Assay for the detection of a wide range of organophosphate (including thiophosphate), and carbamate pesticides in water (drinking water, ground water, surface water and well water). This assay can also be used for testing these compounds collected as dislodgeable residues from a surface wash, as well as pesticide residues prepared as a dry extract (please contact Eurofins Abraxis technical support for information). The test is a qualitative, colorimetric assay (modification of the Ellman method) for the detection of organophosphates and carbamates, based on a modification of their inhibition of the enzyme Acetyl Cholinesterase (ACh-E). Ach-E hydrolyzes acetylthiocholine (ATC) which reacts with 5,5'-Dithio-bis(2-Nitrobenzoic Acid) [DTNB] to produce a yellow color which is read at 405 nm. If OP or Carbamate pesticides are present in a sample, they will inhibit ACh-E and therefore the color formation will be reduced or absent depending on their concentration. Detection limits of the various OP/C pesticides differ depending on their ability to inhibit the enzyme. If it has been established that only a single OP/C is present, the test can be used in conjunction with appropriate standards for quantitative testing.