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[[File:Silicon firefighter tag.jpg|thumb|A [[firefighter]] wearing a [[silicone]] passive sampler on an elastic necklace, shaped like a [[dog tag]]]]
'''Passive sampling''' is an [[Environmental monitoring|environmental monitoring]] technique involving the use of a collecting medium, such as a man-made device or biological [[Organism|organism]], to accumulate chemical [[Pollutant|pollutantspollutant]]s in the environment over time. This is in contrast to [[Environmental monitoring#Grab samples|grab sampling]], which involves taking a sample directly from the media of interest at one point in time. In passive sampling, average chemical concentrations are calculated over a device's deployment time, which avoids the need to visit a sampling site multiple times to collect multiple representative samples.<ref name = Main>{{cite journal |last1=Górecki |first1=Tadeusz |last2=Namieśnik |first2=Jacek |title=Passive sampling |journal=Trends in Analytical Chemistry |date=2002 |volume=21 |issue=4 |accessdatepages=31276–291 May|doi=10.1016/S0165-9936(02)00407-7 2018}}</ref> Currently, passive samplers have been developed and deployed to detect toxic metals, [[Pesticide|pesticidespesticide]]s, [[Drug|pharmaceuticals]], [[Radionuclide|radionuclidesradionuclide]]s, [[Polycyclicpolycyclic aromatic hydrocarbon| polycyclic aromatic hydrocarbons]]s (PAHs), [[Polychlorinatedpolychlorinated biphenyl|polychlorinated biphenyls]]s (PCBs), and other organic compounds in water,<ref name = Chem1>{{cite journal |last1=Charriau |first1=Adeline |last2=Lissalde |first2=Sophie |last3=Poulier |first3=Gaëlle |last4=Mazzella |first4=Nicolas |last5=Buzier |first5=Rémy |last6=Guibaud |first6=Gilles |title=Overview of the Chemcatcher® for the passive sampling of various pollutants in aquatic environments Part A: Principles, calibration, preparation and analysis of the sampler |journal=Talanta |date=2016 |volume=148 |urldoi=https:10.1016//wwwj.sciencedirecttalanta.com/science/article/pii/S0039914015301041?via%3Dihub2015.06.064 |accessdatepages=31556–571|pmid=26653485 May 2018}}</ref><ref name = Chem2>{{cite journal |last1=Lissalde |first1=Sophie |last2=Charriau |first2=Adeline |last3=Poulier |first3=Gaëlle |last4=Mazzella |first4=Nicolas |last5=Buzier |first5=Rémy |last6=Giubaud |first6=Giles |title=Overview of the Chemcatcher® for the passive sampling of various pollutants in aquatic environments Part B: Field handling and environmental applications for the monitoring of pollutants and their biological effects |journal=Talanta |date=2016 |volume=148 |urldoi=https:10.1016//wwwj.sciencedirecttalanta.com/science/article/pii/S00399140153011812015.06.076 |accessdatepages=31572–582|pmid=26653486 May 2018}}</ref><ref name = Brumbaugh>{{cite journal |last1=Brumbaugh |first1=WG |last2=Petty |first2=JD |last3=Huckins |first3=JN |last4=Manahan |first4=SE |title=Stabilized Liquid Membrane Device (SLMD) for the Passive, Integrative Sampling of Labile Metals in Water |journal=Water, Air, and Soil Pollution |date=2002 |volume=133 |urlpages=109–119 |doi=https://link.springer.com/article/10.1023/A:1012923529742 |accessdatebibcode=312002WASP..133..109B May|s2cid=93497819 2018}}</ref><ref name = POCISSPMD>{{cite web |title=Guidelines for the Use of the Semipermeable Membrane Device (SPMD) and the Polar Organic Chemical Integrative Sampler (POCIS) in Environmental Monitoring Studies |url=https://pubs.usgs.gov/tm/tm1d4/ |publisher=United States Geological Survey |accessdateaccess-date=30 May 2018}}</ref> while some passive samplers can detect hazardous substances in the air.<ref name = Sigma>{{cite web |title=Passive (Diffusive) Sampling Overview |url=https://www.sigmaaldrich.com/analytical-chromatography/air-monitoring/passive-sampling.html |website=Sigma-Aldrich |accessdateaccess-date=31 May 2018}}</ref><ref name = LichData>{{cite web |title=Lichen Monitoring in US National Forests and Parks Reports, Publications and Other Resources |url=http://gis.nacse.org/lichenair/?page=reports |website=National Lichens & Air Quality Database and Clearinghouse |publisher=United States Forest Service |accessdateaccess-date=31 May 2018}}</ref><ref name = Tubes>< /ref>
==Theory and application==
The underlying principle of passive sampling is the flow of contaminant molecules or ions from the sampling medium (air or water) onto a collecting medium (the passive sampler), due to [[Fick's laws of diffusion|Fick's first law of diffusion]] and, depending on the passive sampler, a greater [[Binding constant|binding affinity]] of contaminants with the collecting medium as compared to the sampling medium. As a result, contaminants concentrate on the collecting medium over time until they reach [[Chemical equilibrium|equilibrium]] with the surrounding medium. The use of passive sampling provides time-averaged concentrations of contaminants over the sampler's deployment period.<ref name = Main>< /ref>
It is important to distinguish passive sampling from ''active sampling'', which has the same underlying principle but employs moving parts, such as pumps, to force the sampling medium onto a collecting medium. <ref>{{cite web |last1=Salter |first1=Eddie |title=Active versus passive air sampling |url=https://www.envirotech-online.com/article/health-and-safety/10/skc/active-versus-passive-air-sampling-eddie-salter/923 |website=Environmental Technology |publisher=Labmate Online |accessdateaccess-date=4 June 2018}}</ref> Passive sampling solely relies on [[Molecular diffusion|molecular diffusion]] and the sorbing or binding of contaminants to agents in the samplers, which is why passive sampling is also called ''diffusive sampling''.<ref name = Sigma>< /ref>
Passive sampling is also distinct from grab sampling, which is the collection of an air, water, or soil sample to analyze directly for contaminants. These samples represent a single point in time and provide information about contaminant concentration at one point in time, unlike passive sampling devices or organisms.
Many different kinds of passive samplers have been developed and have sampled many different contaminants, including:
*[[Antibiotic|Antibiotics]]s<ref name = DGT>< /ref>
*[[Bisphenol|Bisphenols]]s<ref name = DGT>< /ref>
*[[DioxinDioxins and dioxin-like compounds|Dioxins]]<ref name = POCISSPMD>< /ref>
*[[Flame retardant|Flame retardants]]s<ref name = POCISSPMD>< /ref>
*[[Furan|Furans]]s<ref name = POCISSPMD>< /ref>
*[[Nanoparticle|Nanoparticles]]s<ref name = DGT>< /ref>
*[[Oxyanion|Oxyanions]]s such as [[Phosphate|phosphatesphosphate]]s<ref name = DGT>< /ref>
*[[Polybrominated diphenyl ethers|Polybrominated diphenyl ethers (PBDEs)]]<ref name = POCISSPMD>< /ref>
*[[Polycyclic aromatic hydrocarbons|Polycyclic aromatic hydrocarbons (PAHs)]]<ref name = POCISSPMD>< /ref>
*[[Polychlorinated biphenyl|Polychlorinated biphenyls (PCBs)]]<ref name = POCISSPMD>< /ref>
*[[Pesticide|Pesticides]]s<ref name = POCISSPMD>< /ref>
*[[Pharmaceutical|Pharmaceuticals]]s<ref name = POCISSPMD>< /ref>
*[[Radionuclide|Radionuclides]]s<ref name = Chem1>< /ref><ref name = Chem2>< /ref>
*Toxic metals (Such as [[copper]], [[zinc]], and [[lead]])<ref name = Brumbaugh>< /ref><ref name = DGT>< /ref>
==Passive sampling in water==
Several kinds of passive sampling devices exist for monitoring pollutants present in water. In addition to these devices, organisms, such as [[Mussel|musselsmussel]]s, living in the environment also "passively sample" contaminants ([[Bioaccumulation|bioaccumulation]]) and can be used to monitor water pollution ([[Aquatic biomonitoring|biomonitoring]]).<ref name="Mussel">{{cite journal |last1=Sericano |first1=JL |last2=Wade |first2=TL |last3=Jackson |first3=TJ |last4=Brooks |first4=JM |last5=Tripp |first5=BW |last6=Farrington |first6=JW |last7=Mee |first7=LD |last8=Readmann |first8=JW |last9=Villeneuve |first9=JP |last10=Goldberg |first10=ED |title=Trace Organic Contamination in the Americas: An Overview of the US National Status & Trends and the International 'Mussel Watch' Programmes |journal=Marine Pollution Bulletin |date=1995 |volume=31 |issue=44–12|pages=214–225 |doi=10.1016/0025-12326X(95)00197-U |bibcode=1995MarPB..31..214S }}</ref>
===Chemcatcher===
{{Main|Chemcatcher}}
Chemcatcher<sup>®</sup> has many configurations, which collectively can passively sample [[Inorganic compound|inorganic]] pollutants (metals) and a wide range of [[Organic compound|organic]] pollutants. It is composed of a single-use disc, with or without a [[Membrane|membrane]], sealed into a plastic support. Types of receiving phases and membranes vary greatly, depending on the target chemicals to be sampled. Time-averaged water concentrations of many chemical pollutants can be determined from Chemcatcher<sup>®</sup> sampling as long as its sampling rate and the water flow rate are known.<ref name = Chem1>< /ref><ref name = Chem2>< /ref>
===Diffusive gradients in thin films (DGT)===
{{Main|Diffusive gradients in thin films}}
Diffusive gradients in thin films (DGT) samplers passively sample [[Ion|ionicion]]ic trace metals, as well as [[Antibiotic|antibioticsantibiotic]]s, [[Oxyanion|oxyanionsoxyanion]]s, [[Bisphenol|bisphenolsbisphenol]]s, and [[Nanoparticle|nanoparticlesnanoparticle]]s in different configurations. They are composed of plastic pistons and caps, with a window that exposes a binding gel, diffusive gel, and filter membrane to the sampling water. They can be used in both freshwater and marine environments, as well as in in the water located between freshwater and marine [[Sediment|sediment]] particles, called ''pore water'' or ''interstitial water''. Once the mass of accumulated contaminants on the DGT sampler is known, the DGT equation (based on [[Fick's law]]) can be used to calcuatecalculate the time averaged water concentration of contaminants.<ref name="DGT">{{cite journal |last1=Zhang |first1=Chaosheng |last2=Ding |first2=Shiming |last3=Xu |first3=Di |last4=Tang |first4=Ya |last5=Wong |first5=Ming H |title=Bioavailability assessment of phosphorus and metals in soils and sediments: a review of diffusive gradients in thin films (DGT) |journal=Environmental Monitoring and Assessment |date=2014 |volume=186 |issue=11|pages=7367–7378 |doi=10.1007/s10661-014-3933-0 |pmid=25015347 |bibcode=2014EMnAs.186.7367Z |s2cid=25854461 }}</ref>
=== Microporous polyethylene tubes (MPT) ===
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.<ref>{{Cite journal|last1=Fauvelle|first1=Vincent|last2=Kaserzon|first2=Sarit L.|last3=Montero|first3=Natalia|last4=Lissalde|first4=Sophie|last5=Allan|first5=Ian J.|last6=Mills|first6=Graham|last7=Mazzella|first7=Nicolas|last8=Mueller|first8=Jochen F.|last9=Booij|first9=Kees|date=2017-03-07|title=Dealing with Flow Effects on the Uptake of Polar Compounds by Passive Samplers|journal=Environmental Science & Technology|volume=51|issue=5|pages=2536–2537|doi=10.1021/acs.est.7b00558|pmid=28225255|bibcode=2017EnST...51.2536F|s2cid=206567423 |issn=0013-936X|doi-access=free}}</ref> The diffusive polyethylene layer prevents the thickness of the water-boundary layer (which is affected by flow) from dominating diffusion.<ref name=":0">{{Cite journal|last1=Fauvelle|first1=Vincent|last2=Montero|first2=Natalia|last3=Mueller|first3=Jochen F.|last4=Banks|first4=Andrew|last5=Mazzella|first5=Nicolas|last6=Kaserzon|first6=Sarit L.|date=2017|title=Glyphosate and AMPA passive sampling in freshwater using a microporous polyethylene diffusion sampler|journal=Chemosphere|volume=188|pages=241–248|doi=10.1016/j.chemosphere.2017.08.013|issn=1879-1298|pmid=28886558|bibcode=2017Chmsp.188..241F}}</ref> The tube is filled with sorbents depending on the chemicals or chemical groups being sampled and has been successfully used to sample glyphosate, AMPA, illicit drugs and pharmaceuticals and personal care products.<ref name=":0" /><ref>{{Cite journal|date=2020-02-20|title=Calibration and validation of a microporous polyethylene passive sampler for quantitative estimation of illicit drug and pharmaceutical and personal care product (PPCP) concentrations in wastewater influent|url=https://www.sciencedirect.com/science/article/abs/pii/S0048969719358863|journal=Science of the Total Environment|language=en|volume=704|article-number=135891|doi=10.1016/j.scitotenv.2019.135891|issn=0048-9697|last1=McKay|first1=Sarah|last2=Tscharke|first2=Ben|last3=Hawker|first3=Darryl|last4=Thompson|first4=Kristie|last5=O'Brien|first5=Jake|last6=Mueller|first6=Jochen F.|last7=Kaserzon|first7=Sarit|pmid=31838300|bibcode=2020ScTEn.70435891M|s2cid=209386153 |url-access=subscription|hdl=10072/396186|hdl-access=free}}</ref>
===Peepers===
Peepers are passive [[Diffusion|diffusion]] samplers used for metals in freshwater and marine [[Sediment|sediment]] pore water, so they can be used to find areas that may have metal-contaminated sediments. Peepers are plastic vessels filled with clean water and covered in a [[Dialysis_Dialysis (biochemistry)|dialysis membrane]], which allows metals in sediment pore water to enter the water inside the peeper.<ref name="Peeper1">{{cite journal |last1=Serbst |first1=JR |last2=Burgess |first2=RM |last3=Kuhn |first3=A |last4=Edwards |first4=PA |last5=Cantwell |first5=MG |title=Precision of Dialysis (Peeper) Sampling of Cadmium in Marine Sediment Interstitial Water |journal=Archives of Environmental Contamination and Toxicology |date=2003 |volume=45 |urlissue=https:3 |pages=297–305 |pmid=14674581 |doi=10.1007//wwws00244-003-0114-5|bibcode=2003ArECT.ncbi.nlm45.nih.gov/pubmed/14674581297S |s2cid=23462490 }}</ref> They are usually placed deep enough into sediment to be in an [[Anoxic waters|anoxic]] environment, in which metals will be soluble enough to sample.<ref name = Missouri>< /ref> If the peepers are deployed long enough so the sediment pore water and contained peeper water reach equilibrium, they can accurately provide metal concentrations in sampled sediment pore water.<ref name = Peeper1>< /ref>
===Polar organic chemical integrative sampler (POCIS)===
{{Main|Polar organic chemical integrative sampler}}
Polar organic chemical integrative samplers (POCIS) sample [[Chemical polarity|polar]] organic contaminants with a log [[octanol-water [[Partition coefficient|partition coefficient]] (K<sub>ow</sub>) value that is less than 3. Examples of these types of chemicals include polar pesticides, pharmaceuticals, [[Recreational drug use|illicit drugs]], [[Flameflame retardant|flame retardants]]s, and drug [[Metabolite|metabolitesmetabolite]]s. The POCIS is composed of variable numbers of solid sorbent discs attached to a support rod and encased in a metal cage, and has two possible sorbent configurations, the pesticide-POCIS and pharmaceutical-POCIS. As long as the amount of water passing over the sampler is known, polar organic contaminant water concentrations can be calculated after extracting sorbed contaminants from a POCIS.<ref name = POCISSPMD>< /ref>
===Semipermeable membrane devices (SPMDs)===
{{Main|Semipermeable membrane devices}}
Semipermeable membrane devices (SPMDs) passively sample [[Chemical polarity|nonpolar]] organic contaminants with a log octanol-water partition coefficient (K<sub>ow</sub>) value greater than 3. Examples of these types of chemicals include [[polycyclic aromatic hydrocarcbonshydrocarbons]] (PAHs), [[polychlorinated biphenyls]] (PCBs), [[Polybrominated diphenyl ethers|polybrominated diphenyl ethers]] (PBDEs), chlorinated pesticides, [[DioxinPolychlorinated dibenzodioxins|dioxins]], and [[FuranPolychlorinated dibenzofurans|furans]]. SPMDs are composed of sealed plastic tubing filled with [[Triolein|triolein]], in which nonpolar organics are very soluble and which serves as a representation of the fatty tissues of aquatic organisms. The tubing is then weaved between metal rods and enclosed in a metal cage. The sampler can be made in varying lengths of tubing for different applications, since sampling rate depends on the surface area of tubing exposed to the water. As long as the amount of water passing over the sampler is known, nonpolar organic contaminant water concentrations can be calculated after extracting contaminants from a SPMD.<ref name = POCISSPMD>< /ref>
[[File:Stabilized liquid membrane device (SLMD).jpg|thumb| 75px |A 7.5 centimeter SLMD, filled with a 1:1 mixture of Kelex-100 and oleic acid.]]
===Stabilized liquid membrane devices (SLMDs)===
{{main|Stabilized liquid membrane devices}}
Stabilized liquid membrane devices (SLMDs) passively sample [[Ion|ionicion]]ic metals in freshwater. They are made of [[Low-density polyethylene|low-density polyethylene]] plastic tubing sections that are sealed on both ends and filled with an equal mixture of [[Oleic acid|oleic acid]] and metal [[Chelation|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.<ref name = Brumbaugh>< /ref> 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.<ref name="Missouri">{{cite journal |last1=Brumbaugh |first1=William G |last2=May |first2=Thomas W |last3=Besser |first3=John M |last4=Allert |first4=Ann L |last5=Schmitt |first5=Christopher J |title=Assessment of Elemental Concentrations in Streams of the New Lead Belt in Southeastern Missouri, 2002–05 |datejournal=2007USGS Report |accessdateseries=3Scientific JuneInvestigations 2018Report |date=2007 |page=78 |publisher=United States Geological Survey|doi=10.3133/sir20075057 |bibcode=2007usgs.rept...78B }}</ref> Metal weight accumulated by a SLMD over its deployment period can be calculated and divided by the SLMD deployment time to get an average metal weight accumulated per time unit, but currently, no method has been developed to convert this to an average metal concentration. In addition, SLMD sampling rates greatly vary with water flow rate, which plastic housings can be used to control.<ref name = Brumbaugh>< /ref><ref name = Missouri>< /ref>
==Passive sampling in air==
Passive sampling can also be accomplished for contaminants in the air, including airborne particles and hazardous vapors and gases. This can be done with man-made devices or with biomonitoring organisms, such as [[Lichen#Effects of air pollution|lichens]].<ref name = LichData>< /ref><ref name="Lichen">{{cite journal |last1=Garty |first1=J |title=Biomonitoring Atmospheric Heavy Metals with Lichens: Theory and Application |journal=Critical Reviews in Plant Sciences |date=2001 |volume=20 |issue=4 |urlpages=https://www.tandfonline.com/309–371 |doi/abs/=10.1080/20013591099254 |bibcode=2001CRvPS..20..309G |s2cid=59062166 }}</ref>
===Sorbent tubes===
{{Main|Sorbent tube}}
Sorbent tubes are passive samplers for [[Volatilevolatile organic compound|volatile organic compounds]]s (VOCs). They are glass tubes filled with adsorbing materials, such as [[Charcoal|charcoal]] or [[Silica gel|silica gel]], which the air to be sampled passes through. The adsorbing materials remove VOCs from the air that passes through them, and the VOCs can be desorbed and analyzed. Air concentrations can be calculated using the amount of air that flowed through the sorbent tube and the amount of contaminants desorbed.<ref name="Tubes">{{cite web |title=Sorbent tubes |url=http://airsamplingsolutions.com/index.php/sorbent-tubes/ |website=Air Sampling Solutions |publisher=Casella |accessdateaccess-date=3 June 2018}}</ref>
==Advantages==
Contaminant concentrations from passive sampling reflect average contamination throughout the sampler deployment time, meaning the sample will capture contaminant concentration fluctuations over the whole deployment period. Traditional grab sampling does not do this, since collected samples only represent a single moment in time and multiple grab samples must be taken to observe variation in contaminant concentrations over time.<ref name = Main>< /ref> This integrative sampling method can also can result in the detection of chemicals present at such low concentrations that they would be undetected in a grab sample, due to concentration of the chemicals on the sampler over time. As a result, passive sampling has the potential to be a less time-intensive, less expensive and more accurate sampling method than grab sampling.
In addition, passive samplers are often easy to use and deploy, have no pumps or moving parts, and do not require electricity, since they rely on the [[Molecular diffusion|molecular diffusion]] of contaminants or binding of contaminants to agents within the samplers, unlike active sampling.<ref name = Sigma>< /ref> They may also be inexpensive and simple to construct, such as SLMDs, which only require sealed plastic tubing and two chemical components.<ref name = Brumbaugh>< /ref>
Passive sampling may also more accurately reflect metal concentrations that are [[Bioavailability|bioavailable]] to organisms than other sampling methods. For example, the [[semipermeable membrane devices|SPMD]] sampler uses a semipermeable membrane and [[Triolein|triolein]] (a [[Triglyceride|triglyceride]]), both of which mimic [[Toxicant|toxicant]] uptake by organism fatty tissue.<ref name = POCISSPMD>< /ref> However, this depends on the type of passive sampler used, since some samplers, such as peepers, rely solely on molecular diffusion,<ref name = Peeper1>< /ref> which may be too simple to be reflective of the [[Toxicokinetics|complex processes of contaminant uptake]] in an organism.
==Disadvantages==
Since passive sampling provides information about average contaminant concentrations, all possible concentrations over the sampler deployment time are included in this average value. 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.<ref name = Main>< /ref> If high and low concentrations of contaminants throughout the sampling period are needed, other sampling methods should be used in conjunction with passive sampling.
Not all passive samplers have universally accurate ways to convert contaminant masses accumulated into water concentrations, which are used in government regulation, such as the [[United States Environmental Protection Agency]] [[Clean Water Act]].<ref name="EPA">{{cite web |title=National Recommended Water Quality Criteria - Aquatic Life Criteria Table |url=https://www.epa.gov/wqc/national-recommended-water-quality-criteria-aquatic-life-criteria-table |publisher=United States Environmental Protection Agency |accessdateaccess-date=4 June 2018|date=2015-09-03 }}</ref> With some samplers, as with the DGT, this can be done using equations developed for the samplers, but not all samplers have these. Passive sampler deployment time is also limited depending on the sampler's capacity; for example, SLMDs have been deployed for month-long periods, but may reach saturation and stop sampling much sooner if metal concentrations and water flow rates are high enough.<ref name = Brumbaugh>< /ref> However, this issue is avoidable if literature on the relevant passive sampler is examined for background information about sampler capacity and ideal deployment times prior to deployment.
==References==
<references />
[[Category:Environmental monitoring]]
[[Category:Sampling techniques]]
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