Environmental Health - Contaminant Biology

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Metals in Acid Mine Drainage Affect Aquatic Insects

View of two streams. Left with low metals. Right with high metals.
Two streams (North Fork of South Platte and Handcart Gulch) spanning the gradient of aqueous metal from natural weathering and hard-rock mining in the Colorado Mineral Belt. Floating traps capture emerging adult aquatic insects. Photo Credit: Johanna Kraus, USGS.

Studies conducted in subalpine streams in Colorado by U.S. Geological Survey (USGS) scientists found that aqueous metals resulting from acid mine drainage and natural weathering can almost eliminate adult insect emergence from streams, even at metal levels too low to reduce aquatic larval densities. This pattern suggests that adult insects might be a more sensitive indicator of metals than juvenile (larval) insects and that adults are not as protected from aquatic contaminants as currently thought. Results of the studies were published in the journals Ecological Applications, and Environmental Science and Technology.

Most aquatic insects live in freshwater as larvae but move to land as flying adults to complete their life cycle. These adults are a major source of food to terrestrial food webs. When aquatic contaminants kill insects before they become adults, predators such as spiders, birds, and bats lose a rich food source. On the other hand, if contaminants accumulate in larvae and persist in adult bodies, terrestrial predators are exposed to elevated contaminant concentrations.

A systematic analysis of literature reviewed for these studies indicated that insect metamorphosis from larva to adult has strong effects on contaminants in insect bodies. For example, some metals are almost completely eliminated from insect bodies during metamorphosis while concentrations of certain organic contaminants, such as polychlorinated biphenyls (PCBs), increase. Because the uptake of contaminants in insect bodies varies, predator exposures to contaminants vary, depending on whether larvae or adult insects are eaten.

These findings inform regulators and resource managers about the broader impacts of aquatic contaminants on resource availability for terrestrial consumers. Furthermore, understanding changes in insect chemistry related to metamorphosis will help predict and potentially mitigate the cascading effects of contaminants across perceived ecosystem boundaries and will improve risk management of contaminated sites.

Funding for this study was provided by the USGS Mendenhall Research Fellowship, Mineral Resources, and Contaminant Biology Programs; and the U.S. Environmental Protection Agency.


Metamorphosis alters contaminants and chemical tracers in insects--Implications for food webs: Environmental Science and Technology, 2014, doi:10.1021/es502970b.

Metamorphosis enhances the effects of metal exposure on the mayfly, centroptilum triangulifer: Environmental Science and Technology, 2014, v. 48, no. 17, p. 10415-10422, doi:10.1021/es501914y.

Emergence flux declines disproportionately to larval density along a stream metals gradient: Environmental Science and Technology, 2013, v. 47, no. 15, p. 8784-8792, doi:10.1021/es3051857.

More Information

This article was featured as an article in the USGS GeoHealth Newsletter, Vol. 11, No. 1, 2014


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