458 (FRA-1117-851238) Chronic waterborne and dietborne cadmium exposures to juvenile rainbow trout: physiological and molecular endpoints.
Start time: 8:20 AM
Franklin, N¹, Galvez, F¹, Wood, C¹, ¹ McMaster University, Hamilton, Ontario, Canada
Previous research has shown that the gill epithelium of freshwater fish undergoes significant alterations in calcium transport during chronic exposure to waterborne cadmium. However, the effects of chronic dietary exposure and possible interactions between waterborne and dietary cadmium uptake have been largely overlooked. The present study uses a novel radiotracer technology to evaluate the relative contribution and potential interaction of each exposure pathway to fish. Juvenile rainbow trout were fed diets containing control (0.1 mg Cd/kg) or elevated dietary Cd (500 mg Cd/kg, radiolabelled with ¹⁰⁹Cd) in combination with either background (0.04 g Cd/L) or moderately elevated waterborne Cd (3g Cd/L) for 28 d. To further investigate the importance of dietary calcium on cadmium exposure via the different routes, each diet was also supplemented with elevated Ca (60 mg/g as CaCO₃; control diet = 15 mg Ca/g). The combined waterborne/dietborne Cd exposure produced significantly greater mortality (13%) than either exposure alone (<2%), and Ca in the diet was shown to protect against short-term Cd toxicity. Dietary Cd uptake contributed the majority (70 – 100%) of the body′s Cd accumulation from a combined exposure, and resulted in a significant gill Cd burden (35 – 65%). Results indicate that tissue accumulation of Cd via each exposure pathway is largely additive with prolonged exposure, and suggests that assumptions of additivity used to model chronic metal accumulation and toxicity may hold true for non-nutrient metals such as Cd. We are currently using quantitative PCR to assess possible changes in the expression of various genes encoding calcium transporters which may be altered by chronic cadmium exposure. (Funded by ILZRO, ICA, CDA, NiPERA, Noranda-Falconbridge, Teck Cominco, and an NSERC CRD grant).

459 (MCG-1117-861066) The influence of acclimation to Cu or Cd on the toxicity and bioaccumulation of Cu and Cd in rainbow trout and Daphnia magna.
Start time: 8:40 AM
McGeer, J¹, Nadella, S², Wood, C², ¹ Natural Resources Canada, Ottawa² McMaster University, Hamilton
The understanding of the potential impacts of chronic metal exposure is complicated by the fact that responses of fish to long term metal exposure can be variable, for example gill metal burden can change considerably, and as well, many metals induce acclimation. This study examines the influence of pre-exposure to chronic sublethal waterborne Cu or Cd on the subsquent uptake and distribution of Cu and Cd in both rainbow trout and Daphnia magna. In the trout experiments fish were exposed to either 3 ug/L Cd or, 75 ug/L Cu for one month with minimal mortality and no effect on growth. Chronic sublethal exposure to metal resulted in acclimation (resistance to acute challenge) to the metal of exposure as well as cross acclimation to the other metal. Exposure also resulted in significant accumulations of metal (either Cd or Cu) in the gill, kidney and liver. Accumulations of Cd were highest in the gill while those of Cu were greatest in the liver. Following a month of exposure to either Cd or Cu, metal uptake into gills, blood, liver, kidney, gastrointestinal tract and whole body was studied over time using radioisotopes (109Cd or 64Cu). Acclimation to Cd resulted in a reduction in the rate of Cd uptake into the gills and whole body compared to uptake rates of naive fish exposed to 3 ug/L Cd. When challenged at the higher level of 10 ug/L Cd, acclimated fish had significantly higher rates of gill Cd uptake and previous exposure to Cu similarly enhanced Cd uptake. In addition, chronic metal exposure resulted in altered routing of new metal through different body compartments. In Daphnia magna experiments whole body metal accumulation and acclimation were assessed. The results illustrate the changes in metal uptake and internal distribution that occur during chronic sublethal exposures and help to build an understanding of the physiology of acclimation responses in rainbow trout and Daphnia magna.

460 (CHO-1117-238003) Chronic exposure of rainbow trout to dietary cadmium: physiological responses and acclimation.
Start time: 9:00 AM
Chowdhury, M.¹, Pane, E.², Wood, C.³, ¹ US EPA-MED, Duluth, MN, U.S.A.² Monterey Bay Aquarium Research Institute, Moss Landing, CA, U.S.A.³ McMaster University, Hamilton, ON, Canada
Chronic effects of dietary metals in fish are not yet well defined. We examined a suite of physiological parameters (respiratory, acid-base, ionoregulatory, haematological, stress, and renal) in adult rainbow trout (Oncorhynchus mykiss) after chronic exposure to a sublethal level of dietary Cd (500 mg/kg diet) for 45 - 52 d. Blood sampling via an indwelling arterial catheter revealed that dietary Cd exposure had no major effects on blood gases, acid-base balance, and plasma ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl^-), but resulted in an increase in hematocrit (49 %) and hemoglobin (74 %) and a decrease in the plasma total ammonia (43%) and glucose (49%). Urine sampling via a urinary bladder catheter showed a significantly higher excretion rate of ions(Zn²⁺, K⁺, Na⁺, Cl^-), glucose and protein in Cd exposed trout relative to non-exposed naïve trout, with no changes in glomerular filtration rate (GFR) and urine flow rate (UFR). When both groups were challenged with waterborne Cd (10 g/L, ∼ 50% of the 96-h LC50) for 72 h, fish exposed to dietary Cd showed acclimation with increased protection against the effects of waterborne Cd on arterial blood P_aCO2 and pH, plasma ions and stress indices. After waterborne Cd challenge, plasma Ca²⁺ levels declined from the pre-challenge level, but the effect was more pronounced in non-acclimated fish (44 %) than in Cd-acclimated fish (14%) by 72 h. Similarly, plasma K⁺ and four traditional stress-parameters (plasma total ammonia, cortisol, glucose, and lactate) were elevated only in the non-acclimated fish. However, urinary loss of ions and protein, not glucose, remained elevated in the Cd pre-exposed trout during waterborne Cd challenge. Thus, chronic exposure to dietary Cd produces acclimation in trout with increased protection against additional stress caused by waterborne Cd. It appears that such acclimation also involves some physiological costs in terms of renal dysfunction and elevated urinary losses (Supported by NSERC, ICA, CDA, NiPERA, ILZRO, Teck-Cominco, Noranda-Falconbridge, & Inco).

(58125) COFFEE BREAK.
Start time: 9:20 AM

462 (KLE-1117-564015) Adaptation to metals in aquatic organisms: lessons learned from Foundry Cove and beyond.
Start time: 10:20 AM
Klerks, P¹, Xie, L¹, Levinton, J², ¹ University of Louisiana, Lafayette, Louisiana, USA² State University of New York, Stony Brook, New York, USA
Individuals of a population may differ genetically with respect to their sensitivity to metal toxicity. The selective pressure exerted by long-term exposure to toxic metal levels may thus result in the evolution of resistance in populations inhabiting metal-contaminated sites. The ultimate fate of such adapted populations can depend on fitness costs associated with the adaptation, while implications for the ecosystem may depend on the resistance mechanisms. These various issues are important when assessing metal risks and when setting environmental quality criteria. This presentation will address the occurrence of adaptation, associated fitness costs, and resistance mechanisms, focusing mainly on the oligochaete Limnodrilus hoffmeisteri inhabiting Cd-contaminated Foundry Cove and on a laboratory selection experiment with the least killifish Heterandria formosa selected during six generations for an increased resistance to cadmium. Results show that resistance can evolve very rapidly (though some populations fail to adapt), and that resistance may also be lost rapidly once a population is no longer exposed to the pollution. Various fitness costs were identified in the laboratory-selected population, but were less evident in the natural population in Foundry Cove. Metal accumulation and detoxification differed between adapted and control populations, indicating that the presence of metal-adapted populations affects the potential for trophic transfer of a metal.

463 (COU-1117-642195) Metabolic cost of chronic metal exposure in wild yellow perch.
Start time: 10:40 AM
Couture, P.¹, Pyle, G.², ¹ Institut National de la recherche scientifique, centre Eau, Terre et Environnement, Québec, QC, Canada² Nipissing University, North Bay, ON, Canada
The overall objective of this investigation was to examine the extent of metabolic impairment and adaptation in wild yellow perch historically exposed to elevated aqueous and dietary metal contamination. Sampling was carried out in metal gradients around Sudbury and Rouyn-Noranda, two major Northeastern Canadian copper and nickel mining and smelting areas. Yellow perch is a freshwater species that is widely distributed across North America. It is also metal tolerant and is the only abundant fish species remaining in the most contaminated lakes studied. Fish from the two regions demonstrated pronounced differences in tissue metal accumulation patterns in response to environmental contamination. Increasing metal contamination was associated with consistent increases of liver and muscle aerobic capacities in Rouyn-Noranda, but not Sudbury yellow perch. In contrast, previous research had clearly demonstrated that at the whole organism level, the aerobic capacity of metal-contaminated yellow perch from Sudbury was impaired, as measured by aerobic swim performance and respiration rates. Overall, our results indicate that chronic metal exposure and adaptation in wild yellow perch lead to metabolic costs but that metal acclimation strategies vary regionally, likely at least partly due to genetic differences induced by varying selective pressures. We also hypothesize that oxidative stress at the mitochondrial level plays a key role in chronic metal toxicity and metabolic costs for wild fish.

464 (CLE-1117-747533) Adaptation and acclimation of benthic macroinvertebrates to heavy metals increases susceptibility to novel anthropogenic stressors.
Start time: 11:00 AM
Clements, W¹, Kashian, D¹, Harrahy, E², Courtney, L³, ¹ Colorado State University, Fort Collins, CO, USA² Wisconsin &#65279;Department of Natural Resources, Madison, WI, USA³ University of Colorado, Boulder, CO, USA
Populations exposed to heavy metals often exhibit enhanced tolerance compared to naive or unexposed populations. Although increased tolerance to low levels of metals is often protective of subsequent pulsed exposure, the physiological and genetic mechanisms responsible for tolerance may have specific costs. We conducted stream microcosm experiments designed to assess the tolerance and associated costs of macroinvertebrate communities exposed to heavy metals. Communities collected from reference and metal-impacted streams in Colorado were subsequently exposed to combinations of heavy metals and other biotic and abiotic stressors (reduced pH, UV-B radiation, predation by stoneflies). In all instances, organisms collected from metal-polluted streams were more tolerant of metals than naive organisms. However, despite greater tolerance to metals, assemblages from metal-polluted streams were more sensitive to UV-B radiation, acidification, and predation. Because of the ubiquitous nature of heavy metal pollution in Rocky Mountain streams, these results have significant implications for understanding interactions between heavy metals and other anthropogenic stressors. If increased susceptibility to novel stressors is widespread in metal-tolerant populations, it is likely these populations will be disproportionately affected by other anthropogenic stressors.

465 (MUY-1117-541526) Multi-generation zinc acclimation and cost of tolerance in Daphnia magna.
Start time: 11:20 AM
Muyssen, B.¹, Janssen, C.¹, ¹ Ghent University, Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent, Belgium
The acclimation potential of Daphnia magna to zinc was investigated by means of an extensive laboratory multi-generation study. In the first generation exposed to concentrations up to 195 g Zn²⁺/L reproduction was stimulated. After 5 generations, however, an optimal concentration range could be observed at concentrations of 2 to 19 g Zn²⁺/L with deficiency and toxicity symptoms outside this range. The same trends were found for carapax length and energy reserves. Acclimated organisms were a factor of 3 more tolerant in acute toxicity tests than non-acclimated daphnids. Also in chronic tests it was found that 8th generation daphnids acclimated to concentrations equal or higher than 0.7 g Zn²⁺/L and exposed to 86 g Zn²⁺/L performed significantly better than organisms acclimated to lower concentrations, except for zinc-deprived animals in which reproduction was stimulated. In an additional study in which D. magna was acclimated to environmentally realistic zinc concentrations ranging from 0.02 to 74 g Zn²⁺/L acute nor chronic zinc tolerance was increased. However at test concentrations below the 21dEC50, acclimation to 6 to 22 g Zn²⁺/L did significantly increase reproductive rates, which corresponds to the previously established optimal range. Generally in toxicity testing, acclimation (deliberate or not) of test organisms should be taken into account and especially the use of zinc-deprived test organisms should be avoided as this renders organisms unnaturally sensitive. Finally, in an attempt to unravel processes underlying chronic zinc toxicity in D. magna, it was found that organisms show recovery of acute zinc toxicity between day 7 and day 14 of exposure. In surviving animals, the body calcium content was restored as well as filtration rate, energy reserves and reproduction. The use of genomic tools will help to further elucidate acclimation mechanisms.