What are passive samplers and how are they used?

Modified on: Mon, 18 Mar, 2019 at 9:51 AM


Passive sampling devices are techniques for monitoring environmental contaminants over time. The principle of operation is slow diffusion of the target parameter(s) into a collecting medium, until an equilibrium is reached with the surrounding environment. These techniques are called "passive" is because there are no moving parts or components that would force the contaminants into the sampling media. 

This is in contrast to a grab or discrete sampling approach, which comprises the majority of the samples that we receive (sampling the media of interest directly, at one point in time or compositing). 

Passive samplers are often deployed for extended periods of time and this factors in to calculating the concentration of target parameter(s). There are a variety of such devices and specific to the group of contaminants or compounds: semivolatiles, metals, volatiles. Passive samplers as described here pertain to water media only (although passive air sampling devices are often deployed as well). 

Advantages

The use of passive samplers allows for determination of average concentrations of contaminants over the duration of deployment. This means that any variations or fluctuations in concentrations will be captured and a more accurate representation of average environmental conditions is represented. 

The absence of a matrix that may otherwise present with significant interferences means that contaminants may be tested for at lower detection limits. Lastly, this sampling methodology is much more efficient at measuring contaminant concentrations in the dissolved phase, since the presence of particulates or excessive sediment have no consequence. 

Disadvantages

The first point described above as an advantage is also a disadvantage. For a site or an environment that may experience high and low levels of contaminant concentrations, passive samplers are not suitable to determine what these extremes are. Additional grab samples would have to be employed in parallel to or in place of passive samplers.

There is no universally accurate method or approach to back-calculate contaminant masses from the passive sampling material to water concentration for all devices. Although this is likely less of a concern since the types of sampling devices that have the appropriate equations developed would be known ahead of selection and deployment. 

Lastly, the use of passive samplers is a significantly more costly approach than traditional methods of sample collection and because of the extended deployment period, rush assessments can't be accommodated.

Types

PDB (Passive Diffusion Bags) - VOCs
Regenerated Cellulose Diffusion Samplers - Metals, Ions, DOC, VOCs
Peepers - Metals, Ions, DOC, VOCs

DGT (Diffusive Gradients in thin films) - Heavy metals, trace metals, radionuclides
SPMD (Semipermeable membrane devices) - PAHs, PCBs, PHCs

POCIS (Polar organic chemical integrative sampler) - Pharmaceuticals and Personal Care Products
Chemcatcher - Pharmaceuticals and Personal Care Products  



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