Experimental verification of a model describing solid phase microextraction (SPME) of freely dissolved organic pollutants in sediment porewater

To verify a theoretical mass balance and multiple compartment partitioning model developed to predict freely dissolved concentrations (FDCs) of hydrophobic organic chemicals (HOCs) using negligible depletion-solid phase microextraction (nd-SPME), a series of sediment slurry experiments were performed using disposable poly(dimethyl)siloxane (PDMS) coated-SPME fibers and (14)C-radiolabeled HOC analogs. First, pre-calibration of disposable PDMS coated fibers for four model compounds (phenanthrene, PCB 52, PCB 153 and p,p'-DDE) with good precision (<or=10%) was achieved. Second, sediment slurries spiked and aged with the radiolabeled analogs were extracted by SPME with manipulation of the sediment slurry mass (m(s)) or the PDMS coating volume (V(f)). The measured extent of depletion by SPME (x(e)) decreased with increasing sediment mass (m(s)); conversely, x(e) increased with increasing V(f), which is consistent with the theoretical prediction from our previous model [Yang, Z.-Y., Zeng, E.Y., Maruya, K.A., Mai, B.-X., Ran, Y., 2007b. Predicting organic contaminant concentrations in sediment porewater using solid-phase microextraction. Chemosphere 66, 1408-1414]. Moreover, the SPME-measured FDCs (C(pw,SPME)) followed the order of phenanthrene>PCB 52>PCB 153, and the measured and predicted C(pw) values were not substantially different from empirically determined values except for p,p'-DDE.

Geographic specificity of Aroclor 1268 in bottlenose dolphins (Tursiops truncatus) frequenting the Turtle/Brunswick River Estuary, Georgia (USA)

Coastal marine resources are at risk from anthropogenic contaminants, including legacy persistent organic pollutants (POPs) with half-lives of decades or more. To determine if polychlorinated biphenyl (PCB) signatures can be used to distinguish among local populations of inshore bottlenose dolphins (Tursiops truncatus) along the southeastern U.S. coast, blubber from free-ranging and stranded animals were collected along the Georgia coast in 2004 and analyzed for PCB congeners using gas chromatography with electron capture and negative chemical ionization mass spectrometric detection (GC-ECD and GC-NCI-MS). Mean total PCB concentrations (77+/-34 microg/g lipid) were more than 10 fold higher and congener distributions were highly enriched in Cl(7)-Cl(10) homologs in free-ranging animals from the Turtle/Brunswick River estuary (TBRE) compared with strandings samples from Savannah area estuaries 90 km to the north. Using principal components analysis (PCA), the Aroclor 1268 signature associated with TBRE animals was distinct from that observed in Savannah area animals, and also from those in animals biopsied in other southeastern U.S estuaries. Moreover, PCB signatures in dolphin blubber closely resembled those in local preferred prey fish species, strengthening the hypothesis that inshore T. truncatus populations exhibit long-term fidelity to specific estuaries and making them excellent sentinels for assessing the impact of stressors on coastal ecosystem health.

Determination of poly(dimethyl)siloxane–water partition coefficients for selected hydrophobic organic chemicals using 14C-labeled analogs

Aqueous solutions of (14)C-labeled analogs of seven hydrophobic organic chemicals (HOCs) were subject to solid-phase microextraction (SPME) under static conditions to assess their multi-compartment distribution and to compare poly(dimethyl)siloxane (PDMS)-water partition coefficients (K(f) values) with previously reported values. To accomplish this, a protocol for quantitative desorption of radiolabelled HOCs from SPME fibers using hexane was developed. Time series extractions indicated that loading of SPME fibers had reached steady-state by day 8 for PCBs 52, 77 and 153, phenanthrene, benzo[a]pyrene, p,p'-DDT and p,p'-DDE. The recovery of spiked radioactivity among the (residual) aqueous phase, the PDMS coating, and all remaining wetted experimental surfaces ranged between 80 and 120%. K(f) values based on (14)C-labeled analogs were in good agreement with previously published values that were determined at (or closely approaching) equilibrium conditions and without significant chemical depletion and/or uncorrected system losses. Because it allows for the direct determination of HOCs associated with the residual aqueous and experimental surface compartments, the use of radiolabelled HOC analogs is a powerful tool in discriminating among competing sorptive compartments encountered in most SPME fiber calibration methodologies employed to date.

Predicting organic contaminant concentrations in sediment porewater using solid-phase microextraction

Because of its cost and time saving features, solid-phase microextraction (SPME) is a leading candidate as a biomimic technique in assessing the bioavailable fraction of hydrophobic organic contaminants (HOCs) in sediment porewater. However, no predictive modeling framework in which to systematically address the effect of key parameters on SPME performance for this application exists. In this study, we derived two governing equations to predict (1) the minimum sediment volume (V(s)min) required to achieve non-depletive conditions, and (2) dissolved phase HOC porewater concentrations (C(pw)) as functions of HOC- and sediment specific characteristics in a conceptual three compartment system. The resulting model predicted that V(s)min was independent of HOC concentrations both in sediment and porewater, but did vary with hydrophobicity (characterized by logK(ow)), the fraction of sediment porewater (f(pw)), and the volume (V(f)) of the SPME sorbent phase. Moreover, the effects of these parameters were minimized (i.e., V(s)min reached plateaus) as logK(ow) approached 4-5. Model predictions of C(pw), a surrogate for SPME-based detection limits in porewater, decreased with increasing sediment volume (V(s)) at low V(s) values, but rapidly leveled off as V(s) increased. A third result suggested that the sediment HOC concentration required for SPME is completely independent of K(ow). These results suggest that relatively small sediment volumes participate in exchange equilibria among sediment, porewater and the SPME fiber, and that large sediment HOC reservoirs are not needed to improve the detection sensitivity of SPME-based porewater samplers. The ultimate utility of this modeling framework will be to assist future experimental designs and help predict in situ bioavailability of sediment-associated HOCs.

Application of a static solid-phase microextraction procedure combined with liquid–liquid extraction to determine poly(dimethyl)siloxane–water partition coefficients for selected polychlorinated biphenyls

A static solid-phase microextraction (SPME) procedure combined with liquid-liquid extraction (LLE) was used to determine the poly(dimethyl)siloxane (PDMS)-water partition coefficients (K(f)) for selected polychlorinated biphenyl congeners (PCBs), including PCB 1, 15, 28, 47, 101, 153, 180, 202, 206, and 209. The accuracy for the measurements of analyte concentrations in the aqueous phase was ensured with a one-to-one recovery correction strategy employing one 13C-labeled PCB congener as a surrogate standard for each unlabeled PCB counterpart. The effects of coating thickness (7, 30, and 100 microm) and sample volume (130 mL and 2 L) on the K(f) values were examined experimentally and confirmed with paired t-tests. Significant dependence of K(f) values on coating thickness was found for a few heavily chlorinated congeners only, and was tentatively attributed to the use of the inaccurate effective coating volumes and the structural variation with these PDMS coatings. In addition, no significant differences in the log K(f) values of all analytes except for PCB 206 were found between the sample sizes of 130 mL and 2 L for both the 7- and 100-microm coatings. Overall, K(f) values obtained with 2-L sample containers were consistently higher than those reported in the literature, which is attributable to the selection of appropriate equilibrium times for SPME and direct measurements of aqueous analyte concentrations with LLE in the present study.

Polychlorinated biphenyls and toxaphene in preferred prey fish of coastal southeastern U.S. bottlenose dolphins (Tursiops truncatus)

Legacy organochlorine (OC) contaminants continue to pose a potential risk to ecological and human health in coastal aquatic ecosystems of the southeastern United States. Polychlorinated biphenyls (PCBs) and toxaphene (TOX) were analyzed by gas chromatography with electron capture detection and negative chemical ionization mass spectrometry in 77 composites of four inshore fish species commonly preyed upon by bottlenose dolphins (Tursiops truncatus) from estuaries near Savannah, Georgia (SAV), Brunswick, Georgia (BRN), and Jacksonville, Florida (JAX), USA. Whereas seasonal and species-specific differences were minimal, differences among mean total PCB concentrations (sigmaPCBs) by estuary (42.0 +/- 48.3, 1.59 +/- 1.24, and 0.281 +/- 0.075 microg/g lipid for BRN, JAX, and SAV, respectively) were highly significant. This estuary-specific trend also held true for mean total toxaphene concentrations (sigmaTOX): 49 +/- 100 (BRN), 1.2 +/- 0.52 (JAX), and 0.40 +/- 0.19 microg/g lipid (SAV). Congener profiles of PCBs also were found to be significantly different among estuaries, with BRN and (to a lesser extent) JAX samples enriched with highly chlorinated homologs associated with Aroclor 1268, a legacy OC linked to a historical point source in Brunswick. The observed spatial heterogeneity in OC concentrations and PCB congener profiles suggests that contaminated fish from Brunswick pose the greatest risk to ecological and human health via biomagnification and seafood consumption; highly chlorinated PCBs (and possibly toxaphene) are transported in a southerly, alongshore direction; and the uniqueness of Aroclor 1268 underscores its utility as a signature proxy in future regional ecotoxicological studies.

Distribution and mass inventory of total dichlorodiphenyldichloroethylene in the water column of the southern California bight

A large-scale survey on the area and depth stratified distribution of dichlorodiphenyltrichloroethane (DDT; mainly p,p'- and o,p'-dichlorodiphenyldichloroethylene (DDE)) contamination in the water column of the Southern California Bight (SCB) was conducted in 2003-2004 using a solid-phase microextraction-based sampling technique. Dissolved-phase DDEs were clearly widespread, with the central SCB containing the highest levels, and the Palos Verdes Shelf sediments have remained the dominant source of DDT compounds to the SCB. The p,p'- and o,p'-DDE concentrations ranged from < 0.073 to 2.6 ng/L and from < 0.043 to 0.26 ng/L, respectively, clearly elevated with respect to measured values from across the globe. DDEs were hypothesized to have been transported from the historically contaminated zone on the Palos Verdes Shelf to other areas via a repeated process of sediment resuspension/deposition and short-range advection. Total mass inventories were estimated at 14 and 0.86 kg for p,p'- and o,p'-DDE, respectively, for the sampled area, resulting in p,p'- and o,p'-DDE mass inventories for the entire SCB of 230 and 14 kg, respectively. Furthermore, total fluxes of p,p'-DDE were estimated to be in the range of 0.8 to 2.3 metric tons per year. These results suggest that the SCB has been and continues to be a significant source of DDT contamination to the global oceans.

Temperature and congener structure affect the enantioselectivity of toxaphene elimination by fish

Recent advances in enantioselective separation techniques have enabled scientists to investigate environmental fate processes of chiral pollutants. In this study, congener- and enantiomer-specific toxaphene residues were monitored in captive, naturally contaminated fish (Fundulus heteroclitus) to characterize the effect of temperature and compound structure on the enantioselectivity of the elimination process. A previous study performed under warm water conditions (Tmean = 25 degrees C) demonstrated relatively rapid (t(1/2) approximately = 7-14 d) and enantioselective elimination of the reductive dechlorination metabolites 2-exo,3-endo,6-exo,8,9,-10-hexachlorobornane (B6-923 or Hx-Sed) and 2-endo,3-exo,5-endo,6-exo,8,9,10-heptachlorobornane (B7-1001 or Hp-Sed). As expected, repetition of this experiment at cooler water temperatures (Tmean = 15 degrees C) resulted in a decrease in overall (i.e., both enantiomers) first-order elimination rate constants. Enantiomer fractions or ratios (EFs/ERs) during elimination, however, varied by congener, ranging from racemic for very rapidly eliminated Cl5 homologues to increasingly nonracemic for selected Cl6-Cl8 homologues (including 86-923, several unknown Cl7 compounds, B8-1414, and B8-1945). As a result, we propose a classification to describe the environmental persistence of chiral toxaphene pollutants based on congener-specific elimination kinetics and susceptibility to biotransformation as measured by EFs/ERs.

Residues of toxaphene in insectivorous birds (Petrochelidon spp.) from the Rio Grande, Texas

Although it has been documented that wildlife in the Rio Grande Valley (RGV) contain increased concentrations of organochlorine (OC) contaminants, particularly DDE, little has been published on residues of toxaphene throughout this major North American watershed. In this study, 28 liver composites from adult swallows (Petrochelidon spp.) collected along the Rio Grande from 1999 through 2000 were analyzed for toxaphene residues using congener-specific gas chromatography-electron-capture negative ionization-mass spectrometry. Estimated total toxaphene concentrations ranged from 12 to 260 ng/g wet wt and were highest in samples from the lower RGV near Llano Grande Lake in Hidalgo and Cameron counties (Texas). Toxaphene congener profiles were relatively invariant throughout the watershed and were dominated by 2,2,5-endo,6-exo,8,8,9,10-octachlorobornane (P-42a or B8-806) with lesser amounts of several other Cl(7)-Cl(9) compounds, many of which remain unidentified. Petrochelidon spp. liver profiles appear to be intermediate in complexity between those in invertebrates and fish (more complex) and mammals (less complex) and differs somewhat from those reported for other avian species. In addition to other legacy OC contaminants, toxaphene residues were most concentrated in the lower RGV and accumulated at up to hundreds of parts per billion in these insect-eating birds, underscoring their utility as avian bioindicators of persistent organic pollutants.

Exposure of grass shrimp to sediments receiving highway runoff: Effects on reproduction and DNA

A grass shrimp bioassay was carried out on sediments from three estuarine stations which were different distances from a highway storm drain. Total polycyclic aromatic hydrocarbon (PAH) concentrations were 29, 1.5 and 0.1 microg/g sediment at stations A (next to drain), B (100 m from drain) and C (500 m from drain), respectively. Lower embryo production and embryo hatching rates and a higher level of DNA strand breaks (comet assay) were observed in grass shrimp exposed to stations A and B sediments. There appeared to be an association between reproduction abnormalities and increased DNA strand breaks as a result of grass shrimp exposure to estuarine sediments receiving highway runoff.

Toxicity assessment of sediments associated with various land-uses in coastal South Carolina, USA, using a meiobenthic copepod bioassay

Coastal urbanization supplies surrounding estuarine environments with urban-related contaminants such as polycyclic aromatic hydrocarbons (PAHs), metals and pesticide mixtures. In our study, adult female and male copepods (Amphiascus tenuiremis) were chronically exposed to 18 sediment samples collected from sites influenced by different land-uses. Sediment samples were collected from three major suburban areas (Hilton Head, Kiawah Island and the Okatee River watershed) and a pristine site (North Inlet) in coastal South Carolina. Three-sediment bioassays (six sites per bioassay) were conducted by culturing copepods for 14 days in quadruplicate test sediments under flow-through conditions at 20 degrees C and 12:12 LD cycles. Adult survival and copepod reproductive output were quantified. Sediment samples were also analyzed by GC-MS for low and high molecular weight PAHs. Minimal adult mortality was observed in most sediment samples. However, sediments from Hilton Head Island and the Okatee River showed significant effects on copepod reproductive output (i.e., nauplii, copepodites and clutch size). Thus, we determined that reproductive endpoints rather than adult copepod survivorship were more sensitive to effects of contaminated sediments on A. tenuiremis. Furthermore, six (33%) of the 18 sites had a >25% reduction in copepod bioassay endpoints relative to controls, suggesting a high risk to long term A. tenuiremis population maintenance.

Anaerobic transformation of compounds of technical toxaphene. 2. Fate of compounds lacking geminal chlorine atoms

The major toxaphene metabolites in sediment and soils (2-exo,3-endo,6-exo,8,9,10-hexachlorobornane [B6-923] and 2-endo,3-exo,5-endo,6-exo,8,9,10-heptachlorobornane [B7-1001]) were incubated with the isolated gram-negative bacterium Dehalospirillum multivorans. Within 14 d, biotransformation of B7-1001 was nearly quantitative, resulting in two penta- and six hexachlorobornanes, as well as one unsaturated hexachloro compound of technical toxaphene. The major transformation product (approximately 50% of all metabolites) was identified as 2-exo,3-endo,5-exo,8,9,10-hexachlorobornane (B6-903). Abiotic dehydrochlorination of B7-1001 with methanolic KOH resulted in the formation and subsequent identification of the lone unsaturated compound as 2,5-endo,6-exo,8,9,10-hexachloroborn-2-ene. Thus, dehydrochlorination was found to be a minor process of the anaerobic transformation of toxaphene. Biotransformation of 70% of amended B6-923 within 14 d demonstrated that reductive dechlorination was not exclusively associated with geminal Cl atoms, as previously suggested. Three pentachlorobornanes were identified as transformation products, one of which was identical with a transformation product of B7-1001. This commonality unequivocally proves this metabolite to be 2-exo,3-endo,8,9,10-pentachlorobornane. Fifteen previously unknown metabolites of B6-923, B7-1001, and other toxaphene compounds identified in this study were detected in sediment from Lake Ontario (Canada), underscoring the importance of microbial toxaphene transformation in natural, aquatic environments.

Dehalogenation of 2,6-dibromobiphenyl and 2,3,4,5,6-pentachlorobiphenyl in contaminated estuarine sediment

Estuarine sediments from a USEPA Superfund site in coastal Georgia were extensively contaminated with Aroclor 1268, a mixture of highly chlorinated polychlorinated biphenyls used by a former chlor-alkali plant. Batch slurries of contaminated sediment were incubated for 1 yr with amendments of 2,6-dibromobiphenyl (26-BB) and 2,3,4,5,6-pentachlorobiphenyl (23456-CB) under anaerobic, sulfate-reducing conditions and different pH (5.5-7.5). Organic extracts of slurry sub-samples in a time series were analyzed by congener-specific GC-MS. Dechlorination of 23456-CB was pH dependent and occurred via two routes with the sequential loss of (1) meta and para chlorines and (2) para, ortho, and meta chlorines. Quantitative dehalogenation of 26-BB was observed at all pH. Supplementation of nonachlorobiphenyls (as primers) did not induce dechlorination of native Aroclor 1268 nor of the primers themselves. While contaminated estuarine sediments possess microbial consortia with diverse dehalogenating activities, lack of dechlorination of Aroclor 1268 and spiked nonachlorobiphenyl congeners suggests a bioavailability limitation or enzyme-substrate incompatibilities.

Di- and tribromoindoles in the common oyster (Crassostrea virginica)

The sources/origins, fate and impacts of naturally occurring organobromine compounds in the marine environment are largely unknown. Soft tissue composites of the common oyster (Crassostrea virginica) collected from coastal Georgia (USA) were analyzed for organobromines by gas chromatography. Three simple bromoindoles (BIs)--two dibromo- and one tribromo congener--were detected and their molecular formulas elucidated by electron and negative chemical ionization GC-MS. Semi-quantitative estimates of BI concentrations in these samples using GC-ECD indicated that oysters sampled in November 1999 contained 5-10 times more BIs than those sampled in August 2000 and March 2001. Although their bromine substitution patterns are presently unknown, this first ever report of bromoindoles in C. virginica, a prolific and important commercial and ecological species, underscores its potential utility as a bioindicator of organobromines in the coastal marine environment.

Predicting bioavailability and bioaccumulation with in vitro digestive fluid extraction

Bioavailability of sediment-associated contaminants was assessed in parallel tests by means of a bivalve (Macoma nasuta) bioaccumulation assay and a novel in vitro digestive fluid extraction procedure. Digestive fluid was obtained from the deposit-feeding polychaete Arenicola brasiliensis and used to extract sediments from a U.S. Navy facility. Both the digestive fluid extraction and the bivalve bioaccumulation test identified Cd, Pb, high molecular weight polycyclic aromatic hydrocarbons (HPAHs), and polychlorinated biphenyls (PCBs) as the contaminants of concern; both procedures indicated that As, Cu, Hg, Ni, Zn, and low molecular weight polycyclic aromatic hydrocarbons were rarely, if ever, of concern. The only contaminant for which the techniques consistently differed was Cr, a result attributable to constraints on intestinal absorption of the metal by the bivalves. For Cd and Pb, the concentration attained in digestive fluid during a brief extraction was highly correlated with concentration attained in the bivalve after a 28-d exposure; correlation was marginal for HPAHs and was nonsignificant for PCBs. However, bulk sediment concentrations were equally good predictors of bioaccumulation because of minimal differences in bioavailability from the most contaminated sediments. In vitro contaminant extraction with the digestive fluid assay has potential as a screening tool to predict relative bioaccumulation risk, and has several advantages over traditional tests.

Interpreting nonracemic ratios of chiral organochlorines using naturally contaminated fish

Although reports of nonracemic proportions of chiral organochlorine pollutants in the environment are widespread, the interpretation of such data is not well developed. Using GC/MS and a chiral stationary phase consisting of 25% tert-butyldimethylsilylated beta-cyclodextrin in PS086 (beta-BSCD), we followed the change in the enantiomeric signature of 2-exo,3-endo,6-exo,8,9,10-hexachlorobornane (B6-923) in naturally contaminated fish maintained under toxaphene-free conditions. Whereas the enantiomeric ratio (ER) of B6-923 was near racemic at the start of the elimination experiment, it had increased severalfold by the end of 60 d. On the basis of first-order kinetics, one enantiomer of B6-923 was eliminated twice as fast as its mirror image, resulting in half-lives of 7 and 13 d, respectively. Enantioselective elimination by our test fish (Fundulus sp.) strongly suggests active biotransformation of B6-923; however, bioprocessing throughput estimates suggest a very low in situ rate of natural attenuation. These results confirm that the relatively constant ERs observed for chiral organochlorines in a given species are the result of competing processes, e.g., uptake vs elimination. Our experiments also further illustrate the utility of enantioselective analysis in characterizing the biotransformation of persistent organochlorine pollutants.

Characterization of the B12- and iron-sulfur-containing reductive dehalogenase from Desulfitobacterium chlororespirans

The United Nations and the U.S. Environmental Protection Agency have identified a variety of chlorinated aromatics that constitute a significant health and environmental risk as "priority organic pollutants," the so-called "dirty dozen." Microbes have evolved the ability to utilize chlorinated aromatics as terminal electron acceptors in an energy-generating process called dehalorespiration. In this process, a reductive dehalogenase (CprA), couples the oxidation of an electron donor to the reductive elimination of chloride. We have characterized the B12 and iron-sulfur cluster-containing 3-chloro-4-hydroxybenzoate reductive dehalogenase from Desulfitobacterium chlororespirans. By defining the substrate and inhibitor specificity for the dehalogenase, the enzyme was found to require an hydroxyl group ortho to the halide. Inhibition studies indicate that the hydroxyl group is required for substrate binding. The carboxyl group can be replaced by other functionalities, e.g. acetyl or halide groups, ortho or meta to the chloride to be eliminated. The purified D. chlororespirans enzyme could dechlorinate an hydroxylated PCB (3,3',5,5'-tetrachloro-4,4'-biphenyldiol) at a rate about 1% of that with 3-chloro-4-hydroxybenzoate. Solvent deuterium isotope effect studies indicate that transfer of a single proton is partially rate-limiting in the dehalogenation reaction.

Structure of a persistent heptachlorobornane in toxaphene (b7-1000) agrees with molecular model predictions

A Cl(7) component of technical toxaphene (CTT), previously detected in marine mammals and fish and referred to as "7-1", was isolated from contaminated estuarine sediment using preparative solid-liquid chromatography followed by reversed-phase HPLC. The structure of this compound, elucidated by GC/MS and (1)H NMR, was 2-endo,3-exo,5-endo,6-exo,8,8,10-heptachlorobornane (hereafter referred to as B7-1000). This newly identified CTT eluted in the nonpolar fraction from silica and shares the alternating endo-exo chlorine substitution pattern with other relatively nonpolar, persistent congeners (e.g., B8-1413 and B9-1679). Based on ECNI-MS response, levels of B7-1000 in tissue samples of various higher organisms including humans were as high as 16% of B8-1413. Enantioselective determination of B7-1000 using a modified cyclodextrin chiral stationary phase (beta-BSCD) resulted in enantiomer ratios that were depleted in adipose tissue of a marine bird (skua) and Weddell seal blubber (0.3 and 0.5, respectively), but not in elephant seal blubber (1.1). Elucidation of the structure of B7-1000 thus validates previous predictions of persistence based on structure-activity relationships, chromatographic properties, and molecular modeling.

Induction of the P450 reporter gene system bioassay by polycyclic aromatic hydrocarbons in Ulsan Bay (South Korea) sediments

Polycyclic aromatic hydrocarbons (PAHs) and induction of the P450 reporter gene system (RGS) for 6- and 16-h exposure periods were determined in organic extracts of Ulsan Bay (South Korea) sediments to assess the utility of this bioassay as a screening tool for PAH contamination. The sum of the concentrations of 23 individual PAHs in 30 sediment samples (sigma PAH) based on GC-MS analysis ranged from 0.05 to 6.1 micrograms/g dry wt. P450 RGS fold induction ranged from 4.0 to 320 micrograms/g based on benzo[a]pyrene toxic equivalents (BaPEq). P450 RGS BaPEq and the 'chemical BaPEq', defined as the sum of the products of individual PAH concentrations and pre-determined toxic equivalency factors, exhibited very strong positive correlations with sigma PAH (r2 > 0.90; P < 0.001). Fold induction did not increase (and in some cases decreased) after the optimal incubation period (6 h) for PAHs, indicating that other compounds known to induce the P450 RGS (e.g. chlorinated organics) were not present at levels effecting significant induction. This was supported by GC-ECD analysis where non-ortho and mono-ortho polychlorinated biphenyls (PCBs) known to be strong P450 RGS inducers were found to be at very low or non-detectable levels in samples with the highest P450 RGS responses. The profound difference in PAH profiles for the two most contaminated sites suggested that this assay is especially sensitive for selected PAHs with greater than four rings. Combined with previous results, the P450 RGS shows promise as a useful screening tool for predicting deleterious biological effects resulting from CYP1A1-inducing, sediment-associated chemicals, particularly high molecular weight PAHs.

DNA strand breaks (comet assay) and embryo development effects in grass shrimp (Palaemonetes pugio) embryos after exposure to genotoxicants

Grass shrimp embryos develop in egg sacs (stages 1-10) attached to the female for 14-20 days after which they 'hatch' from the egg sacs into a swimming zoea stage (stage 11). Until they emerge from the egg sacs, embryos depend on lipids and lipovitellin stored within the egg. The percent of embryos which hatch after exposure to toxicants relative to controls was the basis of an embryo development assay. Exposure of embryos to chromium(III) chloride, sodium chromate, mercuric chloride, and 2-methyl-1,2-naphthoquinone (MNQ) resulted in a reduced hatching rate. In addition to effects on embryo development, DNA strand damage tests were carried out on contaminant-exposed embryos, using the single-cell electrophoresis method often referred to as comet assay. Development of stage 4 embryos was more affected by MNQ exposure than stage 7 embryos. The hatching rates of stages 4 and 7 embryos exposed to MNQ (172 micrograms/l) were 0 and 90%, respectively. DNA strand damage, measured as DNA tail moments, were 3.4 and 4.4, respectively. Thus, exposure of an early embryo stage to MNQ prevented full embryo development while development of later embryo stages was not affected. It may be that the DNA repair systems are more efficient in later embryo stages than in early stages and thus DNA damaged in the early stages affects development.

Fungal biomass in saltmarsh grass blades at two contaminated sites

Ascomycetous fungi are the principal drivers of the decomposition of shoots of smooth cordgrass (Spartina alterniflora). Shoots of smooth cordgrass move into the saltmarsh food web via the decomposition system. Therefore, influences on saltmarsh ascomycetes by pollutants of saltmarshes could have far-reaching impacts. Earlier examination of impacts of severe contamination of a Georgia saltmarsh by mercury and polychlorinated biphenyls (PCBs) revealed little or no influence of the toxicants on living standing crops or sexual productivities of cordgrass ascomycetes. Extension of the examination of saltmarsh-ascomycete response to sites containing other toxic pollutants (the chlorinated organocyclic insecticide toxaphene; chromium, copper, and lead; and polycyclic aromatic hydrocarbons [PAHs]) has shown that none of the additional toxicants engendered saltmarsh-fungal responses in the form of reduced living standing crops or sexual productivities. Thus the ascomycetes of the cordgrass-decay system appear to be as resistant to anthropogenic-pollutant poisoning as smooth cordgrass itself. Unless the fungal and plant resistance mechanisms involve degradation of the toxicants, this may imply that saltmarshes are especially dangerous as receiving sites for toxic waste because they may have the potential to readily move toxicants into the food web.