Omega-3 Fatty Acids in Lake Superior Fish

Proximate analysis and fatty acid composition of eight commercially important species of Lake Superior fish were determined. Palmitic acid (C16:0) was the predominant saturated fatty acid, accounting for 68–79% of total saturated acids. Oleic acid (C18:1) was the most abundant monounsaturated fatty acid. Linoleic acid (C18:2), linolenic acid (C18:3), eicosapentaenoic acid (C20:5) and docosahexaenoic acid (C22:6) were the predominant polyunsaturated fatty acids. Brining, smoking and refrigerated storage caused a reduction in total lipid, but only a small loss in n-3 fatty acids. The data revealed that most Lake Superior fish examined were excellent sources of polyunsaturated fatty acids with very high levels of omega-3 (n-3) fatty acids, especially eicosapentaenoic and docosahexaenoic acids.     

Effect of microbes on contaminant transfer in the Lake Superior food web

The partitioning of PCBs to natural populations of aquatic heterotrophic bacteria from Lake Superior was measured in both field and laboratory studies to better understand the role of bacteria and the microbial food web in persistent, bioaccumulative, toxic organic contaminant (PBT) transfer. A filtration method that separated material >1 microm from that <1 microm was used to collect and measure PCB concentrations in the bacterial fraction. We used bacterial biovolume and a conversion factor to calculate bacterial carbon, which was used to normalize PCB concentrations. The range of total PCB concentrations in the bacterial fraction (61-337 ng/g organic carbon; OC) was similar, but generally higher than that of the total particulate fraction (36-324 ng/g OC). Measured log bioaccumulation factors (BAFoc, bacterial fraction; Koc, total particulate) were significantly greater in the bacterial fraction than in the total particulate fraction (bacterial range 6.7-7.3, total particulate range 5.8-7.0). Laboratory experiments demonstrated that a hexachlorobiphenyl reached steady state with a natural community of Lake Superior bacteria within 48 h and had a mean log BAFoc of 7.5 +/- 1.9. The octanol/ water partition coefficient (Kow) consistently under-predicted BAFoc, however, the magnitude of the under-prediction was still within the range of uncertainty in food web modeling (factors of 3-9). Food web modeling and risk assessment of PBT bioaccumulation in aquatic systems could be improved by considering the microbial food web (bacteria and its protozoan grazers) as a previously unaccounted for pathway of contaminant transfer.     

Distribution and fluxes of total and methylmercury in Lake Superior

Despite the importance and size of Lake Superior, little is known regarding the biogeochemical cycling or distribution of mercury within its waters. We present the results from two research cruises on total Hg (HgT) and methylmercury (MeHg) distributions in aqueous and particulate phases, and in offshore sediments. Open waters of Lake Superior are similar in HgT content to Lakes Michigan and Ontario (sub-ng L(-1)), whereas MeHg was only 1% of HgT. Seasonality in aqueous HgT distribution was observed, most likely from tributary inputs during Spring snowmelt. Suspended particles were enriched in MeHg relative to water and surficial sediments, suggesting enhanced particle partitioning followed by demethylation in the water column and in surface sediments. Distribution coefficients for mercury in surficial sediments were lower than those in suspended material, likely due to remineralization. Preliminary estimates of mass balance indicate that air-water exchange processes such as evasion and wet deposition dominate the HgT budget, due to the basin's relatively small watershed area relative to lake area. In contrast, methylmercury cycling within Lake Superior is influenced more strongly by watershed sources, as well as by sedimentary sources and photodemethylation. The Hg cycle in Lake Superior is unique in that it is more similar in many aspects to that in marine systems than in small lakes, where management data for freshwaters typically originates.     

Spatial and temporal distribution of singlet oxygen in Lake Superior

A multiyear field study was undertaken on Lake Superior to investigate singlet oxygen ((1)O(2)) photoproduction. Specifically, trends within the lake were examined, along with an assessment of whether correlations existed between chromophoric dissolved organic matter (CDOM) characteristics and (1)O(2) production rates and quantum yields. Quantum yield values were determined and used to estimate noontime surface (1)O(2) steady-state concentrations ([(1)O(2)](ss)). Samples were subdivided into three categories based on their absorbance properties (a300): riverine, river-impacted, or open lake sites. Using calculated surface [(1)O(2)](ss), photochemical half-lives under continuous summer sunlight were calculated for cimetidine, a pharmaceutical whose reaction with (1)O(2) has been established, to be on the order of hours, days, and a week for the riverine, river-impacted, and open lake waters, respectively. Of the CDOM properties investigated, it was found that dissolved organic carbon (DOC) and a300 were the best parameters for predicting production rates of [(1)O(2)](ss). For example, given the correlations found, one could predict [(1)O(2)](ss) within a factor of 4 using a300 alone. Changes in the quantum efficiency of (1)O(2) production upon dilution of river water samples with lake water samples demonstrated that the CDOM found in the open lake is not simply diluted riverine organic matter. The open lake pool was characterized by low absorption coefficient, low fluorescence, and low DOC, but more highly efficient (1)O(2) production and predominates the Lake Superior system spatially. This study establishes that parameters that reflect the quantity of CDOM (e.g., a300 and DOC) correlate with (1)O(2) production rates, while parameters that characterize the absorbance spectrum (e.g., spectral slope coefficient and E2:E3) correlate with (1)O(2) production quantum yields.     

Polybrominated diphenyl ethers in the sediments of the Great Lakes. 1. Lake Superior

Sediment cores were taken in 2001 and 2002 in Lake Superior at six locations away from lakeshores and segmented at 0.5-5 cm intervals. The year of sediment deposition was estimated for each segment of four cores using the 210Pb dating technique. Samples were Soxhlet-extracted and cleaned up by silica gel fractionation, and the concentrations of 10 polybrominated diphenyl ethers (PBDEs) and 19 polychlorinated biphenyls (PCBs) were measured by GC-MS in SIM mode. In contrast to recent declining or level-off trends in PCB fluxes, the sedimentary records of PBDEs generally show a significant increase in recent years. The load of total PBDEs to Lake Superior was estimated to be 2-6 metric tons, and the current loading rate was about 80-160 kg yr(-1). With the exclusion of decabromodiphenyl ether (BDE209), the surficial concentration of sumPBDE (sum of 9 congeners) ranged from 0.5 to 3 ng g(-1), and the current sumPBDEs flux was 8-31 pg cm(-2) yr(-1). The concentrations of BDE209 were about an order of magnitude higher than the sum of other congeners, comprising 83-94% of the total PBDE inventory in the sediments. Among the other nine PBDEs detected, congeners 47 and 99 were the most abundant, and congeners 100, 153, 154, and 183 were also detected in all the cores. Congener analysis demonstrated that the pattern of PBDEs in Lake Superior sediments differs from those in air and fish.     

Deposition versus photochemical removal of PBDEs from Lake Superior air

Analysis of a sediment core collected from Siskiwit Lake, located on a remote island in Lake Superior, provides evidence that polybrominated diphenyl ethers (PBDEs) are removed effectively from the atmosphere via deposition processes during long-range transport. A mass balance model based on photochemical rate constants and data from atmospheric samples was created to understand the relative importance of various photochemical and deposition processes in removing PBDEs from the atmosphere. Photolysis rate constants were derived from UV absorption spectra of 25 PBDEs recorded in isooctane over the range of 280-350 nm at 298 K. Photolysis decays measured for BDE-3 and -7 in the gas phase were substantial compared to a well-defined chemical actinometer, indicating that their photolysis quantum yields are significant. Dibenzofuran production was observed when PBDE congeners containing ortho-bromines were photolyzed in helium. From estimates of removal rates of PBDEs from the lower troposphere, we find that wet and dry deposition accountfor >95% of the removal of BDE-209, while photolysis accounts for -90% of the removal of gas-phase congeners such as BDE-47. These results help explain the deposition patterns of PBDEs found in lake and river sediments and have important implications concerning the inclusion of photolysis as a fate process in multimedia models.     

Organochlorine compounds in Lake Superior: chiral polychlorinated biphenyls and biotransformation in the aquatic food web

The enantiomeric composition of seven chiral PCB congeners was measured in the Lake Superior aquatic food web sampled in 1998, to determine the extent of enantioselective biotransformation in aquatic biota. All chiral PCB congeners studied (CBs 91, 95, 136, 149, 174, 176, and 183) biomagnified in the Lake Superior aquatic food web, based on biomagnification and food web magnification factors greater than unity. PCB atropisomers were racemic in phytoplankton and zooplankton, suggesting no biotransformation potential toward PCBs for these low trophic level organisms. However, Diporeia and mysids had significantly nonracemic residues for most chiral congeners studied. This observation suggests that these macrozooplankton can stereoselectively metabolize chiral congeners. Alternatively, macrozooplankton obtained nonracemic residues from feeding on organic-rich suspended particles and sediments, which would imply that stereoselective microbial PCB biotransformation may be occurring in Lake Superior sediments at PCB concentrations far lower than that previously associated with such activity. Widely nonracemic PCB residues in forage fish (lake herring, rainbow smelt, and slimy sculpin) and lake trout suggest a combination of both in vivo biotransformation and uptake of nonracemic residues from prey for these species. Minimum biotransformation rates, calculated from enantiomer mass balances between predators and prey, suggest metabolic half-lives on the order of 8 yr for CB 136 in lake trout and 2.6 yr for CB 95 in sculpins. This result suggests that significant biotransformation may occur for metabolizable PCB congeners over the lifespan of these biota. This study highlights the potential of chiral analysis to study biotransformation processes in food webs.     

Beach sand and sediments are temporal sinks and sources of Escherichia coli in Lake Superior

The Duluth Boat Club (DBC) Beach, located in the Duluth-Superior harbor of Lake Superior, is frequently closed in summer due to high counts of Escherichia coli, an indicator of fecal contamination. However, the sources of bacteria contributing to beach closure are currently unknown. In this study, we investigated the potential sources of E. coli contaminating the DBC beach by using modified rep-PCR (HFERP) DNA fingerprinting. Over 3600 E. coli strains were obtained from 55 lake water, 25 sediment, and 135 sand samples taken from five transects at the DBC beach at 11 different times during the summer through fall months of 2004 and 2005. Potential sources of E. coli at this beach were determined by using a known-source DNA fingerprint library containing unique E. coli isolates from wildlife, waterfowl, and treated wastewater obtained near Duluth, MN. Amounts E. coli in the samples were enumerated by membrane filtration counting, and the presence of potentially pathogenic E. coli was determined by using multiplex PCR. E. coli counts in all samples increased during the summer and early fall (Julyto September). While E. coli in spring samples originated mainly from treated wastewater effluent, the percentage of E. coli from waterfowl increased from summer to fall. DNA fingerprint analyses indicated that some E. coli strains may be naturalized, and autochthonous members of the microbial community in the beach sand and sediments were examined. However, multiplex PCR results indicated that <1% of the E. coli strains at the DBC was potentially pathogenic. Our results also suggest that wave action may influence the early colonization and homogeneous distribution of E. coli in beach sand and the subsequent release of sand or sediment-borne E. coli into lake water. Taken together, these results indicate that sand and sediment serve as temporal sources and sinks of human and waterfowl-derived E. coli that contribute to beach closures.     

Evaluation of novel techniques for measurement of air-water exchange of persistent bioaccumulative toxicants in Lake Superior

We report initial measurements of concentrations and net air-water exchange fluxes of target persistent bioaccumulative toxicants (PBTs) in Lake Superior utilizing techniques not previously applied for this purpose. Gaseous PBTs are collected in diffusion denuders containing sections of commercial chromatography columns and subsequently thermally extracted into the cooled injection inlet of a high-resolution gas chromatograph. The PBT sampling/analytical methods enable accurate determination of gas-phase PBT concentration and micrometeorological measurement of fluxes to be carried out. PBT fluxes are measured by the modified Bowen ratio technique in which sensible heat flux is related to PBT flux, with the assumption of identical transfer velocities of heat and PBTs between two heights in the atmospheric surface layer. Micrometeorological measurement of flux accounts for all sources of resistance to mass transfer, including atmospheric stability effects, surface films, waves, sea spray, and bubbles. The sensible heatflux, PBT concentration, and PBT flux measurements carried out in 14 2- or 3-h periods during seven sampling events in Lake Superior in summer and fall 2002 and spring 2003 demonstrate advantages under the constraints of the techniques. The uncertainty of the flux measurements was typically in the range from 1% to 160%. Gaseous concentrations of a-hexachlorocyclohexane (alpha-HCH) and hexachlorobenzene (HCB) over Lake Superior were in the range from 6 to 170 and 12-95 pg/m3, respectively. Fluxes out of Lake Superior were measurable in 75% of the cases in which a concentration gradient was measured, and were in the range from -0.17 to +0.064 ng/m2 x h for alpha-HCH and from -0.60 to -0.093 ng/m2 x h for HCB.     

Chlorinated hydrocarbons in the daily diet]

The gas chromatographic analysis of the daily diets (without beverages) of men consuming at maximum 4000 kcal per day, in spring, summer and autumn 1971, revealed always residues of chlorinated hydrocarbons. With an average food amount of 1635 g per day, each subject (having an average body weight of 65 kg) ingested 105 mug of DDT, 20 mug of DDE, 20 mug of DDD, and 149 mug of total DDT and 10 mug of lindane, respectively. The contamination was inferior to the ADI values recommended by the WHO/FAO. From winter 1971 to autumn 1972, the authors also analysed the daily diets (including beverages) of 1-3-year-old children (having an average body weight of 12 kg) in a week-nursery. The average food amount of 1230 g per day contained 42 mug of DDT, 12 mug of DDE, 8 mug of DDD, and 64 mug of total DDT and 7 mug of lindane, respectively. From these values a total DDT intake of 5.3 mug/kg of body weight was calculated which exceeds the ADI value for adults. The claim for a zero tolerance for victuals and ready-to-use baby foods is corroborated. Consequently the complete replacement of DDT by other insecticides is a measure which is imperative not only from the viewpoint of prophylaxis but also from that of health policy.     

Chlorinated solvents in groundwater of the United States

Four chlorinated solvents-methylene chloride, perchloroethene (PCE), 1,1,1-trichloroethane, and trichloroethene (TCE)-were analyzed in samples of groundwater taken throughout the conterminous United States by the U.S. Geological Survey. The samples were collected between 1985 and 2002 from more than 5,000 wells. Of 55 volatile organic compounds (VOCs) analyzed in groundwater samples, solvents were among the most frequently detected. Mixtures of solvents in groundwater were common and may be the result of common usage of solvents or degradation of one solvent to another. Relative to other VOCs with Maximum Contaminant Levels (MCLs), PCE and TCE ranked high in terms of the frequencies of concentrations greater than or near MCLs. The probability of occurrence of solvents in groundwater was associated with dissolved oxygen content of groundwater, sources such as urban land use and population density, and hydraulic properties of the aquifer. The results reinforce the importance of understanding the redox conditions of aquifers and the hydraulic properties of the saturated and vadose zones in determining the intrinsic susceptibility of groundwater to contamination by solvents. The results also reinforce the importance of controlling sources of solvents to groundwater.     

Episodic particle transport events controlling PAH and PCB cycling in Grand Traverse Bay, Lake Michigan

To evaluate the influence of episodic events on particle and hydrophobic organic contaminant (HOC) cycling in the Great Lakes, we deployed sequencing sediment traps at two locations in the western arm of Grand Traverse Bay, Lake Michigan. The traps collected integrated samples of settling particles every 2 weeks from May 1997 to September 1999. The total polycyclic aromatic hydrocarbon (t-PAH) and total polychlorinated biphenyl (t-PCB) settling fluxes from the surface waters in the southern site were significantly greater than those from the northern site. In addition, there were more frequent brief increases in the mass flux to the southern site than to the northern site. These episodic events, which occurred only 20% of the time, accounted for 65% of both the mass flux and t-PAH flux. The t-PCB flux was not influenced by these episodic events, and only 18% of the t-PCB flux occurred during these events. PAHs and PCBs appear to be tracing different types of particles in the water column. Several large mass flux events characteristic of seiches were observed simultaneously in the benthic nepheloid layer (BNL) at both the northern and the southern sites. The particles settling as a result of these resuspension events had lower t-PCB and t-PAH concentrations than particles settling at other times. This suggests that the material settling into the traps on the high mass flux days is composed of a mixture of the less contaminated underlying resuspended sediment and the "regular" contaminant-rich particles settling into the BNL.     

湖光岩水体与泥层中真菌的分离鉴定及抗菌活性研究

从湖光岩的湖水、泥土中分离出30株真菌,根据形态特征确定其种属,通过管碟法测定其抗菌活性。结果表明青霉属15株、曲霉属4株、酵母属4株、木霉属2株、毛霉属1株、粘帚霉属1株、根霉属1株。具有抗菌活性的菌株11株:9株具有抗金黄色葡萄球菌活性;1株具抗金黄色葡萄球菌活性及抗枯草芽孢杆菌活性;1株有抗大肠埃希氏菌活性、抗金黄色葡萄球菌活性及抗枯草芽孢杆菌活性。     

Effects of aryl hydrocarbon receptor-mediated early life stage toxicity on lake trout populations in Lake Ontario during the 20th century

Lake trout embryos and sac fry are very sensitive to toxicity associated with maternal exposures to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and structurally related chemicals that act through a common aryl hydrocarbon receptor (AHR)-mediated mechanism of action. The loading of large amounts of these chemicals into Lake Ontario during the middle of the 20th century coincided with a population decline that culminated in extirpation of this species around 1960. Prediction of past TCDD toxicity equivalence concentrations in lake trout eggs (TEC(egg)s) relative to recent conditions required fine resolution of radionuclide-dated contaminant profiles in two sediment cores; reference core specific biota--sediment accumulation factors (BSAFs) for TCDD-like chemicals in lake trout eggs; adjustment of the BSAFs for the effect of temporal changes in the chemical distributions between water and sediments; and toxicity equivalence factors based on trout early life stage mortality. When compared to the dose-response relationship for overt early life stage toxicity of TCDD to lake trout, the resulting TEC(egg)s predict an extended period during which lake trout sac fry survival was negligible. By 1940, following more than a decade of population decline attributable to reduced fry stocking and loss of adult lake trout to commercial fishing, the predicted sac fry mortality due to AHR-mediated toxicity alone explains the subsequent loss of the species. Reduced fry survival, associated with lethal and sublethal adverse effects and possibly complicated by other environmental factors, occurred after 1980 and contributed to a lack of reproductive success of stocked trout despite gradually declining TEC(egg)s. Present exposures are close to the most probable no observable adverse effect level (NOAEL TECegg = 5 pg TCDD toxicity equivalence/g egg). The toxicity predictions are very consistent with the available historical data for lake trout population levels in Lake Ontario, stocking programs, and evidence for recent improvement in natural reproduction concomitant with declining levels of persistent bioaccumulative chemicals in sediments and biota.