Environ. Sci. Technol. 1985, 19, 454-457
Isacsson, U.; Wettermark, G. Anal. Chim. Acta 1978,83,
(17) Silverman, R. A.; Gordon, G. Anal. Chem. 1974,46, 178. (18) “CRC Handbook of Chemistry and Physics”,60th ed.; CRC Press: Boca Raton, FL, 1980. (19) Aieta, E. M.; Roberts, P. V.; Hernandez, M. J.-Am. Water Works Assoc. 1984, 76, 64. (20) Bull, R. J. J.-Am. Water Works Assoc. 1980, 72, 299. (21) Pilosof, D.; Nieman, T. A. Anal. Chem. 1980, 52, 662. (22) Crank, J.; Park, G. S. ”Diffusion in Polymers”; Academic Press: New York, 1968. (23) Wheeler, G. L.; Lott, L. F. Microchem. J . 1978, 23, 160.
227.
Isacsson, U.; Wettermark, G. Anal. Lett. 1978, 11, 13. Smart, R. B. Anal. Lett. 1981, 14, 189. Nau, V.; Nieman, T. A. Anal. Chem. 1979,51,424. Saksa, D. J. M.S. Thesis, West Virginia University,Morgantown, WV, 1984. “Standard Methods for the Examination of Water and Wastewater”, 15th ed.; American Public Health Assoc., American Water Works Assoc., and Water Pollution Control Federation: Washington, DC, 1980. Masschelein, W. J. “Chlorine Dioxide”;Ann Arbor Science: Ann Arbor, MI, 1979.
Received for review August 24, 1984. Accepted November 21, 1984.
Laboratory Evaluation of Chemical Dispersants for Use on Oil Spills at Sea J. W. Anderson,* D. L. McQuerry, and S. L. Kiesser Batteiie, Marine Research Laboratory, Sequim, Washington 98382
Data on toxicity and effectiveness of 14 chemical dispersants were combined in a straightforward equation to provide an overall assessment of the relative merits of the oil spill chemicals. When a decision is made by regional response authorities to mitigate the damage of spilled oil to the shoreline, our findings should aid in the selection of an effective low toxicity product. Products were evaluated by using standard toxicity tests with a mysid shrimp (Mysidopsis bahia) and a standard effectiveness test using the Mackay-Nadeau-Steelman (MNS) apparatus. Ratios of dispersant to oil required to maintain 90% dispersions of oil in seawater (15 “C and 30%) with a standard mixing energy (1.0 in. of water pressure) of air flow were derived for each chemical by using Prudhoe Bay crude oil. Toxicity tests with M. bahid were conducted at 25 OC and 25%0 by using freshly hatched juveniles (15 per concentration times 5 concentrations) in small dishes in an incubator.
Introduction There is still considerable controversy regardig the use of oil spill chemicals on spills in U.S. coastal waters. While it is recognized that the magnitude of toxicity produced from the chemical products has decreased considerably with the development of new chemicals, state and federal regulatory agencies generally require approval on a caseby-case basis. Field tests have been conducted to determine the effectiveness of arid application and the resulting concentrations of petroleum hydrocarbons in the water (1). Mackay and Wells (2) have attempted to model the potential impacts of dispersant and dispersed oil under actual spill conditions. We feel that both regulatory agencies and spill response authorities need a sound base of comparative data on a variety of chemical dispersants to properly evaluate the ability to disperse a spill and the outcome of the application. The decision process for responding to oil spill begins with an evaluation of the response options available to authorities, and these have been described elsewhere (3). For the purposes of this paper, it will be assumed that all chemical dispersants tested are available for use with the suitable application equipment. In actuality the response authorities might select one or more of the chemicals to stockpile at strategic locations. The possibility exists that the conditions and location of the spill will not require careful assessment to select a dispersant. If there is little possibility of damage to marine life from the use of available equipment and chemicals, 454
Environ. Sci. Technol., Vol. 19, No. 5, 1985
then application could proceed. In many cases, however, it will be important to consider the relative effectiveness and toxicity of the candidate chemical dispersants. In this event, two different points in a decision tree illustrated (Figure 1) provide for the evaluation of experimental data on effectiveness, cost, and toxicity of the candidate dispersant. The response authority can make much more accurate predictions regarding dispersant application if these data are presented in a clear comparative manner and if the analyses of individual factors have been combined to produce an overall ranking. The objective of this paper is to present values for relative effectiveness and toxicity and show how they can be combined with cost data to provide potential users a means of selection.
Materials and Methods A relatively sensitive marine organism (mysid, Mysidopsis bahia) and an effectiveness system called the Mackay-Nadeau-Steelman (MNS) test were used ( 4 , 5 ) . The mysid has been an important species in tests by the U S . EPA regarding acute and chronic toxicity of several different toxic chemicals (6). Freshly hatched juvenile mysids were placed separately in plastic Petri dishes with 100 mL of the five different dilutions of dispersant (in 25% seawater) and these (15 per concentration) were placed in an incubator at 25 OC. Since the animals have a low capability to store energy reserves, a few (20-50) brine shrimp nauplii were added to each dish a t 48 h. While mortality was recorded on a daily basis, only the 96-hvalues are reported, and logit analysis was used to produce 96-h LCm values and the 95% fiducial limits. The MNS test has been used extensively throughout the U.S., Canada, and Europe, and an intercalibration (round robin) exercise has been conducted (Cashion, personal communication). This testing apparatus is now the designated method for use in Canada to determine the acceptability of oil spill dispersants (7), while a different testing method is used in the United States (8). Our toxicity and effectiveness test results are presented, recognizing that other types of tests will likely produce somewhat different findings. When this research project was initiated (Oct 1981) there were 16 products designated as dispersants on the EPA Acceptance List. Subsequently, our purchase requests to the manufacturers produced the 12 oil spill dispersants used in the majority of testing. In 1983, two dispersants (products N and P) were sent directly from the manufacturers after discussions with the
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Table I. Relative Effectiveness and Toxicity of Chemical Dispersants (15 “C) (25 “C) dispersankoil 96-h LCm, ratio (DORW)” ppm
dispersant Atlantol AT-7 (A) BPllOOWD (B) Finsol OSR-7 (C) Arcochem D-609 (D) Corexit 9527 (E) Corexit 7664 (F) Corexit 8667 (G) Petrocon N/T#4
95% fudicial limits
RETb
4.2-10.5
197
0.130
6.6
0.009 0.038
1.4 204.0
0.5-2.0 165.6-250.5
64 2
0.007
29.0
19.0-45.3
2
0.009 0.500 0.028 0.018
31.9 515.0 2.0 15.0
15.9-64 436-547 1-20 5.6-39.9
3 10 140 12
0.110
6.7
2.2-20.0
170
0.240 0.580 0.150 0.012
16.0 3.5 17.0 8.0
10.4-24.0 2.2-5.7 8.3-34.5 5.1-22.0
150 170
0.008
3.7
(HI Flgwe 2. Relationship of data on dispersed 011 at varlolus dispersantoil ratios (DOR) to model curves. Parameters A-D are determined by characteristicsof the di, dispersants, and test condblons. Y = percent oil dispersed during mixing and X = dispersant to oil volume ratio.
Emergency Response Division of EPA. Toxicity tests were conducted with these two chemicals, and preliminary effectiveness studies were completed. The standard oil used in all tests was Prudhoe Bay crude, since we have been conducting extensive studies on the toxicity of this chemically dispersed oil for marine species (9-11).
Results Effectiveness. Figure 2 shows the results of tests with one of the more effective dispersants and the fit of the data to an equation provided by the first description of the
Ameriod OSD/LT (I) Slick-A-Way (J) Conco K (K) BPllOOX (L) Magnus Maritec
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(N)
Petromend (P)
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22
ODORBois the ratio of dispersant to oil required to disperse 90% of the oil. bRET = relative effective toxity = (DORMX 104)ILCm.
MNS method (revision is in progress) and one developed by our laboratory. It is clear that the more complex exponential model fits the data quite closely, providing an accurate estimate of the dispersant to oil ratio required to produce a 90% dispersion of oil (DORgO). The results of all effectiveness tests with the 14 chemical dispersants are shown in Table I. There are four chemEnviron. Sci. Technol., Voi. 19, No. 5, 1985
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DISPERSWNT EFFECTIVENESS CDOR= @SI
9 OURING
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Figure 3. Dispersant effectiveness during and after (5 min) mixing (in MNS apparatus) at a DOR of 0.05. Only those products producing a 50% or greater dispersion during mixing were compared.
icals (B, D, E, and P) which are very effective, as demonstrated by DO& values of less than 0.01. Another group including C, G, €3, and N exhibit DORgOvalues between 0.01 and 0.10. Dispersants A, F, and I-L are the least effective, with DORw values b e t w e p 0.1 and 0.6. These latter values can be more easily interpreted by considering the fact that it would be necessary to apply the chemicals at a ratio of from 10% to 60% of the volume of the spilled oil to produce a 90% oil dispersion in the water column. No single laboratory test will be capable of producing all the information necessary to accurately rank the effectiveness of a chemical dispersant. It has been pointed out that the true test of these chemicals is in a real field situation. There are, however, difficulties and much expense in assessing the degree of dispersion produced (and maintained) in the open ocean. There is also the problem of obtaining permission to introduce pollutants into the sea, even for scientific purposes. The potential toxicity of dispersants and dispersed oil will be addressed in the following section, but first some variables associated with effectiveness should be considered. In the actual field situation it is clearly an advantage to produce a stable dispersion of the spilled material such that a new slick does not appear minutes later. The MNS test includes sampling during mixing (after 10 min, Table I) and sampling of 5 min following the termination of mixing. Data taken a t the two time intervals can be compared to determine the relative stability of the oil dispersion. Only eight chemicals which had been thoroughly tested (N and P not included) and which produced 50-90% dispersions of oil during mixing a t a ratio of 1:20 (DOR = 0.05) are compared in Figure 3. It is apparent that two products (D and E) produce very stable dispersions with no significant decrease in the amount of oil dispersed after 5 min of settling. Product B, which was one of the most effective chemicals in Table I, did not rank as high in stability as D and E. Other products (G-I) produced dispersions of oil in this apparatus which were even less stable. Presumably the primary factory leading to the stability of the various dispersions is the mean size of oil droplets produced. It was shown (IO)that the mean size of droplets produced by chemical E is about half the size of those generated in the same system by product B (about 2 pm for E compared to 4 pm for B). Another factor that should be considered for selection of an effective dispersant is the ability of the product to disperse spilled material at ambient temperature. It might 456
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1°t
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5
10
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20
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be assumed that temperatures higher than 15 "C (used in all of our tests) would result in a greater degree of dispersion with these test products, since the oil would be less viscous. However, the potential effects of lower temperatures cannot be made without testing several products. One test conducted with product D is illustrated in Figure 4. For a 90% dispersion of oil a t 0 OC it was necessary to increase the ratio of dispersant to oil by approximately 10 times. After further testing was done with other products, it should be possible to determine whether or not this is a consistent relationship among the most effective products. Toxicity. Toxicity tests with the dispersants (at 25 "C and 25 %o) using the mysid Mysidopsis bahia are presented in Table I, including the 95% fiducial limits around each value. Seven of the products tested produced 50% mortality in 96 h at concentrations between 1and 10 parts per million (pprn). Three chemicals (H, J, and L) exhibited LCs0 values between 15 and 17 ppm, and two (D and E) were substantially less toxic (LC50 of 29 and 32 ppm, respectively). Only two products could be defined as nontoxic, since the concentrations of these chemicals required to produce 50% mortality (C = 204 ppm and F = 515 ppm) would not likely ever be reached in a field situation. The same procedure was used to test the comparative toxicity of a standard toxicant, dodecyl sodium sulfate (DSS),and a 201 dispersion of Prudhoe Bay oil (with product E) for these mysids. The DSS produced a 96-h LC, value of 8.7 ppm with 95% fiducial limits of 6.6-11.5 ppm. Dispersed oil provided a 96-h LC50 of 4.0 ppm (2.4-6.8 ppm) which is about one-tenth the 96-h LC, value for product E alone. Questions regarding impacts from oil dispersed into the water with the aid of these chemicals are of major concern, but that subject is beyond the scope of this paper.
Discussion The information presented provides independent evaluations of the effectiveness and toxicity of each of the 14 products tested. It is, of course, possible to study these values and derive a decision on the product best suited for a given spill of toxic material. To aid in this decision process, the data have been combined. When DORS0 values are combined with 96-h LC, values for mysids, we can provide an estimate of the interactions between two selection criteria (Table I). The column in Table I incorporating these criteria is entitled relative effective toxicity (RET). When the DORgOincreases in the nu-
merator or the LCs0 in the denominator decreases, the RET becomes larger, which indicates a less acceptable product. Thus, the chemicals with the lowest RET values (best products) are those that require less dispersant volume to disperse a spill or are less toxic (higher LC50 value) or when the two factors are combined produce the lowest ratio. As a result, for example, products C-E exhibit very low RET values, indicating the best combination of low toxicity and high effectiveness. From low to high, these values represent the relative ranking of the 14 products tested. Products C-E rank the highest, and they are rather widely separated from the other chemicals. Three chemicals rank rather closely around the value of 10 (F,H, and N). Between 20 and 100, products P, L, B, J, and G (respectively) form an intermediate group of chemicals. Only three chemicals (A, I, and K)exhibit combined ranking values that would place them quite low on a list of acceptable products. It may be valuable for the potential dispersant user to consider cost in the final evaluation of a chemical dispersant. The DORw defines the ratio of dispersant to oil needed to produce a 90% dispersion. A calculation can be made t o determine the volume (and subsequent expense) of dispersant required per unit volume of oil on the water. At the 90% effectiveness level two or more dispersants can be compared for relative effective costs (REC),including delivery to the site. Since a low REC and a high LC50 value (low toxicity) are desirable, a division of REC by the LCm will produce the lowest values for the most acceptable products. It should be noted that the system used in this paper gives equal weighting to the toxicity and effectiveness of the dispersants. In certain instances the potential users of dispersant may wish to heavily weight the selection toward only one of the factors evaluated in this paper. The type of data required to make these decisions has been supplied. The reader now has the necessary information on the relative merits of each chemical regarding effectiveness and toxicity to feedback an evaluation into the decision process on Figure 1. He may choose to also consider the relative costs of a smaller group of chemicals. The final decision, to disperse or consider an alternate response, will ultimately be negotiated by response authorities, but it is hoped that the findings presented in this paper will clarify differences between candidate products. Registry No. A, 75602-59-4; B, 63653-52-1; C, 67298-33-3; D, 95312-89-3; E, 60617-06-3; F, 12774-30-0; G, 95312-90-6; H, 95312-92-8; I, 75602-56-1; J, 95312-94-0; L, 39403-84-4; N, 95312-91-7; P, 95312-93-9.
Literature Cited (1) McAuliffe, C. D.; Steelman, B. L.; Leek, W. R.; Fitzgerald, D. E.; Ray, J. P.; Barker, C. D. In “1981 Oil Spill Conference”;American Petroleum Institute: Washington, DC, 1979; pp 269-282. (2) Mackay, D.; Wells, P. G. In “1983 Oil Spill Conference”; American Petroleum Institute: Washington, DC, 1983; pp 65-71. (3) U.S. Environmental Protection Agency “Manual of Practice-Chemical Agents in Oil Spill Control”; U.S.Environmental Protection Agency: Washington, DC, 1982; EPA-600/8-82-010, (4) Mackay, D. S.; Nadeau, S.; Ng, C. ASTMSpec. Tech. Publ. 1978. STP 659. (5) Mackay, D.; Watson, A.; Ng, C.; Nadeau, S. In “1979 Oil Spill Conference Proceeding*; American Petroleum Institute: Washington, DC, 1979; pp 447-452. (6) Nimmo, D. R.; Bahner, L. H.; Rigby, R. A.; Sheppard, J. M.; Wilson, A. J., Jr.; Mayer, F. L.; Hamilink, J. L., Eds. ASTM Spec. Tech. Publ. 1977, STP 634, 109-166. (7) Environment Canada, Environmental Protection Service “Guidelines on the Use and Acceptability of Oil Spill Dispersants”, 2nd ed.; Environment Canada: Ottawa, Ontario, Canada, 1984; EPS 1-EP-84-1, p 31. (8) U.S.Environmental Protection Agency “Revised Standard Dispersant Effectiveness and Toxicity Tests”; U S . Environmental Protection Agency: Washington, DC, 1983. (9) Anderson, J. W.; Kiesser, S. L.; Bean, R. M.; Riley, R. G.; Thomas, B. L. In “1981 Oil Spill Conference”; American Petroleum Institute: Washington, DC, 1981; pp 69-75. (10) Anderson, J. W., final report to the American Petroleum Institute, Washington, DC, 1984, pp 1-58. (11) Anderson, J. W.; Kiesser, S. L.; McQuerry, D. L.; Riley, R. G.; Fleischmann, M. L. In “OilSpill Dispersants: Five Years of Research”; American Society for Testing and Materials: Philadelphia, PA, 1984; STP-40, pp 14-22.
Received for review August 6,1984. Accepted December 17,1984. This work was performed for the Environmental Protection Agency under a Related Services Agreement with the Department of Energy under Contract DE-ACO6-76RLO 1830. The Marine Research Laboratory is part of the Pacific Northwest Laboratory, which is operated for the Department of Energy by Battelle Memorial Institute under Contract DE-ACO6-76RLO 1830. Although the research described in this article has been funded wholly or in part by the Environmental Protection Agency through Interagency Agreement EPA-82-D-X0533 to the Pacific Northwest Laboratory, it has not been subjected to agency review and therefore does not necessarily reflect the views of the agency, and no official endorsement should be inferred. The registered trademarks are referenced for reader convenience in replicating experiments and do not represent endorsement by Pacific Northwest Laboratory.
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