Kate Magee CK Associates
IPEC Houston, TX October 16, 2014 } Metalloid
} Ubiquitous ∑ Elemental ∑ Minerals ∑ Soil ∑ Rivers ∑ Oceans ∑ Groundwater http://www.knowledgedoor.com http://www.inorganicventures.com ∑ Food
} Most abundant in rocks , commonly } Redox Active Species associated with shales , deep-sea ∑ 3+, 5+ are most common clays , iron oxides , sulfur minerals , ∑ 1+, 2+, 3- are less common volcanic sediments Arsenate (5+) Arsenite (3+) Monomethyl- arsonic acid
Monomethyl- Dimethylarsinic Dimethylarinous arsonous acid acid acid
Hughes M F et al. Toxicol. Sci. 2011;123:305-332. Published by Oxford University Press on behalf of the Society of Toxicology 2011. http://www.mineraltest.ca/wp-conte nt/uploads/2012/11/arsenic-skin-lesion-300x300.jpg
Arsenic Toxicity
Hughes M F et al. Toxicol. Sci. 2011;123:305-332. Published by Oxford University Press on behalf of the Society of Toxicology 2011. } Poison - Poison of Kings
} Medicinal - Fowler’s Solution Forwler’s Solution, Dave Ward/Flickr } Hardening alloys
} Glass manufacturing
} Electrical device component
} Semiconductor
} Pesticides
} Pigments Dusting cotton, 1934/USDAgov/Flickr
} Wood preservation
CCA wood preservatives, 2011/npic.orst.edu } Production tubing corrosion inhibitor (Frenier et al., 1989)
} Produced water (Gallup et al., 1996)
} Crude oils (Magaw et al., 2001) ∑ ~60 ug /L (average of 26 crude samples )
} Gas condensate (Krupp et al., 2007) ∑ 33-122 ug/L
} Released hydrocarbons can liberate arsenic from soils
http://www.cjstech.com/wp-content/uploads/2013/07/Truck-and-Spool.jpg Quiruvilca Mine (La Libertad Mine; ASARCO Mine), Quiruvilca Panasqueira Mine (Couto Mineiro da District, Santiago de Chuco Province, La Libertad Department, Panasqueira), Panasqueira, Covilhã, Castelo Peru © Christian Bracke Branco District, Portugal © Kristalle and Crys http://www.minfind.com
As2S3 FeAsS As4S4
} More than 150 arsenic-bearing minerals
} Arsenic has an affinity for iron and sulfur
FeAsS
Dissolution 3+ Adsorption As (aq) As 5+ Precipitation (aq) Desorption
Mobile in Immobile Immobile Groundwater
Iron pH Redox Oxides 5+ } pKa 1= 2.2 Arsenate (As )
- 2- H2AsO 4 HAsO 4 1 H AsO 3- + - 3 4 AsO 4 H3AsO 4° ‰ H + H2AsO 4
} pKa 2= 6.97
- + 2- H2AsO 4 ‰ H + HAsO 4 Relative Abundance Abundance Relative Relative 0 1 3 5 7 9 11 13 } pKa = 11.53 3 pH
22- + 3- HAsO 44 ‰ H + AsO 4 pKa 1 pKa 2 pKa 3 } pKa = 9.22 1 Arsenite (As 3+ )
H AsO + - 1 3 3 H AsO - H3AsO 3° ‰ H + H2AsO 3 2 3
2- HAsO 3 } pKa 2= 12.13
- + 2- H2AsO 3 ‰ H + HAsO 3 Abundance Abundance Relative Relative
3- AsO 3 0 } pKa 3= 13.4 1 3 5 7 9 11 13
2- + 3- HAsO 3 ‰ H + AsO 3 pKa 2
pKa 1 pKa 3 2 in
} Metal oxyhydroxides can act as a sink and source of arsenic Raven et al., 1998
Positive PZC Negative Surface Charge Surface Charge } Ligand Exchange Reactions (phosphate , sulfate, carbonate, silicate)
Fe oxide–As(V) + phosphate ‰ Fe oxide–PO4 + As(V)
} Reductive Dissolution
Dissolution As 3+ 2+ (aq) Fe (aq) + 5+ As (aq)
[As] GW ↑ Mobile 1 Groundwater Oxidized } Arsenate more prevalent H3AsO 4
- H2AsO 4 } Arsenic will be 0.5
predominantly immobile 2- HAsO 4
Eh (volts) (volts) Eh Eh H3AsO 3 0 3- AsO 4
2- HAsO 3 H AsO - -0.5 2 3 AsO 3- [As] GW ↓ 3
0 2 4 6 8 10 12 14 pH } Arsenic more likely 1 to be mobile H AsO Sample Identification Sample 13 Sample4 2 Sample 3 Sample 4 Hydrocarbon Status LNAPL Unaffected Dissolved Phase Dissolved Phase - H2AsO 4 } Arsenite more 0.5 Iron (III) Oxide Arsenic Speciation (1362A) prevalent 2- Arsenic (III), mg/L 0.164 0.146 0.392HAsO 4 0.444 Arsenic∑ (V), mg/L ND (volts) (volts) Eh Eh H3NDAsO 3 0.033 0.056 H3AsO 3° 0 3- Inorganic Arsenic, mg/L 0.164 0.148 Iron (II)0.425 AsO0.5004
2- Oxidation Reduction Potential -154.2 -115.5 -82.4 -82.4 HAsO 3 Groundwater H AsO - Dissolved Oxygen, mg/L 0.10-0.5 0.31 0.092 3 0.09 AsO 3- Reduced 3 [As] GW ↑ 0 2 4 6 8 10 12 14 pH } Arsenic will be predominantly immobile 1 H3AsO 4
- H2AsO 4 } Orpiment, arsenopyrite, 0.5
pyrite precipitate (bind 2- HAsO 4
arsenic) (volts) (volts) Eh Eh 0 3- AsO 4
[As] ↓ -0.5 GW Sulfidic Conditions
0 2 4 6 8 10 12 14 pH
Reeder et al., 2006 EPA adopts Congress passed Safe Arsenic rule EPA affirms standard standard of 50 ug/L Drinking Water Act became effective (0.010 mg/L) 1975 08-06-1996 03-25-2002 03-25-2003
10-22-2001 1988 10-23-2006 EPA sets new EPA declares As Compliance date for drinking water standard a carcinogen new standard (10 ug/L) } “National Primary Drinking Water Regulations ; Arsenic and Clarifications to Compliance and New Source Contaminants Monitoring” published in Federal Register (66 FR 6976 )
} Maximum Contaminant Level (MCL) = 0.010 mg/L ∑ Enforceable
} Maximum Contaminant Level Goal (MCLG) = 0 mg/L ∑ Non-enforceable
} Applies to public water systems 10 ug/L Site 5 ug/L Specific
10/1,000/ 100 ug /L 10 ug /L 10,000 ug/L
10 ug/L Or Background 10/1,000 10/50- ug/L 22,000 ug/L State Agency Standard (ug/L) Guidance National EPA 10 https://federalregister.gov/a/01-1668 http://www.deq.louisiana.gov/portal/Portals/0/t Louisiana Department of Louisiana 10/50-22,000 echnology/recap/2003/RECAP%202003%20Text Environmental Quality %20Table%201.pdf Montana Department of http://www.deq.mt.gov/StateSuperfund/PDFs/D Montana 10 Environmental Quality EQ7_2012.pdf NJ Department of Environmental New Jersey 5 http://www.nj.gov/dep/rules/rules/njac7_9c.pdf Protection New Mexico Environmental http://www.nmenv.state.nm.us/gwb/documents New Mexico 100 Department /2062NMAC-Amended2014.pdf North Dakota Department of Health Chapter 33-16-02.1 Standards of Water Quality North Dakota Site Specific Waste Management of the State Oklahoma Department of Oklahoma 10/Background http://www.deq.state.ok.us/rules/690.pdf Environmental Quality PA Department of Environmental http://www.pacode.com/secure/data/025/chapt Pennsylvania 10/1000/10,000 Protection er250/chap250toc.html Texas Commission on Environmental http://www.tceq.state.tx.us/remediation/trrp/trr Texas 10/1000 Quality ppcls.html } Arsenic is present in groundwater due to natural and anthropogenic sources
} The two major valence states of arsenic in groundwater are 3+ (arsenite) and 5+ (arsenate) – mobility and toxicity differences
} Arsenic concentrations increase as pH increases, under post - oxic conditions
} Arsenic immobilized under oxidizing conditions, sulfidic conditions
} Regulation of arsenic varies by state ∑ No valence state standards } Hughes et al. 2011. Arsenic Exposure and Toxicology: A Historical Perspective. Toxicol. Sci. 123 (2): 305-332 .
} Raven et al. 1998. Arsenite and arsenate adsorption on ferrihydrite: Kinetics, equilibrium, and adsorption envelopes. Environ. Sci. Technol. 32:344 –349.
} Reeder et al. 2006. Reviews in Mineralogy and Geochemistry . 64 (1): 59-113.