Macroinvertebrate Bioaccumulation Analysis

Samples of macroinvertebrates were used to measure the bioaccumulation of metals in Montezuma Creek in 1995 and 1996. Invertebrates were used, because fish were absent from the creek in the study area. Samples of invertebrates were taken from each site, separated to taxon and feeding group. In 1995 fewer specimens required grouping by feeding group, while in 1996 separate taxa could be used. These samples were used for ICP/MS analysis, gross alpha and beta activity, and gamma spectroscopy.
Arsenic, cobalt, molybdenum, selenium, and vanadium showed spatial pattern of contamination with highest values at sites in Montezuma Creek closest to the mill site. At the most downstream site, the levels for these metals were similar to levels in Verdure Creek (Figure 1).

Uranium was also elevated in macroinvertebrate samples from Montezuma Creek, but did not decline with distance downstream.

Gross alpha activity was higher at sites below the mill than at sites above the mill. Beta activity was similar among all the sites and gamma spectroscopy did not find any radioisotopes in the macroinvertebrate samples.

Figure 1. Representative patterns of metal bioaccumulation levels in benthic macroinvertebrates in Montezuma and Verdure creeks.

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Last Modified: April 17, 2001