Atrazine Adsorption by Soil Colloids and Co‐Transport through Subsurface Environments

Abstract

This study evaluated the potential of water‐dispersible soil colloids with diverse physicochemical and mineralogical characteristics to adsorb and mediate the transport of atrazine through macropores of intact soil columns. The soil columns were taken from the upper solum of an Alfisol (Maury) and a Mollisol (Loradale) in the Bluegrass region of Kentucky. Six different colloid suspensions mixed with atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine] were introduced at a constant flux into the undisturbed soil columns. The eluents were collected and analyzed periodically for colloid and herbicide concentrations. Colloid recovery in the eluents ranged from 45 to 90%. The presence of colloids enhanced the transport of atrazine by 2 to 18%, depending on colloid type and mobility. Colloids with higher pH, total exchangeable bases (TEB), cation‐exchange capacity (CEC), organic carbon (OC), surface area (SA), and electrophoretic mobility (EM), showed greater mobility, greater affinity for atrazine, and greater potential to co‐transport atrazine. In contrast, increased levels of kaolinite, Fe, and Al inhibited atrazine adsorption and transport. Soil columns with higher hydraulic conductivity, well‐developed macropore system, and lower surface reactivity (Maury) also transported more atrazine. In spite of the increased transportability of atrazine by the presence of soil colloids, the colloid‐bound herbicide fraction contributed ≤1% to the observed increase. This suggests that matrix‐surface‐site exclusion and blocking mechanisms induced by the presence of colloids are more important than colloid sorption in promoting atrazine mobility in subsurface soil environments.

Atrazine and picloram adsorption in organic horizon forest samples under laboratory conditions

“…The atrazine isotherm resulted in high Freundlich constants (Table 4). As K f ind ica tes the str eng th or deg ree of the adsorption and 1/n indicates the curve slope (Sonon and Scwab, 1995), results show that atrazine has high adsorption to the 0 horizon. This behavior was expected sinc e atrazin e shows high adsorption to soil particles and low solubility.…”

“…The adsorption pattern of atraz ine and picloram was fit to the Freundlich isotherm, whi ch is in agr eement wit h other studie s (Gover, 1971;Sonon and Scwab, 1995). The Freundlich isotherm has been commonly used in studies of adsorption, and it is well suited to the adsorptive behavior of herbicide (Ebato et al, 2001).…”

“…This behavior was expected sinc e atrazin e shows high adsorption to soil particles and low solubility. The high adsorption to the 0 horizon can be noted when comparing the atrazi ne K f value (67 .54 ) to the fou nd for atr azi ne adsorption to whole soil particles (1.0 to 4.0) (Barriuso et al, 1992;Nakagawa et al, 1995;Seta and Karathanasis, 1997;Gomes et al, 2002). On the oth er han d, the amount of atrazine adsor bed by the amount of litt er, represented by the normalized mass (Table 3) was lower in the 0 horizon (1.01 µg g -1 ) when compared to 6.35 µg g -1 obtained by (Huang et al, 1984) for clay particles.…”

“…Ma ny st udie s ha ve be en re port ed on the adsorption of herbicides on different soils and soil constituents (Barriuso et al, 1992;Gover, 1971;Huang et al, 1984;Seta and Karathanasis, 1997;Wauchope and Myers, 1985) but few studies have reported herbicide ads orp tion to for est soi l org ani c hor izo ns (Sundaram, 1995). Adsorption of herbicides within organic horizons of forested SMZs may play an important role in limiting herbicide movement from recently treated sites under conditions where high precipitation generates surface runoff.…”

The significance of colloids in the transport of pesticides through Chalk

“…Numerous studies have been undertaken that show pesticide can sorb to colloids and potentially enhance their transport (e.g. Vinten et al, 1983;Worrall et al, 1999;Seta and Karathanasis, 1997;Kulikova and Perminova, 2002).…”