Characterization of heavy metal concentrations in the Mahoning River bottom sediments

Abstract

Over the past ten years, a decrease in heavy metal loadings to the Mahoning River has occurred. Due to the closing of several steel mills and stringent effluent limitations being imposed on discharge sources, the Mahoning is expected to show a slow recovery, in which heavy metal levels in the river bottom sediments will decrease.

Variations in heavy metal concentrations with depth and length along the course of the Mahoning River were investigated in this study. Grab samples and core samples of river sediment were taken, air dried, pulverized, and digested, then analyzed with flame Atomic Absorption analysis. The metals analyzed were calcium, chromium, copper, iron, lead, manganese, nickel and zinc. Based on the data generated, a consistent trend was noticed in the sediment metal concentrations as a function of river mile. The overall tendency was for the metal levels to increase dramatically at the beginning of the industrialized section of the river. Following the initial spike, there was a net decrease in metal levels the closer to the river's mouth the samples were taken. As for variation with sediment depth, it was difficult to distinguish a consistent trend for the entire river. Even at the individual corning locations, heavy metal profiles varied along the channel cross section. Based on the data collected for the core samples taken across the river channel, the metal concentrations in the river sediments show increasing concentrations, decreasing concentrations and no distinct trend in metal concentrations varying with depth.