Date of Award


Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)


Ecology and Environmental Sciences


Howard H, Patterson

Second Committee Member

Joan Trial

Third Committee Member

Adria Elskus


Pesticide application on blueberry fields is a primary non-point source (NPS) of pollution in the Pleasant and Narraguagus River watersheds (Maine, USA). The common practice of taking a grab sample (1 to 4 L) for pesticide analysis measures only instantaneous concentrations and cannot estimate time-weighted average (TWA) concentration of contaminants, as a fundamental part of the ecological risk assessment process. The use of passive samplers has emerged recently to mimic the exposure of organisms to chemicals over extended time periods. While several passive sampling studies have been conducted, the influence of the exposure time on the TWA concentration of contaminants has seldom been evaluated. Here, conventional grab sampling was compared with sequential deployments of the Polar Organic Chemical Integrative Sampler (POCIS) for the monitoring of pesticides chlorothalonil, propiconazole, hexazinone and phosmet, in surface waters in the above-mentioned watersheds.

Pesticide sampling rates (Rs), defined as the volume of water extracted daily by POCIS, determined in the laboratory, showed that, for all pesticides, the level of natural organic matter (NOM) in the water had no effect on the magnitude of the Rs (p > 0.05), whereas values were significantly increased by flow and turbulence (p < 0.001). The results indicate that the Rs generated from laboratory experiments simulating field conditions can be used to estimate ambient water concentration of the studied pesticides without correction for sorption to NOM.

POCIS deployed in the field accumulated quantifiable levels of pesticides that were not detected in grab samples. Pesticide water concentrations estimated from POCIS ranged from <0.02 to 2.943 μL-1 and were consistent with previous surveys conducted in the study area and elsewhere. Estimates of annual mass transport indicated that about 14 kg of chlorothalonil, 20 kg of propiconazole (isomers a & b) and 27 kg of hexazinone were discharged into the Narraguagus River.

POCIS estimated ambient water concentrations of pesticides within a factor of 1.2 on average, compared with means from grab samples. POCIS integratively accumulated pesticides over time, with one exception. The observed departure from linearity at one site was probably due to exceptional increases in flow and sediments in the stream channel during the POCIS deployment period and requires further research to correct POCIS concentrations for these variables. Nonetheless, the findings of this study indicate that POCIS can be used as a cost-effective alternative to repetitive grab samplings for monitoring pesticides in Maine surface waters.