Assessment of Potential Interferences and Technical Strategies to Minimize False Positive Bias in Analytical Testing for Organochlorine Pesticides Dieldrin, Endrin, and DDT in River Water Samples

Aldrin, Dieldrin, Endrin, Endrin Ketone, Endrin Aldehyde and DDT and its isomers are organochlorine pesticides (OCPs) widely used as pesticides between the 1950s and 1970s when concerns about toxicity and persistence in the environment resulted in regulatory bans. Residual concentrations of OCPs in soils, groundwater and agricultural runoff continue to contaminate surface water largely from soil erosion. This paper investigates ambient background of OCPs in the Atibaia River in Sao Paulo, Brazil where detections of OCPs (banned in 1985) became more frequent with the introduction of lower detection limit methods in 2021. This study investigates why OCPs were detected more frequently decades after agricultural application. Although reliable for pesticides analysis, USEPA Method 8081 (dual column GC/ECD) can be prone to interferences, particularly at low levels. The purpose of the investigation presented in this paper was to determine if other substances in the river water could bias the detection of organochlorine pesticides at low concentrations near the method detection limit. Analysis of the laboratory surface water data suggests detections of these OCPs at very low levels near the method detection limit are potentially caused by non-target analyte (NTA) interferences associated with other natural and anthropogenic substances that may result in false positives and positive bias. This paper recommends several possible modifications to the analytical method that could minimize this bias in samples collected during future sampling campaigns.