This ESTCP project was designed to demonstrate and validate an innovative technique for evaluating potential risks to amphibians in palustrine wetland environments. This technique builds on previous Department of Defense (DoD) research, which resulted in the development of a tiered amphibian ecological risk assessment (ERA) protocol, as well as laboratory toxicity tests for evaluating potential risks to amphibians due to exposure to contaminated soils and sediments (referred to herein as the soil protocol and sediment protocol, respectively). The soil protocol evaluates impacts to adult salamanders, and the sediment protocol evaluates impacts to larval tadpoles.
When selecting appropriate receptors to derive ERA-based remedial goals, amphibians should be considered since these species play a key ecological role in wetlands and are an important link in ecological food chains, serving both as predators and prey items. However, there is a relative lack of available toxicity data for amphibians. As a result, remedial decisions at sites are often based on data from aquatic or terrestrial species that are not typical of wetlands. These species may be more or less sensitive to chemical stressors than amphibians. This project presents a methodology for evaluating potential risks to amphibians in wetlands and for deriving remediation goals based on these important ecological receptors.
The demonstration was conducted to achieve the following objectives:
These objectives were met by evaluating sediment and hydric soil samples collected from two DoD sites. Based on the results of the toxicity testing and the evaluation of the analytical data, the protocols were deemed appropriate for use at both demonstration sites. In addition, they were sensitive enough to detect lethal and sub-lethal impacts due to firing range contaminant exposure. The ERA framework and lead and copper screening values were also applicable at both demonstration sites.
Traditional ERA methods include the use of non-amphibian benchmarks and toxicity tests to evaluate potential risks to amphibians in wetland environments. The tiered amphibian ERA framework and the soil and sediment exposure protocols were developed to provide a more appropriate assessment of potential risks to amphibians. The amphibian ERA framework is designed to be a part of wetland site investigations and incorporates a variety of field and laboratory methods. These include comparing media concentrations to benchmarks, conducting laboratory toxicity tests, and performing field surveys to evaluate habitat and amphibian populations. Not all methods will be employed at all sites.
Travis Air Force Base (AFB) in California and the Aberdeen Proving Ground (APG) in Maryland were selected as the demonstration sites. Both have amphibian habitat co-located with contamination and associated with firing ranges. The field demonstration focused on lead because copper levels at the selected sites were not expected to be present at levels high enough to result in significant adverse impacts to amphibians.
Soil and sediment exposure tests were conducted with samples containing lead concentrations up to approximately 17,000 mg/kg. The test results demonstrated that field-collected soils and sediments were substantially less toxic than the laboratory-spiked soils and sediments. Therefore, the ecological screening levels derived based on the laboratory validation testing with spiked soils and sediments would have the potential to be overly conservative in assessing risks to amphibians exposed to lead under field conditions.
The application of the tiered amphibian ERA framework, incorporating the soil and sediment exposure protocols, resulted in a more appropriate site-specific assessment of potential risks to amphibians than would have been accomplished using more traditional ERA methods.
The performance objectives for the field demonstration effort were met. Results indicate that the sediment exposure protocol and the amphibian ERA framework are both applicable tools for potential impact investigation to amphibians at wetland sites. Although the soil exposure protocol is a valid approach to investigating toxicity from chemicals in soil to a terrestrial salamander, ethical and financial obstacles preclude its regular application as part of site characterization efforts. However, this method may be appropriate for controlled toxicological investigations designed to derive safe soil levels for particular compounds.
Implementation of this technology will provide a methodology for evaluating potential risks to amphibians in wetlands and for deriving more appropriate remediation goals. The costs for this demonstration indicated that implementation of the sediment exposure protocol will be within ± 20% of the costs of testing with more traditionally used species (i.e., benthic invertebrates). However, the value in expending this additional amount is achieved when making an informed decision about incurring the financial burdens associated with unnecessary wetland remediation and the preventable loss of valuable wetland resources.
Limitations exist for the application of these toxicity testing protocols. Due to the potential seasonal availability of amphibians, the use of these protocols may be limited to times of year when the test organisms are available (generally spring, late fall, and winter for frog eggs and February through May for salamanders). The availability of frog eggs caused a delay in the start of the sediment toxicity tests for both demonstration sites. These seasonal limitations are known to be potential concerns when using field-collected or laboratory-spawned test organisms. These types of seasonal limitations need to be considered when developing a sampling and testing program in support of a site investigation.
In addition to seasonal limitations on the availability of salamanders, the soil exposure protocol requires several dozen adult test organisms and could lead to local extirpation of populations. Based on these limitations, as well as the expense of the assay and supporting parameters, the soil exposure protocol is not likely to be feasible for most site investigations. However, the protocol may be appropriate for controlled toxicological investigations designed to derive safe soil levels.
The transition of the technology to stakeholders and end users is in progress.
These endorsements should facilitate regulatory (e.g., USEPA) acceptance.
Although copper and lead were the focus of this ESTCP project, it is anticipated that these methodologies would be applicable to many different wetland contaminants.