The primary goal of this dissertation was to develop and evaluate an improved aquatic passive sampling device (PSD) for measurement of polar organic contaminants. Chemical uptake of current polar-PSDs (e.g., POCIS – polar organic chemical integrative sampler) is dependent on the specific environmental conditions in which the sampler is deployed (flow-rate, temperature), leading to large uncertainties when applying laboratory-derived sampling rates in-situ. A novel configuration of the diffusive gradients in thin-films (DGT) passive sampler was developed to overcome these challenges. The organic-DGT (o-DGT) configuration comprised a hydrophilic-lipophilic balance® sorbent binding phase and an outer agarose diffusive gel (thickness = 0.5–1.5 mm), notably excluding a polyethersulfone protective membrane which is used with all other polar-PSDs. Sampler calibration exhibited linear uptake and sufficient capacity for 34 pharmaceuticals and pesticides over typical environmental deployment times, with measured sampling rates ranging from 9–16 mL/d. Measured and modelled diffusion coefficients (D) through the outer agarose gel provided temperature-specific estimates of o-DGT sampling rates within 20% (measured-D) and 30% (modelled-D) compared to rates determined through full-sampler calibration. Boundary layer experiments in lab and field demonstrated that inclusion of the agarose diffusive gel negated boundary layer effects, suggesting that o-DGT uptake is largely insensitive to hydrodynamic conditions. The utility of o-DGT was evaluated under a variety of field conditions and performance was assessed in comparison to POCIS and grab samples. o-DGT was effective at measuring pharmaceuticals and pesticides in raw wastewater effluents, small creeks, large fast-flowing rivers, open-water lakes, and under ice at near-zero water temperatures. Concentrations measured by o-DGT were more accurate than POCIS when compared to grab samples, likely resulting from the influence in-situ conditions have on POCIS. Modelled sampling rates were successfully used to estimate semi-quantitative water concentrations of suspect wastewater contaminants using high-resolution mass spectrometry, demonstrating the unique utility of this o-DGT technique. This dissertation establishes o-DGT as a more accurate, user-friendly, and widely applicable passive sampler compared to current-use polar-PSDs. The o-DGT tool will help facilitate more accurate and efficient monitoring efforts and ultimately lead to more appropriate exposure data and environmental risk assessment.