Fate of pendimethalin in soil and characterization of non-extractable residues (NER)

Abstract One important route of degradation of herbicide pendimethalin in soil leads to formation of non-extractable residues (NER). To investigate NER nature (irreversibly, chemically bound, including possible biogenic NER, or strongly sorbed and entrapped) residues of 14C-labelled pendimethalin in soil were investigated after conventional extraction with organic solvents by silylation. After 400 days of incubation, 32.0% of applied radioactivity (AR) was transformed into NER, 39.9% AR remained extractable. Mineralization reached 26.2% AR. Additionally, 14C-pendimethalin was incubated in soil amended with compost for 217 days to investigate the influence of organic amendments on NER formation. NER amounted to 37.8% AR, with 57.9% AR remaining extractable. Mineralization was negligible (1.4% AR). For all sampling times only low amounts of radioactivity were entrapped ( It can be concluded that no parent pendimethalin was found and NER of pendimethalin in soil are mainly formed by covalent binding to organic matrix with only low potential of remobilization under natural conditions.