Summary


1
Stable isotope analysis has improved understanding of trophic relationships among biota. Coupled with contaminant analysis, stable isotope analysis has also been used for tracing the pattern and extent of biomagnification of contaminants in aquatic food webs.

2
Combined analysis of nitrogen (δ 15 N) and carbon (δ 13 C) isotopes from fish species in a sub-Arctic lake were related to tissue mercury (Hg) concentrations to assess whether carbon sources influenced Hg accumulation in fish, in addition to trophic position.

3
Statistical models were used to estimate Hg biomagnification and uptake, to elucidate Hg accumulation dynamics and to appraise the relative importance of Hg exposure routes for the fish species.

4
Species Hg contamination increased as a function of trophic position (δ 15 N) and was inversely related to the δ 13 C signature. Species connected to the benthic food chain had lower Hg concentrations than species connected to the pelagic food chain. Species undergoing ontogenetic dietary shifts with increasing size, e.g. lake trout Salvelinus namaycush , also showed increased Hg concentrations with increasing reliance on pelagic fish as prey.

5
The results indicate that both vertical (trophic) and horizontal (habitat) food web structure influence Hg concentrations in fish tissue.

6
The biomagnification and uptake models indicated that contamination at the base of the food chain in the lake exceeded estimates for more southerly environments, thereby demonstrating the importance of dietary and water column Hg exposure routes in the sub-Arctic for determining Hg concentrations in fish.

7
Overall, the data reported here demonstrate how a combination of ecological concepts (food webs), developing ecological methods (stable isotopes) and environmental geochemistry can combine profitably to indicate the risks of exposure to environmental contaminants. Additional studies of the dynamics of Hg accumulation in the food webs of sub-Arctic lakes are needed, particularly in the light of the estimated high biomagnification rates and the heavy reliance of Inuit communities on subsistence fish harvests.

Mercury accumulation in the fish community of a sub‐Arctic lake in relation to trophic position and carbon sources

Radiotracer techniques were employed to quantify the rates of uptake from aqueous and dietary sources, and rates of elimination of Cd, Se and Zn by a marine predatory fish, the mangrove snapper Lutjanus argentimaculatus. The relative significance of bioaccumulation of metals by fish from water and food and the food chain transfer factor were then assessed using a kinetic modeling approach. Cd and Zn in the aqueous phase exhibited an approximately linear uptake pattern over a 1 to 2 d exposure, whereas Se exhibited a 2-compartmental uptake at a low ambient concentration, with a slow initial uptake followed by a rapid increase in Se influx. Most of the accumulated aqueous Se and Zn were incorporated into the muscles, whereas Cd was evenly distributed in the viscera and the remaining tissue, with a lower proportion in the gills. The influx rates were dependent on the ambient metal concentration and were tissue-specific for each metal. The assimilation efficiency of trace metals in fish ingesting different prey (copepods, Artemia sp. and clam tissue) ranged from 6 to 24% for Cd, 32 to 68% for Se and 15 to 46% for Zn, and decreased with an increase in ingestion rate. The efflux rate constant of Cd in fish following uptake from the dietary phase (0.047 d -1 ) was higher than that following aqueous uptake (0.025 d -1 ), whereas the efflux rate constants of Se and Zn were comparable between these 2 exposure pathways. Our modeling calculations indicate that dietary uptake of Cd and Zn dominates their accumulation in fish when zooplankton are the main prey, whereas aqueous uptake may be the dominant pathway when planktivorous fish are the dominant prey for the predatory fish. Dietary uptake always dominates Se accumulation in these fish. The modeling results also indicated that the food chain transfer factor of Cd was <0.5 in the fish regard- less of the ingestion rate and the assimilation efficiency, consistent with the results of field studies. However, Se and Zn may potentially be biomagnified when the ingestion rate and assimilation effi- ciency are at the high end of the range possibly encountered by the predatory fish.

/pdf/exposure-and-potential-food-chain-transfer-factor-of-cd-se-1s277x2omt.pdf

Exposure and potential food chain transfer factor of Cd, Se and Zn in marine fish Lutjanus argentimaculatus

The uptake of radioactive trace metals by suspended particles in natural aquatic systems is often slow and the time constants for scavenging are of the same order of magnitude as the residence times of particles in the water column. Therefore, models simulating removal of radioactive trace metals from water to sediments in shallow aquatic systems with short particle residence times need to include sorption (i.e. scavenging) kinetics. We present a numerical kinetic transport model designed to simulate tracer movements from a well mixed water column where particles are generated by both primary production and sediment resuspension processes. Tracers are allowed to penetrate into underlying sediments by diffusion and particle and porewater mixing. All model parameters can be experimentally determined either in the ecosystem itself or in separate laboratory experiments. Model simulations of three kinds of experiments are presented: tracer diffusion in benthic flux chambers, and tracer removal in marine mesocosms and in lacustrine limnocorrals. Limited sensitivity analyses and simulations of actual experiments indicate that under conditions of particle cycling in the sediments and the water, tracer removal can be affected and-in the case of high particle fluxes, as in summer- even be limited by the slow kinetics of tracer uptake by suspended particles. The model is also useful in identifying and quantifying critical pathways in the complicated web of interrelated processes of an aquatic ecosystem.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1986.31.2.0277

The relevance of scavenging kinetics to modeling of sediment‐water interactions in natural waters1,1

Elevated levels of selenium have resulted in the degradation of several ecosystems and have been linked to reproductive impairment in important fish and waterfowl populations in several lakes and reservoirs, indicating the need for a better understanding of the bioaccumulation of selenium by aquatic organisms. Because space limitations prevent an exhaustive review, this paper focuses on the processes and mechanisms of bioconcentration and biomagnification. Comparative uptake and accumulation of selenite, selenate, and selenomethionine are examined, as well as the relative importance of waterborne and foodborne exposure. The observed toxicity of selenium in lakes and reservoirs is briefly discussed. Finally, this information is summarized, pointing out key trends in the uptake and accumulation of selenium. Perhaps the most important information generated by this review involves comparative metabolism of selenite and selenate; selenite is readily reduced and metabolized, while reduction and metabol...

https://www.tandfonline.com/doi/pdf/10.1080/07438148809354824

Michael A. Turner

Papers

Fates of metal radiotracers added to a whole lake: Accumulation in slimy sculpin (cottus cognatus) and white sucker (catostomus commersoni)