Laboratorium Estimering af Net Trofiske overføringseffektiviteter af PCB-til Lake Trout (<em> Salvelinus namaycush</em>) Fra sit bytte
Summary
En teknik til laboratorium estimering af netto trofisk overførsel effektivitet polychlorerede biphenyler (PCB) kongenere til fiskeædende fisk fra deres bytte præsenteres. For at maksimere anvendeligheden af laboratorieresultater til feltet, bør fiskeædende fisk fodres bytte fisk, der typisk spises i marken.
Abstract
En teknik til laboratorium estimering af netto trofisk overførsel effektivitet (γ) af polychlorerede biphenyler (PCB) kongenere til fiskeædende fisk fra deres bytte er beskrevet heri. Under en 135-dages laboratorium eksperiment, vi fodres bloater (Coregonus hoyi), der var blevet fanget i Lake Michigan til sø ørred (Salvelinus namaycush) holdt i otte laboratorie tanke. Bloater er en naturlig føde for sø ørred. I fire af tankene blev en relativ høj strømningshastighed anvendes til at sikre relativt høj aktivitet ved søen ørred, mens en lav strømningshastighed blev brugt i de fire andre tanke, der giver mulighed for lav sø ørred aktivitet. På en tank-for-tanken grundlag blev mængden af mad spist af søørred på hver dag i forsøget registreres. Hver sø ørred blev vejet ved begyndelsen og slutningen af forsøget. Fire til ni søørred fra hver af de otte tanke blev aflivet ved starten af eksperimentet, og alle 10 søørred tilbage i hver af tankene var euthanteriseret ved slutningen af eksperimentet. Vi bestemmes koncentrationer af 75 PCB-i sø ørred ved starten af eksperimentet, i søen ørred i slutningen af eksperimentet, og bloaters fødes til sø ørred under eksperimentet. Baseret på disse målinger blev γ beregnes for hver af 75 PCB-congenere i hver af de otte tanke. Mean γ blev beregnet for hver af de 75 PCB-kongenere for både aktiv og inaktiv søørred. Fordi forsøget blev gentaget i otte tanke, standardafvigelsen omkring betyde γ kan anslås. Resultater fra denne type eksperiment er nyttige risikovurderingsmodeller at forudsige fremtidig risiko for mennesker og dyreliv spise forurenede fisk under forskellige scenarier for miljøforurening.
Introduction
Of all of the factors affecting the rate at which fish accumulate contaminants, the efficiency with which fish retain contaminants from the food that they eat is one of the most important1-3. Risk assessment models have been developed to predict future risks to both people and wildlife eating contaminated fish under various scenarios of environmental contamination, and the reliability of these predictions critically depends on the accuracy of the estimates of the efficiency at which fish retain contaminants from their food4.
The efficiency with which the contaminant in the food ingested by the predator is transported through the gut wall is known as gross trophic transfer efficiency5. A portion of the quantity of the contaminant transported through the gut wall of the predator may eventually be lost through depuration and/or metabolic transformation. The efficiency with which the contaminant in the food ingested by the predator is retained by the predator, including any losses due to elimination and metabolic transformation, is known as net trophic transfer efficiency6.
Gross trophic transfer efficiency of organic contaminants to fish from their prey appears to vary with the contaminant’s chemical properties, including lipid affiliation as measured by the octanol-water partition coefficient, Kow3,7. According to an empirical relationship developed by Thomann3, gross trophic transfer efficiency is relatively high when log Kow is equal to a value between 5 and 6. Gross trophic transfer efficiency declines exponentially at a rate of 50% per unit of log Kow as log Kow increases from 6 to 10, according to the Thomann3 relationship.
Nevertheless, the gross and net trophic transfer efficiencies of polychlorinated biphenyl (PCB) congeners to fish from their prey do not appear to follow the Thomann3 relationship in most cases. Although the trophic transfer efficiencies of PCB congeners to lake whitefish (Coregonus clupeaformis) from its food followed the relationship proposed by Thomann8, trophic transfer efficiencies of PCB congeners were either just weakly related or not related at all to log Kow for Atlantic salmon (Salmo salar)9, rainbow trout (Oncorhynchus mykiss)10, coho salmon (Oncorhynchus kisutch)11, and northern pike (Esox lucius)11.
The overall goal of this study was to present a laboratory technique for estimating the net trophic transfer efficiencies of PCB congeners to a piscivorous fish from its prey. Lake trout (Salvelinus namaycush) was chosen as the piscivorous fish for our experiment because lake trout are relatively easy to maintain in laboratory tanks. Bloater (Coregonus hoyi) was selected as the prey fish to be fed to the lake trout because bloater is eaten by lake trout in its natural setting12. In addition, we determined whether the net trophic transfer efficiencies for lake trout estimated from our laboratory experiment followed the Thomann3 relationship. We also determined whether the degree of activity by the lake trout had a significant effect on net trophic transfer efficiency (γ) of the PCB congeners. Activity by lake trout in the Laurentian Great Lakes is believed to have recently increased because changes in the food webs have caused lake trout to allocate more energy toward searching for food13. Lake trout were forced to exercise in one set of tanks by subjecting these lake trout to relatively high flow rates, whereas the other lake trout were permitted to remain relatively inactive by subjecting them to relatively low flow rates. Finally, the specific details of our laboratory procedure that need to be carefully followed to ensure the highest degree of accuracy in the γ estimates and to make the laboratory results applicable to the field are discussed, as well as future directions for research building on our laboratory technique. Net trophic transfer efficiency can be estimated both in the laboratory and in the field, and advantages and disadvantages are associated with both approaches. Accuracy in the estimate of γ depends on the accuracy of the estimate of food consumption. The amount of food eaten by fish in the laboratory can be accurately determined when proper protocols are followed, whereas the amount of food eaten by fish in the field is typically estimated via bioenergetics modeling. Use of bioenergetics modeling to derive the amount of food eaten has the potential to introduce a substantial amount of uncertainty into the estimates of food consumption. Fish bioenergetics models have been shown to estimate food consumption with no detectable bias for the case of lake trout14,15, but considerable bias in bioenergetics model estimates of food consumption has been detected for the case of lake whitefish15,16. On the other hand, estimates of net trophic transfer efficiency estimated in the laboratory may not be applicable to the field due to a difference in feeding rates between the laboratory and the field17. Evidence from both the laboratory and the field suggest that feeding rate can influence γ14,17.
The methodology used in the present study for estimating γ in the laboratory is applicable to situations where the predator fish is fed prey fish, and the amount of prey fish eaten by the predator can be accurately tracked. To accomplish this, the experimenter must weigh all of the food before placement in the tank; and the experimenter must be able to remove all of the uneaten food from the tank, and then weigh the uneaten food. In addition, an adequate suite of mixers and blenders should be available to obtain a sufficient degree of homogenization of the samples of both predator and prey fish. Finally, the gas chromatography – mass spectrometry instrumentation used to determine the PCB congener concentrations must be capable of detecting and quantifying individual PCB congeners at relatively low concentrations.
Protocol
Representative Results
Discussion
Til de mest nøjagtige estimater af γ skal forsøgslederen være i stand til præcist at spore både mængden af fødevarer er placeret i hver af tankene, og mængden af Foderrester i hver af tankene i løbet af eksperimentet. For at opnå dette, skal forsøgslederen være i stand til at fjerne alle de Foderrester fra tankene og præcist bestemme dens vægt. Foruden nøjagtig sporing af fødevarer faktisk spist af rovfisk, kan nøjagtig estimering af γ også afhænge af tilstrækkelig varighed af eksperime…
Disclosures
The authors have nothing to disclose.
Acknowledgements
This work was funded, in part, by the Great Lakes Fishery Commission and the Annis Water Resources Institute. Use of trade, product, or firm names does not imply endorsement by the U. S. Government. This article is Contribution 1867 of the U. S. Geological Survey Great Lakes Science Center.
Materials
| Name | Company | Catalog Number | Comments |
| 870-L fiberglass tanks | Frigid Units | RT-430-1 | |
| 2,380-L fiberglass tanks | Frigid Units | RT-630-1 | |
| Tricaine methanesulfonate (Finquel) | Argent Chemical Laboratories, Inc. | C-FINQ-UE-100G | Eugenol could also be used as an anesthetic. |
| Ashland chef knife | Chicago Cutlery | SKU 1106336 | |
| Cutting board | Williams-Sonoma | 3863586 | |
| Hobart verical mixer (40 quart) | Hobart Corporation | ||
| 1.9-L food processor | Robot Coupe, Inc. | RSI 2Y1 | |
| Polyethylene bags (various sizes) | Arcan Inc. | ||
| I-Chem jars | I-Chem | 220-0125 | |
| Top-load electronic balance | Mettler Toledo | Mettler PM 6000 | |
| Sodium sulfate, anhydrous – granular | EMD | SX0760E-3 | |
| Glass extraction thimbles (45 mm x 130 mm) | Wilmad-Lab Glass | LG-7070-114 | |
| Teflon boiling chips | Chemware | 919120 | |
| Rapid Vap nitrogen sample concentrator | Labconco | 7910000 | |
| N-Vap nitrogen concentrator | Organomation | 112 | |
| Soxhlet extraction glassware (500 mL) | Wilmad-Lab Glass | LG-6900-104 | |
| Hexane | Burdick & Jackson | Cat. 211-4 | |
| Dichloromethane | Burdick & Jackson | Cat. 300-4 | |
| Silica gel | BDH | Cat. BDH9004-1KG | |
| Labl Line 5000 mult-unit extraction heater | Lab Line Instruments | ||
| Agilent 5973 GC/MS with chemical ionization | Agilent | 5973N | |
| Internal standard solution | Cambridge Isotope Laboratories | EC-1410-1.2 | |
| PCB congener calibration standards | Accustandard | C-CSQ-SET | |
| DB-XLB column (60m x 0.25mm, 0.25 micron) | Agilent/ J&W | 122-1262 |
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