Degradation Kinetics of Perchlorate in Sediments and Soils

Abstract

This study investigated the intrinsic perchlorate (ClO4-)degradation kinetics of sediments and soils from multiple sites in microcosm studies, including the influence of varying nitrate concentration (NO3--N from 1 to 22.8 ppm) and up to 300 ppm sulfate. The first-order degradation rates and lag times of both ClO4- and NO3- degradation were site-specific and dependent on environmental conditions such as organic substrate availability, nitrate, initial ClO4- concentration, and prior ClO4- exposure. At an initial ClO4- concentration of 5 ppm, ClO4- degradation rates ranged from 0.13 to 0.46 day-1, and lag times of ClO4- degradation ranged from 0 to 60.0 days; while NO3- degradation occurred at rates ranging from 0.03 to 1.42 day-1, with lag times ranging from 0 to 29.7 days. Under the same treatment conditions, NO3- degradation rates were relatively higher than that of ClO4-. Perchlorate degradation rates remained constant at both lower (0.5 ppm) and higher (5 ppm) ClO4- concentrations. Generally, ClO4- rates were affected by the availability of organic substrate, which was represented here by Total Volatile Solids (TVS) of sediments and soils, and not by NO3-. Nitrate did increase the lag time of ClO4- degradation, which may account for the persistence of ClO4- in the environment, especially when ClO4- is typically ppb levels in the environment compared to ppm levels of NO3-. This study showed rapid intrinsic ClO4- degradation in sediments and soils of contaminated sites, and highlighted the potential for natural attenuation of ClO4- in the environment.