ARS | Publication request: EVALUATION OF ATRAZINE POSITIVE AND FALSE POSITIVE IMMUNOASSAY DETECTIONS IN GROUND WATER

Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 8, 1997
Publication Date: N/A

Interpretive Summary: There is considerable public concern about the presence of pesticides in ground water. Thus, it is important to have reliable and affordable methods for the detection of pesticides. There are several different ways to detect if pesticides are present. We used a recently developed technology, immunoassay, to determine if pesticides were present in ground water samples. The immunoassay test uses enzymes to find pesticides. The enzymes are selected to detect a specific compound; however, they may also detect compounds that are similar to the ones they were selected to find. When the enzymes identify the presence of a compound other than the one it was specifically selected to detect, that detection is called a "false positive." We analyzed 1800 samples with the immunoassay. Any time this test indicated pesticides present, the sample was retested by a second, more precise but more expensive, method to verify the results. It was discovered that false positive detections often occurred. We found that 57% of our detections were actually false positives.

Technical Abstract: False positive responses on an atrazine (6-chloro-N-ethyl-N'-(1-methylethyl -1,3,5-triazine-2,4-diamine) immunoassay kit were investigated to explain possible causes for these occurrences. Ground water samples were evaluated with the immunoassay kit and positive responses were confirmed using gas chromatography/mass spectrometry (GC/MS). Non-confirming samples (false positives) were analyzed for seven additional compounds on GC. Resulting GC/MS and GC analyses showed that 70% of the false positives could be attributed to two compounds. Prometon (6-methoxy-N,N'-bis(1-methylethyl)-1,3,5-triazine-2,4-diamine) was responsible for the majority (64%) of the false positive responses. The atrazine metabolite, deethylatrazine (2-chloro-4-amino-6-isopropylamino -1,3,5-triazine), was responsible for the other 6% of the false positives measured. Unattributed false positives (30%) were probably due to an overestimation of pesticide concentrations in the kit's lower detection range.