1University of Massachusetts at Amherst Department of Chemistry

Project 2: Gutzeit Method for Determination of As in Soils

Method: using field kits (used for water) to measure arsenic in soils and digital image analysis for quantification.

2University of Massachusetts at Amherst Department of Chemistry

Allowable Levels of Arsenic in Soils

Contaminant Lined Landfills (mg kg-1) Unlined Landfill (mg kg-1)

Total Arsenic 40 40

Total Cadmium 80 30

Total Chromium 1,000 1,000

Total Lead 2,000 1,000

Total Mercury 10 10

The Massachusetts DEP, www.mass.gov/dep/service/regulations/proposed/aisfindr.pdf, (accessed August, 2010)

Massachusetts: The allowable level is 20 mg kg-1 (ppm) in soil

3University of Massachusetts at Amherst Department of Chemistry

Key Issues Surrounding Arsenic in Soil

Sources:• Naturally Occurring• Mining • Wood Treatments for Preservation• Bactericides, Fungicides, Pesticides and Insecticides

Areas of Concern:• Arsenic in soil is mobile into water and plant sources. • Is there bioaccumulation in rice? • What are the average concentrations in soil and rice?• Why is it more important to measure arsenic in soil than

water?

Quandt, S. A.; Jones, B.T.; Talton, J. W.; Whalley, L.E.; Galvan, L.; Vallejos, Q.M.; Grzywacz, J. G.; Chen, H.; Pharr, K.E.; Isom, S.; Arcury, T.A. Heavy metals exposures among Mexican farm workers in eastern North Carolina, Envir. Res. 2010 110, 83-88

4University of Massachusetts at Amherst Department of Chemistry

The Soil, Rice and Water Connection

Average rice consumption between 400 and 650 g/day by typical adults in the arsenic-affected areas of Bangladesh, the intake of arsenic through rice stood at 0.20-0.35 mg/day.

Daily water consumption of 4 L drinking water, arsenic intake through drinking water stands at 0.2 mg/day.

Background arsenic concentration ranges from 2.35 to 0.18 mg kg-1 (ppm) in dry soil and from 50.6 to 0.03 mg kg-1 (ppm) in wetlands.

Rahman, A.M.; Hasegawa, H.; Rahman, M. M.; Rahman, A. M.; Miah, M.M.; and Miah, M.A.M.Arsenic accumulation in rice (Oryza sativa L.): Human exposure through food chain.Eco. and Enviro. Safety, 2008, 69, 317-342

Chen, M., Ma, L.Q., Harris, W.G. Arsenic concentrations in Florida surface soils: Influence of soil type properties, Soil Sci. Soc. of Amer. J., 2002, 66, 632-640

5University of Massachusetts at Amherst Department of Chemistry

Portable XRF Technology

“Accurate, fast measurement of arsenic in the field remains a technical challenge. Technological advances in a variety of instruments have met with varying success. However, the central goal of developing field assays that reliably and reproducibly quantify arsenic has not been achieved.”

Melamed, D. Anal. Chim. Acta, 2005, 532, 1-13.

• There is a spectral interference between Arsenic and Lead

• Arsenic detection limit of 7 mg kg-1 (ppm) and Lead 13 mg kg-1 (ppm)

• Cost: $25,000Innov-A-Systems XRF Report on Detection Limit.http://www.equipcoservices.com/pdf/manuals/AsinSoilApp.pdf, (accessed February, 2010)

6University of Massachusetts at Amherst Department of Chemistry

Plot of Blue Pixel Count Versus Concentration of Arsenic at Varied Mass

Blue pixel count versus concentration of arsenic in mg kg-1 for five mass values at 1-20 reacted 20 minutes, 0.1 g (diamond), 0.5 g (square), 1 g (triangle), 5 g (x with a line), 10 g (x).

7University of Massachusetts at Amherst Department of Chemistry

Plot of Blue Pixel Count Versus Concentration of Arsenic at 0.5 g soil and a Large Range of Concentrations at Different Times

Plot of concentration of blue pixel value versus arsenic for 0.1 grams mass soil at 1-1000 mg kg-1 for four time periods; 1 hour(diamond), 45 min. (square), 30 min. (triangle), 20 min.(x).

8University of Massachusetts at Amherst Department of Chemistry

Plot of Blue Pixel Count Versus Concentration of Arsenic at Varied Soil Mass and Time

Plot of concentration of arsenic in mg kg-1 versus average blue values for 0.05 g mass soil at 1 to 1000 mg kg-1for four time periods, 20 min.(x), 30 min. (triangle), 45 min. (square), 1 hour (diamond)

9University of Massachusetts at Amherst Department of Chemistry

Extraction of Arsenic from Soils with Different Solvent

Plot of concentration of arsenic in mg kg-1 versus average blue values for 0.1 g mass soil at 20 to 1000 mg kg-1for three extracting solvents, sulfamic acid 1 M (blue diamond), phosphoric acid 1 M (red square), phosphoric acid 1 M at 24 hours (green triangles).

10University of Massachusetts at Amherst Department of Chemistry

Future Work

Soils: experiment with a variety of soils containing wide ranges of particle distribution.

Solvents: use extraction procedures to determine if extraction enhances sensitivity.

Time: continue to investigate the relationship between time of exposure and ability to extract the metals from the soil matrix.

Kits: experiment with different manufacturer’s kits.