What do Total and Dissolved Metal Concentrations in Groundwater Samples Really Tell Us? Part 1: Metal Speciation, Analytical Definition and Toxicity Elizabeth Haack, Ph.D., P.Chem. WaterTech 2013, April 11 2013, Banff, AB.
Contemplated Policy – AESRD Wallace (2012)
Unfiltered, Field Acidified Filtered 0.45 µm filter, Field Acidified
Note: Best way to sample metals in water is a source of ongoing debate globally (US, European Union) 2
Will we necessarily obtain meaningful and scientifically-defensible data using this approach?
Meaningful Data Exceedingly difficult question to answer based on the sampling objectives, being: To determine whether or not specific anthropogenic activities are affecting natural levels? To predict potential adverse health effects to receptors at the point of exposure. • • •
Human ingestion (and dermal exposure) – treatment? Shallow groundwater (eco direct contact) Discharge point to surface water body – conditions along flow path?
Overarching Challenge: “Operational” Definition Absolute Total Concentration of a Metal “Dissolved”
Particulate/Suspended
Passes through 0.45 µm filter
Retained by 0.45 µM filter
Colloidal (0.001 µm - 1 µm); Guo and Santschi 2007 “Trully” Dissolved (< 1 nm: Hydrated ions, Low Molecular Weight Fraction)
Field Acidification
Strong Acid Extractable
Very Strong acids
Nitric/Hydrochloric Acid Digestion (USEPA, 2010)
(solubilize metals from crystal structure)
Overarching Challenge Speciation
Metals are associated with matter (ligands, colloids, particles) that spans a continuum of sizes • will be partitioned amongst all fractions in accordance with properties of both metal and matter • Not static – perturbation of conditions will affect partitioning
A metal/trace element’s mobility, bioavailability and toxicity is almost always dependent on its speciation.
“Speciation” involves a myriad of considerations: • • • • • •
oxidation state / redox conditions presence and activity of microbes solubility of mineral phases ligands reactions at the solid-solution interface presence of other metals/ions
To meet objectives…. Rigorous science requires that the following a true: 1.
Field methods obtain “representative” samples of the relevant fractions.
2.
There is a good understanding of what the relevant forms (chemical species) of the metal will be.
3.
Analytical methods exist that can accurately quantify total metals as well as relevant species concentrations
4.
Toxicological data exists that allows us to assess the (relative) bioavailability and toxicity of all forms.
Ken’s Talk - Next
Example: Chromium
Why Chromium? Growing concern over Cr(VI) carcinogenicity by oral exposure route State of California: Groundwater Ambient Monitoring and Assessment (GAMA) Program (2011) >47 % of wells tested, Cr(VI) exceeded the detection limit for the purposes of reporting of 1µ/L (1 ppb) Public Health Goal of 20 ng/L (20 ppt) published in 2011 (OEHHA) Science behind existing Total Cr criteria (50 ppb, Canada) outdated US EPA currently considering a Maximum Concentration Limit for Cr(VI alone).
1. Do we understand the relevant forms? Present naturally in groundwater through weathering of Cr-containing soils and rocks (secondary minerals, chromic oxide, chromite) electroplating factories, leather tanneries and textile manufacturing facilities Aqueous Speciation: Cr(III) (cationic) and Cr(VI) (anionic) Cr (III) to Cr (VI): Mn oxides and bacterial oxidation, kinetics slow
McNeill et al., 2006
Not the whole story - mixed species - Non-equilibrium conditions - Complexes with OM
1. What are the relevant forms that are not “trully” dissolved
From McNeill et al. 2012, 4 mg/L Fe(OH)3, 5 µg/L Cr(III) or Cr(VI
2. Can we analyze total and all the species concentrations? Previous slides indicate that both in filtered and non-filtered samples, may have a complex combination of species Total Cr by ICP-MS • • • •
No speciation Prone to interferences (ArC, ClO) Stong acid digest may not be effective (Kumar and Riyazuddin 2009) Detection limits are not in line with levels proposed for Cr(VI) (~0.5 µg/L)
Speciation Analysis - Cr(VI) by Ion Chromatography (McNeill et al., 2012) • • •
New methodologies (US EPA Method 218.7) mean that laboratories are capable of detection limits required for ppt-level criteria and does not require filtration (Ask your commercial lab) May be some issues with respect to contamination of Cr(VI) with reagents used to adjust pH Field filtration may not be necessary
3. So what? What is important to my receptor? Hexaaquachromium ion; not actively transported Cr in soils/particulates (largely Cr) does not appear to be bioavailable through leaching tests that simulates stomach and intestinal environment
Similarity of the Cr(VI) ion to sulphate – readily taken up Mammal Studies indicate mutagenic effects
Hold up on regulatory criteria: BIOAVAILABILITY OF Cr(VI) – critical factor linking aqueous phase concentration to the toxic dose -Cr(VI) reduced to Cr(III) in saliva and G.I. tract - Amount not reduced unknown Zhitkovich, 2011
Summary - Cr
Speciation, analytical and toxicology are all “somewhat understood”
Studies suggest that risks overwhelmingly related to Cr(VI) in samples
Proposed approach (i.e. total vs. dissolved) is not likely to significantly increase our understanding of risks
Interim – reasonable because of unknown potential for Cr(III) oxidation
Other Metals
Other Metals/Trace Elements “Simpler Biogeochemistry” - predominantly present in groundwater as divalent cations – behaviour largely sorption-controlled, or complexation with organic ligands: • • • • •
Cu(II) Cd(II) Zn(II) Ni(II) Co(II)
Thermodynamic Equilibirum models (Biotic Ligand Model; WHAM) can be used with water quality data to evaluate/predict available concentrations
“Complex Biogeochemistry” that includes consideration of bioaacumulation and potential biomagnification • Selenium and Mercury • Studies have not shown that water concentrations are not a good predictor of risk to higher-level organisms. • Ecological Tissue-based criteria
Emerging/Applied Methods
Approaches to Consider
“Bioanalogical Sensors” (Van Leeuwen et al. 2005): • • • •
Diffusive Gradient Thin Films Gel-Integrated Microelectrodes Permeation Liquid Membrane Voltammetry
Time-averaged, preconcentration - Mobile and Labile forms Operationally Defined; Not all elements
Bioavailability to specific organisms:
Sensitivity and Specificity may not be sufficient
• Biosensors/Bioluminescence Sensors - (Ivask et al. 2009) • Wholeistic: In Situ effects monitoring – caged test species
Toxicology – “Omics” Sciences:
Quality Control and Standards Lacking
• Revolutionizing toxicology (Cohen 2004; North and Vulpe 2010) • Cheaper, faster, number of endpoints less limited than trad. animal testing • Can test mixed systems (i.e. where more than one contaminant is present) Significant technical expertise to use/deploy and interpret
Concluding Thoughts
Difficulty in assessing the meaningfulness of data from the proposed approach is in line with ongoing debate globally (e.g. responses to the dissolved-phase decision as part of the Water Framework Directive of the European Union)
Approach is arbitrary, and considered here to be an interim approach based on current science.
In the short term, from the standpoint of the realities of monitoring wells, system complexity, analytical constraints, and the varied receptors to be accounted foremost in decision-making around metals sampling should be sound professional judgment and interpretation based on understanding of biogeochemistry and potential risks.
In the medium-long term - a new paradigm whereby effects monitoring, monitoring of specific “high-risk species”, or evaluation of tissue-based concentrations (for some elements) to emerge that provides a lines-ofevidence approach to risks from metal/trace element concentrations at a Site.
Elizabeth Haack WorleyParsons Canada Services Ltd. 905-614-2844
[email protected]
Thank You – Questions?
References – 1 of 2
Cohen, S. 2004. Risk Assessment in the Genomic Era. Toxicologic Pathology. 32, 3.
Eaton, A., Ramirez, L.M. and Haghani, A., 2001. The Erin Brokovich Factor – Analysis of Total and Hexavalent Chromium in Drinking Waters. AWWA Water Quality Technology Conference, Nashville, TN.
Groundwater Ambient Monitoring and Assessment (GAMA) Program . Groundwater Information Sheet: Hexavalent Chromium. www.swrcb.ca.gov/gama/docs/coc_hexchromcr6.pdf
Guo, L., and Santschi, P.H., 2007. Ultrafiltration and its applications to sampling and characterisation of aquatic colloids. Environmental Colloids and Particles: Behaviour, Separation and Characterisation. edited by Kevin J. Wilkinson, Jamie R. Lead. 159-222. John Wiley & Sons, Ltd. England.
Ivask, A., Rõlova, T., and Kahru, 2009. A. A suite of recombinant luminescent bacterial strains for the quantification of bioavailable heavy metals and toxicity testing. BMC Biotechnology 2009, 9:41.
Kumar, A.R., and Riyazuddin, P., 2009. Comparative Study of Analytical Methods for the Determination of Chromium in Drinking Water Samples Containing Iron. Microchemical Journal. 93, 236.
McNeill, A., McLean, J., Edwards, M., and Parks, J., 2012. State of the Science of Hexavalent Chromium in Drinking Water. Water Research Foundation. Updated May 2012.
References – 2 of 2
Morman, S.A., Plumlee, G.S., and Smith, D.B., 2009. Application of in vitro extraction studies to evaluate element bioaccessibility in soils from a transect across the United States and Canada. Applied Geochemistry, v. 24 14541463).
North, M., and Vulpe, C.D., 2010. Functional Toxicogenomics: Mechanism-Centered Toxicology. International Journal of Molecular Sciences. 11, 4796-4813.
Sharma, V.K., and Sohn, M., 2009. Aquatic arsenic: Toxicity, speciation, transformations, and remediation. Environment International 35.743–759.
US EPA. 2010. UCMR3 Laboratory Approval Requirements and Information Document, EPA, 815-R-10-004, USEPA Office of Water, Cincinnati, OH.
Wallace, 2012. Alberta Water Policy Update. Brief to Water Technologies Symposium 2012. April 12, 2012. http://www.esaa-events.com/proceedings/watertech/2012/pdf/P4.pdf
WHO (World Health Organization), 1988. Environmental Health Criteria 61, Chromium, 1988.
Van Leeuwen et al., 2005. Dynamic Speciation Analysis and Bioavaibility of Metals in Aquatic Systems. Environmental Science and Technology, 39, 8545-8556.
Zhitkovich, A, 2011. Chromium in Drinking Water: Sources, Metabolism, and Cancer Risks. Chemical Research in Toxicology, 24., 1617–1629.
