Studies on bound (14)C-chlorsulfuron residues in soil

Area of Science:

• Environmental Chemistry
• Soil Science
• Agrochemicals

Background:

• Chlorsulfuron is a widely used herbicide, but the phytotoxicity of its bound residues to rotational crops remains poorly understood.
• Nonextractable (bound) residues of pesticides in soil can pose risks to subsequent crops.

Purpose of the Study:

• To investigate the formation and distribution of nonextractable chlorsulfuron residues in soil organic matter fractions.
• To determine the bioavailability of bound chlorsulfuron residues under specific soil conditions.

Main Methods:

• Radiolabeled (14)C-chlorsulfuron was applied to soil, and residue fractions were analyzed over 150 days.
• Soil organic matter was fractionated into humic acid (HA), fulvic acid (FA), and humin.
• Autoclaving was used to assess the release of bound residues.
• Gas chromatography-mass spectrometry (GC-MS) identified released degradation products.

Main Results:

• Over 150 days, extractable chlorsulfuron decreased to 25.1%, while bound residues increased to 47.1%.
• Bound residues were distributed in soil organic matter fractions as: humic acid (HA) < humin < fulvic acid (FA).
• Autoclaving soil released bound (14)C-chlorsulfuron residues, yielding 2-amino-4-hydroxyl-6-methyl-1,3,5-triazine.

Conclusions:

• Bound chlorsulfuron residues form in soil and accumulate in organic matter fractions, particularly FA and humin.
• Bound chlorsulfuron residues can become bioavailable, potentially leading to phytotoxicity in rotational crops.
• Understanding residue dynamics is crucial for managing herbicide carryover and preventing crop damage.