IMMUNOLOGICAL DETERMINATION OF TRIAZINE PESTICIDES BOUND TO SOIL HUMIC ACIDS (BOUND RESIDUES)

An immunological method for the determination of triazine herbicides c ovalently bound to soil humic acids has been developed. A sandwich-imm unoassay has been performed, based on both polyclonal humic acid-antib odies and monoclonal triazine-antibodies. A peroxidase-labelled third antibody has been used for the photometric detection. A triazine-humic acid conjugate served as calibration standard. The coupling density f or this conjugate has been determined by measuring the difference of f ree amino groups both with ninhydrin and with the trinitrobenzene sulf onic acid method. In addition, the coupling density has been confirmed by scintillation counting using a C-14-atrazine derivative. Due to no nspecific interactions between antibody proteins and humic acids, diff erent blocking steps had to be performed. Finally, the assay has been applied to a triazine contaminated soil sample. Humic acids (including bound residues) have been extracted by diluted sodium carbonate solut ion. Concentrations of bound atrazine residues have been found in the range of 2 mg/kg soil on fields where triazine herbicides has been app lied over a period of 21 years. These results are comparable to both t he applied amount and the nonextractable fraction.