Implementation of bioavailability under the Water Framework Directive

1. Implementation of bioavailability under the Water Framework Directive Scientific underpinning of the bioavailability approach Implementation of Bioavailability

2. Outline • Introduction • What are Biotic Ligand Models and where do they come from? • How do they work - provenance and validation of the biotic ligand models….. • Simplified biotic ligand models • Construction • Important input parameters • Performance against original biotic ligand models • Questions NOT remaining • Questions remaining

3. Important considerations for metals ERA • There is extensive evidence that neither total nor dissolved aqueous concentrations are good predictors of metal bioavailability and toxicity • Uptake and toxicity of cationic trace metals is best predicted by the aqueous concentration (or activity) of the free metal ion (FIAM – Morel and Hering 1993, Campbell 1995) Relationship between Cd concentrations in Chaoborus species from various lakes and free Cd ion concentrations normalized for competition between H+ and free Cd ions for biological uptake sites (Hare and Tessier 1998)

4. What are Biotic Ligand Models and where do they come from? • Gill Surface Interaction Model – Pagenkopf 1983 • Describes interaction of metals with fish gills and competition from other ions • Humic Ion Binding Model V – Tipping 1992 • Describes binding of metals with natural organic matter and competition from other ions • Biotic Ligand Model – Di Toro 2001 • Combines both of these models to describe toxicity as a function of water chemistry

5. How do they work?

6. PROS Quantitatively addresses the question of bioavailability from solution Mechanistically based, more robust and flexible than empirical approaches Considers relevant uptake mechanisms Conceptual model for toxicity that is testable, can be (field) validated, modified and improved upon CONS Originally used for predicting the acute toxicity of metals in few selected species BLM implicitly assumes that the properties of the epithelial-binding site or biotic ligand are constant and unaffected by general water chemistry (pH, hardness) or by pre-exposure to metals Assumes that metal toxicity can be predicted on the basis of waterborne exposures and that other sources of exposure are less important Advantages and limitations of BLM

7. Waterborne vs dietary metal exposure • Experimental evidence regarding the role of dietary metals in toxicity is limited and contradictory: • Hook and Fisher (2001) found that diet-borne Zn and Cd were the main contributors to chronic toxicity in invertebrates • Kraemer et al. (2006) and Cooper et al. (2010) showed that water is the main source of Cd respectively for juvenile yellow perch and freshwater bivalves using biodynamic modeling • Results seemingly depend on the metal, species and organs

8. Waterborne vs dietary exposure • Some studies have shown that toxicity can be caused by metals from dietary exposures • Assimilation efficiencies of metals from the diet can be low • Are metal concentrations in food linked to waterborne exposures? • Are toxic exposures via food sources likely to occur at water concentrations below the EQS or PNEC?

9. BLMs vs current standards? BLMs Hardness Banding Many sub-chronic tests Main focus on fish, algae not always included Always applied (no boundaries considered) Unvalidated • Chronic effects • 3 trophic levels (fish, invertebrates, and algae) • Defined region of applicability (boundaries) • Validated in the field Monitoring of metal concentrations in suspended particulate matter has also been used in some areas. This focuses on the fraction of least relevance to potential toxic effects, although it may be useful in terms of understanding loads and fluxes.

10. BLMs vs current standards? Comparison of Cu and Ni standards for 545 freshwater monitoring sites in Scotland, calculated using the current EQS and the BLMs for these metals. Current standards are hardness banded and were set under the DSD.

11. How well do they work? Validation of the biotic ligand models….. Predictive capacity of NiBLM for C.dubia for natural waters Validation of manganese BLMs algae (circles), invertebrates (diamonds), and fish (squares). Predictions for individual species in field collected waters typically within a factor of 2 of the BLM predictions

12. Comparisons with Field Evidence Variation in snail abundance, relative to a reference condition, with bioavailable nickel exposure in UK freshwaters. Snails are expected to be one of the most sensitive groups of aquatic organisms to nickel toxicity.

13. How are they applied? • Species Sensitivity Distribution includes many species • Sensitivity of each species adjusted according to water chemistry conditions • Most appropriate BLM applied to each species • SSD recalculated using normalised data • HC5 or PNEC derived for site specific conditions from normalised SSD • Most sensitive species depends on conditions

14. Applying BLMs to other species • Prediction of variation in the sensitivity of a rotifer (top) and a snail (bottom) to Ni using BLMs developed for daphnids. • The intrinsic sensitivity is adjusted for each species, but other BLM parameters remain the same. • Suggests comparability between how different species respond to metal toxicity.

15. Comparability Between Different BLMs a - De Schamphelaere & Janssen 2004 Environ Toxicol Chem23:1365 b - De Schamphelaere & Janssen 2004 Environ Sci Technol38:6201 c - De Schamphelaere et al. 2006 Environ Toxicol Chem24:1190 d - Deleebeeck et al. 2008 Environ Toxicol Chem27:2097 e - Binding constant for the toxic metal

16. BLMs vs measurement approaches? • BLMs predict effects on organisms as a function of water chemistry from a few simple measurements (pH, DOC, Ca) • Speciation measurements tend to be complicated and expensive to perform • Speciation measurements cannot currently take account of competitive effects at the “biotic ligand” • Techniques such as DGT, DMT, ASV

17. Using the BLMs • Several possible approaches • BLM software (Hydroqual) • Usually used for individual species models • Mostly used for acute BLMs • Adapted for chronic Cu BLM to include full normalisation of the SSD • Chemical speciation model (e.g. WHAM6) and separate “biotic ligand” calculations (e.g. in Excel) • More flexible, not limited to a single speciation model • Currently used for Ni and Mn BLMs

18. Using the BLMs • Full water chemistry required • pH, DOC, Ca, Mg, Na, K, Cl, SO4, alkalinity, temp • Complicated and time consuming • Separate calculations required for each species at each site (automated in the Cu BLM) • Not practical for routine regulatory use • Too costly in terms of time and effort required • A quicker and simpler approach is required

19. User Friendly Biotic Ligand Models Full BLM User Friendly BLMs

20. User Friendly Biotic Ligand Models • Two approaches have been taken so far • Look-up tables of BLM calculations • Estimation using simple algorithms • Simplified input requirements • Look–up tables • Can give more accurate results • Algorithms • Can be more easily automated • Both approaches use large sets of full BLM calculations in their development

21. User Friendly BLM development • Look-up tables of BLM calculations • Large numbers of BLM calculation results are entered into look-up tables • Interpolation to provide results • Estimation using simple algorithms • Large numbers of BLM calculation results are used to train simple algorithms • Results calculated by simple algorithms

22. User Friendly Biotic Ligand Models

23. User Friendly Biotic Ligand Models

24. User Friendly Biotic Ligand Models Performance against original biotic ligand models

25. User Friendly Biotic Ligand Models Performance against original biotic ligand models

26. User Friendly Biotic Ligand Models Performance against original biotic ligand models

27. Which Metals? Which metals are BLMs, or other bioavailability corrections, currently available for or in development? • Currently available • Cu, Zn, Ni, Cd (hardness correction), Mn • Currently under development • Pb, Co, Al, Fe, Ag

28. Questions NOT remaining Biotic Ligand Models are not recent innovations and the science is well developed. Regulatory acceptability of the models Scientific support of the use of the models in regulatory approaches Technical support for the use of the models in a tiered approach

29. Questions remaining • Use of measurements as an alternative to prediction of bioavailability? • Accumulation in sediments? • Application to waters outwith boundary conditions? • Importance of other routes of exposure? no doubt other questions......