Modeling the transport of organic chemicals between polyethylene passive samplers and water in finite and infinite bath conditions

Abstract

Understanding the transfer of chemicals between passive samplers and water is essential for their use as monitoring devices of organic contaminants in surface waters. By applying Fick's second law to diffusion through the polymer and an aqueous boundary layer, the authors derived a mathematical model for the uptake of chemicals into a passive sampler from water, in finite and infinite bath conditions. The finite bath model performed well when applied to laboratory observations of sorption into polyethylene (PE) sheets for various chemicals (polycyclic aromatic hydrocarbons, polychlorinated biphenyls [PCBs], and dichlorodiphenyltrichloroethane [DDT]) and at varying turbulence levels. The authors used the infinite bath model to infer fractional equilibration of PCB and DDT analytes in field-deployed PE, and the results were nearly identical to those obtained using the sampling rate model. However, further comparison of the model and the sampling rate model revealed that the exchange of chemicals was inconsistent with the sampling rate model for partially or fully membrane-controlled transfer, which would be expected in turbulent conditions or when targeting compounds with small polymer diffusivities and small partition coefficients (e.g., phenols, some pesticides, and others). The model can be applied to other polymers besides PE as well as other chemicals and in any transfer regime (membrane, mixed, or water boundary layer-controlled). Lastly, the authors illustrate practical applications of this model such as improving passive sampler design and understanding the kinetics of passive dosing experiments.

Determination of silicone rubber and low‐density polyethylene diffusion and polymer/water partition coefficients for emerging contaminants

“…The model of Equation is approximate because it assumes a constant δ p / D p . The concentration gradient that establishes in the polymer over time will result in a ratio that will not remain constant over time .…”

“…The model of Equation 1 is approximate because it assumes a constant d p / D p . The concentration gradient that establishes in the polymer over time will result in a ratio that will not remain constant over time [23]. Equilibrium between the concentration in water and that in the sampler is reached when a sampler is deployed for a sufficiently long period.…”

Calibration of silicone rubber rods as passive samplers for pesticides at two different flow velocities: Modeling of sampling rates under water boundary layer and polymer control

“…Each transport mechanism contributes to the resistance to mass transfer (1/k o ), calculated using Equation 1, with k w and k s as the mass transfer coefficients in the water and the silicone rubber polymer respectively, and K sw the silicone/water partition coefficient [26,29,30]. We focused only on the theory for membrane-free or monophasic samplers, such as silicone rubber plates.…”

“…It is a simple and approximated model, unlike the 2-phase Fickian model [29] (considering a time-dependent D s and resulting in nonlinear diffusion profiles in the polymer) that would lead to more accurate results. It is a simple and approximated model, unlike the 2-phase Fickian model [29] (considering a time-dependent D s and resulting in nonlinear diffusion profiles in the polymer) that would lead to more accurate results.…”

“…Transport across the biofilm layer for long exposure in water was neglected in the present work. Each transport mechanism contributes to the resistance to mass transfer (1/k o ), calculated using Equation 1, with k w and k s as the mass transfer coefficients in the water and the silicone rubber polymer respectively, and K sw the silicone/water partition coefficient [26,29,30].…”