Matching analytical methods with EQS values for water and sediment

Transcription

1 Matching analytical methods with EQS values for water and sediment Frank Van Assche International Zinc Association 168 Avenue de Tervueren 1150 Brussels

2 contents Monitoring metals in water total versus dissolved Preparing dissolved fractions Data needed for bioavailability assessment/data sources Metal assessment using the tiered approach Regional examples Bioavailability assessment in sediment

3 Monitoring metals in water Metals EQS are set using ecotoxicity data expressed as dissolved (bioavailable) metal concentrations EQS are also expressed as a dissolved metal concentration Compliance with metal EQS must be checked using dissolved metal concentrations Total metal concentrations should not be used for checking compliance

4 Partitioning of metals in water Zn 2+ Total metal content has no relation to toxicity Zn 2+ Zn 2+ Ni 2+ Solid suspended material Cu 2+ Cu 2+ Zn 2+ 4

5 Dissolved metal concentrations can cause an effect Dissolved metal is the active fraction Zn 2+ Zn 2+ 5

6 Competing cations Ca 2+ Mg 2 + The «Biotic Ligand Model» (after Janssen et al, 2003) Na + DOC H + Organic and inorganic complexation ph Me 2+ MeOH + Alkalinity MeCO 3 Bioavailability determines metal toxicity 6

7 Measuring dissolved metals is not easy For determining the dissolved fraction, the water sample needs to be filtered (0.45µm) Can be done on-site or off-site in the lab Possible sources of major error: Contamination of sample Preservation of sample before filtering

8 Contamination of water samples Metals are naturally present in soil, etc Labware may contain significant amounts of metals that can leach into the sample Filter material, rubber, plastics syringes, stoppers, tubes, valves, beakers, lab gloves E.g.: cases where [Me]dissolved > [Me] total (%) River province Cu Zn Ni Dommel Regge & Dinkel Schieland (after Zwolsman & De Schamphelaere 2007) Blancs should always be used!

9 Do not preserve sample before filtering Older guidance may leave the option to stabilise sample before filtering Me extraction!! % increase in Me-recovery from Belgian waters, stabilised or not before filtering (ECTX 2013) river Susp. Solids (mg/l) % Cd % Cu % Ni % Pb % Zn Dommel > Dommel Grote Nete > Scheldt

10 Metals have natural background e.g. Zinc AIR: ng Zn/m 3 SOIL: mg Zn/kg DW WATER: µg dissolved Zn/l BIOMASS: µg Zn/g DW 10

11 FOREGS (2006): Zinc in Stream water Background is variable Can be high due to e.g. metal-geology Can be taken into account in compliance checking Zinc: «added PNEC» :10.9µg/l FOREGS Geochemical atlas of Europe (2006)

12 Data needed for bioavailability assessment Ideally, local data on ph, hardness and DOC are available If not, more regional data can be used for local assessment e.g.: data from the area ( ecoregions ) or more general data e.g. FOREGS

13 Dissolved Organic carbon concentrations in Europe (FOREGS 2006)

14 How to assess compliance of metals with the EQS? [Me] dissolved / Reference EQS [Me] dissolved can be: measured (preference) Calculated as from the total [Me] using the water-suspended solids partition coefficient Kd Depending on the metal, and available knowledge, a tiered approach can be applied at the regional and local level

15 Programmes of measures Classification The Tiered Approach [Me]-dissolved 1. Comparison with generic EQS generic EQS is set to protect all waters - 95% of waters in the most sensitive region EXCEEDANCE Pass 2. Use of user-friendly screening tool BLM Bioavailability correction EXCEEDANCE Pass 3. Consideration of local ambient background concentrations EXCEEDANCE Pass 4. Remedial measures No further action necessary 15

16 Zinc in Norwegian waters (2010) EU-WISE dataset 46 sampling points on zinc Total Zn concentration calculate dissolved Zn Using Kd (EU risk assessment 2007) local SPM data

17 Zinc in Norwegian waters (2010)(2) Bioavailability assessment using conservative estimations of background, DOC, Ca, ph (10P WISE) After bioavailability assessment, no exceedance anymore at the 1 sampling point with [Zn] > EQS

18 Programmes of measures Classification The Tiered Approach: compliance checking Norway 2010 [Zn]-dissolved: 46 stations 1. Comparison with generic EQS EXCEEDANCE 1 Bioavailability correction 2. Use of user-friendly screening tool BLM EXCEEDANCE 0 3. Consideration of local ambient background concentrations EXCEEDANCE 4. Remedial measures generic EQS is set to protect all waters - 95% of waters in the most sensitive region 45 1 Pass Pass Pass No further action necessary 18

19 Regional assessment Case: Zinc in Swedish waters WISE dataset Total zinc monitoring data ~=70 sampling points ph and Ca reported for the sampling points Missing information: DOC minimum value or 10P of FOREGS (SE) was used Calculations with the BIOMET tool Background Zn concentrations: Local Zn concentration or 10P value of FOREGS was used

20 Distribution (%) Distribution (%) Distribution (%) Bioavailability parameters in Sweden ph and Ca: data available in Wise library; DOC data available from FOREGS 1 1,2 0,8 0,6 0,4 Ca (mg/l) 10P=2.36 mg/l 90P= mg/l 1,0 0,8 0,6 0,4 10P= P= 7.5 ph 0,2 0, Ca (mg/l) 0, ph 1,2 1 0,8 0,6 0,4 0,2 DOC (mg/l) 10P= 7.36 mg C/L 90P= mg C/L DOC (mg C/L)

21 zinc in Swedish water: 2010 Number of stations measuring Zn : 72 Zn concentrations were expressed as total concentrations Zn dissolved = Zn total /(1 + Kd* Cs* 10-6 ) where [Zn dissolved ] and [Zn total ] are the dissolved and total Zn concentration (μg/l). Kd is the equilibrium partitioning coefficient (L/kg). Cs is the concentration of suspended solids (mg/l). The 50P of 13 SPM data given in the dataset of 2009 for lakes was used (3,75 mg/l)

22 Distribution (%) 1,2 1 Sweden : Exposure assessment ,8 0,6 0,4 Total Zn Dissolved Zn 0, µg Zn/L Percentile µg Zn (total)/l µg Zn (dissolved)/l

23 Programmes of measures Classification Sweden: compliance checking 2010 N=72 1. Comparison with generic EQS N=69 EXCEEDANCE 2. Use of user-friendly screening tool BLM N=90 EXCEEDANCE N=29 N=624 N=61 3. Consideration of local ambient background concentrations EXCEEDANCE N=3 N=0 4. Remedial measures EXCEEDANCE N=0 BG =1µg Zn/L N=0 BG = Foregs N=3 Pass Pass Pass No further action necessary (Calculations at minimum DOC)

24 The tiered approach If dissolved metal concentration is < EQS, water is compliant as such Only in case dissolved metal concentration is EQS, the assessment can be refined by considering metal bioavailability and/or metal background Models exist for a number of metals to calculate their bioavailability based on physchem parameters Bioavailability models should have been validated in natural waters that are relevant for the area under assessment and be based on agreed datasets e.g. in the EU risk assessment

25 The marine environment For marine waters, EQS are different EQS freshwater Cu 8 5,2 Ni 4.0 8,6 Zn 10,9 (background to be added) EQS marine Bioavailability models for freshwater do NOT apply to the marine water Bioavailability studies are ongoing (DOC corrections?) 6.9 Cd ,2 Pb 1.2 1,3

26 Metal bioavailability in sediment: the SEM-AVS concept In sediments, metals form very stable Me-Sulphides Me ++ bound to sulphides is not bioavailable Order of metal affinity for S: Cu > Pb > Cd > Zn > Ni AVS = Acid Volatile Sulfides: sulfides liberated by the cold extraction of sediment in approximately 1 M HCl SEM = Simultaneously Extracted Metals: refers to the metals associated with the sulfides and any other metal bearing phase that is extracted in the cold HCl extraction used for AVS 26

27 Predicting metal bioavailability in sediment: The SEM-AVS concept SEM Me AVS < 0 : No toxicity predicted AVS Ni Zn Cd Pb Cu All metal bound AVS Ni Zn Cd Pb Cu DOC Bound metal Metal not bound on DOC = available AVS > SEM No bioavailability, no toxicity AVS < SEM Part of zinc, and Ni possibly bioavailable 27

28 Why zinc gets sequestered in the sediment Covariance between AVS Zn and SEM Zn in European sediments (taken from Vangheluwe et al 2003). Analysis of the data suggests that a coupling (covariance) of SEM Zn and ΔAVS Zn occurs (EU RA 2008).

29 Percentile 100 P Cu AVS-SEM data for Flanders Cases: Cu, Zn SEM Cu - AVS -0.7 µmol/g dry wt mg/kg dry wt (µmol/g dry wt) 100 P Zn SEM Zn - AVS Exc(Zn) (µmol/g dry wt) µmol/g dry wt 70.1 mg/kg dry wt coupled data of the Flanders database, with an indication of the 90P (Vangheluwe et al, 2003, 2005)

30 Conclusions Metal EQS are related to dissolved concentrations Monitoring for dissolved metals fraction must be done with care Specific methodology exists for compliance checking of metals to EQS in water The tiered approach with bioavailability (and possibly background) correction allows more efficient assessment, and more efficient management, if needed The AVS/SEM concept allows for estimating bioavailability of metals in the sediment

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