Sorption of acetochlor, S‐metolachlor, and atrazine in surface and subsurface soil horizons of Argentina

Abstract

Understanding herbicide sorption within soil profiles is the first step to predicting their behavior and leaching potential. Laboratory studies were conducted to determine the influence of surface and subsurface soil properties on acetochlor, atrazine, and S-metolachlor sorption. Soil samples were taken from horizons A, B, and C of two loamy soils of the humid pampas of Argentina under no-till management; horizon A was divided into two layers, A(0) (0-5 cm) and A(1) (5 cm to the full thickness of an A horizon). Sorption isotherms were determined from each sampled horizon using the batch equilibrium method and seven concentrations (0, 0.1, 0.5, 2.0, 5.0, 10.0, and 20.0 mg L(-1)). Sorption affinity of herbicides was approximated by the Freundlich equation. The sorption strength K(f) (mg(1 - 1/n) kg(-1) L(1/n) ) over the soils and horizons studied followed the order S-metolachlor (16.51-29.19) > atrazine (4.85-12.34) ≥ acetochlor (5.17-11.97), which was closely related to the hydrophobicity of herbicides expressed as octanol-water partition coefficient (K(OW) ). The K(f) values of the three herbicides were positively correlated with soil organic carbon, with a significance of p < 0.01. Values of K(f) for the three herbicides decreased with depth in the two soils, indicating greater sorption onto surficial soil horizons and possibly a delayed transport toward subsurface soils and subsequent pollution of groundwater.

Pesticide fate on catchment scale: conceptual modelling of stream CSIA data

“…In support of this assumption, previous studies have found strong sorption of S-metolachlor to surface soils, where the organic matter content is typically higher than at greater depth (e.g. Bedmar et al, 2011;Rice et al, 2002;Si et al, 2009). Subsequently, infiltration of precipitation leads to pesticide desorption and input into the dissolved phase of the source zone reservoir.…”

Effect of precipitation on the dissipation, efficacy and selectivity of three chloroacetamide herbicides in sunflower

“…The metolachlor adsorption in soil is quite high (Bedmar et al 2011) and increases with soil organic carbon content. The selectivity of metolachlor in sunflower is relatively good and, therefore, may also be used for early post-emergent application (Pannacci et al 2007), but spectrum of controlled weed is relatively narrow.…”

Retention characteristics of acetochlor in soils collected from different depths in relation to soil properties (Žitný ostrov area, SW Slovakia)

“…Statistical analyses (Table 3) showed that the sorption of acetochlor in soils was highly correlated with soil organic carbon content (R = 0.99, P < 0.001), and the humic acid and fulvic acid carbon contents (R = 0.98 and R = 0.97, P < 0.001). Several studies have suggested that soil organic matter exhibits a high affinity for acetochlor and plays the most prominent role as a sorbent of acetochlor in soils (Wang et al 1999;Hiller et al 2008;Bedmar et al 2011). The calculated K oc values for acetochlor were similar among the soils, confirming that organic matter of the soils had similar sorption affinity for the herbicide and that TOC was the most important factor for acetochlor sorption in soils.…”

“…The different shapes of sorption isotherms might be attributed to the occurrence of more sorption mechanisms included in the acetochlor sorption, likely due to differences in composition of the soils and their heterogeneous nature. Several authors have reported non-linear isotherms of L-and S-types for acetochlor sorption in soils with contrasting physico-chemical properties (Taylor et al 2004;Hiller et al 2008;Bedmar et al 2011). Based on the K fs values, the extent of acetochlor sorption decreased with increasing soil depth for each soil type (Table 2).…”

“…The propensity of acetochlor to leach downward through the soil profile is dependent primarily on its sorption and desorption behaviour in soil. The sorption of acetochlor in different soil types has been studied by various authors (Wang et al 1999;Lengyel & Földényi 2003;Taylor et al 2004;Hiller et al 2009;Bedmar et al 2011) who proved it to be moderate to strong depending on the soil physico-chemical properties. Reported Freundlich and distribution coefficient (K fs and K d ) values for the sorption of acetochlor in soils range from 1.44 to 16.9 mg…”