Sampling rates , SPMD water

Some introductory comments on the conceptual basis of SPMD uptake (ku) and release (ke) rate constants and the associated sampling rates (i.e., Rs) are in order. The can be conceptualized as the volume of air or water cleared of chemical per unit sampler mass or volume per unit time (e.g., mL g d or mL mL d ) and Rs is the volume of air or water cleared per unit time (e.g., L d ). Thus, the only difference between ku and Rs is that Rs is not normalized to a unit mass or unit volume of sampler. In the context of organism exposure (see Section l.L), the SPMD is equivalent to the encounter volume times the fractional bioavailability of the chemical (which excludes dietary uptake). The release rate constant (d ) is equal to kuK J. 

Huckins, J.N. Petty, J.D. Orazio, C.E. Lebo, J.A. Clark, R.C. Gibson, V.L. Gala, W.R. Echols, K.R. 1999, Determination of uptake kinetics (sampling rates) by lipid-containing semipermeable membrane devices (SPMDs) for polycyclic aromatic hydrocarbons (PAHs) in water. Environ. Sci. Technol. 33 3918-3923. 

When the k and SPMD-water partition coefficient of the PRC are known, its Rs can be calculated from Eq. 3.20. More precisely, we assume that the PRC is representative of the in situ sampling rates of target compounds with similar physicochemical properties as the PRC. Various approaches have been used to estimate sampling rates for all analytes from the PRC-derived sampling rates (see Section 3.6.). 

Table A.5 Water Sampling Rates (/ ss) and Uptake Rate Constants (kys) of 4.5 g, 460 cm SPMDs at a Temperature of 25 °C, and Flow Rates of 0.01 and 50 cm s (Luellen and Shea, 2002)...

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