Assessing Metal Contamination in Lead Arsenate Contaminated Orchard Soils using Near and Mid-Infrared Diffuse Reflectance Spectroscopy.

Historic use of lead-arsenate as a pesticide in apple orchards caused many soils to become contaminated with arsenic (As) and leads (Pb). Human health effects from this contamination are of primary concern for regulatory agencies, and communities. Wet chemistry methods for soil analyses are relatively expensive, time-consuming, and may also generate environmental pollutants. This paper explores the application of rapid and nondestructive infrared spectroscopy for assessing As and Pb, along with other minerals (carbon, nitrogen, iron and phosphorus) in orchard soils. A total of 202 soil samples at the 0-15 cm depth were collected from orchard soils with a history of lead arsenate use from six major apple producing states, Maryland, Michigan, New York, Virginia, Washington and West Virginia. Samples were scanned at near-infrared (400-2498 nm) and mid-infrared (2500 to 25000 mm) wavelength regions using NIR systems. Partial least squares (PLS) with the one-out validation procedure was used to develop calibrations. Results reported various levels of soil metal content (5 - 220 mg kg^-1 for As, 15-325 mg kg^-1 for Pb, 2.5 – 15.0 mg kg^-1 for iron) and other minerals (0.5 to 18 % for carbon, 0.2 – 3.5% for nitrogen, 150 -1250 mg kg^-1 for phosphorus). Mid-infrared spectroscopy performed better compared to Near-infrared spectroscopy. The best coefficients of determination (r²) values for metals (As, Pb and iron) were 0.68, 0.76 and 0.87 respectively. With the exception of phosphorus, Correlations were poor with the other minerals. High carbonates in soil may have affected predictability of carbon. This study demonstrated that the prediction of As and Pb in lead-arsenate contaminated orchard soils is feasible.