How to correct for background and acclimatisation in hazard assessment? Data relevancy.

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1 How to correct for background and acclimatisation in hazard assessment? Data relevancy. Frank Van Assche International Zinc Association 168 Avenue de Tervueren 1150 Brussels

2 Metals are natural, some are essential Metals are components of the natural environment they occur in natural background concentrations in all environmental compartments Moreover, some metals are essential elements and are actively regulated by organisms through homeostasis mechanisms.

3 The Optimal Concentration range for Essential Elements depends on BG Shift to higher sensitivity Shift to lower sensitivity deficiency Optimal dose toxicity 3

4 Consequences for hazard assessment Conditioning to background implies that the sensitivity of organisms to metals in toxicity tests is function of the background concentration they experience(d) not only in the test medium also in the nutrient solution in which they were cultured prior to testing

5 Background is variable Due to underlying geology, metal background can vary significantly E.g. FOREGS (2006) compartment 10P 50P 90P EU Stream waters (µg dissolved Zn/l) EU Top soils (µg Zn/g DW) Organisms may be conditioned/ acclimatised to these varying natural conditions

6 Metal levels in the culture medium can define sensitivity R. subcapitata cultured in different zinc concentration prior to testing showed different sensitivity in the test Zinc in culture medium and OECD 201 medium (µg/l) EC50 growth rate NOEC growth rate 0,3 1, > < /

7 Sensitivity to zinc as function of BG Culture conditions < 2 µg Zn/l 2 < [Zn] < 50 µg Zn/l >50 µg Zn/l species Ephydatia : 3.3 Ephydatia : 34 Hormidium : 1000 corresponding ecosystem Number of species NOECs Daphnia magna : 59 Daphnia magna : 365 Selenastrum c. : 8 Selenastrum c. : 37 Ceriodaphnia: 31 Chroococcus: 200 Synecoccus: 390 Corbicula: 25 Dreissenia: 400 Salvenilus: 530 Potamopyrgus: 75 Jordanella: 51 Hyallella: 42 Pimephales : 78 Phoxinus: 50 Salmo: 210 N-American Great Lakes European lowland rivers Scenedesmus: 1400 Mineralised areas Mean NOEC (µg Zn/l) 36 +/ / /- 1 HC5 (µg Zn/l) /

8 Metals interact with the natural environment e.g.: Ecotoxicity of copper (µg/l) on growth rate of unicellular algae See section: bioavailability

9 Metal exposure is function of environmental parameters Metals interact with the natural environment Me toxicity is determined by the bioavailability of the metal (ion) at target sites on the organism Competition effects e.g. with H +, Ca 2+, Mg 2+ Complexation on e.g.: organic carbon, Environmental relevancy of the test needs consideration

10 Accounting for background and essentiality Ensure that data have been obtained under conditions that are relevant for the environment under study test- and culture medium prior to testing Nutritional requirements for essential elements like Cu, Zn and Ni need be satisfied in both media in order to correctly reflect the toxicity of the metals studied (OECD 2000)

11 Ensuring environmental relevancy of ecotoxicity data Select ecotoxicity data on physico-chemical parameters of test and culture medium e.g.: water: Metal background: set minimum and maximum concentration, relevant for the area (when relevant) ph: idem(e.g.: 6-9) Hardness: idem (e.g.: mg CaCO3/l) (DOC: data often lacking, not added in artificial media) Idem: for other compartments Relevant ranges can be set for area under study, e.g. EU-region

12 Checking reliability Given the importance of the phys-chem conditions of the test, critical parameters need to be documented for the test to be reliable (Kl. 1 or 2), e.g.: Hardness, ph, metal background in test and culture media (Information on origin of test organisms) ECx/NOEC values: Measured metal concentrations include background nominal concentrations do not include background. indication needed that nominal ~= measured

13 summary Conditioning/acclimatisation to natural background and essentiality of metals necessitate a more specific selection of ecotoxity data for hazard/risk assessment. Selection is aimed at ensuring that the data reflect the sensitivity of organisms in the environment studied. Documentation of the critical parameters determining metal toxicity is conditio sine qua non