Oil spill dispersants in freshwater and marine water

​​​Toxicant default guideline values for protecting aquatic ecosystems

October 2000

Description of chemical

Oil spill dispersants are intended to reduce the overall environmental impact of an oil spill, if they can be applied at the appropriate spill location and within the window of opportunity to treat oil slicks. Hence it is necessary to have substantial stocks of dispersants available at strategic locations around the coast of Australia and New Zealand. These dispersants should have undergone prior approval by the relevant authorities. Two key considerations in this management approach are toxicity and efficiency (AMSA 1991). A total of seven oil spill dispersants are currently approved for use in Australian marine waters (Gilbert 1996). These (as registered trade names) are: Ardrox 6120; BP-AB; Corexit 9527; Corexit 9550; Shell VDC; Slickgone NS and Tergo R-40.

In New Zealand up to 25 dispersants are approved, including some of the above, plus others, such as Enersperse 1037, Corexit 9600, Simple Green and Rochem R40 (NZ Marine Protection Rules, Part 132).

The Australian requirements for toxicity testing include testing with Australian tropical (30 ±3°C) and temperate (15 ±3°C) species (AMSA 1991). The only New Zealand requirements are that the tests be internationally recognised and that the organisms are relevant to New Zealand waters. Unfortunately, few of these data have been published in peer-reviewed literature but Gilbert (1996) has tabulated general toxicity rankings for the Australian dispersants and indicated that they mostly fall into IMO GESAMP (1996) slightly toxic (> 10 mg/L) rank or practically non-toxic (100 to 1000 mg/L) rank (Table 8.3.25). These data are mostly from material safety data sheets, restricted investigation reports, laboratory test results and company information.

Table 8.3.25 Oil spill dispersants, type and general toxicity ranking (from Gilbert 1996)

The ‘types I–III’ in Table 8.3.25 refer to the three general types of dispersants, which should not be confused with the older classification of generations. The first generation of dispersants, such as those used in the Torrey Canyon incident in UK in 1967, were a mixture of detergents, degreasers and solvents, and are no longer either in use or approved for use in Australia or New Zealand.

Type I: are hydrocarbon-based for use on foreshores and neat at sea from vessels

Type II: are concentrates that have been diluted with water or use from vessels

Type III: are concentrates for application by air, from vessels or on foreshores.

Most dispersants approved for use in Australia are both type II and type III concentrates.

Oil dispersants work on the principle of breaking up the oil slick into fine suspension so that natural biodegradation processes are enhanced and direct damage to wildlife or foreshores from floating oil is minimised.

The effectiveness of dispersants depends on a number of factors including the type of oil and its weathering properties, the age of the slick, temperature and movement of the oil-water interface to enhance mixing, apart from properties of the dispersant itself (Swan et al. 1994, Gilbert 1996). Dispersants are applied from ship-borne sprays as mixtures with water, from fixed-wing spray aircraft or from helicopters carrying spray buckets.

Use of dispersants in most states is restricted to open waters greater 5 m in depth, to minimise damage to benthic organisms or nursery stocks (SPCC 1981). Chemical dispersants may be used in coastal waters less than 5 m in depth if water circulation, exchange and tidal effects remove the dispersed oil quickly and effectively. In Australia the combating of major oil spills is controlled under the National Plan for Prevention of Pollution of the Sea by Oil (NATPLAN) and, in the case of particular spills, is coordinated by appropriate State authorities. This process assists in targeting of resources for combating spills. Appropriate use of dispersants to minimise environmental damage (both from the oil slick and the dispersed oil) is just one of the considerations in combating an oil spill. Environmental issues and sensitive coastal communities are identified in Coastal Resource Atlases (CRAs) funded under the National Plan and being completed for the whole coast of Australia (e.g. NSW EPA 1994). These CRAs may also specify areas appropriate for dispersant use or areas of environmental concern.

It is generally considered that the toxicity of oil and oil plus dispersant is of greater concern than the dispersant alone (Swan et al. 1994). Wells (1984) concluded that, if third generation dispersants are used at recommended doses, the expected initial concentration in marine waters would be between 0.1 and 10 mg/L, which he considered to be below threshold concentrations that cause toxicity to most pelagic organisms.

Dispersant use in oil spill pollution and emergency situations, and according to established guidelines, such as those specified in the coastal resource atlases, is intended to minimise environmental damage. It would not be appropriate to override contingency planning by imposing guideline levels onto the spill control process. Spiked, declining exposures (SD) are considered to be more indicative of concentrations under conditions of dispersant use in spill situations. SD figures were between 2 and 20 times higher than corresponding standard exposure test figures.

The toxicity of a few of the dispersants is given below. There were insufficient data to derive a freshwater guideline for any of the dispersants and environmental concern level (ECL) values are suggested in the text.

Aquatic toxicology

BP 1100 X (or BP AB)

Marine fish: Pleuronectes platessa (plaice), 48-hour LC50, 7100 mg/L (i.e. x 1000 µg/L).

Marine crustacean: two species (scud and shrimp), 96-hour LC50, 150 to 300 mg/L. An additional species, Carcinus maenus (crab), 48-hour LC50, 20,000 mg/L.

Marine molluscs: two species, 48 to 96-hour LC50, 25 to 3700 mg/L.

Corexit 7664 (CAS 12774-30-0)

Freshwater fish: one species, Oncorhynchus kisutch, 96-hour LC50, 15.8 mg/L (i.e. x 1000 µg/L).

Marine fish: two species, 96-hour LC50, 5000 to 10,000 mg/L.

Marine crustacean: two species, 48-hour LC50, 5000 to 10,000 mg/L.

Marine molluscs: two species, 96-hour LC50, Cardium edule, 1 mg/L and Aequipecten opercularis, 250 mg/L.

Corexit 8667 (CAS 95312-90-6)

Marine crustacean: one species, Artemia sp, 48-hour LC50, 1225 mg/L.

Corexit 9527 (CAS 60617-09-3)

Freshwater fish: one species, O. mykiss, 260 mg/L.

Marine fish: two species, 48 to 96-hour LC50, 2.8 to 115 mg/L. George-Ares and Clark (2000) reported a range of 42 to 293 mg/L for nine species.

Marine crustacean: four species, 48 to 96-h LC50, 4.3 to 217 mg/L. A range of 2.4 to > 1000 mg/L (16 species) was cited by George-Ares and Clarke (2000).

Marine molluscs: no suitable data were available but George-Ares and Clark (2000) cited 48 to 96-h LC50 of 1.6 to 100 mg/L for three species.

Marine macrophytes: one species, Thalassia testudium, 96-hour LC50, 200 mg/L.

Marine algae: 1 sp, 48-hour EC50, 30 mg/L (George-Ares & Clark 2000).

The data from George-Ares and Clark (2000) were not received in time to recalculate the current trigger value but are within the range of sensitivities of the data used.

Field and mesocosm studies: Field and mesocosm studies have largely focussed on toxicity of oil and dispersed oil. See the section on ‘Oil and petroleum hydrocarbons’.

Corexit 9550

It was not possible to adequately evaluate the recent data by George-Ares and Clark (2000) for the current trigger value calculations. However, the unscreened data that met the basic time requirements (≥ 48-hour duration) were used to calculate a trigger value. Marine and freshwater species were grouped together at this stage. There were sufficient data for calculation by the statistical distribution method but, as these had not been fully evaluated, the figure was reported as a low reliability trigger value only.

Fish: seven species, 48 to 96-h LC50, 25 to 354 mg/L; Brachydanio rerio had 24-h LC50 >400 mg/L.

Marine crustaceans: five species, 48 to 96-h LC50, 3.5 to 48 mg/L. A 6-hour LC50 of 8103 mg/L was reported for Palaemonetes varians and spiked declining exposures (107 minutes half-life) were reported for Mysidopsis bahia of 790 to 1038 mg/L and for Holmesimysis costata of 158 to 245 mg/L. These were not used but give an indication of reduced risk for short-term exposures. The NOEC for H. costata was 11 to 142 mg/L.

Marine molluscs: one species, 24-hour EC50, Polinices conicus (snail), 42.3 mg/L. A 48-hour NOEC of 0.7 mg/L was reported for Haliotis rufescens (red abalone), along with spiked declining exposure NOEC of 5.7 to 9.7 mg/L and LC50 of 12.8 to 19.7 mg/L (the latter were not used).

Marine algae: two species, 72 to 96-hour EC50, 0.7 and 20 mg/L.

Australian and New Zealand data

There have been a number of tests conducted on dispersant toxicity in Australia, particularly to satisfy the basic approval requirements of AMSA (1991). Unfortunately, most of these data are in unpublished or confidential reports and cannot be assessed. It is understood that Corexit 9550 was around 2 orders of magnitude less toxic to temperate crustaceans than Ardrox 6120 or Corexit 9527, the latter two being of similar toxicity (T Gilbert, pers. comm. 1997, J Wall pers. comm. 1997).

Ahsanullah et al. (1982) tested the toxicity of BP-AB to the crab Paragrapsus quatridentatus but could not obtain a statistically valid 96-hour LC50. The results appeared to lie between 1300 and 2200 mg/L, indicating low toxicity.

Guidelines

References

Ahsanullah M, Edwards RRC, Kay DG & Negilski DS 1982. Acute toxicity to the crab Paragrapsus quadridentatus (H Milne Edwards), of Kuwait light crude oil, BP/AB dispersants, and an oil-dispersant mixture. Australian Journal of Marine and Freshwater Research 33, 459-464.

AMSA 1991. Oil dispersants: Guidelines for acceptance, Australia. Australian Maritime Safety Authority, Belconnen, ACT.

ANZECC & ARMCANZ 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.

George-Ares A & Clark J R 2000. Aquatic toxicity of two Corexit ® dispersants. Chemosphere 40, 97–906.

Gilbert TD 1996. Proceedings of the Sixth National Plan Scientific Support Coordinators Workshop, Tasmania, December 2–6, Australian Marine Science Association, Belconnen, ACT.

SPCC 1981. Guidelines for controlling oil spills in maritime waters of New South Wales. State Pollution Control Commission, Sydney.

Swan JM, Neff JM & Young PC (eds) 1994. Environmental implications of offshore oil and gas development in Australia: The findings of an independent scientific review. Australian Petroleum Exploration Association, Sydney.

Wells PG 1984. The toxicity of marine oil dispersants to marine organisms: A current perspective. In Oil spill chemical dispersants: Research, experience and recommendations, ed TE Allen, ASTM STP 840, American Society for Testing and Materials, Philadelphia, Pa, 177-202.