The environmental effects of chemicals released into bodies of water (marine or freshwater) depend on several factors. Consequences will depend upon not only the chemical’s toxicity and the quantity released, but also its resulting concentrations, the length of time it is maintained in the water column, and the sensitivity of the organisms in the water. Consequences will also depend upon meteorological conditions and local topography. In calm waters, the area exposed may be relatively small and expand slowly; conversely, in rivers or confined waterways, a moving plume can travel downstream quickly, and the area exposed can expand rapidly. In the open sea, tides, currents, and turbulent diffusion usually speed the dilution of released chemicals.
When released into water, chemicals may evaporate, dissolve, float, sink, react further to produce other chemicals, or a combination of these. Actions taken to control the spread of contamination should consider these behaviors.55 For example, depending on a chemical’s density, actions to stop contaminant dispersal should focus on the surface water, the water column, or the bottom water near the underlying sediment. Thus, simple initial estimations of a chemical’s likely behavior and effects can be made based on the physical properties of the chemical in combination with the environmental conditions (air and water temperature, water movement, wind speed and direction). These estimations should be used to select appropriate control actions. Response actions should be proportional to the threat posed by the volume and hazards associated with the chemicals released, realizing that some chemicals become more toxic when exposed to water.
In water, the following contamination control techniques are commonly, and often concurrently, applied:22,37,55,56
- Containment and recovery. Buoyant chemicals often spread across the water surface, forming a slick in a manner similar to oil, although they may not be visible. Exclusion, diversion, river, and shore-sealing booming techniques are often used to contain and control chemical movement on a body of water’s surface, with the aim of using skimmers and other spill response equipment (including sorbent materials) to recover/ remove the spilled material. Other techniques used to control or contain floating chemical slicks include the construction of beach berms, dikes, or dams. Chemicals that sink have the potential to contaminate the riverbed/lakebed/seabed and may persist in the sediment there, although in some cases, sinking agents may be added to contaminated water in an effort to remove the released substance from the water column. The use of dredgers or pumps/vacuums to recover sunken chemicals and contaminated sediment may be considered, although such actions will generate large quantities of potentially contaminated material for disposal. In some circumstances, in situ ‘capping’ of contained sediment may be an option; here, heavier, clean sediment is dumped on top of contaminated sediment.
- Neutralization. Chemicals that dissolve in water will form a growing plume. Some dissolved plumes may be neutralized by the application of flocculants, gelling agents, activated carbon, complexing agents, oxidizers, or reducers. Here, modeling can help predict plume movement and identify potential hazards to nearby resources such as fisheries, water intakes, and recreational areas. However, the ability to contain dissolved chemicals is limited, especially in open waters (at sea) where there is likely to be a delay between incident and response, and large volumes of water are involved. For chemicals that float in water, in situ burning may be possible.
- Sorption and recovery. The spread of floating chemical slicks may be controlled with the use of passive, sorbent materials to recover/remove the spilled material. Although booms containing absorbent material are commonly used, sorbents are generally less useful in the water than on land due to their cost and the large volumes of contaminated waste that are produced and require specialized disposal.
- Dispersal. In some cases, treatment of floating chemicals with dispersants may be possible. This allows the chemical to break up into small droplets that can be dispersed into the water column, both diluting the chemical and promoting its biodegradation. Dispersants also make it easier for waves to break up the chemical slick, which helps prevent the slick from being driven by wind and currents toward shore and helps prevent dispersed chemical particles from re-coalescing into larger droplets that may recreate sheens. As they speed the removal of the chemical from the water, dispersants can reduce a spill’s potential impact on shorelines, sensitive habitats, and wildlife on or near the sea surface. Dispersants may be effective in situations where booming and skimming may not be possible (e.g., in areas with fast currents or choppy waters).
- Vapor suppression. As on land, released gases or volatile liquids have the potential to generate toxic and/or explosive vapor clouds, threatening the health of nearby populations as well as responders. Again, modeling can help identify areas at risk. If possible, leaking vessels may be maneuvered so that these vapors are carried away from populations. Alternatively, knockdown of a vapor cloud with water sprays or foam to stop or deflect its movement may be possible, depending upon the reactivity of the chemical with water, and considering the concomitant generation of large volumes of contaminated water. In open environments, toxic vapors will usually disperse as a result of natural air movement, and the only feasible response action may be to monitor the cloud and its dispersion.
Response options for inland and near shore waters are wider ranging than for offshore waters due to environmental, meteorological, logistical, and cost constraints. In general, unless the spill involves oil, response options in the open sea are limited. In addition to actions taken at the release site, various actions may be taken to reduce the risks to the surrounding population and the environment. Local authorities may decide to evacuate some areas, prevent recreational activities, close beaches, or impose fishing restrictions to protect fishermen and/or consumer health.56
Footnotes
22. Levy, L., Smithson, A.E. (2000). Rethinking the Lessons of Tokyo. Ataxia: The Chemical and Biological Terrorism Threat and the US Response Stimson Report 35. (pp. 71-111). Global Health Security.
37. U.S. Environmental Protection Agency. (2016). National Response System.
55. Purnell, K. (2014, May 22). Are HNS Spills More Dangerous than Oil Spills? (2009). International Tanker Owners Pollution Federation Ltd. Interspill Conference & the 4th IMO R&D Forum, Marseille, France, May 2009.
56. Chilcott, R.P., Larner, J. & Matar, H. (2018). Primary Response Incident Scene Management (PRISM): Guidance for the Operational Response to Chemical Incidents. 1(2nd ed). Office of the Assistant Secretary for Preparedness and Response, Biomedical Advanced Research and Development Authority.