Abstract:

This dataset includes the concentrations of polycyclic aromatic hydrocarbons (PAHs) in three fractions on the Avicennia germinans (black mangrove) leaf (PAHs in particles on the leaf surface, PAHs partitioned into the leaf cuticle and PAHs in the remaining leaf tissue. PAH concentrations in semipermeable membrane devices in the plant canopy and on the marsh surface were collected simultaneously with these leaf measurements. Finally, marsh soil PAH concentrations were collected on several dates for comparison. These data reflect the continued cycling of PAHs in marsh vegetation years after the spill.

Suggested Citation:

Pardue, John. 2021. Polycyclic aromatic hydrocarbons (PAHs) concentrations in Avicennia germinans plant tissue and semipermeable membrane devices in a crude oil contaminated salt marsh. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/81FCYJBA

Purpose:

The purpose of this dataset is to better understand the cycling of polycyclic aromatic hydrocarbons (PAHs) through the plant canopy, specifically focused on black mangroves, Avicennia germinans.

Data Parameters and Units:

PAH concentrations in plant tissue (mg/kg) PAH concentrations in soils (mg/kg) PAH mass in semipermeable membrane devices (ug)

Methods:

Methodology 1. Leaf sampling and PAH extraction Three black mangrove trees were selected at the oiled site at Bay Jimmy and sampled from July 2016 to February 2017. Three sample sets were randomly collected from each tree during each sampling event: (a) immature leaves; (b) mature leaves; (c) senescing leaves. Immature leaves are identified as being smaller in size and spatially located at the tip of each mangrove branch. Mature leaves are typical of mangrove trees being dark green, thick, and located all along the mangrove branch. Senescing leaves are found at random locations along the mangrove branch and are characterized as yellow, brown. All samples underwent a three stage sequential extraction of PAHs consisting of EDTA contact time, dichloromethane (DCM) contact time, and accelerated solvent extraction (ASE). The sequential extraction was initiated in the field. Sample leaves were placed into a 100 mL solution of EDTA (1 M, pH = 5) and shaken vigorously for 2 minutes, chelating and removing the particulates bound to the surface of the leaves. The leaves were then transferred to 100 mL of pesticide-grade DCM and shaken again for 2 minutes, dissolving the cuticle of the leaves. The leaves were removed from the DCM, placed in a sealed bag, and stored in the dark for transport to the lab for further PAH extraction. In the lab, EDTA was exchanged with cyclohexane using a separatory funnel. The cyclohexane solvent was evaporated at 70°C to 2 mL using a RapidVap N2 Evaporation System (Labconco, USA). The 2 mL cyclohexane was diluted to 20 mL with hexane/acetone (50:50 v/v), evaporated at 70°C to 3 mL, and stored in a scintillation vial before GC-MS analysis. DCM samples were evaporated at 30°C to 2 mL using the RapidVap. The 2 mL DCM was diluted to 20 mL with hexane/acetone (50:50 v/v), evaporated at 70°C to 3 mL, and stored in a scintillation vial before GC-MS analysis. The leaf samples were cut into small pieces, weighed, and mixed with diatomaceous earth to dry the samples in preparation of aggressive tissue extraction of PAHs using accelerated solvent extraction (ASE). Full sample masses were recorded for calculation purposes but only 15 grams or less of leaf mass were used for analysis. The prepared samples were loaded into stainless steel, cylindrical cells and placed in a Dionex Accelerated Solvent Extractor 350 (Thermo Scientific). The ASE extracts oil elements from the samples using hexane/acetone (50:50 v/v) under 1700 psi of pressure at a temperature of 100°C. The hexane/acetone solvent eluate from the ASE was evaporated at 70°C to 3 mL using the RapidVap. The 3 mL hexane/acetone sample from the ASE was processed further using solid phase extraction (SPE) with a silica gel column before GC-MS analysis. The column was activated with 1 mL of water followed by the 3 mL hexane/acetone sample. The column was eluted with 40 mL of 2:3 hexane/acetone. The eluate was evaporated at 70°C to 2 mL on the RapidVap, diluted to 20 mL with hexane/acetone (50:50 v/v), evaporated at 70°C to 3 mL, and stored in a scintillation vial before GC-MS analysis. 2. SPMD samples Semipermeable membrane devices (SPMDs) doped with a small volume of the fat triolein were deployed in both air and the marsh surface at each of the 6 experimental plots at Bay Jimmy at each sampling event. Three plots were located in an area with obvious surface oiling. Three additional plots were located at a reference site with no surface oiling approximately 1 km southeast of the site along the same shoreline. Surface SPMDs were secured to the sediment bed by a rope and pole system. Surface SPMDs were freely exposed to tidal fluctuations, thus experiencing similar environmental conditions as Spartina. Air SPMDs were secured inside a metal cylinder. The paint can was hung upside down just above the canopy to minimize photodegradation processes in the SPMD film. SPMD films were retrieved at each sampling event after an incubation time of 20 to 60 days. The SPMD films were removed from the canisters and washed of solids and salts before PAH dialysis in solvent. The washing process included gentle wiping with gloved fingers followed by rinsing by dilute hydrochloric acid, water, acetone, then hexane. Once washed, the SPMD films were placed in separate jars of 100 mL hexane and incubated for 24 hours. The films were transferred to a fresh 100 mL hexane and incubated for another 24 hours before discarding. The two 100 mL hexane fractions were combined and evaporated to 2 mL at 70°C on the RapidVap, diluted to 20 mL with hexane/acetone (50:50 v/v), evaporated to 3 mL at 70°C, and stored in scintillation vials before GC-MC processing. 3. Soil sampling Surface soil samples were collected from all experimental plots Bay Jimmy to determine PAH source concentrations at plant bases. Samples were stored in dark for transport to the laboratory for processing. Ten grams of soil sample was mixed with diatomaceous earth in preparation of PAH extraction using ASE (described above). The hexane/acetone solvent eluate from the ASE was evaporated at 70°C to 10 mL using the RapidVap and stored in a scintillation vial before GC-MS processing. 4. PAH analysis All samples were prepared for analysis by gas chromatograph-mass selective detection (GC-MS) for targeted PAHs by combining 1 mL of sample eluate with 5 μL of deuterated internal standard (naphthalene, acenaphtheylene, phenanthrene, and chrysene). Samples were analyzed for PAH concentrations by a Hewlett Packard 6890N gas chromatograph equipped with a 5973N mass selective detector and a DB-5 capillary column (30 m x 0.25 mm x 0.25 μm film). The injector temperature was set at 300°C. The detector temperature was set at 280°C. The oven temperature was set at 45°C for 3 minutes, followed by an increase rate of 6°C per minute to 315°C where the temperature was held for 15 minutes. The GC utilized helium as the carrier gas. Quality control blanks (1 mL hexane/acetone at 50:50 by volume with 5 μL internal standard) were placed before and after each run. Continuing calibration standards of known concentrations of PAHs were incorporated in each run as well. Leaf samples were analyzed targeting the following PAH’s: naphthalene, C1-naphthalenes, C2-naphthalenes, C3-naphthalenes, C4-naphthalenes, acenaphthylene, acenaphthene, fluorene, C1-fluorenes, C2-fluorenes, C3-fluorenes, phenanthrene, C1-phenanthrenes, C2-phenanthrenes, C3-phenanthrenes, C4-phenanthrenes, dibenzothiophene, C1-dibenzothiophenes, C2-dibenzothiophenes, C3-dibenzothiophenes, fluoranthene, pyrene, C1-pyrene/fluoranthene, chrysene, C1-chrysenes, C2-chrysenes, and C3-chrysenes. SPMD samples were analyzed targeting the same PAH’s as listed above as well as the following deuterated performance reference compounds: anthracene-d10, fluoranthene-d10, and dibenzo-b,h-anthracene-d14.

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