Comparative sorption, desorption and leaching potential of aminocyclopyrachlor and picloram

• Published in: Journal of environmental science and health. Part B, Pesticides, food contaminants, and agricultural wastes Pesticides, food contaminants, and agricultural wastes, 2013, Vol.48 (12), p.1049-1057
• Main Authors: Oliveira, Rubem S, Alonso, Diego G, Koskinen, William C, Papiernik, Sharon K
• Format: Article
• Language: English
• Subjects: Adsorption; Agronomy. Soil science and plant productions; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Desorption; Fundamental and applied biological sciences. Psychology; Groundwater; Groundwater - analysis; Half-Life; Herbicides; Herbicides - chemistry; hysteresis; Leaching; mobility; Parasitic plants. Weeds; Phytopathology. Animal pests. Plant and forest protection; picloram; Picloram - chemistry; Pyrimidine carboxylic acids; Pyrimidines - chemistry; soil; Soil - chemistry; Soil Pollutants - chemistry; soil properties; Soils; Sorption; sorption isotherms; Water Pollutants, Chemical - chemistry; Weeds
• ISSN: 1532-4109; 0360-1234; 1532-4109
• DOI: 10.1080/03601234.2013.824291

Sorption and desorption of aminocyclopyrachlor (6-amino-5-chloro-2-cyclopropylpyrimidine-4-carboxylic acid) were compared to that of the structurally similar herbicide picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) in three soils of differing origin and composition to determine if picloram data is representative of aminocyclopyrachlor behavior in soil. Aminocyclopyrachlor and picloram batch sorption data fit the Freundlich equation and was independent of concentration for aminocyclopyrachlor (1/n = 1), but not for picloram (1/n = 0.80–0.90). Freundlich sorption coefficients (Kf) for aminocyclopyrachlor were lowest in the eroded and depositional Minnesota soils (0.04 and 0.12 μmol ⁽¹–¹/ⁿ⁾ L¹/ⁿ kg⁻¹) and the highest in Molokai soil (0.31 μmol ⁽¹–¹/ⁿ⁾ L¹/ⁿ kg⁻¹). For picloram, Kf was lower in the eroded (0.28 μmol ⁽¹–¹/ⁿ⁾ L¹/ⁿ kg⁻¹) as compared to the depositional Minnesota soil (0.75 μmol ⁽¹–¹/ⁿ⁾ L¹/ⁿ kg⁻¹). Comparing soil to soil, Kf for picloram was consistently higher than those found for aminocyclopyrachlor. Desorption of aminocyclopyrachlor and picloram was hysteretic on all three soils. With regard to the theoretical leaching potential based on groundwater ubiquity score (GUS), leaching potential of both herbicides was considered to be similar. Aminocyclopyrachlor would be ranked as leacher in all three soils if t₁/₂ was > 12.7 days. To be ranked as non-leacher in all three soils, aminocyclopyrachlor t₁/₂ would have to be