A method and system for enabling the determination of kinetic rates within a fluid of interest including directing fluid flow exiting a test bed to a multi-port switching valve. The multi-port switching valve to switches the fluid to a number of channels connected to in in-flow extraction cartridge. Analytes of interest from the fluid flow our concentrated and captured on an extraction medium. Rates are determined by (i) sequentially channeling the fluid through the each of the plurality of channels for a preselected time duration, (ii) analyzing the extraction cartridges, and computing the kinetic rate of interest.

Contaminant mass collection in saturated sedimentary environments for bioavailability determination. A casing includes a screen between the environment that is subject to sampling, such as a saturated sediment and the device itself. The casing includes a water intake zone, a pump, and sorptive media. The water intake zone, the pump, the screen and the sorptive media, are all operably linked in sequence. The screened casing is secured to form an in situ device; the screen is in fluid communication with the water intake zone and excludes endemic sediments and aquatic life. The in situ device is deployed in the saturated sedimentary environment. The pump operates to concentrate analytes from the selected environment in the sorptive media, where the concentrated analytes include the analyte mass of time-weighted fluid samples.