Pore Water Collection, Analysis and Evolution: The Need for Standardization.

Investigating the ecological impacts of contaminants released into the environment requires integration of multiple lines of evidence. Collection and analysis of interstitial water is an often-used line of evidence for developing benthic exposure estimates in aquatic ecosystems. It is a well-established principle that chemical and toxicity data on interstitial water samples should represent in-situ conditions; i.e., sample integrity must be maintained throughout the sample collection process to avoid alteration of the in-situ geochemical conditions. Unfortunately, collection and processing of pore water is not standardized to address possible geochemical transformations introduced by atmospheric exposure. Furthermore, there are no suitable benchmarks (ecological or human health) against which to evaluate adverse effects from chemicals in pore water; i.e., empirical data is lacking on the toxicity of inorganic contaminants in sediment interstitial water. It is clear that pore water data is best evaluated by considering the bioavailability of trace elements and the partitioning of contaminants between the aqueous and solid phases. It is also evident that there is a need for sediment researchers and regulatory agencies to collaborate in developing a standardized approach for sediment/pore water collection and data evaluation. Without such guidelines, the number of different pore water collection and extraction techniques will continue to expand, and investigators will continue to evaluate potentially questionable data by comparison to inappropriate criteria.

Natural attenuation of coal combustion waste in river sediments.

The weathering of coal combustion products (CCPs) in a lotic environment was assessed following the Tennessee Valley Authority (Kingston, TN) fly ash release of 2008 into surrounding rivers. Sampled materials included stockpiled ash and sediment collected from 180 to 880 days following the release. Total recoverable concentrations of heavy metals and metalloids in sediment were measured, and percent ash was estimated visually or quantified by particle counts. Arsenic and selenium in sediment were positively correlated with percent ash. For samples collected 180 days after the release, total concentrations of trace elements downstream of the release were greater than reference levels but less than concentrations measured in stockpiled ash. Total concentrations of trace elements remained elevated in ash-laden sediment after almost 2.5 years. A sequential extraction procedure (SEP) was used to speciate selected fractions of arsenic, copper, lead, nickel, and selenium in decreasing order of bioavailability. Concentrations of trace elements in sequentially extracted fractions were one to two orders of magnitude lower than total recoverable trace elements. The bulk of sequentially extractable trace elements was associated with iron-manganese oxides, the least bioavailable fraction of those measured. By 780 days, trace element concentrations in the SEP fractions approached reference concentrations in the more bioavailable water soluble, ion exchangeable, and carbonate-bound fractions. For each trace element, the percentage composition of the bioavailable fractions relative to the total concentration was calculated. These SEP indices were summed and shown to significantly decrease over time. These results document the natural attenuation of leachable trace elements in CCPs in river sediment as a result of the loss of bioavailable trace elements over time.

Using artificial burrows to evaluate inhalation risks to burrowing mammals.

Since the onset of plutonium production at the U.S. Department of Energy's Hanford Site, several hundred cubic meters of carbon tetrachloride (CCl4) has been discharged to the soil column, resulting in a dispersed CCI4 vapor plume in the subsurface. Inhalation of volatile organic chemicals could be an important exposure pathway for burrowing animals there. Historical levels of CCl4 in soil pore gas exceeded the inhalation ecological screening level for CCl4. Thus, the inhalation exposure pathway was evaluated with the use of artificial burrows deployed at locations that had elevated levels of CCl4 in soil gas. Artificial burrows were designed on the basis of information available for Hanford Site fossorial wildlife. After installation, the artificial burrow atmosphere was sampled and analyzed for CCl4 and its degradation products: chloroform, methylene chloride, and chloromethane. Sampling was repeated on 3 occasions to capture varying atmospheric conditions affecting exposure concentrations. CCl4 was detected in the artificial burrows, and maximum exposures were observed during relatively low barometric conditions. The highest CCl4 detections were still well below the inhalation-based ecological screening level and CCl4 degradation products were never detected. This study shows that artificial burrows are an efficient method for obtaining relevant exposure data and illustrates the utility of directly measuring the medium for exposure under ecologically realistic conditions.

Collection and evaluation of existing data: an ecological risk assessment perspective.

All scientific disciplines rely to some degree upon existing data to design new studies, test hypotheses, and make decisions. Because existing data can take many forms, a framework for addressing the quality of these data must be general and comprehensive. By nature of this inclusiveness, quality categories for existing data are necessarily broad. Effective employment of existing data requires the development of specific acceptance criteria from broad data quality categories. A framework is presented for collecting and evaluating existing data with examples of Environmental Protection Agency projects employing a tiered data review. The systematic planning inherent in a tiered review is described and attendant data quality considerations are developed in the context of an ecological risk assessment; specifically, the process is illustrated by defining an ecologically protective concentration of a chemical in soil.