Regional assessment of marine and estuarine sediment toxicity in Southern California, USA

Sediment toxicity was investigated at 222 stations in the Southern California Bight (SCB) during 2008. This represented the first time that assessment methods established by California's new Sediment Quality Objectives program were employed in a survey of this scale. The goal was to determine the extent and magnitude of sediment toxicity in the SCB, how toxicity compared among specific environments, and whether toxicity has changed over the last decade. Two toxicity tests were used: the 10-day amphipod whole sediment survival test with Eohaustorius estuarius and a 48-h embryo development test with the mussel Mytilus galloprovincialis exposed at the sediment–water interface. Less than 1 % of the area of the SCB was found to be toxic to the amphipod test. No toxicity was found in offshore stations, but 14 % of embayment areas were toxic to the amphipods. The mussel test identified 13 % of the embayment areas to be toxic. Estuary and marina locations had the greatest areal extent of toxicity for both tests. The two toxicity methods agreed that sediments were not toxic at over half of the stations tested. The mussel test showed a greater magnitude of response than the amphipod. Sediment toxicity was shown to have declined in both extent and magnitude from levels measured in 1998 and 2003.     

Mercury contamination in three species of anuran amphibians from the Cache Creek Watershed, California, USA

Fish and wildlife may bioaccumulate mercury (Hg) to levels that adversely affect reproduction, growth, and survival. Sources of Hg within the Cache Creek Watershed in northern California have been identified, and concentrations of Hg in invertebrates and fish have been documented. However, bioaccumulation of Hg by amphibians has not been evaluated. In this study, adult and juvenile American bullfrogs (Lithobates catesbeianus) and foothill yellow-legged frogs (Rana boylii), adult Northern Pacific treefrogs (Pseudacris regilla), and larval bullfrogs were collected and analyzed for total Hg. One or more species of amphibians from 40% of the 35 sites had mean Hg concentrations greater than the US Environmental Protection Agency’s tissue residue criterion for fish (0.3 μg/g). Of the bullfrog tissues analyzed, the liver had the highest concentrations of both total Hg and methyl mercury. Total Hg in carcasses of bullfrogs was highly correlated with total Hg in leg muscle, the tissue most often consumed by humans.     

Conservation and management applications of the REEF volunteer fish monitoring program

The REEF Fish Survey Project is a volunteer fish monitoring program developed by the Reef Environmental Education Foundation (REEF). REEF volunteers collect fish distribution and abundance data using a standardized visual method during regular diving and snorkeling activities. Survey data are recorded on preprinted data sheets that are returned to REEF and optically digitized. Data are housed in a publicly accessible database on REEF's Web site (http: //www.reef.org). Since the project's inception in 1993, over 40,000 surveys have been conducted in the coastal waters of North America, tropical western Atlantic, Gulf of California and Hawaii. The Fish Survey Project has been incorporated into existing monitoring programs through partnerships with government agencies, scientists, conservation organizations, and private institutions. REEF's partners benefit from the educational value and increased stewardship resulting from volunteer data collection. Applications of the data include an evaluation of fish/habitat interactions in the Florida Keys National Marine Sanctuary, the development of a multi-species trend analysis method to identify sites of management concern, assessment of the current distribution of species, status reports on fish assemblages of marine parks, and the evaluation of no-take zones in the Florida Keys. REEF's collaboration with a variety of partners, combined with the Fish Survey Project's standardized census method and database management system, has resulted in a successful citizen science monitoring program.     

An assessment of fecal indicator and other bacteria from an urbanized coastal lagoon in the City of Los Angeles, California, USA

A study was performed in Del Rey Lagoon, City of Los Angeles, to determine if the lagoon was as a source or sink for fecal indicator bacteria (FIB: total coliforms, Escherichia coli, enterococci) and to screen for the presence of other potentially pathogenic bacteria. The lagoon receives tidal flows from the adjacent Ballona Estuary whose water usually is contaminated with FIB originating from the highly urbanized Ballona Creek Watershed. During 16 sampling events from February 2008 through March 2009, replicate water samples (n?=?3) were collected 1 h prior to the high tide and 1 h prior to the following low tide. FIB concentrations were measured by the defined substrate method (IDEXX, Westbrook, Me) followed by culturing of bacterial isolates sampled from positive IDEXX Quanti-Tray wells and were identified using the Vitek 2 Compact (bioMérieux, Durham, NC). Mean concentrations of FIB often differed by an order of magnitude from flood to ebb flow conditions. The lagoon tended to act as a sink for total coliforms based on the ratio of mean flood to ebb densities (R _F/E) >1.0 during 56 % of the sampling events and during ebb flows, as a source for E. coli and enterococci (R _F/E <1.69 % of events). Approximately 54 species were identified from 277 isolates cultured from the IDEXX Quanti-Trays. Of these, 54 % were species known to include pathogenic strains that can be naturally occurring, introduced in runoff, or originated from other sources. Diversity and cluster analyses indicated a dynamic assemblage that changes in species composition with day-to-day fluctuations as well as tidal action. The concept of monitoring the lagoon and estuary as a sentinel habitat for pathogenic assemblages is discussed.     

Interpretation of roadside PM10 monitoring data from Sunderland,United Kingdom

Roadside PM₁₀ has been monitored by Partisol® at three sitesin Sunderland between August 1997 and February 1998. The sites chosen were an inner city kerbside site; a roadside site adjacentto a dual carriageway on the outskirts of Sunderland with an openaspect; and a rural site.The results indicate that there is a seasonal variation in the relationship between the sites in terms of monitored PM₁₀.In the winter there is a poor correlation between the sites whereas in the summer significant correlations are obtained. Of the sites monitored PM₁₀ is consistently highest at the inner city roadside site. During the summer, exceedances of theU.K. 50 g m^-3 standard (DETR, 2000) are associated with conditions suitable for the build-up of photochemical pollutionhowever during the winter period exceedances are recorded duringa variety of weather conditions.At the dual carriageway site PM_2.5 has also been recorded and contributions to measured PM₁₀ are 77% in summer and68% in winter. The results illustrate a number of inconsistencies between this study utilising the Partisol® andothers reporting results where PM₁₀ has been monitored by TEOM®.     

Comparative Water Quality of Lightly- and Moderately-Impacted Streams in the Southern Blue Ridge Mountains, USA

For less-developed regions like the Blue Ridge Mountains, data are limited that link basin-scale land use with stream quality. Two pairs of lightly-impacted (90–100% forested) and moderately-impacted (70–80% forested) sub-basins of the upper Little Tennessee River basin in the southern Blue Ridge were identified for comparison. The pairs contain physically similar stream reaches, chosen for the purpose of isolating forest conversion as a potential driver of any detected differences in water quality. Streams were sampled during baseflow conditions twice monthly over a six-month period from September 2003 through February 2004. Parametric t-tests were run for each parameter measured between the lightly-and moderately-impacted streams within each pair. Statistically significantly higher mean values of suspended and dissolved solids, nitrate, specific conductivity, turbidity, and temperature were observed in the moderately impacted streams versus the lightly impacted streams in both pairs, while dissolved oxygen levels were lower in the moderately-impacted streams. No significant differences were demonstrated in orthophosphate or ammonium concentration. A near-bankfull runoff event on February 6, 2004, was sampled for stormflow values, and the results support baseflow findings. The water quality of these streams is very good when compared with lower relief areas like the Piedmont, and none of the parameters measured in this study exceeds levels of known threat to stream biota. However, the demonstration that moderate reductions in forest cover are associated with stream water quality degradation carries important implications for stream management in this rapidly developing mountainous region.     

Copper, zinc, and cadmium body concentrations in Hexaplex trunculus collected from the Tunisian coast

Copper, Zn, and Cd were analyzed in the soft tissues of the edible gastropod Hexaplex trunculus collected from seven localities along the Tunisian coast. The body concentration of these metals was significantly different depending on the gender and site. Copper and Zn varied, respectively, from 47.70 to 343.64 μg/g dry weight (dw) and 149.46 to 530.44 μg/g dw, being higher in males. Cadmium varied from 0.22 to 18.95 μg/g dw and was always higher in females. Overall, the highest concentrations of the three metals were all recorded in Gabès fishing harbor. Comparison of metal concentrations with the European standards compiled by the Food and Agriculture Organization showed that values exceeded standards in several localities. Imposex had been previously recorded in H. trunculus along the Tunisian coast; however, it does not seem to be related with Cu, Zn, and Cd pollution because the body concentration of these metals is not correlated with imposex degree. Nevertheless, interactive effects resulting from the combination of different pollutants and other stressors cannot be disregarded.     

Chlorinated, brominated, and perfluorinated compounds, polycyclic aromatic hydrocarbons and trace elements in livers of sea otters from California, Washington, and Alaska (USA), and Kamchatka (Russia)

Concentrations of organochlorine pesticides (DDTs, HCHs, and chlordanes), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), perfluorinated compounds (PFCs), and 20 trace elements were determined in livers of 3- to 5-year old stranded sea otters collected from the coastal waters of California, Washington, and Alaska (USA) and from Kamchatka (Russia). Concentrations of organochlorine pesticides, PCBs, and PBDEs were high in sea otters collected from the California coast. Concentrations of DDTs were 10-fold higher in California sea otters than in otters from other locations; PCB concentrations were 5-fold higher, and PBDE concentrations were 2-fold higher, in California sea otters than in otters from other locations. Concentrations of PAHs were higher in sea otters from Prince William Sound than in sea otters from other locations. Concentrations of several trace elements were elevated in sea otters collected from California and Prince William Sound. Elevated concentrations of Mn and Zn in sea otters from California and Prince William Sound were indicative of oxidative stress-related injuries in these two populations. Concentrations of all of the target compounds, including trace elements, that were analyzed in sea otters from Kamchatka were lower than those found from the US coastal locations.     

Analysis of diazinon monitoring data from the Sacramento and Feather River watersheds: 1991-2001

The objectives of this study were to: (1) analyzehistorical diazinon water column monitoring data frominconsistent monitoring programs in mainstem and tributary sitesin the Sacramento and Feather River watersheds from 1991 to 2001to assess possible spatial and temporal trends and (2) determinethe probability of measured diazinon concentrations by site orsimilar pooled sites exceeding various proposed effectsbenchmarks such as Water Quality Criteria and 10th centilesderived from species sensitivity distributions proposed as targetconcentrations for Total Maximum Daily Loads (TMDLs). An analysisof diazinon monitoring data from both fixed and rain eventsampling from the Sacramento/Feather River watersheds from 1991to 2001 showed that 90th centiles for 27 different mainstemand tributary sites ranged from 12 to 14,897 ng L^-1. The 90th centiles were generally higher at tributary sites (as compared to mainstem sites) during rain event sampling prior to 1995. A comparison of rain event samples for similar sites sampled in 1994 and 2000 showed that 90th centiles were lower in seven of eight sites in 2000. A comparison of pooled mainstemsites between 1994 and 2000 for rain event data showed a lower90th centile value for 2000; 90th centiles were alsolower in 2000 at all pooled tributary sites and all sites whendata from a highly influential site was removed. For varioussite designations (all sites, pooled mainstem sites etc.) theprobability of exceeding the acute and chronic diazinon targetsdeveloped by California Department of Fish and Game decreasedfrom 1994 to 2000. These data clearly show progress in the 6 yrperiod in reducing environmental concentrations of diazinon.Probability of exceeding the 10th centile targets based onspecies sensitivity distributions for arthropods (the mostsensitive taxa to diazinon exposure) was similar and fairly lowbetween years; the highest percent probability of exceedance forany site designation was 20%.Results from a two-way ANOVA using individual measurementsfrom all sites sampled showed a significant decrease during rainevents between 1994 and 2000, although the decrease was notequivalent for all sites. Sources of uncertainty identified inthe analysis of rain event data from 1994 and 2000 wereinconsistent frequency of sampling during rain events for eachyear, unknown definition of rain events between the two years andnon-defined measurement point within the hydrograph of rainevents sampled in each year. Analysis of diazinon trends fromfixed sampling was limited due to lack of yearly data by site;therefore, only parametric analysis could be conducted. Based onparametric analysis of diazinon monitoring data from fixedsampling sites, the percent detected concentrations were greaterthan 20% for 12 tributary sites and 5 mainstem sites fromsamples collected during January-March. On the average over allsites and months, diazinon concentrations have decreased at fixedsampling sites in the Sacramento/Feather River watershed from1991 to 2001.     

Critical evaluation of PAH source apportionment tools using data from the Swiss soil monitoring network

In this study a large dataset on the polycyclic aromatic hydrocarbon (PAH) content of Swiss soils was analysed to evaluate two source apportionment tools, i.e., characteristic PAH ratios/molecular markers and a linear mixing model. Population density and total organic carbon (TOC) content were identified by a multiple regression model as independently and positively influencing the PAH concentrations in Swiss background soil. Specifically, TOC was more strongly positively correlated with the sum of light PAH (naphthalene to phenanthrene) than with the sum of heavy PAH (anthracene to benzo[ghj]perylene), whereas population density was more strongly positively correlated with the sum of heavy PAH than with light PAH. In addition, the sum of the heavy PAH as well as the total sum correlated negatively with sample site altitude. It is therefore hypothesised that heavy PAH are less mobile, whereas light PAH were closer to equilibrium with TOC in the soil. Similar results were found for polychlorinated biphenyls (PCB). The characteristic ratios and molecular markers pointed to pyrogenic origin of PAH in Swiss background soil but did not allow for further differentiation of individual fuel contributions, even though attempts to take environmental fractionation processes into account were made. The comparison of three soil profiles identified with a linear mixing model from the pattern of 16 PAH with >300 PAH emission profiles from the literature suggested urban dust, wood combustion and binders from asphalt as PAH sources. However, also here, environmental fractionation processes probably obscured source characteristic PAH ratios and fingerprints, which thus need to be interpreted with caution.     

Spatiotemporal classification of environmental monitoring data in the Yeongsan River basin, Korea, using self-organizing maps

Environmental monitoring data for planning, implementing and evaluating the Total Maximum Daily Loads (TMDL) management system have been measured at about 8-day intervals in a number of rivers in Korea since 2004. In the present study, water quality parameters such as Suspended Solids (SS), Biochemical Oxygen Demand (BOD), Dissolved Oxygen (DO), Total Nitrogen (TN), and Total Phosphorus (TP) and the corresponding runoff were collected from six stations in the Yeongsan River basin for six years and transformed into monthly mean values. With the primary objective to understand spatiotemporal characteristics of the data, a methodologically systematic application of a Self-Organizing Map (SOM) was made. The SOM application classified the environmental monitoring data into nine clusters showing exclusively distinguishable patterns. Data frequency at each station on a monthly basis identified the spatiotemporal distribution for the first time in the study area. Consequently, the SOM application provided useful information that the sub-basin containing a metropolitan city is associated with deteriorating water quality and should be monitored and managed carefully during spring and summer for water quality improvement in the river basin.     

An assessment of the optimal scale for monitoring of MODIS and FIA NPP across the eastern USA

Robust monitoring of carbon sequestration by forests requires the use of multiple data sources analyzed at a common scale. To that end, model-based Moderate Resolution Imaging Spectroradiometer (MODIS) and field-based Forest Inventory and Analysis (FIA) data of net primary productivity (NPP) were compared at increasing levels of spatial aggregation across the eastern USA. A total of 52,167 FIA plots and colocated MODIS forest cover NPP pixels were analyzed using a hexagonal tiling system. A protocol was developed to assess the optimal scale as an optimal size of landscape patches at which to map spatially explicit estimates of MODIS and FIA NPP. The optimal mapping resolution (hereafter referred to as optimal scale) is determined using spatially scaled z-statistics as the tradeoff between increased spatial agreement as measured by Pearson’s correlation coefficient and decreased details of coverage as measured by the number of hexagons. Spatial sensitivity was also assessed using land cover assessment and forest homogeneity using spatially scaled z-statistics. Pearson correlations indicate that MODIS and FIA NPP are most highly correlated when using large hexagons, while z-statistics indicate an optimal scale at an intermediate hexagon size of 390 km². This optimal scale had more spatial detail than was obtained for larger hexagons and greater spatial agreement than was obtained for smaller hexagons. The z-statistics for land cover assessment and forest homogeneity also indicated an optimal scale of 390 km².     

Optimum spatial analysis of monitoring data on temperature,salinity and nutrient concentrations in the Baltic Proper

In spite of the large number of monitoring data on hydrography and nutrients collected from the Baltic Sea, it is still difficult to describe large-scale distribution patterns of these variables. We therefore suggest a stochastic approach that allows the spatial reconstruction of the fields for the entire sea. The Baltic Sea monitoring data on temperature, salinity and nutrient concentrations from the years 1972–1991 are each divided into twenty data sets: five regions, times four seasons. The spatial regions are the Southern Baltic Proper, the Northern and Central Baltic Proper, both above and below halocline, and the region of the Gulf of Finland and the Gulf of Riga. The four seasons consist of three-month periods: January–March (winter), April–June (spring), July–September (summer) and October–December (fall). Each monthly subset of a regional and seasonal data set is modeled as a sample out of a monthly realization of a random field. The data sets are decomposed into mean and fluctuational components. The mean is determined as an average over the space cells with dimensions of standard sampling depth intervals vertically, 10 in meridional (south-north), 20 in zonal (west-east) directions and over five-year periods in time. The fluctuation fields are considered second-order stationary, homogeneous and horizontally isotropic. Estimated horizontal (surface) and vertical (depth) components of the spatial correlations are approximated by Gaussian functions. The correlation scales for the fields of the Baltic Proper are mostly larger than 100 nautical miles horizontally and 40 m vertically and their dependence on the sea region or season is relatively weak. The most probable noise-to-signal ratio values of the data lie in the interval 0.6 to 1.2. The estimated correlation functions and noise-to-signal ratios allow the optimum analysis technique to assess the correctness of each datum of a sample on the background of the field statistics. The outliers of each monthly sample are excluded from the analysis. The observed fluctuations are interpolated into locations with missing data by an optimum interpolation procedure. The discrete cell-and-five-year mean values are interpolated by a different, piece-wise linear technique. Since the data number for the mean interpolation considerably exceeds the data number for the fluctuation interpolation, the interpolation errors for the mean are assumed negligible compared to the interpolation errors for the fluctuation. The sums of the mean and fluctuation, interpolated into the withheld observation points, are compared to the actually observed values and to some other linear interpolation estimates. In all test cases the optimum interpolation procedure performs the best.     

Chemical and biological recovery from acid deposition within the Honnedaga Lake watershed,New York,USA

Honnedaga Lake in the Adirondack region of New York has sustained a heritage brook trout population despite decades of atmospheric acid deposition. Detrimental impacts from acid deposition were observed from 1920 to 1960 with the sequential loss of acid-sensitive fishes, leaving only brook trout extant in the lake. Open-lake trap net catches of brook trout declined for two decades into the late 1970s, when brook trout were considered extirpated from the lake but persisted in tributary refuges. Amendments to the Clean Air Act in 1990 mandated reductions in sulfate and nitrogen oxide emissions. By 2000, brook trout had re-colonized the lake coincident with reductions in surface-water sulfate, nitrate, and inorganic monomeric aluminum. No changes have been observed in surface-water acid-neutralizing capacity (ANC) or calcium concentration. Observed increases in chlorophyll a and decreases in water clarity reflect an increase in phytoplankton abundance. The zooplankton community exhibits low species richness, with a scarcity of acid-sensitive Daphnia and dominance by acid-tolerant copepods. Trap net surveys indicate that relative abundance of adult brook trout population has significantly increased since the 1970s. Brook trout are absent in 65 % of tributaries that are chronically acidified with ANC of <0 μeq/L and toxic aluminum levels (>2 μmol/L). Given the current conditions, a slow recovery of chemistry and biota is expected in Honnedaga Lake and its tributaries. We are exploring the potential to accelerate the recovery of brook trout abundance in Honnedaga Lake through lime applications to chronically and episodically acidified tributaries.     

Integrating in-situ, Landsat, and MODIS data for mapping in Southern African savannas: experiences of LCCS-based land-cover mapping in the Kalahari in Namibia

Integrated ecosystem assessment initiatives are important steps towards a global biodiversity observing system. Reliable earth observation data are key information for tracking biodiversity change on various scales. Regarding the establishment of standardized environmental observation systems, a key question is: What can be observed on each scale and how can land cover information be transferred? In this study, a land cover map from a dry semi-arid savanna ecosystem in Namibia was obtained based on the UN LCCS, in-situ data, and MODIS and Landsat satellite imagery. In situ botanical relevé samples were used as baseline data for the definition of a standardized LCCS legend. A standard LCCS code for savanna vegetation types is introduced. An object-oriented segmentation of Landsat imagery was used as intermediate stage for downscaling in-situ training data on a coarse MODIS resolution. MODIS time series metrics of the growing season 2004/2005 were used to classify Kalahari vegetation types using a tree-based ensemble classifier (Random Forest). The prevailing Kalahari vegetation types based on LCCS was open broadleaved deciduous shrubland with an herbaceous layer which differs from the class assignments of the global and regional land-cover maps. The separability analysis based on Bhattacharya distance measurements applied on two LCCS levels indicated a relationship of spectral mapping dependencies of annual MODIS time series features due to the thematic detail of the classification scheme. The analysis of LCCS classifiers showed an increased significance of life-form composition and soil conditions to the mapping accuracy. An overall accuracy of 92.48% was achieved. Woody plant associations proved to be most stable due to small omission and commission errors. The case study comprised a first suitability assessment of the LCCS classifier approach for a southern African savanna ecosystem.     

Fluvial transport and surface enrichment of arsenic in semi-arid mining regions: examples from the Mojave Desert, California

As a result of extensive gold and silver mining in the Mojave Desert, southern California, mine wastes and tailings containing highly elevated arsenic (As) concentrations remain exposed at a number of former mining sites. Decades of weathering and erosion have contributed to the mobilization of As-enriched tailings, which now contaminate surrounding communities. Fluvial transport plays an intermittent yet important and relatively undocumented role in the migration and dispersal of As-contaminated mine wastes in semi-arid climates. Assessing the contribution of fluvial systems to tailings mobilization is critical in order to assess the distribution and long-term exposure potential of tailings in a mining-impacted environment. Extensive sampling, chemical analysis, and geospatial mapping of dry streambed (wash) sediments, tailings piles, alluvial fans, and rainwater runoff at multiple mine sites have aided the development of a conceptual model to explain the fluvial migration of mine wastes in semi-arid climates. Intense and episodic precipitation events mobilize mine wastes downstream and downslope as a series of discrete pulses, causing dispersion both down and lateral to washes with exponential decay behavior as distance from the source increases. Accordingly a quantitative model of arsenic concentrations in wash sediments, represented as a series of overlapping exponential power-law decay curves, results in the acceptable reproducibility of observed arsenic concentration patterns. Such a model can be transferable to other abandoned mine lands as a predictive tool for monitoring the fate and transport of arsenic and related contaminants in similar settings. Effective remediation of contaminated mine wastes in a semi-arid environment requires addressing concurrent changes in the amounts of potential tailings released through fluvial processes and the transport capacity of a wash.     

Distribution of mercury in the tissues of five species of freshwater fish from Lake Mead, USA

Total mercury (Hg) concentrations were determined in seven tissues (skeletal muscle, liver, blood, gonad, brain, gill, and heart) of 59 striped bass and four tissues (muscle, liver, blood, and gonad) of 69 largemouth bass, 76 channel catfish, 12 bluegill, and 22 blue tilapia collected from Lake Mead, USA. Mercury levels generally increased according to trophic level and fish length. For striped bass, mean Hg levels (ng g(-1), wet mass) were highest in the liver (531), followed by muscle (309), heart (186), gonad (136), brain (77), gill (52), and blood (36). Similarly, Hg levels in the catfish and tilapia were liver > muscle > gonad > blood. In contrast, largemouth bass and bluegill had the highest levels in muscle, followed by liver, gonad, and blood. Generally, Hg levels were strongly correlated among the tissues, especially for blood/muscle and blood/liver. As the body burden of Hg increased, the concentration in blood and organs increased relative to the concentration in muscle. The trend was most pronounced for the liver. These relationships could form the basis of a predictive model and suggest that blood and muscle (plugs) could be useful for a non-lethal measure of Hg concentration and exposure in fish. For the striped bass, elevated Hg levels in the tissues were also correlated with degree of emaciation. Liver-to-muscle ratios were similar to literature values, except for tilapia with an average ratio of approximately 1.7, which is higher than generally reported for non-piscivores. Finally, this study demonstrates the usefulness of a solid sampling approach in trace element monitoring, especially as pertaining to in vivo analysis, analysis of a large number of samples and reduction of contamination risk.     

Dietary exposure of three passerine species to PCDD/DFs from the Chippewa, Tittabawassee, and Saginaw River floodplains, Midland, Michigan, USA

Dietary exposure of house wrens (Troglodytes aedon), tree swallows (Tachycineta bicolor), and eastern bluebirds (Sialia sialis) to polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs) near Midland, Michigan (USA) was evaluated based on site-specific data, including concentrations of residues in bolus samples and individual invertebrate orders and dietary compositions by study species. Site-specific dietary compositions for the three species were similar to those reported in the literature, but differed in their relative proportions of some dietary items. Oligocheata (non-depurated) and Brachycera (Diptera) contained the greatest average concentrations of ??PCDD/DFs of the major site-specific dietary items collected via food web-based sampling. Average ingestion values of ??PCDD/DFs from site-specific bolus-based and food web-based dietary concentrations for nestlings at study areas (SAs) were 6- to 20-fold and 2- to 9-fold greater than at proximally located reference areas (RAs), respectively. Average ingestion values of total 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQ_WHO???Avian) from site-specific bolus-based and food web-based dietary concentrations for nestlings at SAs were 31- to 121-fold and 9- to 64-fold greater than at proximally located RAs, respectively. Estimates of ??PCDD/DFs and TEQ_WHO???Avian tissue concentrations based on nestling dietary exposures were greater than those measured. Plausible explanations include nestling metabolism of 2,3,7,8-tetrachlorodibenzofuran and assimilation rates of less than the 70% assumed to occur over the nestling growth period. Profiles of the relative concentrations of individual PCDD/DF congeners in samples of invertebrates and bolus at SAs on the Tittabawassee River downstream of the source of contamination were dominated by 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin (22% to 44%) and 2,3,7,8-tetrachlorodibenzofuran (18% to 50%).