Passive sampling
Passive sampling is an environmental monitoring technique involving the use of a collecting medium, such as a man-made device or biological organism, to accumulate chemical pollutants in the environment over time.
In addition to these devices, organisms, such as mussels, living in the environment also "passively sample" contaminants (bioaccumulation) and can be used to monitor water pollution (biomonitoring).
[2][3] Diffusive gradients in thin films (DGT) samplers passively sample ionic trace metals, as well as antibiotics, oxyanions, bisphenols, and nanoparticles in different configurations.
[10] Microporous polyethylene tubes (MPT) attempt to mitigate the flow-dependency of other kinetic passive samplers such as Chemcatcher and POCIS by introducing a thicker membrane.
[5] Semipermeable membrane devices (SPMDs) passively sample nonpolar organic contaminants with a log octanol-water partition coefficient (Kow) value greater than 3.
Examples of these types of chemicals include polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), chlorinated pesticides, dioxins, and furans.
They are made of low-density polyethylene plastic tubing sections that are sealed on both ends and filled with an equal mixture of oleic acid and metal chelating agent.
They work by interacting with calcium and magnesium ions in freshwater, which forms a hydrophobic film on the outside the SLMD plastic membrane in which the chelating agent can bind to metals in the sampling water.
[4] They have been deployed for up to month-long periods in the field, alone or covered by a plastic tube housing to mediate water flow.
[4][16] Passive sampling can also be accomplished for contaminants in the air, including airborne particles and hazardous vapors and gases.
They are glass tubes filled with adsorbing materials, such as charcoal or silica gel, which the air to be sampled passes through.
For example, the SPMD sampler uses a semipermeable membrane and triolein (a triglyceride), both of which mimic toxicant uptake by organism fatty tissue.
However, there is no way of finding out the complete range of contaminant concentrations over the deployment time at a single site with only passive sampling.
