Characterization of soil organic matter by FT-IR spectroscopy and its relationship with chlorpyrifos sorption

Abstract

Sorption of non-ionic organic compounds to soil is usually expressed as the carbon-normalized partition coefficient (K_OC) assuming that the main factor that influences the amount sorbed is the organic carbon content (OC) of the soil. However, K_OC can vary across a range of soils. The influence of certain soil characteristics on the chlorpyrifos K_OC values variation for 12 representative soils of the Northpatagonian Argentinian region with different physicochemical properties was investigated for this study. The chlorpyrifos sorption coefficients normalized by the OC content were experimentally obtained using the batch equilibrium method; the K_OC values ranged between 9000-20,000 L kg^-1. The soil characteristics assessed were pH, clay content and spectral data indicative of soil organic matter (SOM) quality measured by FT-IR on the whole soil. The bands considered in the spectroscopic analyses were those corresponding to the aliphatic components, 2947-2858 cm^-1 (band A) and the hydrophilic components, 1647-1633 cm^-1 (band B). A significant relationship was found (R² = 0.66) between chlorpyrifos sorption (K_OC) and the variables pH and A/B height band ratio. The correlation between the values predicted by the derived model and the experimental data was significant (r = 0.89 p < 0.05). Thus, this methodology could be used to estimate chlorpyrifos sorption coefficient through the use of a simple, rapid, and environmentally-friendly measurement. K_OC analysis in relation to soil properties represents a valuable contribution to the understanding of the attenuation phenomena of the organic contaminants off-site migration in the environment.

Keywords: FT-IR spectroscopy; Organic matter; Pesticides; Sorption.