Surface-washing agents

Effectiveness and Toxicity of Some Surface-Washing Agents... 

Photo 89 Surface-washing agents are often applied with small back-mounted sprayers. 

As with dispersants, the use of surface-washing agents is subject to rules and regulations in both Canada and the United States. Only a few products have passed... 

While it has been proposed that surface-washing agents be used on land spills, this is forbidden in most jurisdictions because it moves the oil to the groundwater. It is much more difficult and expensive to clean up subsurface spills or groundwater than to physically remove a surface layer contaminated with oil. 

Photo 90 The person in the foreground is applying a surface-washing agent, while the person in the background is rinsing the treated oil down to a recovery area. (Oil Spill Response Limited)... 

Surface-washing agents contain surfactants, but unlike dispersants, they are used to remove oil from shorelines or similar surfaces. 

While chemical agents other than beach cleaners or surface-washing agents are sometimes suggested for shoreline cleanup, they should not be used as they are not effective and can cause additional problems. Dispersants generally increase the penetration of the oil, which makes them unsuitable for use on shorelines. Solidifiers or recovery agents do not assist with oil recovery. 

Surface-washing agents — Sometimes referred to as dispersants, although the surfactants in surface-washing agents are more soluble in water than in oil. They are applied to shorelines or structures to release oil from the surface. 

Many surfactant mixtures for treating oil spills have been promoted in the past two decades to overcome the extensive problems and costs of physical recovery. Of particular interest to this volume are dispersants, surface-washing agents, and emulsion breakers and inhibitors. All of these are formulations containing surfactants as active ingredients. Dispersants, in particular, promise to reduce the efforts and costs of cleaning up oil spills. 

Dispersants are formulated to disperse oil slicks into the sea or another water body. Surface-washing agents, or beach cleaners as they are sometimes called, are surfactant formulations designed to remove oil from surfaces such as beaches. Emulsion breakers and inhibitors are intended to break water-in-oil emulsions or to prevent their formation. 

There is some concern about whether surface-washing agents can result in appreciable amounts of dispersed oil. Some products currently listed as surface-washing agents do disperse the oil given moderate agitation or sea energies. If this occurs, the situation can be similar to that with dispersants. 

At this time, the only product approved by Environment Canada as a surface-washing agent is Corexit 9580 from Exxon [96]. The U.S. Environmental Protection Agency has approved the following seven agents Corexit 9580, Corexit 7664, Topsail 30, CN-110, Premier 99, Simple Green, and Aquaclean [97]. 

Formulations. Little information is available on specific formulations for surface-washing agents because the formulations vary extensively and many are not patented. Several basic types of formulations... 

Figure 13. Application of a surface-washing agent to an oiled beach during an experiment.

Effectiveness. Field Trials. Several tests of the effectiveness of surface-washing agents have been conducted at actual spills. The results of some of these tests are listed in Table 12 [119, 122, 126-135], Effectiveness was not quantified in any of these field tests, however, in every case, except where dispersants were used in earlier years, the tests were declared to be successful. The earlier dispersant trials showed variable effectiveness and, where penetration was measured, showed that dispersants promoted penetration of the oU into the sub-sediments [135],... 

Table 12. Use of Surface Washing Agents and Major Field Tests... 

Figure 14. Close-up of the sloped-trough test for evaluating surface-washing agents.

Toxicity. The acute lethal toxicity of many surface-washing agents is shown in Table 13 [47, 49], Unlike dispersants, the aquatic toxicity of surface-washing agents varies from nontoxic (> 1000 mg/L) to... 

Clayton, J.R. Tsang, S. F. Frank, V. Marsden, P. Chau, N. Harrington, J. Chemical Surface Washing Agents for Oil Spills, U.S. Environmental Protection Agency Report, EPA/600/SR-93/113,1993. 

---