Heavy metal distribution and bioaccumulation in Chihuahuan Desert Rough Harvester Ant (Pogonomyrmex rugosus) populations

Background/Question/Methods Heavy metal contaminants are known to negatively impact ecosystem function and structure.  Previous studies in the Northern Chihuahuan Desert have shown that the area has been subjected to considerable amounts of heavy metal contamination due to copper refining activities. However, a thorough examination of the distribution and accumulation patterns of heavy metals in multiple desert trophic levels has not been completed. In this study we analyzed the distribution and bioaccumulation of As, Cd, Cu, Pb and Zn in seeds and Pogonomyrmex rugosus populations of the Chihuahuan Desert in the west Texas, USA region. Our objectives were (1) to conduct a survey of the heavy metal distribution in ants of the region and ultimately provide a framework for objective 2; (2) to use high, medium and low contamination sites to evaluate the bioaccumulation factors for the heavy metals of interest. Sampling was conducted at 17 sites during 2007 and 3 sites during 2008. All samples were digested and analyzed for metals using an ICP-OES.

Results/Conclusions We identify a logarithmic contamination gradient as a function of distance from the suspected point source for As, Cd, Cu and Pb. No such trend was observed in Zn. All the metals considered in this study show significant bioaccumatlion trends in the granivorous ant trophic level. The bioaccumulation factors for the metals are identified as follows: As (1.56 X), Cd (9.00 X), Cu (3.63 X), Pb (2.84 X), and Zn (3.60 X).  All mean metal concentrations were compared using a single factor ANOVA and significant increases in concentrations from the seeds to the ants (p≤0.05) were observed in all metals of interest.