Preparation for battlefield conditions requires military training activities using the cover of smokes and obscurants (S&O). S&O release active chemicals into the environment. The need to effectively quantify the emissions resulting from the use of S&O, and assess the potential health and environmental impact of these emissions, has become an important issue. In particular, the impact of S&O on the vitality and survivability of threatened and endangered species (TES) that cohabit training areas must be ascertained.
The objective of this project was to study the effects of S&O on fish, cover plants, and insect prey relative to toxicity, fecundity, and food chain disruption. This information will ultimately assist efforts to develop and refine approaches for the conservation, management, and recovery of aquatic TES and ecosystems.
This project studied the direct and indirect effects of actual field deposition of the most common military S&O, fog oil (FO), on relevant surrogate aquatic species for threatened and endangered insect-eating fish, threatened or endangered fish, the insect prey of these fish, and habitat plants using lethal and sub-lethal endpoints such as survivorship, growth, and fecundity. Laboratory and field data were obtained and analyzed to help predict the impacts, effects, and mortality on these relevant aquatic species from exposure to varying concentrations of S&O. Specific measurements on the effects of S&Os included insect larvae and pupae survival, adult emergence, and oviposition; survival, condition, and egg hatching of fish; amount of new growth and biomass for plants; and bioaccumulation of chemicals in tissue residues for all species.
Because U.S. military forces were actively engaged in combat during this project, S&O were largely unobtainable for release testing. Field testing as well as chemical testing and toxicological studies were conducted with the FO quantities present at the time in the laboratory and on the relevant organic dyes that are currently contained in military colored smoke grenades.
Each type of S&O examined has an optimal substrate material for collection. This work reaffirmed that military fog oils are complex hydrocarbon mixtures composed of a multitude of chemically similar components. Their complete analysis and characterization is difficult, if not impossible. Two-dimensional chromatography, despite its enhanced resolution over one-dimensional gas chromatography, is not able to completely characterize such samples.
While field deposition rates are variable, FO and other S&O deposition is generally undetectable beyond 50 m downwind of the source. While varying ambient field conditions pose a number of challenges to acute toxicity testing with FO, the results showed that acute toxicity to a common freshwater crustacean (Daphnia magna) was measurable under field conditions. Also while low levels of FO deposition did not have significant effects on a suite of variables related to midge development from larva to adult, a higher dose of oil resulted in decreased numbers of larvae pupating and successfully emerging from the water surface as adults.
Under field conditions, this project was unable to detect any acute toxicity at other trophic and phylogenetic levels involving green algae, submersed vascular plants, several species and genera of fish, and a common amphibian.
Studies showed that photolysis of FO on water can dramatically increase the toxicity of FO by increasing the amount of water soluble components. At the FO levels observed in the field, photolysis does not increase the toxic effects of the water beneath the oil layer, but at much higher FO concentrations, the water did become highly toxic. Fountain darter larvae are sensitive to relatively low concentrations (e.g., 10 ppm) of photolyzed FO in water. Darter adults, eggs, and juvenile fish are much less sensitive. The duration of this increased sensitivity is unknown, but nonetheless it is limited to the time of emergence from the egg until some point in physiological development to juvenile status.
Based on the results of this project, it was concluded that FO toxicity to aquatic organisms in the field, while measurable, is low and preventable provided that the generation point is located greater than 50 m from a water body containing TES or their prey items and aquatic plant cover.
This distance protection can be enhanced by refraining from FO use during periods when larvae of endangered fish are most likely to be present. Continued buildup of FO on a controlled volume of water can eventually result in a concentration that proves toxic to fish larvae, but this is unlikely in the field where continual water exchange occurs and the environmental water volume is much greater. Conservatively, FO training exercises should be limited to five consecutive days.