Contact-time-dependent atrazine residue formation in surface soils

Area of Science:

• Environmental Chemistry
• Soil Science
• Agrochemicals

Background:

• Atrazine is a widely used herbicide.
• Understanding the fate of herbicides in soil is crucial for environmental protection.
• Nonextractable residues (NER) represent a significant portion of applied pesticides.

Purpose of the Study:

• To evaluate the formation of nonextractable atrazine residues in sterilized agricultural and woodland soils.
• To determine the influence of soil-herbicide contact time on atrazine extractability and NER formation.
• To investigate the association of NER with soil organic matter components (fulvic acid, humic acid, humin/mineral).

Main Methods:

• Sterilized agricultural and woodland soils were pre-loaded with (14)C-atrazine for various contact periods.
• Sequential fill-and-draw extractions (water, ethylacetate/water, alkali) were used to determine extractability.
• Soil components (fulvic acid, humic acid, humin/mineral) were separated to quantify (14)C-activity associated with each.

Main Results:

• Increased herbicide-soil contact time led to decreased water extractability and increased NER formation.
• At the longest contact periods, 35-50% of the pre-loaded atrazine was recovered in fulvic acid, humic acid, and humin/mineral fractions.
• Woodland soil, with higher humic acid and humin content, showed greater contribution to NER formation compared to agricultural soil.

Conclusions:

• Physicochemical processes within soil mineral and organic matter matrices significantly influence the long-term fate of atrazine.
• Nonextractable residue formation is a dynamic process influenced by contact time and soil properties.
• These findings highlight the importance of considering intra-soil interactions in pesticide fate assessments.