Contaminated sediments are a global environmental issue known to affect North America, Europe and Australasia [1
]. This is because sediments serve as an efficient sink for many anthropogenic contaminants associated with various types of industrial activity including nonionic organic chemicals (NOCs) like polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) and cationic metals like cadmium, copper, nickel and lead. For example, in the United States, the U.S. Environmental Protection Agency’s Contaminated Sediment Inventory (CSI) and the National Oceanic and Atmospheric Administration (NOAA) Status and Trends Program have reported large areas of sediments contaminated with anthropogenic chemicals [2
]. The affected areas have been quantified to represent billions of metric tons of contaminated sediment. The presence of these contaminants can have several adverse effects to the environment ranging from acute and sublethal toxicity to invertebrates and fish to benthic community impairments [4
]. The implications of these effects are both ecological and economic in nature. For example, severely toxic sediments may significantly impair a benthic invertebrate community fed upon by a commercially important fish. In turn, the lack of the benthic community may result in a nonviable fishery.
The principle approach to clean-up such contaminated sediments is through remediation. Currently, contaminated sediment remediation methods includes environmental dredging in which the contaminated sediments are removed from a site, monitored natural recovery (MNR) where the site is allowed to bury the contaminated sediments naturally through siltation with clean sediments, and in situ capping [6
]. Capping is similar to MNR, but is enhanced by placing material on top of the contaminated site. In many instances, capping material is simply sand; however, other more chemically-active capping materials have been investigated including the addition of various forms of activated carbon [6
]. The addition of active capping materials seeks to enhance the sequestering of contaminants within the cap and reduce the transport and bioavailability of toxic chemicals associated with the contaminated sediments. Recently, the use of activated carbon as a sediment amendment and potential active capping material has been explored for PCBs, PAHs and pesticides [7
]. These evaluations have also shown promise for possible field application [11
]. For example, for sediments from the Lake Hartwell Superfund site (SC, USA), Werner et al. [12
] reported reducing PCB aqueous concentrations by up to 95% and accumulation by semi-permeable membrane devices (SPMDs) by 78% after one month of activated carbon-sediment interaction. Further, in a preliminary field study at Hunter’s Point Shipyard (San Francisco, CA, USA), Cho et al. [11
] demonstrated activated carbon could be effectively distributed into contaminated sediments and result in evidence of reduced PCB bioavailability to the bivalve Macoma nasuta
several months following activated carbon deployment.
Coal fly ash, another material that has a long history of use in pollution control [13
], is now being considered for capping. Coal fly ash is most often formed during the combustion of coal in the production of electricity at power plants. Like activated carbon, fly ash is formed in a process that can produce a type of refractory and highly sorptive black carbon. In recent studies, black carbon has been shown to strongly adsorb many NOCs [15
]. Several studies have examined the interaction of NOCs and cationic metals with fly ash demonstrating strong adsorption under some conditions [16
]. Fly ash is an appealing remedial material because it is inexpensive, readily available from the very large quantities produced annually from the burning of coal, and reuses a waste substance. For example, according to the American Coal Ash Association and European Coal Combustion Products Association, in 2004 the United States and Europe, generated 64,500 and 43,500 kilotons of fly ash, respectively, of which only approximately 45% was reused (www.ecoba.org
). One of the most common uses of coal fly ash is as an additive in making concrete while the remaining ash is often landfilled.
While several studies have examined the chemical interactions of fly ash and contaminants, few studies have investigated the effects of fly ash on the bioavailability and toxicity of NOCs associated with sediments. In the present study, the objective was to evaluate how effectively several samples of coal fly ash affect the toxicity and geochemistry of a marine sediment environmentally contaminated with PAHs. For this evaluation, a marine amphipod (Ampelisca abdita
) and mysid (Americamysis bahia
) were used. This study is an evaluation of coal fly ash as a possible remedial substance for capping aquatic contaminated sites. For comparison, a form of activated carbon, powdered coconut charcoal, which has been shown to very effectively reduce the toxicity of NOCs in sediments [21
], was included in the study. Finally, to assess the effects of fly ash addition on the nutritional condition of benthic organisms and uptake of possible contaminants, a preliminary 28 d bioaccumulation study with a marine polychaete (Nereis virens
) was performed using reference sediment amended with fly ash and the effects on organism tissue and lipid mass and PAH and mercury accumulation were evaluated.