ATRAZINE INTERACTION WITH TROPICAL HUMIC SUBSTANCES BY ENZYME-LINKED-IMMUNOSORBENT-ASSAY

Enzyme-Linked Immunosorbent Assay (ELISA) has been evaluated by analyz ing rich-humic water samples from tropical rivers. The samples were sp iked with atrazine at ppb level Different pHs (4 to 9) and humic conce ntrations (2.5 to 40 mg L-1) were investigated. The assay performance showed a strong dependence on the pH values and amount of humic matter at low atrazine concentration. From all the conditions studied the lo w pH (pH 4) and high humic substances concentrations (40 mg L-1) showe d the greatest influence. The IC50 value to control sample (no humic) diminished from 0.28 nmol L-1 to 0.64 nmol L-1 to humic acid solution. This effect is specially noted for the humic acid fractions, since fu lvic acid fractions showed no significant change on the immunoassay re sults. Additionally, it has been demonstrated that at basic pH the mat rix effect produced by the natural Brazilian water sample containing h umic substances even at 40 mg L-1 disappears. Therefore, the ELISA met hod used to determine atrazine, can be employed to determine this pest icide in water samples containing humic substances without prior prepa ration.