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Title: Assessing mercury exposure and biomarkers in largemouth bass (Micropterus Salmoides) from a contaminated river system in California
Description: We evaluated mercury (Hg) exposure and two biomarkers, metallothionein (MT) gene expression and histopathological alterations in a wild fish species, largemouth bass (Micropterus salmoides), collected from the Sacramento-San Joaquin Delta, CA, a region polluted with Hg from historic mining activities. Hg is highly toxic and can disrupt multiple physiological systems in vertebrate species, including the immune system. Total mercury (THg) concentration in muscle tissue ranged from 0.12 to 0.98 ppm (wet weight) and was not related to body condition (r 2 = 0.005, p = 0.555). Using linear regression analysis, we found a positive relationship between MT gene expression (as determined using quantitative polymerase chain reaction) and copper, zinc, manganese, aluminum, and nickel (decreased to one variable by way of principal component analysis) (r 2 = 0.379, p = 0.044), a negative relationship with selenium (r 2 = 0.487, p = 0.017), and a weak, negative relationship with THg concentrations (r 2 = 0.337, p = 0.061). Juvenile largemouth bass collected from Hg-contaminated areas displayed histopathological features of immunosuppression compared with those collected from less contaminated areas as evidenced by significantly lower macrophage density in kidney and liver tissue (p = 0.018 and 0.020, respectively), greater trematode density in liver tissue (p = 0.014), and a greater number of adult trematodes. Our results suggest that largemouth bass may be experiencing sublethal effects from chronic Hg exposure. Furthermore, our findings illustrate the utility of examining multiple sublethal markers of effect to assess the impacts of contaminant exposure on physiological function in wild species. © 2012 Springer Science+Business Media New York., Fish and Fisheries, CODEN: AECTC
Author: Gehringer, Finkelstein, Coale, Stephenson, Geller
Date: 2013-01-01T00:00:00Z

Title: Elevated concentrations of mercury in mussels (Mytilus californianus) associated with pinniped colonies,
Description: The geographic distribution of mercury concentrations in the California mussel Mytilus californianus, collected from 1977-1978 at 43 sites along the western coastline of the continental United States is marked by consistently elevated levels at two locations. These two sites, which are relatively isolated from anthropogenic inputs and mercury-rich minerals, both contain large pinniped and marine bird populations. The relatively elevated mercury levels measured in the excrement of a pinniped from one of those locales indicate that the concentrated discharge of mercury-rich waste products from the marine ecosystem's top carnivores is contaminating lower trophic levels., Cited By (since 1996):1, Ecology, CODEN: MBIOA, ,
Author: Flegal, Stephenson, Martin, Martin
Date: 1981-01-01T00:00:00Z

Title: Mercury cycling in agricultural and managed wetlands, Yolo Bypass, California: Spatial and seasonal variations in water quality,
Description: Abstract The seasonal and spatial variability of water quality, including mercury species, was evaluated in agricultural and managed, non-agricultural wetlands in the Yolo Bypass Wildlife Area, an area managed for multiple beneficial uses including bird habitat and rice farming. The study was conducted during an 11-month period (June 2007 to April 2008) that included a summer growing season and flooded conditions during winter. Methylmercury (MeHg) concentrations in surface water varied over a wide range (0.1 to 37 ng L− 1 unfiltered; 0.04 to 7.3 ng L− 1 filtered). Maximum MeHg values are among the highest ever recorded in wetlands. Highest MeHg concentrations in unfiltered surface water were observed in drainage from wild rice fields during harvest (September 2007), and in white rice fields with decomposing rice straw during regional flooding (February 2008). The ratio of MeHg to total mercury (MeHg/THg) increased about 20-fold in both unfiltered and filtered water during the growing season (June to August 2007) in the white and wild rice fields, and about 5-fold in fallow fields (July to August 2007), while there was little to no change in MeHg/THg in the permanent wetland. Sulfate-bearing fertilizer had no effect on Hg(II) methylation, as sulfate-reducing bacteria were not sulfate-limited in these agricultural wetlands. Concentrations of MeHg in filtered and unfiltered water correlated with filtered Fe, filtered Mn, DOC, and two indicators of sulfate reduction: the SO42 −/Cl− ratio, and δ34S in aqueous sulfate. These relationships suggest that microbial reduction of SO42 −, Fe(III), and possibly Mn(IV) may contribute to net Hg(II)-methylation in this setting., , ,
Author: Alpers, Fleck, Marvin-DiPasquale, Stricker, Stephenson, Taylor
Date: 2014-06-15T00:00:00Z

Title: Sediment quality in Los Angeles Harbor, USA: A triad assessment,
Description: Sediment quality in the Los Angeles and Long Beach Harbor area of southern California, USA, was assessed from 1992 to 1997 as part of the California State Water Resources Control Board's Bay Protection and Toxic Cleanup Program and the National Oceanic and Atmospheric Administration's National Status and Trends Program. The assessment strategy relied on application of various components of the sediment quality triad, combined with bioaccumulation measures, in a weight-of-evidence approach to sediment quality investigations. Results of bulk-phase chemical measurements, solid-phase amphipod toxicity tests, pore-water toxicity tests with invertebrate embryos, benthic community analyses (presented as a relative benthic index), and bioaccumulation measures indicated that inner harbor areas of this system are polluted by high concentrations of a mixture of sediment-associated contaminants and that this pollution is highly correlated with toxicity in laboratory experiments and degradation of benthic community structure. While 29% of sediment samples from this system were toxic to amphipods (Rhepoxynius abronius or Eohaustorius estuarius), 79% were toxic to abalone embryos (Haliotis rufescens) exposed to 100% pore-water concentrations. Statistical analyses indicated that amphipod survival in laboratory toxicity tests was significantly correlated with the number of crustacean species and the total number of species measured in the benthos at these stations. Triad measures were incorporated into a decision matrix designed to classify stations based on degree of sediment pollution, toxicity, benthic community degradation, and, where applicable, tissue concentrations in laboratory-exposed bivalves and feral fish., Cited By (since 1996):36, Rocks and Cores, CODEN: ETOCD, ,
Author: Anderson, Hunt, Phillips, Fairey, Roberts, Oakden, Puckett, Stephenson, Tjeerdema, Long, Wilson, Lyons
Date: 2001-01-01T00:00:00Z

Title: A field bioassay approach to determining tributyltin toxicity to oysters in California,
Description: , , Field experiments were conducted with oysters, Crassostrea gigas to determine the toxicity of tributyltin (TBT). Oysters were transplanted to over one hundred stations distributed in 25 marinas usually in a transect of four or five stations along a gradient next to vessels extending to station locations distant from vessels. In almost every bay in California there are many vessels, the TBT levels in water are > 50 ng/liter (parts per trillion), and the oysters exhibit a chambering response similar to the chambering response that was indicative of the destruction of the oyster industry in France. Although oysters were transplanted to stations that had extreme environmental conditions (near sewer and petroleum refinery discharges) no evidence of chambering was observed indicating that the chambering response does not occur with every type of environmental stress. In addition, oysters transplanted to a marina that had been abandoned for 18 months did not show a chambering response, whereas those transplanted in marinas that had vessels always showed a chambering response. The use of field techniques in determining toxicity responses worked in this case but the response could have been more clearly defined if more stations were added in each marina and the dose response determined on a marina by marina basis. More TBT measurements in water would have also helped to refine the dose-response relationship. A first estimate of a toxicity value can be determined from these data to be less than 40 ng/liter., , ,
Author: Stephenson
Date: 1991-01-01T00:00:00Z

Title: Assessment of sediment toxicity and chemical concentrations in the San Diego Bay region, California, USA,
Description: Sediment quality within San Diego Bay, Mission Bay, and the Tijuana River Estuary of California was investigated as part of an ongoing statewide monitoring effort (Bay Protection and Toxic Cleanup Program). Study objectives were to determine the incidence, spatial patterns, and spatial extent of toxicity in sediments and porewater; the concentration and distribution of potentially toxic anthropogenic chemicals; and the relationships between toxicity and chemical concentrations. Rhepoxynius abronius survival bioassays, grain size, and total organic carbon analyses were performed on 350 sediment samples. Strongylocentrotus purpuratus development bioassays were performed on 164 pore-water samples. Toxicity was demonstrated throughout the San Diego Bay region, with increased incidence and concordance occurring in areas of industrial and shipping activity. Trace metal and trace synthetic organic analyses were performed on 229 samples. Copper, zinc, mercury, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and chlordane were found to exceed ERM (effects range median) or PEL (probable effects level) sediment quality guidelines and were considered the six major chemicals or chemical groups of concern. Statistical analysis of the relationships between amphipod toxicity, bulk phase sediment chemistry, and physical parameters demonstrated few significant linear relationships. Significant differences in chemical levels were found between toxic and nontoxic responses using multivariate and univariate statistics. Potential sources of anthropogenic chemicals were discussed., Cited By (since 1996):36, Rocks and Cores, CODEN: ETOCD, ,
Author: Fairey, Roberts, Jacobi, Lamerdin, Clark, Downing, Long, Hunt, Anderson, Newman, Tieerdema, Stephenson, Wilson
Date: 1998-01-01T00:00:00Z

Title: Intense and localized benthic marine pollution around McMurdo Station, Antarctica,
Description: Cited By (since 1996):61, CODEN: MPNBA, Benthic sediments and animals are highly modified by human activities at McMurdo Station, the largest human settlement in Antarctica. The quantity of anthropogenic debris, contamination of marine sediments with hydrocarbons and metals, and gross changes in benthic communities are largely confined to Winter Quarters Bay, adjacent to the former dump site and the ice dock used by visiting ships. Levels of purgeable hydrocarbons in bay sediments are as high as 4500 ppm. Metal levels are mostly high within the bay, but are not greater than in the most polluted temperate habitats. Levels of anthropogenic chemicals are significantly higher in the back bay compared to stations established at different distances from the bay (along three potential contamination gradients), including reference sites many kilometres away. There are significant negative correlations between the total number of infauna or epifauna and the concentrations of hydrocarbons and most metals in sediments. The few animals living in the back bay are motile polychaete worms with opportunistic life histories, primarily Capitella capitata antarcticum and Ophryotrocha claparedii. Fortunately, the local physical setting apparently permits little transport of contaminated sediments from the bay, which is flanked on one side by a large submarine ridge and on the other by Hut Point. Hut Point also protects the bay from oceanic conditions. The back bay is over 30 m deep and the ridge top is only 18 m deep. The gradient of chemical and community change is extremely steep, but there are observable ecological impacts outside the bay along the front of the station. Although most historical inputs of pollution are removed or reduced and continued cleanup is planned, Winter Quarters Bay may require many decades to recover., ,
Author: Lenihan, Oliver, Oakden, Stephenson
Date: 1990-01-01T00:00:00Z

Title: Comparison of marine sediment toxicity test protocols for the amphipod Rhepoxynius abronius and the polychaete worm Nereis (Neanthes) arenaceodentata,
Description: The 10-d amphipod survival toxicity test protocol using Rhepoxynius abronius was compared to the 20-d polychaete worm growth and survival protocol using Nereis (Neanthes) arenaceodentata. Of the 341 sediment samples collected in California and tested over a 2-year period, 78% significantly inhibited R. abronius survival, whereas 2 and 26% significantly inhibited N. arenaceodentata survival and biomass, respectively. Statistical power associated with each protocol endpoint was determined by calculating the minimum significant difference (MSD) for each test protocol for this data set. The 90th percentile MSDs for R. abronius survival and N. arenaceodentata survival and biomass were 16, 36, and 56%, respectively. Survival of R. abronius was significantly negatively correlated with a number of toxicants including metals, pesticides, polycyclic aromatic hydrocarbons, and polychlorinated bipbenyls. No significant correlations were determined between N. arenaceodentata survival or biomass and contaminants measured. Amphipod survival was also negatively correlated with sediment total organic carbon and grain size, but when samples with a high percent fine grain size (>90% fines) were eliminated from consideration, the overall conclusions of the study were not altered. The 10-d amphipod survival protocol using R. abronius was a more sensitive indicator of toxicity, but the results indicate that this was due to greater statistical power rather than greater sensitivity of the test organisms or endpoints., Cited By (since 1996):16, ,
Author: Anderson, Hunt, Phillips, Tudor, Fairey, Newman, Puckett, Stephenson, Long, Tjeerdema
Date: 1998-01-01T00:00:00Z

Title: Mercury in sport fish from the Sacramento-San Joaquin Delta region, California, USA,
Description: Total mercury (Hg) concentrations were determined in fillet tissue of sport fish captured in the Sacramento-San Joaquin River Delta and surrounding tributaries, a region particularly impacted by historic gold and mercury mining activity. In 1999 and 2000, mercury concentrations were measured in 767 samples from ten fish species. Largemouth bass (Micropterus salmoides), the primary target species, exhibited a median Hg concentration of 0.53 μg g- 1 (N = 406). Only 23 largemouth bass (6%) were below a 0.12 μg g- 1 threshold corresponding to a 4 meals per month safe consumption limit. Most of the largemouth bass (222 fish, or 55% of the sample) were above a 0.47 μg g- 1 threshold corresponding to a 1 meal per month consumption limit. Striped bass (Morone saxatilis), channel catfish (Ictalurus punctatus), white catfish (Ameirus catus), and Sacramento pikeminnow (Ptychocheilus grandis) also had relatively high concentrations, with 31% or more of samples above 0.47 μg g- 1. Concentrations were lowest in redear (Lepomis microlophus) and bluegill (Lepomis macrochirus) sunfish, with most samples below 0.12 μg g- 1, suggesting that targeting these species for sport and subsistence fishing may reduce human dietary exposure to Hg in the region. An improved method of analysis of covariance was performed to evaluate spatial variation in Hg in largemouth bass captured in 2000, while accounting for variability in fish length. Using this approach, Hg concentrations were significantly elevated in the Feather River, northern Delta, lower Cosumnes River, and San Joaquin River regions. In spite of elevated Hg concentrations on all of its tributaries, the central Delta had concentrations that were low both in comparison to safe consumption guidelines and to other locations. © 2007 Elsevier B.V. All rights reserved., Cited By (since 1996):16, CODEN: STEVA, ,
Author: Davis, Greenfield, Ichikawa, Stephenson
Date: 2008-01-01T00:00:00Z

Title: Evidence for the decline of silver and lead and the increase of copper from 1977 to 1990 in the coastal marine waters of California,
Description: Data collected from 1977 to 1990 by the California State Mussel Watch programme was analysed for long-term trends in silver, copper and lead at 20 sites along the California coast. 75% of the sites showed a clear trend in at least one heavy metal. Changes were evident in contaminated harbours as well as remote sites. 55% of the sites showed significant decreases in silver, 25% increased in copper and 40% decreased in lead. Declines in silver and lead appear related to decreased mass emission rates by wastewater treatment facilities, more effective reclamation efforts, and decreases in the use of leaded gasoline. Increase in copper appear related to increased vessel traffic and use of new, copolymer anti-fouling paints. These results suggest that the coastal waters of California are becoming cleaner, at least with respect to silver and lead. However, trends in copper are disturbing. These and other sites should continue to be monitored to document the status of copper and other trace metals in the environment., Cited By (since 1996):34, Oceanography, CODEN: MPNBA, ,
Author: Stephenson, Leonard
Date: 1994-01-01T00:00:00Z

Title: Mercury dynamics in a San Francisco Estuary tidal wetland: Assessing dynamics using in situ measurements
Description: We used high-resolution in situ measurements of turbidity and fluorescent dissolved organic matter (FDOM) to quantitatively estimate the tidally driven exchange of mercury (Hg) between the waters of the San Francisco estuary and Browns Island, a tidal wetland. Turbidity and FDOM-representative of particle-associated and filter-passing Hg, respectively-together predicted 94 % of the observed variability in measured total mercury concentration in unfiltered water samples (UTHg) collected during a single tidal cycle in spring, fall, and winter, 2005-2006. Continuous in situ turbidity and FDOM data spanning at least a full spring-neap period were used to generate UTHg concentration time series using this relationship, and then combined with water discharge measurements to calculate Hg fluxes in each season. Wetlands are generally considered to be sinks for sediment and associated mercury. However, during the three periods of monitoring, Browns Island wetland did not appreciably accumulate Hg. Instead, gradual tidally driven export of UTHg from the wetland offset the large episodic on-island fluxes associated with high wind events. Exports were highest during large spring tides, when ebbing waters relatively enriched in FDOM, dissolved organic carbon (DOC), and filter-passing mercury drained from the marsh into the open waters of the estuary. On-island flux of UTHg, which was largely particle-associated, was highest during strong winds coincident with flood tides. Our results demonstrate that processes driving UTHg fluxes in tidal wetlands encompass both the dissolved and particulate phases and multiple timescales, necessitating longer term monitoring to adequately quantify fluxes. © 2012 The Author(s)., Cited By (since 1996):1
Author: Bergamaschi, Fleck, Downing, Boss, Pellerin, Ganju, Schoellhamer, Byington, Heim, Stephenson, Fujii
Date: 2012-01-01T00:00:00Z

Title: Evaluation and use of sediment toxicity reference sites for statistical comparisons in regional assessments,
Description: Sediment reference sites were used to establish toxicity standards against which to compare results from sites investigated in San Francisco Bay (California, USA) monitoring programs. The reference sites were selected on the basis of low concentrations of anthropogenic chemicals, distance from active contaminant sources, location in representative hydrographic areas of the Bay, and physical features characteristic of depositional areas (e.g., fine grain size and medium total organic carbon [TOC]). Five field-replicated sites in San Francisco Bay were evaluated over three seasons. Samples from each site were tested with nine toxicity test protocols and were analyzed for sediment grain size and concentrations of trace metals, trace organics, ammonia, hydrogen sulfide, and TOC. The candidate sites were found to have relatively low concentrations of measured chemicals and generally exhibited low toxicity. Toxicity data from the reference sites were then used to calculate numerical tolerance limits to be used as threshold values to determine which test sites had significantly higher toxicity than reference sites. Tolerance limits are presented for four standard test protocols, including solid-phase sediment tests with the amphipods Ampelisca abdita and Eohaustorius estuarius and sea urchin Strongylocentrotus purpuratus embryo/larval development tests in pore water and at the sediment-water interface (SWI). Tolerance limits delineating the lowest 10th percentile (0.10 quantile) of the reference site data distribution were 71% of the control response for Ampelisca, 70% for Eohaustorius, 94% for sea urchin embryos in pore water, and 87% for sea urchins embryos exposed at the SWI. The tolerance limits are discussed in terms of the critical values governing their calculation and the management implications arising from their use in determining elevated toxicity relative to reference conditions., Cited By (since 1996):19, Rocks and Cores, CODEN: ETOCD, ,
Author: Hunt, Anderson, Phillips, Newman, Tjeerdema, Fairey, Puckett, Stephenson, Smith, Wilson, Taberski
Date: 2001-01-01T00:00:00Z

Title: Long-term trends in DDT, polychlorinated biphenyls, and chlordane in California mussels,
Description: The California State Mussel Watch program is a long-term monitoring program conducted by the State Water Resources Control Board and the Department of Fish and Game. In a fifteen year time span, from 1977-1992, mussels were collected at 378 stations. From these stations, 47 were chosen to conduct statistical analysis based on the criteria that they had been sampled at least 6 times for total DDTs, total polychlorinated biphenyls (PCBs), and total chlordanes. Declines of total DDTs and chlordanes were noted at approximately half of the stations. Declines of total PCBs were noted at approximately one-quarter of the stations. Declines of PCBs but not DDTs in mussels near Los Angeles County's sewer discharge corresponded to declines of these contaminants in treated effluent., Cited By (since 1996):29, Invertebrates, Ecology, CODEN: AECTC, ,
Author: Stephenson, Martin, Tjeerdema
Date: 1995-01-01T00:00:00Z

Title: Trace metals in mussels transplanted to San Francisco Bay,
Description: Mussels (Mytilus californianus) transplanted to San Francisco Bay exhibited elevated trace metal concentrations compared with those in other mussel watch studies on the west coast of the United States. The highest concentrations of Ag, Cu, Hg, Mn, Pb and Zn were at the South Bay stations, and often in the Redwood Creek area. Ag and Hg concentrations were linearly correlated with station distance from the North Bay (San Pablo Bay), indicating that the South Bay is a major reservoir of these pollutants within San Francisco Bay. © 1986., Cited By (since 1996):7, CODEN: ETOCD, ,
Author: Smith, Stephenson, Flegal
Date: 1986-01-01T00:00:00Z

Title: Mercury cycling in agricultural and managed wetlands: A synthesis of methylmercury production, hydrologic export, and bioaccumulation from an integrated field study
Description: With seasonal wetting and drying, and high biological productivity, agricultural wetlands (rice paddies) may enhance the conversion of inorganic mercury (Hg(II)) to methylmercury (MeHg), the more toxic, organic form that biomagnifies through food webs. Yet, the net balance of MeHg sources and sinks in seasonal wetland environments is poorly understood because it requires an annual, integrated assessment across biota, sediment, and water components. We examined a suite of wetlands managed for rice crops or wildlife during 2007-2008 in California's Central Valley, in an area affected by Hg contamination from historic mining practices. Hydrologic management of agricultural wetlands for rice, wild rice, or fallowed - drying for field preparation and harvest, and flooding for crop growth and post-harvest rice straw decay - led to pronounced seasonality in sediment and aqueous MeHg concentrations that were up to 95-fold higher than those measured concurrently in adjacent, non-agricultural permanently-flooded and seasonally-flooded wetlands. Flooding promoted microbial MeHg production in surface sediment of all wetlands, but extended water residence time appeared to preferentially enhance MeHg degradation and storage. When incoming MeHg loads were elevated, individual fields often served as a MeHg sink, rather than a source. Slow, horizontal flow of shallow water in the agricultural wetlands led to increased importance of vertical hydrologic fluxes, including evapoconcentration of surface water MeHg and transpiration-driven advection into the root zone, promoting temporary soil storage of MeHg. Although this hydrology limited MeHg export from wetlands, it also increased MeHg exposure to resident fish via greater in situ aqueous MeHg concentrations. Our results suggest that the combined traits of agricultural wetlands - slow-moving shallow water, manipulated flooding and drying, abundant labile plant matter, and management for wildlife - may enhance microbial methylation of Hg(II) and MeHg exposure to local biota, as well as export to downstream habitats during uncontrolled winter-flow events.
Author: Windham-Myers, Fleck, Ackerman, Marvin-DiPasquale, Stricker, Heim, Bachand, Eagles-Smith, Gill, Stephenson, Alpers
Date: 2014-01-01T00:00:00Z

Title: Spatial and habitat-rased variations in total and methyl mercury concentrations in surficial sediments in the San Francisco Bay-Delta,
Description: Recent studies indicate significant amounts of mercury (Hg) are annually transported into the San Francisco Bay-Delta (Bay-Delta) as a result of historic gold and Hg mining activities. We examined temporal and spatial variation in concentrations of total Hg (HgT) and monomethylmercury (MMHg) in surficial sediments of various ecosystem types in the Bay-Delta. We sampled surficial sediments across the Bay-Delta system and found HgT sediment concentrations in the central Delta were generally 100-200 ng g -1 and increased westward through Suisun Bay to 250-350 ng g -1. MMHg concentrations in the central Delta were between 1 and 3 ng g-1, while those in sediments in the perimeter waterways and adjacent bays were less than 1 ng g-1. Six sites were monitored monthly for over a year to identify seasonal changes in Hg sediment concentrations. Hg T sediment concentrations ranged from 48 to 382 ng g-1 and varied as a function of location not season. However, MMHg concentrations varied seasonally, increasing from 1 ng g-1 during winter months to 6 ng g-1 during spring and summer. Transects conducted at three marshes in the central Delta revealed MMHg sediment concentrations of 4-8 ng g-1at the interior and 2 ng g-1 at the exterior of the marshes. Habitat type was a major factor controlling MMHg concentration and the MMHg to HgT ratio in sediments of the Bay-Delta. MMHg was significantly correlated to HgT (r2 = 0.49) in marsh sediments. © 2007 American Chemical Society., Cited By (since 1996):24, Oceanography, CODEN: ESTHA, ,
Author: Heim, Coale, Stephenson, Choe, Gill, Foe
Date: 2007-01-01T00:00:00Z

Title: Determination of tributyltin in tissues and sediments by graphite furnace atomic absorption spectrometry,
Description: A method for the determination of tributyltin (TBT) in tissue and sediments has been developed for environmental samples. The technique involves extraction with methylene chloride and isolation of TBT from mono- and dibutyltin with a sodium hydroxide wash. The TBT is then back extracted and converted to elemental Sn with nitric acid. Analysis is by Zeeman graphite furnace atomic absorption spectrophotometry. Recoveries of spiked samples were between 99 % and 111% for mussel and fish tissues and 72% and 99% for various sediments. The limit of quantification was 0.0025 μg/g for tissue (on a wet weight basis). This technique was developed in response to our need to process large numbers of environmental samples with a minimum time investment., Cited By (since 1996):9, ,
Author: Stephenson, Smith
Date: 1988-01-01T00:00:00Z

Title: A large-scale categorization of sites in San Francisco Bay, USA, based on the sediment quality triad, toxicity identification evaluations, and gradient studies,
Description: Sediment quality was assessed in San Francisco Bay, California, USA, using a two-tiered approach in which 111 sites were initially screened for sediment toxicity. Sites exhibiting toxicity were then resampled and analyzed for chemical contamination, recurrent toxicity, and, in some cases, benthic community impacts. Resulting data were compared with newly derived threshold values for each of the metrics in a triad-based weight-of-evidence evaluation. Sediment toxicity test results were compared with tolerance limits derived from reference site data, benthic community data were compared with threshold values for a relative benthic index based on the presence and abundance of pollution-tolerant and -sensitive taxa, and concentrations of chemicals and chemical mixtures were compared with sediment quality guideline-based thresholds. A total of 57 sites exceeded threshold values for at least one metric, and each site was categorized based on triad inferences. Nine sites were found to exhibit recurrent sediment toxicity associated with elevated contaminant concentrations, conditions that met program criteria for regulatory attention. Benthic community impacts were also observed at three of these sites, providing triad evidence of pollution-induced degradation. Multi- and univariate correlations indicated that chemical mixtures, heavy metals, chlordanes, and other organic compounds were associated with measured biological impacts in the Bay. Toxicity identification evaluations indicated that metals were responsible for pore-water toxicity to sea urchin larvae at two sites. Gradient studies indicated that the toxicity tests and benthic community metrics employed in the study predictably tracked concentrations of chemical mixtures in Bay sediments., Cited By (since 1996):36, CODEN: ETOCD, , , Rocks and Cores
Author: Hunt, Anderson, Phillips, Tjeerdema, Taberski, Wilson, Puckett, Stephenson, Fairey, Oakden
Date: 2001-01-01T00:00:00Z

Title: Factors influencing methylmercury contamination of black bass from California reservoirs
Author: Melwani, Negrey, Heim, Coale, Stephenson, Davis