Comparison of time-integrated pesticide concentrations determined from field-deployed passive samplers with daily...

The rate of release of three performance reference compounds (PRCs) from passive samplers when deployed in rivers with variable flow and temperature were compared with their release from passive samplers in a laboratory continuous-flow system. The passive samplers used in the current study were constructed from low-density polyethylene bags containing trimethylpentane solvent (TRIMPS). The half-lives for release from the TRIMPS of the PRCs tributylphosphate, endosulfan sulfate, and chlorpyrifos-ethyl were 7.3, 20.8, and >75 d, respectively, when deployed in rivers, compared with half-lives of 10.4, 26.5, and approximately 73 d in a laboratory flow system. The mean pesticide concentrations taken up by TRIMPS deployed for periods from 7 to 22 d in rivers adjacent to cotton fields were determined during two studies in the austral summer of 2000/2001 and 2001/2002. During the studies, mean total endosulfan and chlorpyrifos-ethyl concentrations were also determined from daily river-water extractions. Regression equations established in previous laboratory studies related the concentration factors into TRIMPS to the time of deployment for a number of pesticides, including endosulfan and chlorpyrifos-ethyl. The laboratory-derived calibration factors were used to determine the mean pesticide concentrations for each deployment period, and these were compared with the cumulative mean concentrations calculated from the daily extractions. The pesticide concentrations determined using the TRIMPS were within twofold of the cumulated mean of the daily river-water extractions of endosulfan and chlorpyrifos-ethyl for deployment periods of 7 to 22 d when the mean river-water concentrations were >0.005 microg/L.