Review and Synthesis of Evidence Regarding Environmental Risks Posed by Munitions Constituents (MC) in Aquatic Systems

Dr. Todd Bridges | U.S. Army Engineer Research and Development Center (ERDC)

ER-2341

Objective

A result of military training and weapons testing activities, munitions are present at numerous current and former DoD sites. Many active and former military installations have ranges and training areas that include aquatic environments, such as ponds, lakes, rivers, estuaries and coastal zones. In addition, until 1970, it was accepted practice to dispose of wastes — including excess, obsolete and unserviceable munitions — in deep water areas. Munitions are also present in water bodies around the world due to combat and training operations. 

The overarching objective of this project was to improve the understanding of the fate and environmental risks of munitions constituents (MC) released from munitions present at underwater military munitions (UWMM) sites. Specific objectives were to (i) compile and review existing evidence regarding environmental exposure and risks posed by MC in aquatic systems impacted by the presence of unexploded or munitions discarded underwater; (ii) decrease uncertainty concerning environmental exposure by summarizing and analyzing environmental fate data collected from the scientific literature; (iii) estimate the release of munitions compounds into the underwater environment under realistic scenarios; (iv) decrease uncertainty concerning hazard by compiling and summarizing ecotoxicity data;  (v) provide revised aquatic criteria and screening benchmarks for MC for use in site-specific ecological risk assessment; and (vi) conduct a screening-level generic risk assessment of MC at UWMM sites.

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Technical Approach

Available data on MC concentrations in exposure media (water and sediment) and biota for marine and freshwater UWMM sites were compiled into a user-friendly database. In addition, concise summaries of MC contamination were prepared for UWMM sites throughout the world. Available data on environmental properties of MC, including dissolution rate constants, sorption constants on soils and sediments, biotic and abiotic degradation rate constants, mobility parameters were compiled and analyzed. To provide further understanding on the fate of MC in aquatic systems, experimental research on the tracking, uptake, translocation, and transformation of MC in the marine environment using stable nitrogen (SERDP project  ER-2122) was summarized. 

Fugacity model calculations were developed for predictions of MC environmental fate. Exposure estimates were enhanced by utilizing multivariate analysis to create a mathematical function correlating published literature data for sediment properties to MC residence time in biphasic sediment systems to provide a more accurate estimate of MC residence time in systems containing solid-phase sediment materials. Existing fate and transport models were integrated into a comprehensive modeling approach to predict MC concentration in sediment and water to estimate the distribution of MC and exposures to organisms. Worst-case scenarios, where a large mass of MC are released to open water were assumed. Model calculations allowed estimates of potential exposure based on initial loading and system residence times based on the inter-media transport of the MC solutes.

A release rate function developed under a previous SERDP project ( ER-1453) was used to provide representative MC source terms via release from munitions under various states of integrity at known UWMM sites. Due to the paucity of data describing the numbers of such potentially breached munitions at such sites, a probabilistic approach was employed using known and statistical distributions for the environmental process parameters that dictate MC release. Such an approach allowed for a cumulative distribution function to be derived for the total release at the former Vieques Navy Training Range (FVNTR), a site for which sufficiently robust numbers of total munitions are known. The total release at this site was then used to provide a conservative concentration estimate for comparison and validation of empirical data collected at the site. Data validated in this manner is suitable for MC source term characterization, and subsequent fate and transport of aqueous MC chemical species at an UWMM site in the overall risk assessment process.

Available data on the biological effects of MC, including lethal and sublethal toxicity to aquatic vertebrates and invertebrates in exposures to spiked water or sediment were compiled into user-friendly databases and summarized. Compiled toxicity data was used for the development of species sensitivity distributions (SSD). The SSD is a statistical distribution constructed by fitting a cumulative distribution function to a series of species toxicity data against the rank-assigned centile which allows the calculation of hazardous concentration (HC). HC5 values representing the probability of 5% of species being affected were derived for use in risk assessment. In addition, aquatic acute and chronic ambient water quality criteria (WQC) and preliminary sediment screening criteria (SSC) were compiled, and when appropriate, revised using recent toxicity data.

To evaluate whether MC has been released to the biologically accessible environment at UWMM sites at levels that could adversely affect fish and invertebrates inhabiting the impacted area using a screening-level risk assessment (SLRA) approach. SLRA was performed to identify MC that may have posed unacceptable risks and those that could have been conservatively ruled out as posing a concern at UWMM sites. Exposure estimates were based on site-specific data while effects characterization were based on effects benchmarks (HC5, WQC and preliminary SSC). 

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Results

Among UWMM sites evaluated, eight waterbodies from four countries for which data has been incorporated into a detailed database and site summaries, including Bahia Salina del Sur (Puerto Rico, USA), Ostrich Bay and Former Seattle Naval Supply Depot Terminal 91 (Washington, USA), Sea Disposal Sites HI-05 and HI-06 (Hawaii, USA), Canada Coastal Waterbodies (Newfoundland and Labrador and Nova Scotia, Canada), Lakes Thun and Brienz and tributaries (Bern, Switzerland). In addition, site summaries were provided for the Oosterschelde (Netherlands) and various Swedish and Norwegian lakes and coastal sites. The compilation and examination of available data revealed that MC concentrations in water, sediment and biota at UWMM sites were largely below detection, with a few samples indicating contamination as highly localized and typically near the UWM. To complement available site data, fate and transport models predicted concentrations of MC in the water column at UWMM sites of the same magnitude or lower than reported data. Available toxicity data derived for freshwater and marine fish, invertebrates and autotrophs was compiled and species sensitivity distributions were derived. Risk to biota was determined to be low at UWMM sites when measured or modeled site concentrations were compared to toxicity data. 

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Benefits

Information presented are critical for the DoD Munitions Response Program to make scientifically defensible risk management decisions with regard to underwater munitions leave in place mitigation and low order detonation (LOD) vs. removal, or blow-in-place (BIP) options. Information compilation, summary, and analysis presented in this document were expected to be extremely useful for developing data quality objectives for investigations of UWMM sites. The ability to leave munitions in place due to lack of ecological impact could result significant savings to DoD. In addition, the assessment will have direct applicability to developing best management practices for a variety of water ranges. This will be used in maintaining the sustainability of DoD operational ranges.

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Points of Contact

Principal Investigator

Dr. Todd Bridges

U.S. Army Engineer Research and Development Center (ERDC)

Phone: 601-634-3626

Fax: 601-634-3528

Program Manager

Environmental Restoration

SERDP and ESTCP

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