Biomedical subjects

Keith A Maruya

Publications and source records attributed to Keith A Maruya.

10 recordsLinked to original sources

PubMed2006

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.

Algorithms↗

PubMed2006

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.

Dimethylpolysiloxanes↗

PubMed2005

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.

California↗

PubMed2005

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.

Animals↗

PubMed2005

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.

Animals↗

PubMed2004

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.

Animals↗

PubMed2004

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.

Anaerobiosis↗

PubMed2003

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.

Animals↗

PubMed2002

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.

Animals↗

PubMedDate not supplied

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.

Animals↗