| dc.description.abstract | Adult dragonflies are aerial predatory arthropods that occur globally. However, no research on adult dragonflies as potential indicators of metallic elements in the environment or metallic element concentrations and relative contribution patterns between sites, species, size classes, habitat types, and relation to possible pollution sources has been published. There is also no information available about dragonflies and their responses to toxic metals. However, metallic elements are toxic in elevated concentrations to all organisms.
I analysed 105 adult male dragonflies from 21 sites in South Africa for 33 metallic elements including thallium, thorium, zinc, mercury, arsenic, lead, chromium, cadmium, strontium, nickel, phosphorus, sodium, magnesium, potassium, rubidium, silver gold, and platinum. The results indicated that all species of dragonflies, regardless of body size are suitable indicators. Furthermore, differences between habitat differences did not affect the metallic element concentrations on the scale of this study. Interesting patterns were found between sites. Sites located near wastewater treatment plants showed elevated concentrations. Thallium, thorium, zinc, arsenic, phosphorus, sodium, magnesium, potassium, rubidium, and lead were found at elevated concentrations (relative to the other sites) in dragonflies from sites near mining. Dragonflies from sampling sites near potential pollution sources, but seemingly had isolated water sources, showed lower metallic element concentrations when compared with other sites. These observations point to avenues of investigation that can be followed up. Dragonflies are excellent indicators, especially of their immediate environments, because they are aerial predators, large enough for individual sampling and analyses, readily identifiable to species level, and obtaining ethical approval is easier than for vertebrates. Based on these results I conclude that dragonflies would be excellent indicators of environmental metallic elements | en_US |
