Analytical applications of immunoassays in environmental and agricultural chemistry: Study of the fate and transport of herbicides

Abstract

Enzyme-linked immunosorbent assay (ELISA) has become popular recently in the analysis of herbicides in many environmental samples. In this study, interference due to the presence of other herbicides and their degradation products, and other factors that may potentially affect the performance of ELISAs, such as percent dissolved organic matter and solvents used for sample extraction, were investigated. ELISA's for the most widely used herbicides, such as atrazine, alachlor, metolachlor, and 2,4-D, were used to analyze samples from various sources which are representative of the natural environment. These include samples from lakes, rivers, reservoirs, precipitation, and ground-water wells. Selected samples were confirmed by gas chromatography/mass spectrometry or by high-performance liquid chromatography to show the validity of the immunoassay results.

Solid-phase extraction (SPE) was used as a sample pre-concentration step to improve the detection limit of the ELISA for the measurement of low-levels of atrazine in rain and pristine water samples. Also, an SPE method was used to effectively separate alachlor and the alachlor ethanesulfonic acid metabolite (ESA) in order to quantitatively measure the concentration of each compound using the same polyclonal antibodies which recognize both alachlor and ESA.

Polyclonal antibodies were produced against 2,4-D by immunizing rabbits. The polyclonal antibodies generated were used for ELISA and for preparation of immunoaffinity chromatography columns. The use of SPE as a preconcentration step for low-level analysis of 2,4-D was not successful because of the simultaneous isolation of humic substances which interfered with both ELISA and HPLC analysis. The use of immunoaffinity columns for sample preparation of water samples containing 2,4-D reduced the problems associated with humic substances.

This research also identified important degradation products of the widely used chloroacetanilide herbicides, alachlor and metolachlor. It was shown that metolachlor degrades to a metolachlor ESA metabolite, which is analogous to the alachlor ESA. Using the combination of analytical methods developed above, the relative mobility and persistence of both the parent herbicides and metabolites were cost-effectively determined in an experimental field plots. In addition, the leaching potentials of the four chloroacetanilide herbicides, acetochlor, alachlor, metolachlor, and propachlor were compared.