Grantee Research Project Results

Dissolved Organic Carbon Characteristics in Metal-Rich Waters and the Implications for Copper Aquatic Toxicity

EPA Grant Number: FP917448
Title: Dissolved Organic Carbon Characteristics in Metal-Rich Waters and the Implications for Copper Aquatic Toxicity
Investigators: Dee, Kato Tsosie
Institution: Colorado School of Mines
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 2012 through July 31, 2015
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2012) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Environmental

Objective:

This research will test two main hypotheses. First, fractionation of DOC occurs when it is partially removed from stream water by adsorption to precipitated hydrous iron (HFO) and hydrous aluminum oxides (HAO). Secondly, the remaining DOC will have poorer metal binding properties than the fraction that sorbs to the HFO and HAO. An alternative hypothesis also will be examined, namely that variations in DOC characteristics will arise from differences in source (i.e., wetlands, streams, etc.), and this will be more significant than fractionation in defining DOC metal binding properties. The consequence of these processes is that the protective effects of DOC with respect to aquatic metal toxicity will be reduced.

Approach:

The sample collection and analysis methods will focus on aqueous and sediment media associated with AMD impacted aquatic systems that will test the hypothesis. Sites are selected for this research based on their watershed environment and if they are known to have been impacted by AMD. Samples collected at each site will include analysis for metals, water quality parameters (i.e., pH, conductance, etc.), major anions (i.e., sulfate [SO4], chlorine [Cl], etc.), alkalinity and dissolved oxygen. Sediment from each site will be leached with a mild acid to release adsorbed metals and DOC. These results will provide a thorough chemical profile at each site and the impact of AMD. The fulvic acid component of DOC in each sample will be isolated for later use for ultraviolet-visible spectroscopy (UV/VIS) and fluorescence, toxicological and fractionation characterization.

Expected Results:

This research will aim to quantify the effects of fractionation between DOC, HFO, HAO, free copper and the behavior of resultant free DOC in the water column on the toxicological effects of copper. Fractionation between DOC, free metals and iron (Fe) and aluminum (Al) hydroxides will be examined further in this research, particularly in AMD impacted aquatic systems that have variable Fe, Al and DOC chemistry. This variable chemistry likely will demonstrate differences in DOC fractionation with the free metal and HFO/HAO components. It is anticipated that the fraction of DOC remaining in the water will have lesser binding capacity than the fraction that has undergone adsorption or complexation with other ligands. The “depleted” DOC fraction will be characterized by specific UV absorbance and excitation-emission matrix (EEM) analyses. Moreover, the resultant DOC-Copper (Cu) species is especially important for aquatic toxicology applications. A better understanding of the DOC fractionation characteristics as related to bioavailability of free metal ions will provide significant acute and chronic LC50 data to more accurately represent metal-laden AMD impacted waters.

Potential to Further Environmental/Human Health Protection
Results from this project potentially will have significant regulatory impacts that will provide a continuum to improving water quality for human health and aquatic ecosystems. This project likely may provide some better insight to the effectiveness of DOC-rich effluent from treatment systems in mitigating the toxicological effects of heavy metals. As a result, this technology may aid efforts to improve the health of numerous fisheries impacted by AMD originating from abandoned mines and thus potentially lead to improved recreational opportunities and tourism. Regulatory decisions based on utilizing the Biotic Ligand Model for water quality certification standards likely will be enhanced by this research.

Supplemental Keywords:

dissolved organic carbon (DOC), acid mine drainage (AMD), toxic heavy metals

Progress and Final Reports:

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.