Environ. Sci. Technol. 2007, 41, 4774-4780
PCB Bioavailability Control in Lumbriculus Variegatus through Different Modes of Activated Carbon Addition to Sediments XUELI SUN AND UPAL GHOSH* Department of Civil and Environmental Engineering, University of Maryland Baltimore County, Baltimore, Maryland 21250
PCB bioavailability to a freshwater oligochaete (Lumbriculus variegatus) was studied using sediments from a PCBimpacted river that was treated with different modes of granular activated carbon (GAC) addition. For sediment treated with 2.6% GAC and mixed for 2 min prior to L. variegatus addition, the reduction in total PCB biouptake was 70% for 75-300 µm size carbon, and 92% for the 45-180 µm size carbon. For the case where the GAC was placed as a thin layer on top of the sediments without mixing, the reduction in total PCB uptake was 70%. PCB biouptake kinetics study using treated and untreated sediment showed that the maximum PCB uptake in tissue was achieved at 28 days and decreased after that time. Although the absolute uptake of PCB changed over time, the percent reduction in total PCB uptake upon GAC amendment remained constant after the first few days. Our results indicated that PCB bioavailability was reduced upon the addition and little or no mixing of GAC into sediments. PCB aqueous equilibrium concentration and desorption rates were greatly reduced after GAC amendment, indicating reductions in the two primary mechanisms of PCB bioavailability in sediments: chemical activity and chemical accessibility.
Introduction A widely used approach for contaminated sediment remediation is dredging and disposal, which can be expensive and disruptive to existing ecosystems (1). Moreover, contaminants can be released into the water and air environments during sediment dredging, transportation, and storage (2, 3). Capping with clean sediments may not be practicable in sensitive ecosystems such as wetlands and at sites where there are concerns about changing of the sediment bathymetry. New developments in in-situ remediation approaches are needed that can reduce risks to human health and ecosystems from sediment-bound contaminants and that can work in tandem with long-term natural attenuation processes. Recent findings indicate that bioavailability and leachability of contaminants in sediment are affected strongly by the nature of binding of the contaminants to the sediment particle types (4-9). Work with PCB-impacted marine sediments from Hunters Point, CA, demonstrated that amendment of activated carbon reduces total PCB bioaccumulation in three marine organisms (10, 11) and reduces equilibrium PCB concentrations (12). Thus, application of * Corresponding author phone: 410-455-8665; e-mail: ughosh@ umbc.edu. 4774
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 41, NO. 13, 2007
activated carbon to the biologically active layer of PCBimpacted sediment may be an effective in situ stabilization method to reduce contaminant bioavailability to sediment organisms at the base of the aquatic food web. In situ bioavailability reduction using carbon amendment may be applicable at sites where bioaccumulation reduction can reduce exposures and consequent risk to acceptable levels. This research was focused on evaluating the effects of different modes of GAC application to sediment on PCB biouptake in a freshwater oligochaete, Lumbriculus variegatus. This organism is found throughout North America and Europe and prefers habitats at the edges of ponds, lakes, rivers, and marshes where it feeds on decaying vegetation and microorganisms and forms an important component at the base of the aquatic food web. The EPA method for testing of bioaccumulation of PCBs and PAHs in freshwater sediments (13) suggests the use of L. variegatus as test organisms. Benthic organisms can accumulate sediment-associated contaminants into their tissues via two major pathways: uptake from the aqueous phase, and uptake through ingestion of contaminated sediment particles (14, 15). Sediment ingestion was shown to account for 61% of pyrene uptake by L. variegatus (16). Digestion and absorption of food can cause contaminant fugacity in the gut to exceed that in the organism, which leads to net uptake of chemicals in the gut and also to biomagnification (17). However, the transfer of PCBs from native sediment to GAC and/or presence of GAC in the organism gut can reduce PCB fugacity in the gut. McLeod et al. (18) reported that PCB and PAH assimilation efficiency was decreased in a marine clam due to the strong affinity of PCBs to activated carbon. Recent work by Reichenberg and Mayer (19) suggested that the bioavailability through pore water is controlled by “chemical activity”, and the bioavailability through the gut is controlled by “chemical accessibility”. Reductions in these two “complementary sides” of bioavailability can reduce transfer of PCBs and bioaccumulation in the food chain. This new approach for in-situ remediation of contaminated sediments through sorbent amendment is in the development phase, and improved understanding is required to evaluate the applicability for different types of sediments, and effects on biouptake in key test organisms widely used for biouptake studies. Two field demonstration projects are in the initial testing phases, one in Hunters Point Navy Shipyard, San Francisco Bay, and the other in Grasse River, NY. The key objectives of this research were the following: (1) Evaluate the effect of GAC amendment on biouptake reduction in a freshwater oligochaete; (2) Evaluate the effectiveness of different modes of GAC amendment that may be feasible in the field. Past work with GAC amendment had involved mechanical mixing of GAC with sediments for 1 month or longer. In this research we evaluated the effectiveness of placing GAC as a thin layer on sediments, and also mixing for a short duration of 2 min that may be achievable in the field with a mechanical mixing device. (3) Investigate the effect of GAC amendment on PCB uptake kinetics in L. variegatus. Past work had evaluated the effect of GAC on uptake for 28 days exposures and it was not known if the uptake kinetics profiles of untreated and treated sediments were different and if the reductions observed with treated sediments persisted beyond 28-days of exposure. (4) Evaluate the effect of GAC amendment to sediments on the two PCB bioavailability measures of chemical activity (equilibrium partitioning) and chemical accessibility (desorption kinetics). 10.1021/es062934e CCC: $37.00
2007 American Chemical Society Published on Web 05/25/2007
FIGURE 1. When placed as a layer on the sediment surface, activated carbon is slowly worked into the sediment through bioturbation and covered with new layers of worm feces. Image shows the side view of a laboratory microcosm containing L. variegatus 2 days after placement of an uniform layer of activated carbon on sediment.
Materials and Methods Sediment and Activated Carbon. Sediment from the lower Grasse River (Massena, NY) was used in this study after the removal of gravel and debris with diameter larger than 4 mm. The granular activated carbon (GAC) used was type TOG (Calgon Corp. Pittsburgh, PA) with the size range of 75-300 µm (coarse) and 45-180 µm (fine). Culturing of L. Variegatus. Adult mixed age L. variegatus were obtained from Aquarium Center (Randallstown, MD), and temporarily mass cultured in a plastic container with 35 cm × 20 cm × 15 cm (L × W × D) with spring water (pH 7.9, general hardness 220 mg/L as CaCO3, alkalinity 100 mg/L as CaCO3, conductivity 970 µS at 23 °C and ammonia
