Master of Science (MSc)
Faculty of Science
Dr. Jim McGeer
Recent studies have shown that the use of bioaccumulation (tissue residues) as a predictor for toxic effects for metals is a flawed concept.Adams et al. (2010) suggested a novel tissue residue approach (TRA) in which bioaccumulation in resistant organismsis related to toxic effects in sensitive organisms. The goal of this thesis was to test these assumptions in relation to Cd exposure using the great pond snail, Lymnaea stagnalis by developing and improving the understanding of Cd accumulationin aquatic invertebrates.
The relationship between Cd bioaccumulation and its toxicity was studied in L. stagnalisusing acute (96h) and chronic (one month) toxicity tests in moderately hard water (140 mg/L as CaCO3). Two sizes of snails (18 or 25 mm) were tested for acute toxicity and the 96 h LC50 for both sizes of snails were 350 µg Cd/L. Soft tissue accumulation reached 750 µg Cd/g dry wt.in these exposures while the shell accumulation was only 16 µg Cd/g at the highest non-lethal exposures. Three sizes of snails were tested for chronic toxicity. The 31 d LC50s for the small (5 mm), medium (10 mm) and large (15 mm) snails were 13, 50 and 46 µg Cd/L, respectively. In the smaller snails, growth was inhibited at exposure concentrations below 10 µg Cd/L.
In soft water (20 mg/L CaCO3), two chronic (28 d) tests were conducted using juvenile snails (5 mm), the first with exposures from 2.3 – 8.3 µg Cd/L and the endpoints measured were survival, bioaccumulation and growth. The 28 d LC50for the first test was 7.3 µg Cd/L. Cd accumulation within the soft tissue ranged between 7 - 300 µg Cd/g dry wt. Exposure concentrations in the second test ranged from 0.3 – 2.3 µg Cd/L and the endpoints measured were whole and sub-cellular fractionation of Cd. Cd accumulation within the soft tissue reached levels as high as 117 µg Cd/g dry wt. Cd accumulation was dose dependent and reached steady state tissue burden within 14 d. Sub-cellular fractionation was measured after 28d of exposure and increasing amounts of Cd were found in the heat stable proteins and organelle fractions as Cd exposure concentration increased.
Finally, to test the novel TRA approach, a side-by-side exposure using a Cd sensitive organism (Hyalella azteca; based on studies by T. Straus) and a resistant organism (L.stagnalis) was done over 28 d using a toxicologically relevant exposure range (0.4 to 2.6 µg Cd/L). Endpoints were survival, growth (dry wt.) and Cd accumulation. A relationship between mortality in Hyalella (sensitive organism) and accumulation in Lymnaea (resistant organism) was determined for d 28 of exposure. The 28 d LD20 and LD50 in Hyalella were 0.42 and 0.70 µg Cd/L, respectively. The LD20 and LD50 values in Hyalella was associated to 36 and 69 µg Cd/g dry wt. body burden in the soft tissue of Lymnaea. Therefore, this novel TRA shows potential but requires more validation for it to be used in the field.
Pais, Nish M., "Studies on Waterborne Cadmium Exposure to Lymnaea stagnalis in Varying Water Qualities and the Development of a Novel Tissue Residue Approach" (2012). Theses and Dissertations (Comprehensive). 837.