Laboratoire Estimation des gains en efficience de transfert net trophiques des congénères de PCB dans le lac Trout (<em> Salvelinus namaycush</em>) De sa proie
Summary
Une technique pour laboratoire estimation de l'efficacité du transfert trophique net de polychlorobiphényles (PCB) chez les poissons piscivores à partir de leur proie est présenté. Afin de maximiser l'applicabilité des résultats de laboratoire sur le terrain, les poissons piscivores doit être nourri poissons proies qui sont généralement consommés dans le domaine.
Abstract
Une technique pour laboratoire estimation de rendement net trophique de transfert (γ) de polychlorobiphényles (PCB) chez les poissons piscivores à partir de leur proie est décrite ici. Au cours d'une expérience de laboratoire de 135 jours, nous avons nourri de fumage (Coregonus hoyi) qui avaient été pêchés dans le lac Michigan au lac de fontaine (Salvelinus namaycush) conservés dans huit réservoirs de laboratoire. Fumage est une proie naturelle pour le touladi. Dans quatre des réservoirs, un débit relativement élevé a été utilisé pour assurer une activité relativement élevée par la truite de lac, alors qu'un faible débit a été utilisé dans les quatre autres réservoirs, ce qui permet une faible activité du touladi. Sur une base réservoir par réservoir, la quantité de nourriture ingérée par le touladi sur chaque jour de l'expérience a été enregistrée. Chaque truite de lac a été pesé au début et à la fin de l'expérience. Quatre à neuf touladi de chacun des huit réservoirs ont été sacrifiés au début de l'expérience, et les 10 touladi restant dans chacun des réservoirs étaient euthanlisés à la fin de l'expérience. Nous avons déterminé les concentrations de 75 congénères de BPC dans le touladi au début de l'expérience, dans le touladi à la fin de l'expérience, et bouffis nourris à la truite de lac pendant l'expérience. Sur la base de ces mesures, γ a été calculé pour chacun des 75 congénères de PCB dans chacun des huit réservoirs. Mean γ a été calculé pour chacun des 75 congénères de PCB pour la truite de lac à la fois active et inactive. Parce que l'expérience a été répétée dans huit réservoirs, l'erreur-type sur moyenne γ peuvent être estimés. Les résultats de ce type d'expérience sont utiles dans les modèles d'évaluation des risques pour prédire le risque futur pour les humains et la faune de manger du poisson contaminé, selon divers scénarios de contamination de l'environnement.
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
Pour des estimations plus précises de γ, l'expérimentateur doit être capable de suivre avec précision à la fois la quantité d'aliments placés dans chacun des réservoirs et la quantité de la nourriture non consommée dans chacun des réservoirs, au cours de l'expérience. Pour ce faire, l'expérimentateur doit être en mesure d'éliminer tous les restes de nourriture provenant des réservoirs et de déterminer avec précision son poids. En plus de suivi précis de la nourriture réellement c…
Divulgazioni
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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