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PubMed2004

Synergistic impacts of malathion and predatory stress on six species of North American tadpoles.

The decline of many amphibian populations is associated with pesticides, but for most pesticides we know little about their toxicity to amphibians. Malathion is a classic example; it is sprayed over aquatic habitats to control mosquitoes that carry malaria and the West Nile virus, yet we know little about its effect on amphibians. I examined the survival of six species of tadpoles (wood frogs, Rana sylvatica; leopard frogs, R. pipiens; green frogs, R. clamitans; bullfrogs, R. catesbeiana; American toads, Bufo americanus; and gray tree frogs, Hyla versicolor) for 16 d in the presence or absence of predatory stress and six concentrations of malathion. Malathion was moderately toxic to all species of tadpoles (median lethal concentration [LC50] values, the concentration estimated to kill 50% of a test population, ranged from 1.25-5.9 mg/L). These values are within the range of values reported for the few amphibians that have been tested (0.2-42 mg/L). In one of the six species, malathion became twice as lethal when combined with predatory stress. Similar synergistic interactions have been found with the insecticide carbaryl, suggesting that the synergy may occur in many carbamate and organophosphate insecticides. While malathion has the potential to kill amphibians and its presence is correlated with habitats containing declining populations, its actual role in amphibian declines is uncertain given the relatively low concentration in aquatic habitats.

Animals↗
PubMed1978

Cellular Cl content and concentration of amphibian skeletal and heart muscle.

Toads (Bufo marinus) and frogs (Rana pipiens pipiens) were given intraperitoneal injections of Na36Cl and Na235SO4. After in vivo equilibration for 20--180 min, the animals were pithed, and their ventricular and semitendinosus muscles were excised. Measurements of total Cl (by titrimetry) and 36Cl (by radioassay) showed that specific radioactivities of plasma and mus les approached equality within 1 h after injection for toad skeletal and heart muscle and frog ventricles, indicating complete exchange of cellular Cl with 36Cl. From the simultaneously measured muscle water contents and 35SO4 spaces, intracellular Cl concentrations in vivo (in mumol/g cell water) for semitendinosus and ventricular muscles were calculated to be, respectively, 1.4 +/- 0.3 and 2.3 +/- 0.8 for Bufo and 1.7 +/- 0.7 and 4.8 +/- 2.4 for Rana. In view of these low values, active cellular Cl accumulation seems improbable, but cannot be rigorously excluded without simultaneous membrane potential and intracellular ion activity measurements. A high concentration of Cl in the sarcoplasmic reticulum of skeletal muscle is also inconsistent with these measurements.

Animals↗
PubMed2004

Effects of chlorinated solvents on four species of North American amphibians.

Tetrachloroethylene (PCE), a dry cleaning and degreasing solvent, can enter groundwater through accidental leaks or spills, and concentrations as high as 75 mg/L have been reported in Canadian aquifers. Amphibians in wetlands receiving contaminated groundwater may be exposed to PCE and its degradation products, but little information is available on the impacts of these compounds on indigenous amphibian species. Acute (96-h static renewal) exposures to PCE and its major degradation products, trichloroethylene (TCE) and cisand trans-dichloroethylene, were conducted on embryos of four North American amphibian species: wood frogs (Rana sylvatica), green frogs (R. clamitans), American toads (Bufo americanus), and spotted salamanders (Ambystoma maculatum). Subsequently, chronic exposures to PCE and TCE were conducted with the larvae of American toads. Both PCE and TCE were teratogenic to amphibian embryos; median effective concentrations (EC50s) for developmental deformities produced by PCE and TCE exposure for wood frogs and green frogs were 12 and 40 mg/L, respectively. Embryonic survivorship, however, was not compromised at these concentrations. American toads were less sensitive; the EC50 for developmental abnormalities was not attained at the highest test concentrations, 45 and 85 mg/L PCE and TCE, respectively. These results are pertinent in assessing the impact of groundwater pollution on an aquifer-fed wetland.

Amphibians↗