Biogeochemical Analyses of Airborne Deposition of Lead (Pb) Contamination in Aravaipa Creek, Arizona.

Authors: Betsy Grube, Peter Reinthal, Jessica Gwinn, Elizabeth Arnold

Year: 2018

Abstract

The fish community of Aravaipa Creek, Arizona, with seven native species, is considered the foremost remnant assemblage of the imperiled Gila River basin fauna. In 2009, the Klondyke mine tailings were capped with a two-foot clean soil cover and installation of erosion protection on the upstream pile. Previous studies of lead isotopic ratios (208Pb, 207Pb, and 206Pb) of sediments, water and biota in pre-remediation and post-remediation of a mine tailing EPA Superfund site found remediation was effective in curtailing the inputs of contaminants into Aravaipa Creek from sediment and water. However, there was not an observed shift in the biota isotopic signatures of the lead sources. In this study we examine lead contamination in livers and muscles of native fish species, Catastomus insignis, Pantosteus clarki and Gila robusta, pre- and post-remediation with lead levels in livers much lower post-remediation. Muscle tissue was found to have lower levels of lead contamination than livers. However, given there is not a shift in fish lead isotope ratios suggests an alternative source of lead, such as airborne dust, impacting the creek. We assessed spatial patterns of airborne deposition in epilithic lichens in Upper Aravaipa Creek versus Lower Aravaipa Creek to determine spatial differences in airborne lead deposition. Mean lead found in lichens from Upper Aravaipa Creek (19.6 +/- 7.4 ppm dry), near mine tailings, was significantly greater than mean lead values from lower Aravaipa Creek (14.2 +/- 4.8 ppm dry). These data support the hypothesis that lead is entering the biotic food chain via airborne deposition via dust in Upper Aravaipa Creek that is near mine tailings but not in lower Aravaipa Creek, 15 miles downstream where mine tailings are not present.