Treatment with Coated Layer Double Hydroxide Clays Decreases the Toxicity of Copper-Contaminated Water

Abstract

Copper is a common pollutant found in watersheds that exerts toxic effects on both invertebrates and vertebrates. Layer double hydroxide (LDH) clays are able to adsorb a wide range of contaminants through ion-exchange mechanisms. Coating LDH clays with various materials alters the aggregation of clay particles into the nano-size range, thus increasing relative surface area and offering great potential for contaminant remediation. The goal of this study was to determine if treatment with coated LDH clays decreases the toxicity of copper-containing solutions to Daphnia magna. Four LDH clays with different coatings used to alter hydrophobicity were as follows: used: Na⁺ montmorillonite, Zn–Al LDH-nitrate, Zn–Al LDH-stearate, and Zn–Al LDH-carbonate. It was determined that coated LDH clays decreased copper toxicity by decreasing bioavailability and that smaller aggregate sizes decreased bioavailability the most. 96 h LC₅₀ values increased by as much as 4.2 times with the treatment of the solutions with 100 mg/L LDH clay. Copper analysis of the clay and solutions indicated that the clays work by decreasing copper bioavailability by way of a binding mechanism. Coated LDH clays hold promise as a small-scale remediation tool or as an innovative tool for toxicity identification and evaluation characterization of metals.