Metal concentrations and trace metal Al and Fe ratios in soil of the Chenier Plain, Southwest Louisiana coastal zone

Abstract

Soil baseline metal concentrations were determined in 220 surface soil samples collected from the Chenier Plain area of southwest coastal Louisiana. Regression relationships between Al, Fe, and various metals were calculated from the data set. The use of these relationships to identify enhanced metal contents in the Chenier Plain soils is presented. Statistical analyses showed an average Al concentration of 1.6% with a maximum concentration of 4.8% and a minimum concentration of 1.3 mg kg⁻¹. Al concentration in the sediments was positively correlated at the 1% significance level to Cu (r = 0.577**), Pb (r = 0.936**), Cr (r = 0.969**), Ni (r = 0.830**), Cd (r = 0.617**), and Zn (r = 0.506**), but only a 5% significance correlation was found with Mn (r = 0.148*). Average Fe concentration was 1.2% with a maximum value of 3.4% and a minimum concentration of 9.3 mg kg⁻¹. Fe concentration in the sediments was positively correlated at the 1% significance level to Cu (r = 0.586**), Pb (r = 0.847**), Cr (r = 0.875**), Ni (r = 0.932**), Cd (r = 0.803**), Zn (r = 0.551**), and Mn (r = 0.479**). These relationships were used to evaluate sites for metal contamination. Data from two known contaminated sites, Capitol Lake (Baton Rouge, LA) and Bayou Trepagnier (LA), fell well outside the prediction limits developed with the Chenier Plain Al and Fe metal regression lines for Cr and Zn. Pb and Cd at Capitol Lake were also elevated beyond the metal/Al prediction developed for the Chenier Plain, but the prediction was not out of range when using the metal/Fe regression. Samples from additional sites with no known metal contamination fell within the predictive limits of the regression equations except for Cd and Pb at some sites. Data presented showed that metal/Al and metal/Fe regression relationships can be used as a tool for identifying areas of potential metal contamination in the coastal zone, but must be regionally correlated.

Keywords:

• Heavy metals
• wetland soils
• baseline
• Chenier Plain
• coastal zone
• Louisiana

Acknowledgments

Present address for S. Miao is School of Life Sciences, Guangzhou University, Guangzhou, China.