Data Parameters and Units:
The headers are Leaf Type/Location, Date, Lat (latitude), Long (longitude), Tissue/Media n, Avg (average), St. Dev. (standard deviation), St. Error (Standard error), PAH concentration in cuticle (mg/kg), PAH concentration in plant tissue (mg/kg), and PAH mass in SPMD (ug).
Methods:
1. Site location and sampling
Plant and soil samples were collected from two adjacent marshes at Bay Jimmy in Northern Barataria Basin. Samples were collected from two adjacent marsh sites. Site 1 was designated as the control site with no visible traces of oil and site 2 was designated as the oiled site with visible oil along the marsh shoreline. From each site, samples were collected from three plots along the marsh shoreline. The plots were designated as C1, C2, C3 for site 1 and as O1, O2, O3 for site 2. Sampling was done in triplicate in each sampling plot. For each sampling event, nine Spartina alterniflora leaf samples were collected from the two sites, therefore yielding a total of 18 samples from the Bay Jimmy site. Sampling was conducted in the summer and winter months between June 9, 2016 and Feb 3, 2017. Sampling period intervals ranged between 19-72 days.
Field extraction of Spartina leaf cuticle
Bakker et. al., (2001) performed a sequential extraction analysis on the deposition of PAHs in leaves of Plantago. A similar sequential extraction method was implemented for the analysis of PAHs in Spartina. The extraction process was initiated immediately after sampling at each location. Plant leaves were placed in a glass jar and shaken with 50 ml of EDTA solution (0.03M, pH 5) for about 2 minutes. This initial washing of leaves with EDTA solution served to mobilize any high molecular weight PAHs on the surface of the leaves (Bakker et.al., 2001). Following this, leaves were taken out of the EDTA solution and placed in another glass jar containing 50 ml of pesticide-grade dichloromethane (DCM) and again shaken for 2 minutes (Wang et. al., 2008). This served as the second phase of the sequential extraction, which dissolves the leaf cuticle that may contain PAHs localized within it. The leaves were then placed in Ziploc bags and transported to the lab where they were stored at 4oC prior to the complete extraction of the leaf tissue.
Sequential extraction method
The EDTA solution was exchanged in a separatory funnel with cyclohexane. The EDTA solution was shaken for about 1 minute with 50 ml of cyclohexane and allowed to settle. Once the immiscible mixture settled, the bottom layer (EDTA solution) was separated from the top layer (cyclohexane). The EDTA solution was drained and discarded while cyclohexane was retained for further analysis (Bakker et al., 2001). The cyclohexane solution was evaporated at 70oC to 1.5 ml in a RapidVap N2 Evaporation System (Labconco, USA) and then exchanged with a 1:1 hexane acetone solution and once again evaporated at 70oC to a final volume of 3 ml then stored in a scintillation vial. Following the use of 1 ml of the sample for gas chromatography-mass spectrophotometry (GC/MS) analysis of the presence of PAHs.
Similarly, the second extraction phase with the 50 ml of DCM was evaporated at 30oC to 1.5 ml in a RapidVap N2 Evaporation System (Labconco, USA) then exchanged with a 1:1 hexane acetone solution and once again evaporated at 70oC to a final volume of 3 ml and stored in a scintillation vial. Following the use of 1 ml of the sample for gas chromatography-mass spectrophotometry analysis of the presence of PAHs.
The third extraction phase was the complete extraction of the plant leaf tissue using the accelerated solvent extraction method. This involved the use of an Accelerated Solvent Extractor (ASE), which extracts elements from the leaf tissues utilizing a 50:50 mixture of hexane acetone under 17000 psi of pressure at 100 oC. In preparation for accelerated solvent extraction, the leaves were chopped into pieces, weighed, and placed in a beaker mixing them with sodium sulfate and magnesium sulfate to dry out the moisture content. The mixture was loaded into stainless steel cells after which the cells were loaded onto the accelerated solvent extractor. The extracted solvent was evaporated to 3ml at 70oC and passed through silica gel columns for the solid-phase extraction (SPE) cleanup process.
Field deployment of semipermeable membrane devices
Passive sampler, semipermeable membrane devices were purchased from Environmental Sampling Technologies were set up at Bay Jimmy at both sampling locations. These semipermeable membrane devices are composed of a lay-flat, low-density polyethylene tubing containing a thin film of pure, high-molecular-weight lipid triolein (1,2,3-tri-[cis-9-octadecenoyl]glycerol) (Cranor et al. 2009). This polymer allows for the diffusion of hydrophobic organic chemicals such as PAHs which are consequently sequestered in the lipid phase, (EST Inc, 2016). Two devices were set up on the three designated plots for both site 1 and site 2. One device was set up as a passive air sampler and another submerged as a water sampler. With three plots at each sampling location, a total of 12 devices were deployed at both locations for each deployment period. A field blank was kept as a control sample.
The semipermeable membrane devices set in water were deployed in a standard 91.4 cm stainless steel carrier fastened inside a 15 cm high x 16 cm wide stainless steel canister. Fixing the semipermeable membrane devices within the stainless steel canister allows for a fixed sampling location, thus eliminating problems from aquatic life disturbances. The air samplers were fastened inside perforated cans similar in size to the canisters to allow air entrance and circulation. These were mounted on steel rods standing 4 feet high. The incubation period for the samplers after deployment was set between three to six weeks.
Dialysis of semipermeable membrane devices
After the incubation period, the semipermeable membrane devices were removed from the storage container and cleansed immediately. The semipermeable membrane devices were cleaned by scrubbing the surface with a gloved hand proceeded by sequential solvent rinsing. First, with dilute hydrochloric acid to remove any salts, followed by de-ionized water, then a quick surface rinse with acetone then a final rinse with hexane. The cleaned semipermeable membrane devices were then placed in a contaminant-free, air-tight glass jar of a sufficient volume of hexane. Once in the lab, the dialysis containers were placed in an incubator at 18 oC for 24 hrs. After this initial dialysis, the hexane was transferred into a separate container and the second portion of hexane was added and incubated at 18 oC for another 24 hrs. Following this, both volumes of hexane were combined and the semipermeable membrane devices discarded (Alvarez, 2010).
Following dialysis, the hexane was evaporated at 70 oC to 1.5 ml in a RapidVap N2 Evaporation System (Labconco, USA) and then exchanged with a 1:1 hexane acetone solution and once again evaporated at 70 oC to 3 ml and stored in a scintillation vial. Following the use of 1 ml of the sample for gas chromatography-mass spectrophotometry analysis of the presence of PAHs.
Gas Chromatography - Mass Spectrometry Analysis of PAHs
1 ml of all extracted samples were analyzed using a Hewlett Packard 6800 N gas chromatograph with an HP 6890 series autosampler, DB-5 capillary column (30m x 0.25mm X 0.25µm film), and HP 5973 mass selective detector. The injector temperature was set at 300°C, the detector at 280°C, and oven temperature was at 45°C for 3 minutes, and then the temperature was increased to 6°C/minutes to 315°C, and the temperature was held for 15 min. The carrier gas utilized was helium; at 5.7 mL/min. A selected ion-monitoring mode was used for quantification based on internal standards. Quality control was maintained by running blanks (1 mL hexane/acetone at 50:50, 5 μL internal standard) analyzed at the beginning and end of each run. Calibration standards of a known concentration of PAHs were also included in each run with samples.
PAHs targeted from analysis include: naphthalene (C0N), C1-naphthalenes (C1N), C2-naphthalenes (C2N), C3-naphthalenes (C3N), C4-naphthalenes (C4N), acenaphthylene (ACL), acenaphthene (ACE), fluorene (C0F), C1-fluorenes (C1F), C2- fluorenes (C2F), C3-fluorenes (C3F) phenanthrene (C0P), C1-phenanthrenes (C1P), C2-phenanthrenes (C2P), C3-phenanthrenes (C3P), C4-phenanthrenes (C4P), dibenzothiophene (C0D), C1- dibenzothiophenes (C1D), C2- dibenzothiophenes (C2D), C3- dibenzothiophenes (C3D), fluoranthene (FAN), pyrene (PY), C1- pyrene/fluoranthene (C1-PY/FA), chrysene (C0C), C1-chrysenes (C1C), C2-chrysenes (C2C), and C3-chrysenes (C3C). C30-Hopane was also analyzed.
Provenance and Historical References:
Alvarez, David A. 2010. Guidelines for the use of the semipermeable membrane device (SPMD) and the polar organic chemical integrative sampler (POCIS) in environmental monitoring studies: U.S. Geological Survey, Techniques and Methods 1–D4, 28 p.
Bakker, Martine I., Judith W. Koerselman, Johannes Tolls, and Chris Kolloffel. 2001. Localization of deposited polycyclic aromatic hydrocarbons in leaves of Plantago. Environmental Toxicology Chemistry 20(5): 1112−1116. DOI: 10.1002/etc.5620200524.
Cranor, Walter L., David A. Alvarez, James N. Huckins and Jimmie D. Petty. 2009. Uptake rate constants and partition coefficients for vapor phase organic chemicals using semipermeable membrane devices (SPMDs). Atmospheric Environment 43:3211-3219. DOI: 10.1016/J.ATMOSENV.2009.03.043.
Environmental Sampling Technologies. [cited: 2016 11/2]; Available from: http://www.est-lab.com/spmd.php
Wang, Y. Q., Shuangcheng Tao, X. C. Jiao, Raymond Martin Coveney, Shuiping P. Wu and B. S. Xing. 2008. Polycyclic aromatic hydrocarbons in leaf cuticles and inner tissues of six species of trees in urban Beijing. Environmental Pollution 151(1): 158−164. DOI:10.1016/j.envpol.2007.02.005.
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