Levels Shown to Stress Tadpoles
(Beyond Pesticides, July 12, 2005) Pesticides, even at low levels, are one more stress for tadpoles, which in combination with natural stressors can lead to impaired growth and development, lower fecundity, and decreased survival rates. These findings come from a new study published in Environmental Science & Technology, reinforcing a growing body of research that suggests commonly used acute toxicity tests seriously underestimate pesticides' ecological impacts because they do not account for synergistic effects.
Researchers from Sweden's Uppsala University and Finland's University of Helsinki conducted the study. Tadpoles were exposed to either a common fungicide (fenpropimorph), the visual and chemical signals of a natural predator, or both stressors. Using a fungicide exposure level of 2 µg/L, tadpoles exposed to both of the stressors were smaller and developed slower than siblings exposed to a single stressor. The study's analysis points out that such delays lower fecundity later in life, and decrease the likelihood of survival.
What the authors of the paper "have seen was not outright [increased] mortality, but that pesticides, at concentrations found in nature, alter the fitness of amphibian populations," says Christine Bridges, an ecotoxicologist at the Columbia Environmental Research Center of the U.S. Geological Survey. Bridges points out that many more synergistic effects exist in nature. "It is really important to look at more than one factor," she warns.
The researchers also found that at fungicide exposure levels of 11 µg/L, which is still drastically lower than the levels required to be toxic to fish, chronic exposure killed 93% of the tadpoles. This result was independent of the presence or absence of additional stressors showing the effects of fenpropimorph can change dramatically at low levels within a relatively small concentration range.
Professor Rick Relyea found similar results using the popular pesticide Sevin. He found low concentrations of Sevin were up to 46 times more lethal to tadpoles in combination with cues from natural predators then without. (See Daily News)
Such studies help to explain the worldwide decline of amphibian populations. Amphibian exposure to pesticides such as atrazine has also been shown to lead to deformities, hermaphrodism, and weakening of the immune system. (See Daily News)