used to normalize the ecotoxicity data. Appropriate use of normalization of chronic toxicity to soil organisms necessitates that the CEC boundaries of the experimentally derived relationships are defined relative to the environmental conditions considered. Hence data from studies that passed the reliability and relevance criteria in general, but that were conducted on soils that fell outside of this CEC range were not maintained for PNEC derivation. Data from studies that did not report CEC or additional information enabling an estimation of CEC were rejected. Definition of the relevant environmental conditions and the exclusion of otherwise reliable ecotoxicity data relative to these conditions may need to be adapted for other regions.

Extensive chronic soil toxicity data sets exist for soil microbial processes, plants, and invertebrates. More than 250 individual NOEC/EC10 values were screened for quality and relevancy, which resulted in a data set of 173 individual high quality data that covered 42 different species. The selected data set covers 8 different families, different trophic levels and feeding patterns for invertebrates, and microbial activities. Chronic toxicity data for individual species were generated in 16 different soils, enabling a toxicity comparison between soils and the establishment of toxicity soil-type models. This data set is so far the largest data set on a metal for soil.

Effects data set: Data for 12 microbial processes are available, with NOEC/EC10 values range from 28 mg Ni/kg for nitrification to 2,491 mg Ni/kg for respiration. Additional data are available for enzyme activity measured in soil, with NOEC/EC10 values ranging from 7.9 mg Ni/kg for dehydrogenase to 7,084 mg Ni/kg for arylsulfatase activity. Data also exist for the growth of 13 individual microbial species, with EC10 values ranging from 13 mg Ni/kg for Aspergillus clavatus to 530 mg Ni/kg for Trichoderma viride. NOEC/EC10 values are available for 11 plant species, ranging from 10 mg/kg for Spinacea oleracea to 1,127 mg Ni/kg for Hordeum vulgare. Chronic data are available for 6 different species of soil invertebrates, including both soft- and hard-bodied invertebrates. NOEC/EC10 values range from 36 mg Ni/kg for reproduction by the springtail Folsomia candida to 1,140 mg Ni/kg for reproduction by the earthworm Eisenia fetida.

Bioavailability correction: As clear toxicity differences between various soils were observed, bioavailability correction models (7 in total) were established for 2 plant and 2 invertebrate species, and for 3 microbial processes. The toxicity data from the tested soils showed that among the parameters tested, i.e. CEC, pH, organic material (OM), clay and Ni background, the CEC alone consistently explained a large fraction of variability for the 7 species and endpoints tested in the 16 soils (r2 = 0.60 to 0.92). The CEC range is from 1.8 to 52.8 cmol/kg, which covers most soils. Accordingly, the intra-species variability in chronic toxicity to nickel may to a large extent be due to differences in soil chemistry. Hence, to reduce soil-type related impact on the determination of an HC5 (and subsequently the PNEC) for a given soil, all data in the nickel soil ecotoxicity database were normalized to a set of standard soil properties, using the established CEC based models. Although models were established for 7 species, more species were present in the toxicity database. Therefore extrapolation of the normalization model from species with CEC based chronic toxicity models was also performed to species without such a model (cross-species extrapolation, as for the aquatic compartment): for all plants, except L. esculentum which has its own model, a H. vulgare model was used; an E. fetida model was used for all soft-bodied and a F. candida for all hard-bodied invertebrates; for all nitrifying organisms a nitrification model was used, Maize induced respiration was used for all respiration measures and Substance Induced Respiration was used for all microbial biomass measures. Research has demonstrated that chronic toxicity decreases over time, and that the relationship is directly related to pH (i.e., ageing is more pronounced at higher soil pH). The relationship between time (equilibration time, tested for up to 15 months) and chronic toxicity has been demonstrated in 3 soils for the same 7 species/processes for which the soil-type bioavailability models were established. A pH-dependent “ageing factor” has therefore been developed and applied to the toxicity data (cf. also the Zinc SIAR). The purpose of the ageing factor is to place data from laboratory experiments, in which soluble nickel was spiked into test soils, into a field-based context, where the majority of soil-associated nickel has been shown to be in the solid phase. Therefore, the pH-dependent ageing factor is applied prior to CEC normalization.

Ecoregion approach:

As for the aquatic system it was concluded that statistical approaches based on “reasonable worst case” abiotic factor combinations was not relevant. An Ecoregion approach has instead been developed based on 6 reference soil scenarios that represent typical soil conditions. These include agricultural and natural soils that exhibit wide ranges of textures, pH, and CEC. The Ecoregion approach was developed for conditions typically found in EU soils and its applicability for use in other jurisdictions should be evaluated on a case by case basis.

Physico-chemical characteristis for the 6 reference soil scenarios. Soil pH and CEC were used to normalize soil ecotoxicity data for ageing and bioavailability:

Soil type



Organic matter (%)

Clay (%)

CEC (cmol/kg)

Acid sandy soil

Agricultural soil from arable land





Loamy soil

Agricultural soil from

arable land





Peaty soil

Agricultural soil from






Acid sandy soil

Natural soil from

forested land





Clay soil

Natural soil from

wooded land





Different types

Composite of soils


agricultural and

forested land