J. O'Reilly*1, Dr. M. Watts2 and Prof. N. I. Ward1

Field-Based Arsenic Speciation in Water Samples and the Relationship to Human Health

1. ICP-MS Facility, Chemistry, School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey, GU2 7XH

2. British Geological Survey, Keyworth, Nottingham, NG12 5GGINTRODUCTION:A field-based method for the separation and preservation of four arsenic species (As3+, DMA, MMA and As5+) in waters has been developed, utilising disposable Bond Elut SPE cartridges. On-site separation is achievable through strong cation exchange (SCX) and strong anion exchange (SAX) phases connected in series. The arsenic species are then eluted and analysed in the laboratory for total arsenic by ICP-MS. Arsenic species identification was confirmed using HPLC-ICP-MS. The field-based method was employed on natural/acid mine drainage waters collected from two areas: the Devon Great Consol near Tavistock in Devon and rural regions of Argentina. Populations in certain regions of Argentina (La Pampa and San Juan) display human health conditions linked to arsenic exposure, including skin legions, pigmentation changes, hyperkeratosis and various forms of cancer.

FIELD-BASED METHODOLOGY:

REFERENCES: • P. L. Smedley et al., Applied Geochemistry, 2002, 17, 517• Francesconi et al., Analyst, 2004, 129, 373• Martinez-Bravo et al., J. Chrom. A, 2001, 926, 265

Figure 1: Field-Based Set-up

CONCLUSION:• Comparative arsenic studies were carried out between waters analysed from Devon and Argentina using SPE cartridges.• Variable SPE recoveries were reported between spiking tests and real samples.• Use of ascorbic and citric acids as preservatives alters the type of species identified by HPLC-ICP-MS.• Tap water AsT exceeds WHO guidelines. Studies need to be carried out to assess the effect on human and animal health.

DEVON STUDY SITE:

ARGENTINA STUDY SITE:Some remote populations of Argentina rely solely on artesian drinking water supplies. Total Arsenic (AsT) LevelsAnalysis of waters from La Pampa (artesian-tap) and San Juan (artesian/river) show high total arsenic levels, artesian (713-729 μg/l La Pampa; 59-352 μg/l San Juan) and river (67-132 μg/l Rio Blanco, San Juan). Background levels (Rio Negro) were 26.0 - 40.0 µg/l AsT. The highest AsT level was found in Edvardo Castex (La Pampa) tap water with 700 µg/l (Figure 7). The WHO level for drinking water is 10 µg/l AsT.

Figure 5: La Pampa

Figure 7: Arsenic levels in Argentina

Figure 6: Rio Blanco, San Juan

Figure 2: Study site 7

Figure 3: SPE cartridge results

Total Arsenic (AsT) LevelsAsT levels (filtered and unacidified, F/UA) ranged from 5.5 – 1866.3 µg/l. Site 3 was adjacent to the mine tailings area. Background levels were 5.0 - 20.0 µg/l AsT.

SCX Cartridge(DMA)

SAX Cartridge(MMA and As5+)

Sample 1Elution Processes

Elute with HNO3

Elute with acetic acid and HNO3

SCX SAX

Extraction

Elution Processes

As3+ MMA DMA As5+

CALIBRATION:Arsenic species measured over a range of 0 – 100 μg/l using a VG Elemental PQ ExCell ICP-MS gave an r2 value > 0.998.

Cartridge conditioning is carried out to promote adsorption of the arsenic species onto the silica-based resin:• SCX: 15ml 50% v/v MeOH; 15ml 1M H3PO4; 10ml DI water• SAX: 15ml 50% v/v MeOH; 10ml DI water

SPIKED RECOVERY TESTS:Solutions spiked with 10 μg/l arsenic were passed through the field-based set-up (Figure 1). Recoveries for the 4 arsenic species ranged from 85-98%.

Arsenic SpeciationSPE results generally showed As3+ > As5+ > DMA > MMA (Figure 3). Site 3 had the highest As species levels, similar to AsT. Total AsFraction

levels are generally higher than AsT.

The Devon Great Consol (Figure 2) is a former arsenic mine, ceasing production around 1925. Eight sites were selected within the vicinity of the arsenic mine.

HPLC-ICP-MSFigure 4 shows the As speciation for site 3. Filtered water shows As5+ as the predominant species, whereas field SPE analysis (Figure 3) shows As3+ and As5+. It is suggested that As3+ oxidation takes place with water sample storage and transport to the laboratory.

a) Filtered

c) 1 % Citric

b) 1% Ascorbic

Figure 4: Arsenic species for site 3

As5+

As5+

As5+

DMAMMA

    Arsenic Fractions (µg/l)

SiteTotal (AsT)F/UA (µg/l)

As3+ DMA MMA As5+Total

(As Frac.)

1 5.5 6.4 0.2 0.9 10.5 18.0

2 13.1 30.6 7.9 8.1 44.0 90.5

3 1866.3 1902.3 8.3 257.4 1665.1 3833.1

4 2.3 16.2 6.8 7.4 26.4 56.8

5 18.2 96.5 16.0 2.7 14.6 129.7

6 71.6 36.9 5.6 9.0 40.4 91.9

7 9.6 2930.6 7.9 2.1 10.6 2951.2

8 60.4 160.1 5.1 5.0   170.2

Initial preservation studies using 1% ascorbic and citric acids, shows acidification also influences As speciation (Figure 4).

    Arsenic Fractions (μg/l)

SiteTotal (AsT)F/UA (µg/l)

As3+ DMA MMA As5+Total

(As Frac.)

La Pampa (tap) 136.6 394.2 4.7 49.5 706.5 1154.9

San Juan (river) 115.5 137.8 3.3 6.3 3.5 150.9

San Juan (tap) 332.8 219.4 1.4 57.4 63.9 342.1

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Arsenic SpeciationSPE results showed for La Pampa tap water As5+ > As3+ > MMA > DMA, San Juan river water As3+ > MMA > As5+ > DMA and for San Juan tap water As3+ > As5+ > MMA > DMA (Figure 8).

Figure 8: SPE cartridge results

Total AsFraction levels are generally higher than AsT, with a significant variation in levels for La Pampa.

Tap water analysed from La Pampa is used by a family in which 8 members have recently died of arsenic poisoning.

Figure 4a: 10 µg/l arsenic std.

AsBAs3+

DMA MMA

As5+