Soil Organic Matter Composition and pH as Factors Affecting Retention of Carbaryl, Carbofuran and Metolachlor in Soil

Abstract

The majority of studies concerning the environmental behavior of hydrophobic pollutants in soil consider soil organic matter (SOM) content as a main factor influencing chemical retention, whereas the composition of SOM and its individual fraction share are often neglected. In the present paper, carbaryl, carbofuran and metolachlor retention by loamy sand and loam topsoil materials is compared and referred to humic acids (CHA) and the residual carbon (CR) content of SOM. Additionally, the sorption-desorption behavior of agrochemicals in soils was tested at a pH of three to seven. Calculated isothermal parameters point to favorable, spontaneous and physical pesticide sorption. Groundwater ubiquity score (GUS) indexes confirmed the low leaching ability of metolachlor on soils and moderate of carbofuran. The high affinity of carbaryl to CR may explain its pronounced sorption in loam soil and the lowest percolation potential. Carbofuran retention in soils was associated with montmorillonite (Mt) and CR fractions. Meanwhile, metolachlor uptake was related to humic acid and Mt content of the soils. Lower pH enhanced retention of the agrochemicals, except for carbaryl sorption in sandy loam soil. Results of this study highlight that SOM composition and mutual share of individual organic carbon fractions alongside pH may play a crucial role in predicting non-ionic pesticide behavior in soil.

Influence of SOM Composition, Clay Minerals, and pH on 2,4-D and MCPA Retention in Peri-Urban Soils

“…Humic material of the L and C soils was fractionated (Table 3) according to the method recommended by the IHSS, described in Swift [45] with some modification [31,49]. Briefly, carbon of the low-molecular fulvic fraction was obtained by soil sample decalcification with 0.05 M H 2 SO 4 , followed by the centrifugation of the mixture.…”

“…Residual carbon (CR) was calculated by subtracting the sum of the humic and fulvic acids carbons from the total organic carbon (TOC) using the following equation: TOC-total organic carbon; CAC-carbon of low-molecular fulvic fraction, TEC-total extractable carbon (sum of CHA and CFA), CR-residual carbon. Previously published by Ćwiel ąg-Piasecka et al [49]. Additionally, the CHA/CFA index was calculated to evaluate the humification degree of the studied peri-urban topsoils.…”

“…Two sets of soils (L and C) varying in pH (3-7) were prepared according to the procedure described in a previous paper [49]. Briefly, the soils were saturated with distilled water and 1 M HCl solution was added dropwise to the soil slurry, followed by the equilibration of the mixtures until the desired final pH values were obtained.…”

“…In the next step, the samples were centrifuged (15 min, 10,000 rpm), filtered (0.45 µm), and the pesticide concentrations were analyzed with LC/MS-MS (TSQ Quantum Access MAX, Thermo Scientific, Waltham, MA, USA). The detailed quantification procedure can be found in our previously published papers [12,49,51]. In brief, the measuring conditions were as follows: analytical column-TS Hypersil GOLD column, 50 mm × 2.1 mm, with a 1.9 µm particle size; flow rate: 0.50 mL min −1 ; mobile phase A: deionized water with 0.1% of formic acid and 90% acetonitrile; mobile phase B: 10% of deionized water and 0.1% of formic acid; elution conditions: 100% of eluent A at the beginning of the measurement was gradually replaced by eluent B, achieving 100% in 20 min, with a subsequent re-equilibration time of 7 min.…”

The Interaction of Pesticides with Humin Fractions and Their Potential Impact on Non-Extractable Residue Formation

“…For pesticides deposited in the top horizon of soil, the storage capacity and kinetics of sorption control the transport velocity of a compound, as well as the change in its bioavailability over time [2,5]. So, the retention of pesticides largely depends on the soil mineral and soil organic phase (SOM), which influences the bioavailability/bioaccessibility of these compounds [7][8][9][10][11][12][13]. Pesticide binding affinity is the attraction between a pesticide and soil particles with the significant influence of environmental factors (humidity, temperature, insolation, pressure, etc.).…”