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Mineral Particles are a Source of Dietary Metal in Streams

USGS scientist collecting a water sample from a gravel bar on side of a river.
A USGS scientist collects a water sample for analysis of mineral particles know as colloids. Toxic metals (such as copper in excess) bind to the particles, which are then ingested by aquatic animals. Photo credit: Daniel Cain,USGS
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Copper is directly absorbed from mineral particles when aquatic organisms living on the bottom of streams digest their food. Scientists have known that some aquatic organisms absorb metals from the food they eat. Now it appears that the mineral particles are a potentially important source of metals to sediment dwellers and the food web.

USGS scientists developed and applied new techniques to determine how the chemical properties of mineral particles ingested by aquatic organisms affect metal absorption. The bioaccumulation of metals by animals at the base of aquatic food webs is of particular concern because of high concentrations of metals present in sediment and organic matter at contaminated sites, such as streams impacted by acid mine drainage.

In feeding experiments with freshwater animals, such as the common pond snail (Lymnaea stagnalis), isotopically enriched metals were used as tracers to quantify metal absorption. The food source in some experiments was enriched with synthetic or natural metal-bearing particles representative of what’s found in the environment. The scientists also developed a novel reverse labeling technique to study natural particles. The reverse labeling technique involves artificially enriching the test organisms with a rare isotope of the metal under study instead of the natural particles. The scientist then measure the amount of the normal isotope the animals absorb from the food they eat. This allows the scientist to measure the absorption of the metal(s) from natural particles without altering the natural particles.

The studies show that over 75 percent of the copper associated with the synthetic particles and roughly half of the copper associated with the natural particles was absorbed by the test animals. This is an important new finding for scientists, resource managers, and regulators addressing contamination in streams impacted by acid mine drainage.

This study was funded by the USGS Toxic Substances Hydrology Program and Hydrologic Research and Development Program.

References

Cain, D.J., Croteau, M.-N., and Fuller, C.C., 2013, Dietary bioavailability of Cu adsorbed to colloidal hydrous ferric oxide: Environmental Science and Technology, v. 47, no. 6, p. 2869-2876, doi:10.1021/es3044856.

Croteau, M.-N., Cain, D.J., and Fuller, C.C., 2013, Novel and nontraditional use of stable isotope tracers to study metal bioavailability from natural particles: Environmental Science and Technology, v. 47, no. 7, p. 3424-3431, doi:10.1021/es400162f.

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Created on August 09, 2013