Peepers arefilled with distilled water and when positioned in sediment, equilibrates withthe ambient porewater via passive dissemination. Equilibration/deployment timecan be one hour to several months. Equilibration/deployment time depends onmany factors such as membrane/mesh pore size (45µ or 22µ), peeper volume,sediment type, chemical of potential concern, temperature, and study objectivesand ranges from days to months (Schumacher,2002). Following equilibration with ambient porewater, the peeper isrepossessed, and the insides of each dialysis cell are assessed for element ofconcern. It is necessary to note that passive sampling devices, such aspeepers, often deliver only projected concentrations that can be affected basedon numerous variables (e.
g., temperature, time range, membrane pore size,etc.). Subsequently, the confidence level for the analytical results forporewater analyses can fluctuate and should be counted when interpreting data.
Passeport etal. wrote that their study was the first to apply peepers and CSIA in thefield to investigate the procedures and usefulness of natural recovery (NR) insediments at a field site contaminated with pesticides or contaminants such aschlorinated benzenes and benzene (Passeport etal., 2016, Passeport et al.,2014). Although it was the first study that used peepers for NR insediments at a field site, before that we had peepers in many other studiescontaminated with benzenes or for evaluating nutrition in water (Peijnenburg et al., 2014, Niederkorn,2015).
Although Passeport etal in 2016 determined MCB,benzene, sulfate, nitrate, and iron acrossthe sediment profile for different locations (Passeportet al., 2016), they only mentioned that “the peepers were retrievedafter four weeks, which has been shown to allow volatile organic compoundsconcentrations to reach equilibrium”. However, in their studies in 2014, first,they showed that different contaminants have different equilibration time. Theyshowed that for jar and peeper concentrations equilibrated within 11 days for MCBand 1,2- dichlorobenzene, and after 14 days for benzene and toluene, but in2016, they simply said that they have chosen 4 weeks equilibrium time fordifferent contaminants. Although, the first study of Passeport et al agrees with the study ofPeijnenburg et al. (Peijnenburg et al.,2014), the second study is against of it. Peijnenburg et al.
showed that for different metal elements we have different equilibrium times.Moreover, Passeport et al. (Passeport et al., 2016) mentionedthat nitrate concentrations were below detection atall depths in the sediment, and maximum concentrations were lower than 1 mg/Lin the surface water. However, Niederkorn et al. (Niederkorn, 2015) mentioned that for distributions of nutrientelements in the riparian and hyporheic zones, equilibrium time of peepers wassettled in the laboratory to be almost one month. By comparing the study ofPasseport et al.
with Niederkorn et al., the study of Niederkornis clearer than Passorpt el al. They clearly showed that equilibrium of the peepers with the pore waterappeared to occur after third week. As Peijnenburg et al. showedvarious passive sampling devices have been developed for metals, andmetalloids. Another method that worked like peeper are suction devices. Incontrast with peepers, suction devices are not full up with analyte-free waterprior to placement and depend on active suction via a vacuum. Suction directlypulls the porewater from the interstitial sediment spaces into the samplingcontainer.
A tube attached to the buried container allows retrieval of theporewater sample. Porewater gathered with suction devices are more susceptibleto variations in redox conditions than peepers. (Canadian Council of Ministersof the Environment, 2016).Hexachlorocyclohexanes(HCHs) are among the most related persistent organic contaminants.
Because ofthe environmental worries related to HCHs, there is a high demand for studyingtheir sources, potential sinks, and transformation developments. Inconsistencyin the stable isotope ratios of organic compounds, found both in initiallyindustrial chemicals and in environmental samples from contaminated sites, canbe clarified by isotope fractionation happening during the synthesis,purification, handling, storage, application, and eventual degradation of theseelements in the location. To date, mostof the studies aiming to track sources and outcomes of HCHs in the environmenthave focused on carbon isotope analysis.
In several studies, carbon isotoperatios from different sources were reported (Liet al., 2011, Usman et al., 2014, Ivdra et al., 2016). Chartrandet al (Dr.
Passeport) in 2015 emphasised the application of CSIA to distinguishamong several HCH sources (Chartrand et al.,2015). The overall objective of their studywas to develop a methodology for applying CSIA to investigate the origin andoutcome of HCH at polluted field locations. They mentioned that because variousHCH isomers have relatively similar ranges of log Koc and log Kow,their results that carried out for ?-HCH can be generalised for the other HCHisomers. They stated that CSIA can be used to precisely analyze HCH isomers insamples from HCH polluted field sites. They presented that they had almostdetection limit of 40 ?g L–1 for ?-HCH ?13C and proposedthat this detection limit is almost acceptable.
They also wrote thatgroundwater HCH concentrations generally range between 0.1 and 730 ?g L–1.Although, their result is acceptable, aqueous samples at polluted groundwaterlocations can have concentrations meaningfully lower than this value and inremote areas such as the arctic, or in freshwater and ocean water where thewater is moving this could be challenging. Renpenning et al.
used gas chromatography in combinationwith a high-temperature conversion interface, which in the presence of H2changed organic chlorine to gaseous HCl, and then joined to a dual-detectionsystem, uniting an ion trap mass spectrometer (MS) and isotope-ratio massspectrometer (IRMS). Using GC-HTC-MS/IRMS, chlorine isotope analysis atenhanced conversion settings resulted in very precise isotope values formeasured reference material with recognised isotope composition, includingchlorinated ethylene, chloromethane, hexachlorocyclohexane, and trichloroaceticacids. Concerning about detection limits, the detection limit was determined tobe <15 nmol Cl on column with achieved precision of <0.3‰ which was moreaccurate, and the detection limit was below than the study of Passeport etal. <0.
5‰ (Renpenning et al., 2015a).However, in their study there were several limitations such as: I- Constancy ofthe Aluminum Oxide HTC Reactor, II- water creation which can possibly lead tomemory effects, because it may act as a trap for hydrochloric acid, III-Hydrochloric acid, a very sensitive and violent agent, could potentially damagethe IRMS ion source (Renpenning etal.
, 2015b). Moreover, a recent study presents the optimization of anoffline adaptation method for chlorine isotope analysis by dual-inlet- (DI-)IRMS, providing precise and reproducible chlorine isotope ratios for HCHs.Application of these newest expansions permitted us to overwhelmed earlieranalytical limitations for contaminants such as chlorinated organic compounds (Ivdra et al., 2016).