The Global Symposium on Soil Pollution #GSOP18 | 2 - 4 May 2018 | FAO Hq Mr. Koen Oorts, ARCHE Consulting, Belgium

1. 1
A flexible approach for implementation of
bioavailability into derivation of thresholds for
ecotoxicological effects of metals in soil for
varying protection goals
Koen Oorts and Erik Smolders
GLOBAL SYMPOSIUM ON SOIL POLLUTION
FAO, Rome, Italy
3 May 2018

2. 2
Background
• Metals are among the most widely
studied and regulated substances in
soil
• Wide range in threshold concentrations
for metals in soil
• Many data and bioavailability models
for metal toxicity to soil organisms
developed during last two decades
……..
Bioavaila-
bility
Land use
Protection
goal
Soil
Quality
Standard
Soil type
Species
Goal: a flexible and transparent approach for the
application of the available data and improved
scientific methods for derivation of ecotoxicological
threshold values
=> Threshold calculator for metals in soil

3. 3
0
0.1
0.2
0.3
0 1 2 3 4
Fraction
log soil Cu concentration (mg/kg)
Effect concentrations
(reliable chronic EC10
and NOEC values)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0
0.1
0.2
0.3
0 1 2 3 4
Probabilitydensity
Fraction
log soil Cu concentration (mg/kg)
Effect
concentrations
(reliable chronic
EC10 and NOEC
values)
Cu concentrations
in 0-5 cm of soils
from USA
Cu concentrations
in European
arable soils (0-20
cm)
Threshold
Bioavailability corrections
Without bioavailability corrections: no constant protection level across
soils and risk for soil thresholds for metals within range of background
concentrations

4. 4
Metal Lab-to-field correction factor Soil properties used for
normalization
Cu2+ 2 eCEC, %clay, %OC, pH
Zn2+ 3 eCEC, pH, backgr. Zn
Ni2+ 1-3 (increasing as a function
of pH)
eCEC
Co2+ 1.1-3.5 (increasing as a
function of pH)
eCEC
Pb2+ 4 eCEC
MoO4
2- 2 pH, clay
Cd2+ / /
Ag+ 2 pH, eCEC
VO3
- 1.5 /
Bioavailability corrections (OECD, 2016)
OECD. 2016. Guidance on the incorporation of bioavailability concepts
for assessing the chemical ecological risk and/or environmental
threshold values of metals and inorganic metal compounds. OECD
Environment, Health and Safety Publications, Series on Testing &
Assessment No. 259. OECD, Paris

5. 5
Generic approach for derivation of soil
threshold values
Selection relevant and reliable toxicity studies

6. 6
Generic approach for derivation of soil
threshold values
Selection relevant and reliable toxicity studies
Selection effect threshold (ECx)

7. 7
Generic approach for derivation of soil
threshold values
Selection relevant and reliable toxicity studies
Selection effect threshold (ECx)
Correction for lab-to-field differences in toxicity
Normalization to specific soil properties

8. 8
Generic approach for derivation of soil
threshold values
Selection relevant and reliable toxicity studies
Selection effect threshold (ECx)
Correction for lab-to-field differences in toxicity
Data aggregation per species
Normalization to specific soil properties
Uncertainty assessment
Statistical extrapolation and selection protection level (HCp)

9. 9
Construction of species sensitivity distribution +
selection of protection level (HCp)

10. 10
Threshold calculator for metals in soil
• Excel spreadsheet
• Freely available at https://www.arche-consulting.be/tools/threshold-
calculator-for-metals-in-soil/
• Transparent and flexible derivation of soil quality standards by selection
of:
– trophic level of soil organisms to be included (plants, invertebrates, micro-
organisms)
– (de-)selection of individual studies by filtering database
– effects thresholds (ECx, …)
– protection level (HCp of the SSD)
– soil properties and bioavailability corrections for site-specific assessment

11. 11
Database
• 1186 ecotoxicity tests for 7 metals (Cd, Co, Cu, Pb, Mo, Ni and Zn)
• Wide range in species/endpoints and soil properties covered
• No restrictions for soil type, geographical region or species tested
• Clear reporting of study details (65 parameters on test substance,
organism and endpoint, reference, soils tested, test conditions, …)
• All dose-response curve re-fitted with log-logistic model (US EPA TRAP
program, version 1.30a)
𝑌 =
𝑌0
1+𝑒4𝑆(𝑙𝑜𝑔𝑋−𝑙𝑜𝑔𝐸𝐶50)

12. 12
Threshold calculator for metals in soil: input

13. 13
Threshold calculator for metals in soil: output

14. 14
Example: distribution predicted no effect
concentrations (HC5 of EC10) for Cu across
European arable land

15. 15
Summary
• A generic, flexible and transparent approach is proposed for derivation
of threshold values for metals in soil
• Extensive database of reliable effects data for metals to soil organisms
• Variety of simple models and tools are available to take bioavailability
into account, based on standard soil properties (pH, organic carbon
content, clay content and eCEC).
• Free user friendly tool developed to facilitate and improve decision
making for various regulatory purposes, e.g. derivation remediation
thresholds
- maximal use of available toxicity data and bioavailability
corrections
- enhanced transparency in derivation soil quality standards

16. 16
Thank you