Registration Dossier

Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Additional information

Setting the PNECadd soil.

1. Sources of ecotoxicological data

In the EU risk assessment on zinc, an extensive analysis was made of the available terrestrial toxicity data, available at that time (ECB 2008). The data were carefully scrutinised for quality and relevancy by the Rapporteur and member states. In the present exercise, all data that were considered useful for deriving the PNEC soil in the risk assessment, are used. In addition, an update of the terrestrial toxicity data that became available after the closure of the EU RA, has been made. Based on this update, the PNEC derivation for Zn in soils has been revised. This PNEC derivation is now based on the data and bioavailability models presented in the Risk Assessment Report (RAR) for Zn under the existing substances regulation, the comments of the SCHER on this RAR and new reliable data not yet included in the RAR.

All toxicity data judged reliable and relevant in the RAR for Zn are included (171 NOEC or EC10 values). On March 2 2010, an additional literature search was performed covering the scientific literature since 2000 for new reliable toxicity data for Zn on terrestrial organisms (plants, invertebrates and micro-organisms). This new data search resulted in 43 new NOEC or EC10 values.

 

2. Selection of ecotoxicological data

The toxicity data on invertebrates and plants are from single-species tests that study common ecotoxicological parameters such as survival, growth and/or reproduction. The toxicity data on micro-organisms are from tests in which microbe-mediated soil processes, such as C- and N- mineralisation were studied. These microbial toxicity tests are multiple species tests because these microbe-mediated processes reflect the action of many species in soil microbial communities.

Relevance

Biological relevancy

The toxicity data on terrestrial organisms are from ecotoxicity tests that study relevant ecotoxicological parameters such as survival, growth, reproduction, litter breakdown, abundance. Relevant endpoints for soil micro-organisms focused on functional parameters (such as respiration, nitrification, mineralisation) and microbial growth, but also enzymatic processes are considered relevant.

Relevancy of the test media

Only data from observations in natural and artificial (OECD) soil media have been used in this report, tests performed in substrates that were judged as not representative for soils (e.g. nutrient solution, agar, pure quartz sand and farmyard manure) were not included in this effects assessment.

The data used in the effect assessment should be based on organisms and exposure conditions relevant for Europe. Excluding all data derived in non-EU soils would, however, considerably reduce the amount of data to be used. Therefore, also data based on soils collected outside Europe have been used when the soil properties were within the representative range for Europe.

Test duration

What comprises “chronic exposure” is a function of the life cycle of the test organisms. A priori fixed exposure durations are therefore not relevant. The duration should be related to the typical life cycle and should ideally encompass the entire life cycle or, for longer-lived species the most sensitive life stage. Retained exposure durations should also be related to recommendations from standard ecotoxicity (e.g. ISO, OECD, ASTM) protocols.

Typically chronic test duration for the higher plants are within the range of 4 (e.g. the barley root elongation test based on ISO 11269-1 (1995)) and 21 days (e.g. the tomato shoot yield test based on ISO 11269-2 (1995)). OECD n° 208 (plant seedling emergence and growth test, 1984) recommended a test duration of at least 14 days after emergence of the seedlings. For soil invertebrates, assessing the chronic effects of substances on sub-lethal endpoints such as reproduction on oligochaetes has a typical exposure duration of 3 to 6 weeks for the standard organism Enchytraeus albidus (OECD, 2000; ISO 16387). For another standard species Folsomia candida survival and reproduction is typically assessed after 28 days of exposure (ISO 11267, 1999). Reported test duration using soil micro-organisms vary largely but standard tests last 28 days for carbon transformation (OECD n° 216) and for nitrogen transformation (OECD n° 217).

 

Reliability

Type of test

Both standard test organisms and non-standard species can be used in the framework of a risk assessment. In general, toxicity data generated from standardized tests, as prescribed by organizations such as OECD and USEPA will need less scrutiny than non-standardized test data, which will require a more thorough check on their compliance with reliability criteria before being used. GLP and non-GLP tests can be used provided that the latter fulfil the stipulated requirements.

Concentration-effect relationships

Because effect concentrations are statistically derived values, information concerning the statistics should be used as a criterion for data selection. If no methodology is reported or if values are ‘visually’ derived, the data were considered unreliable. Effect levels derived from toxicity tests using only 1 test concentration always results in unbounded and therefore unreliable data. Therefore, only the results from toxicity tests using 1 control and at least 2 Zn concentrations were retained.

Tests that do not comply with the above-mentioned stipulations are rated as not reliable and are not recommended for use in the risk assessment exercise.

 

3. Derivation of EC10/NOEC values

According to the REACH Guidance on information requirements and chemical safety assessment (Chapter R.10.2.2.1), there is a preference to use EC10 values as calculated from the concentration-effect relationship, for derivation of the Predicted No Effect Concentration (PNEC). In some cases no reliable EC10 can be derived because e.g. no significant dose-response curve can be fitted or the EC10 is outside the concentration range tested. When in these cases a bounded NOEC value can be derived, this NOEC value will be used instead of the EC10 for PNEC derivation. No unbounded NOEC (i.e. no effect at highest dose tested) or LOEC (i.e. significant effect at lowest dose tested) values or EC10 values extrapolated outside the concentration range tested are used for derivation of the PNEC.

 

4. Toxicity data

In accordance to the EU RA, all toxicity data are expressed as added Zn concentration in soil, based on either the nominal dose added or on measured, background corrected soil Zn concentrations.

For plants, in total 45 individual high quality NOEC or EC10 values are selected for the PNEC derivation, representing 18 different species. NOEC or EC10 values vary from 32 mg Zn/kg dw for Trifolium pratense and Vicia sativa (Van der Hoeven and Henzen, 1994) to 5855 mg Zn/kg dw for Triticum aestivum (Warne et al., 2008a).

Information on soil properties allowing bioavailability correction for plants (eCEC and pH) is only available for 31 NOEC or EC10 values, representing 9 different plant species and including the same minimum and maximum values as the total dataset for plants.

In total 61 individual high quality NOEC or EC10 values for reproduction of terrestrial invertebrates are selected for the PNEC derivation. Twenty-four NOEC/EC10 values are available for toxicity of Zn to reproduction of terrestrial arthropods, representing 2 different species and ranging between 14.6 and 1000 mg Zn/kg dw (both for Folsomia candida; Lock and Janssen, 2001c and Lock et al., 2003). The other 37 NOEC or EC10 values cover 6 different worm species and vary from 35.7 mg Zn/kg for Enchytraeus albidus (Lock and Janssen, 2001c) to 1634 mg Zn/kg dw for Lumbricus terrestris (Spurgeon et al., 2000).

For all 61 reliable toxicity thresholds, the information on soil properties allowing bioavailability correction for plants (eCEC) is available.

For microbial assays, in total 108 individual high quality NOEC/EC10’s are selected for the PNEC derivation. These values represent 4 nitrogen transformation processes, 5 carbon transformation processes and 8 enzymatic processes and range from 17 mg Zn/kg dw for respiration (Chang and Broadbent, 1981 and Lighthart et al., 1983) to 2623 mg Zn/kg dw for phosphatase (Doelman and Haanstra, 1989).

Information on the background Zn concentration, allowing correction for differences in bioavailability among soils, is only available for 76 NOEC or EC10 values, representing 13 microbial processes (4 for N cycle, 5 for C cycle and 4 enzymatic processes). The total range in NOEC/EC10 values for the dataset with results for background Zn concentration is the same as for the total dataset for micro-organisms.

 

5. Calculation of the HC5-50

The available ecotoxicity database for the effect of Zn to soil organisms is large. Therefore, the use of the statistical extrapolation method is –as specified by the Guidance document on information requirements and chemical safety assessment Chapter R.10.3.1.3– preferred for PNEC derivation rather than the use of an assessment factor on the lowest NOEC. The PNEC will be based on the 50% confidence value of the 5th percentile value (HC5-50) and an additional assessment factor taking into account the uncertainty on the HC5-50 (thus PNEC = HC5-50/AF).

 

5.1. Generic, non-normalised HC5-50

The non-normalised terrestrial HC5-50 was derived based on either all individual reliable NOEC/EC10 values or the species mean NOEC/EC10 values for the most sensitive endpoint. The generic PNEC was derived from using all data. For comparison, distributions where only the data that could be normalised for bioavailability, were also made.

It must be stressed that, considering the important influence of soil properties on bioavailability and toxicity of zinc in soils, the non-normalised HC5-50 is less ecologically relevant compared to the HC5-50 values taking into account correction for bioavailability (both ageing and effect of variation in soil properties). The cumulative frequency distribution (SSD) of the non-normalised species mean NOEC values for Zn is presented in the CSR.

Using statistical extrapolation and the log-normal distribution results in a HC5-50 of 35.6 mg Zn/kg based on all individual NOEC/EC10 data and a HC5-50 of 33.7 mg Zn/kg when using all individual NOEC/EC10 data with information on soil properties allowing correction for bioavailability among soils (Table 1). Based on the Anderson-Darling goodness-of-fit statistics, the log-normal distribution is accepted for all distributions based on both all individual reliable observations and the species/process mean values.

 

Table 1:Generic HC5 and HC5-50 (with 5% and 95% confidence interval) values for toxicity of Zn to the terrestrial environment based on a log-normal distribution of non-normalised NOEC/EC10addedvalues.

Scenario

All individual NOEC/EC10 values

Species/process mean values

 

N

HC5

(mg Zn/kg)

HC5-50

(mg Zn/kg)

N

HC5

(mg/kg)

HC5-50

(mg Zn/kg)

All data

214

35.6

35.6

(29.1-42.5)

43

51.9

51.3

(34.7-69.4)

Data allowing bioavailability correction

168

33.8

33.7

(26.8-41.2)

30

36.5

35.8

(20.4-54.0)

 

Using a species/process mean approach for non-normalised data yields higher HC5-50 values compared to SSD based on all individual values: 51.3 and 35.8 mg Zn/kg for the total dataset or the data with information on soil properties allowing correction for bioavailability among soils, respectively. Averaging (geomean) all the results available for one species/process avoids over-representation of commonly tested species or processes, e.g.Eisenia fetida (29 data) or nitrification (20 data). This species/process mean approach is preferred for data corrected for the differences in soil properties when the intra-species variation can be considered as the main source of variation among data for a given species/process. However, this is not the case for the generic approach (non-normalised data) where variation between toxicity data for a certain species or process is also caused by differences in bioavailability among soils.

 

Table 2:Generic species/process mean values.

All data

Data allowing bioavailability correction

 

Species/microbial process

Mean NOEC/EC10

 

Species/microbial process

Mean NOEC/EC10

 

 

mg Zn/kg

 

 

mg Zn/kg

1

Vicia sativa

32

1

Vicia sativa

32

2

Trifolium pratense

45

2

Hordeum vulgare

33

3

Denitrification

62

3

Denitrification

39

4

Glutamic acid mineralization

64

4

Trifolium pratense

45

5

Nitrate reductase

67

5

Glutamic acid mineralization

55

6

Urease

72

6

Urease

73

7

Respiration

89

7

Zea mais

83

8

Hordeum vulgare

89

8

Respiration

83

9

Enchytraeus albidus

94

9

Enchytraeus albidus

94

10

Vigna mungo L.

100

10

Nitrification

120

11

Nitrification

120

11

Sinella curviseta

180

12

Dehydrogenase

128

12

Dehydrogenase

195

13

Sorghum bicolor

141

13

Allium cepa

200

14

Zea mais

171

14

Avena sativa

200

15

Sinella curviseta

180

15

Trigonella poenum graceum

200

16

N-mineralization

185

16

Glucose mineralization

204

17

Triticum vulgare

200

17

N-mineralization

211

18

Spinacea oleracea

200

18

Maize residue mineralization

241

19

Avena sativa

200

19

Folsomia candida

246

20

Allium cepa

200

20

Eisenia fetida

284

21

Trigonella poenum graceum

200

21

Brassica rapa

300

22

Amidase

200

22

Acetate mineralization

303

23

Glucose mineralization

204

23

Eisenia andrei

320

24

Maize residue mineralization

241

24

Aporrectodea caliginosa

342

25

Folsomia candida

246

25

Arylsulphatase

406

26

Eisenia fetida

284

26

Lumbricus terrestris

520

27

Medicago sativa

300

27

Triticum aestivum

584

28

Beta vulgaris

300

28

Phosphatase

826

29

Brassica rapa

300

29

Ammonification

1000

30

Acetate mineralization

303

30

Lumbricus rubellus

1634

31

Eisenia andrei

320

 

 

 

32

Aporrectodea caliginosa

342

 

 

 

33

Arylsulphatase

378

 

 

 

34

Lactuca sativa

400

 

 

 

35

Pisum sativum

400

 

 

 

36

Lycopersicon esculentum

400

 

 

 

37

Phosphatase

444

 

 

 

38

Lumbricus terrestris

520

 

 

 

39

Triticum aestivum

584

 

 

 

40

Phytase

590

 

 

 

41

Ammonification

1000

 

 

 

42

Lumbricus rubellus

1634

 

 

 

43

Pyrophosphatase

1640

 

 

 

 

There is no clear distinction among the three trophic levels (plants, invertebrates and micro-organisms) in their sensitivity to Zn in soil (Table 2). Both individual and species/process mean toxicity data for the various plant and invertebrates species and microbial processes strongly overlap (see CSR for figures). Therefore, all data are pooled together into one species sensitivity distribution for the derivation of the PNEC value. In this respect, it is also noted that the EU Scientific Committee for Health and Environmental Risks (SCHER) also recommended to merge the different data sets obtained on plants, arthropods, and microbial functions, respectively (SCHER 2007).

 

For 46 NOEC or EC10 values, no information is available on soil properties allowing correction for differences in bioavailability among soils (CEC and pH for plants and background Zn concentration for microbial processes). The toxicity data with information on these soil properties available cover 30 species/processes compared to a total of 43 for the total dataset. Toxicity data for 9 plant species and 4 microbial processes (all enzymatic processes) do not have information on the soil properties required. The reduced dataset however still covers the same extreme values (both minimum and maximum) as the total dataset (Table 2). The HC5-50 values as calculated from a log-normal distribution are consistently lower for the reduced dataset compared to the total dataset (both based on all individual values as based on species/process mean values, Table 1). It can therefore be concluded that the dataset with information on soil properties is both representative for the total dataset and conservative for the assessment of toxicity of Zn to terrestrial organisms.

6. PNECadd soil

Based on an extensive uncertainty analysis (CSR), and in particular the availability of normalisation models (CSR), a large toxicity database covering a representative range in plant and invertebrate species, microbial processes and soil conditions, and an extensive field validation, it can be concluded that the available database and models allow for the derivation of an HC5-50 that is protective for the terrestrial environment by statistical extrapolation.

3 types of PNECadd soil can be considered:

- The generic PNECadd based on the entire ecotoxicity database is 35.6 mg Zn/kg.

-The generic PNECadd can (in accordance with the EU risk assessment) be multiplied with a default “lab-to-field” correction factor of 3 for taking into account differences of zinc bioavailability after ageing (generic PNECadd including ageing= 107mg/kg dw.)

-If information on soil type and soil conditions is available, a soil-specific PNECaddedcan be calculated, by applying a further correction for bioavailability. A tool is available for this. For illustration, some examples were developed in the present analysis resulting in PNECaddedvalues for soil types representative for the EU conditions between approx. 30 and 300mg Zn/kg.