Hyun-Min Hwang

Diversity, Composition, and Geographical Distribution of Microbial Communities in California Salt Marsh Sediments

ABSTRACT The Pacific Estuarine Ecosystem Indicators Research Consortium seeks to develop bioindicators of toxicant-induced stress and bioavailability for wetland biota. Within this framework, the effects of environmental and pollutant variables on microbial communities were studied at different spatial scales over a 2-year period. Six salt marshes along the California coastline were characterized using phospholipid fatty acid (PLFA) analysis and terminal restriction fragment length polymorphism (TRFLP) analysis. Additionally, 27 metals, six currently used pesticides, total polychlorinated biphenyls and polycyclic aromatic hydrocarbons, chlordanes, nonachlors, dichlorodiphenyldichloroethane, and dichlorodiphenyldichloroethylene were analyzed. Sampling was performed over large (between salt marshes), medium (stations within a marsh), and small (different channel depths) spatial scales. Regression and ordination analysis suggested that the spatial variation in microbial communities exceeded the variation attributable to pollutants. PLFA analysis and TRFLP canonical correspondence analysis (CCA) explained 74 and 43% of the variation, respectively, and both methods attributed 34% of the variation to tidal cycles, marsh, year, and latitude. After accounting for spatial variation using partial CCA, we found that metals had a greater effect on microbial community composition than organic pollutants had. Organic carbon and nitrogen contents were positively correlated with PLFA biomass, whereas total metal concentrations were positively correlated with biomass and diversity. Higher concentrations of heavy metals were negatively correlated with branched PLFAs and positively correlated with methyl- and cyclo-substituted PLFAs. The strong relationships observed between pollutant concentrations and some of the microbial indicators indicated the potential for using microbial community analyses in assessments of the ecosystem health of salt marshes.

Aerial distribution, temperature-dependent seasonal variation, and sources of polycyclic aromatic hydrocarbons in pine needles from the Houston metropolitan area, Texas, USA

To investigate the aerial distribution, seasonal variation, and sources of polycyclic aromatic hydrocarbons (PAHs), pine needles were collected from 18 sites in the Houston metropolitan area, Texas, USA. Total PAHs ranged from 209 to 2,226 ng/g (dry wt.), which were similar to those found in other urban areas. The highest and lowest concentrations were found in samples from the inner city of Houston and the outer edge of suburban area, respectively. Aerial distribution of PAHs in pine needles was closely correlated to the proximity to densely occupied residential area and traffic volumes around sampling sites. Seasonal changes of PAHs in pine needles were inversely correlated with ambient temperature with lower levels in warmer months. Calculated concentrations of 3-ring PAHs in the air had a positive correlation with ambient temperature with higher levels in warmer months. Ratios of PAHs in pine needles to PAHs in the air decreased as ambient temperature increased because fugacity (escaping tendency) of PAHs in pine needles is grater in warmer months. The PAH patterns and ratios were fairly constant in all samples, indicating that the whole study area was influenced by the same emission sources, most importantly gasoline vehicle emission. Phenanthrene was the predominant PAH and 3- and 4-ring PAHs were the most abundant in all samples, accounting for 79 to 97% of the total PAHs. The present study provides evidence that pine needle monitoring can be used as a good screening method to assess the atmospheric PAH contamination quickly and at low cost.

Polychlorinated biphenyls in stormwater runoff entering the tidal Anacostia River, Washington, DC, through small urban catchments and combined sewer outfalls

To investigate the loadings, solid-water partitioning, transport dynamics, and sources of polychlorinated biphenyls (PCBs) in urban stormwater runoff entering into the lower tidal Anacostia River, which flows south of Washington, DC, USA, storm and base flow samples were collected in six branches. Stormwater runoff contained elevated levels of PCBs (9.82 to 211 ng/L) higher than base flow by up to 80-fold. The present study suggests that input of PCBs from Lower Beaverdam Creek is likely to be greater than those from the two major branches (Northeast and Northwest Branches) that were believed as primary source areas. PCBs in storm flow were significantly enriched in the particle phase, which accounted for more than 90% of the total PCBs. Particles were the primary vector transporting PCBs into the Anacostia River, suggesting that removal of particles in stormwater runoff using best management practices (BMPs) such as post treatment system likely decrease PCBs significantly. PCB congener patterns found in stormwater samples clearly explain stormwater runoff is a major transport pathway adding substantial amount of PCBs to the tidal Anacostia River.

Tidal salt marsh sediment in California, USA: part 3. Current and historic toxicity potential of contaminants and their bioaccumulation.

To assess potential health risks to benthic organisms from exposure to toxic contaminants, sediment chemistry data from five salt marshes along the coast of California were compared with threshold effects levels (TELs) and probable effects levels (PELs). As an integrated estimate of toxicity potential of multiple contaminants, mean PEL quotients (mPELQs) were used to categorize sampling stations into three groups: high (>0.5), medium (0.1-0.5) and low (<0.1). In all sediments from Stege Marsh located in San Francisco Bay, at least one contaminant exceeded PELs by up to 18-fold and mPELQs were higher than 0.7. Mean PELQs in two core sediments from eastern Stege Marsh ranged from 0.7 to 2.1, indicating that benthic organisms in Stege Marsh may have been adversely affected for several decades. To investigate bioavailability and bioaccumulation of contaminants in sediments, longjaw mudsuckers (Gillichthys mirabilis) were transplanted to six Stege Marsh stations for 60 days. Body burdens of organic contaminants clearly showed that they were readily available for benthic organisms. Measured concentrations of organic contaminants in mudsuckers were similar to estimated levels computed using a theoretical bioaccumulation potential model. Levels of PCBs and arsenic in mudsuckers were higher than screening values set as guidelines for the protection of humans and levels of PCBs and DDTs were higher than criteria for wildlife. The results of this study indicate that the levels of contaminants in Stege Marsh sediments may not fully support the well-being of benthic organisms and also may provoke adverse effects on fish-eating animals and humans through trophic transfer.

Water Quality Evaluation of Leachate Produced from Pavement Specimens under Controlled Laboratory Conditions

ABSTRACT An experimental apparatus and procedures were used to evaluate the organic and inorganic quality of leachate produced from ten different asphalt and concrete pavement specimens under controlled laboratory conditions. Triplicates of both fresh and aged specimens were tested at three controlled laboratory temperatures of 4, 20, and 45 °C. Leachate samples were taken at various times during each experiment for eight hours to examine the metal pollutants concentration variability. Results showed that, in general, the leachate concentrations for most water quality parameters were below or near the method detection limit. However, dissolved chromium and vanadium concentrations were consistently detected from concrete specimens, particularly during the first three hours of the experiment and gradually reduced to below the reporting limit at the conclusion of the experiments. From this study we can conclude that the concentration of chemical constituents solely generated from pavement surfacing materials is negligible and the pollutants in roadway runoff is mostly related to other road use and land use sources.

Anthropogenic impacts on the quality of streambed sediments in the lower Sacramento River watershed, California.

To investigate the occurrence of contaminants and to assess their toxicity potential to benthic organisms, streambed sediments were collected from three agricultural and one urban influenced small waterways in the lower Sacramento River watershed and analyzed for PAHs, organochlorine (OC) and organophosphorus (OP) pesticides, pyrethroids, and metals. These sites had low benthic biotic index scores in earlier field surveys. The occurrence patterns of these contaminants and iron normalized enrichment factors of metals reflect the land use patterns around study sites. DDTs were detected in all samples while chlordanes were found only at the urban influenced site. No OP pesticides were found in any sediment presumably due to their high water solubilities and low solid-water partitioning. DDTs, PAHs, and metals at sites in the Biggs/West Gridley Canal showed a gradient increasing toward downstream. Distribution patterns of individual PAHs and their ratios found in sediment from the Biggs/West Gridley Canal downstream site resemble those of petroleum. PAHs in this site might originate from petroleum oils that have been used as agricultural pesticides. The enrichment factor of vanadium, which is an indicator of petroleum residue, was also higher in this site. The anthropogenic enrichment of copper at all Biggs/West Gridley Canal sites might be because of significant use of copper based pesticides. The high enrichment factor of lead at the urban influenced Dry Creek site might be related to historical use of leaded gasoline. All sediment samples had at least one chemical that exceed the threshold effects concentration (TEC). Total probable effects concentration quotients (tPECQs) were greater than 1 at all sites, indicating that sediment bound contaminants in the study sites can possibly pose toxic effects. This finding can be linked to lower biotic index scores observed in previous regional monitoring studies.

Residue-response relationship between PAH body burdens and lysosomal membrane destabilization in eastern oysters (Crassostrea virginica) and toxicokinetics of PAHs

This study was undertaken to establish residue-response relationship between lysosomal destabilization and body residues of multiple PAHs in eastern oysters (Crassostrea virginica) exposed to a mixture of PAHs for 25 days in laboratory aquariums. The contaminated oysters were then placed in clean aquariums for 20 days to allow them to depurate and recover. The lysosomal destabilization was linearly correlated with the PAH body burdens. Regression analysis showed that critical body residue (CBR), in terms of lysosomal destabilization (at least 50% of destabilized cells), was found at 2,100 ng/g (9.32 nmol/g) of total PAHs. This CBR is much lower than the CBRs for reproduction and death, confirming that lysosomal destabilization, as a cellular level biomarker, appears to be functioning as an early warning indicator that can be used to detect aquatic contamination much before severe effects are observed. During 25 days of exposure, the lysosomal destabilization and PAH body burdens increased from 32 to 75% and 77 to 5,925 ng/g, respectively. After 20 days of elimination period, the lysosomal destabilization and PAH body burdens decreased to 49% and 2,350 ng/g, respectively. Uptake rates of PAHs showed parabolic shaped correlation with hydrophobicity (K ow ). Uptake rate constants of more hydrophobic PAHs (log K ow > 4.6) had a negative correlation with K ow , implying that hydrophobicity alone is not a satisfactory predictor for these PAHs. Elimination half-lives varied from 4 to 96 days and bioconcentration factors ranged from 650 to 160,000. Fugacity ratios (f o /f w ) indicated that equilibrium still was not reached at the end of the uptake period. Data obtained from the three replicate aquariums, which were operated at the same time under the same condition, showed good replicability (RPD < 30%).

Polycyclic aromatic hydrocarbon body residues and lysosomal membrane destabilization in mussels exposed to the Dubai Star bunker fuel oil (intermediate fuel oil 380) spill in San Francisco Bay

Following the spill of bunker fuel oil (intermediate fuel oil 380, approximately 1500-3000 L) into San Francisco Bay in October 2009, polycyclic aromatic hydrocarbon (PAH) concentrations in mussels from moderately oiled areas increased up to 87 554 ng/g (dry wt) and, 3 mo later, decreased to concentrations found in mussels collected prior to oiling, with a biological half-life of approximately 16 d. Lysosomal membrane destabilization increased in mussels with higher PAH body burdens.

Measuring Submicron-Size Fractionated Particulate Matter on Aluminum Impactor Disks

Sub-micron sized airborne particulate matter (PM) is not collected well on regular quartz or glass fiber filter papers. We used a micro-orifice uniform deposit impactor (MOUDI) to fractionate PM into six size fractions and deposit it on specially designed high purity thin aluminum disks. The MOUDI separated PM into fractions 56-100 nm, 100-180 nm, 180-320 nm, 320-560 nm, 560-1000 nm, and 1000-1800 nm. Since the MOUDI has a low flow rate (30 L/min), it takes several days to collect sufficient carbon on 47 mm foil disks. The small carbon mass (20-200 microgram C) and large aluminum substrate (~25 mg Al) present several challenges to production of graphite targets for accelerator mass spectrometry (AMS) analysis. The Al foil consumes large amounts of oxygen as it is heated and tends to melt into quartz combustion tubes, causing gas leaks. We describe sample processing techniques to reliably produce graphitic targets for (14)C-AMS analysis of PM deposited on Al impact foils.