Michael M. Singer

Fate and Effects of the Surfactant Sodium Dodecyl Sulfate

Sodium dodecyl sulfate is the most widely used of the anionic alkyl sulfate surfactants. Its surface-active properties make it important in hundreds of household and industrial cleaners, personal care products, and cosmetics. It is also used in several types of industrial manufacturing processes, as a delivery aid in pharmaceuticals, and in biochemical research involving electrophoresis. SDS synthesis is a relatively simple process involving the sulfation of 1-dodecanol followed by neutralization with a cation source. Purification is accomplished through repeated extraction. It is available commercially in both broad-cut and purified forms. Although its environmental occurrence arises mainly from its presence in complex domestic and industrial effluents, SDS is also directly released in some applications (e.g., oil dispersants and pesticides). Although surfactants are known to significantly contribute to the toxicity of some effluents, no official water quality standards currently exist. Research has shown SDS to be highly biodegradable by a large number of naturally occurring bacteria, and degradation is generally reported to be > or = 90% within 24 hr. The process involves initial enzymatic sulfate liberation and conversion to dodecanoic acid, followed by either beta-oxidative shortening or elongation and desaturation. All surfactant properties are lost after initial sulfate hydrolysis. SDS can enhance absorption of chemicals through skin, gastrointestinal mucosa, and other mucous membranes. Thus, it is used in transepidermal, nasal, and ocular drug delivery systems and to enhance the intestinal absorption of poorly absorbed drugs; enhancement is concentration dependent. Human exposure is mainly through oral ingestion and dermal contact, although cases of respiratory exposure are known. The main sources of daily intake are ingestion of personal care products, residues on insufficiently rinsed utensils, and contaminated drinking water. Uptake, distribution, and excretion of SDS are all rapid. In fish, uptake in various tissues plateaus within 24-72 hr, with elimination occurring within < 24-48 hr; selective accumulation occurs in the hepatopancreas and gall bladder. In mammals, it is readily absorbed via the intestine, colon, and skin. Metabolism is similar in fish and mammals, proceeding from initial omega-oxidation to a carboxylic acid, then to beta-oxidation to butyric acid 4-sulfate, which is finally nonenzymatically desulfurated to gamma-butyrolactone and inorganic sulfate. SDS elicits both physical and biochemical effects on cells, with the membrane the primary target structure. Effects are concentration dependent and range from loss of barrier function and increased permeability to complete cell lysis. Hemolysis in mammals is pH dependent.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of Salinity on Petroleum Accommodation by Dispersants

Abstract The effect of receiving water salinity on the effectiveness of two oil dispersants, Corexits ® 9527 and 9500, was investigated using a recently implemented modified version of the Swirling Flask efficacy test. The dispersants were tested with ten different oils, representing a wide range of physical–chemical properties. Test salinities ranged from 0 to 35 ppt, with temperature held constant at 15°C. Results showed Corexit 9500 to be generally more effective on most of the dispersible oils at most salinities, but performance of both products was significantly affected by salinity. Both dispersants performed best at salinities above 25 ppt, with Corexit 9500 maintaining its effectiveness over a fairly wide range of salinities. Correlations between dispersant effectiveness and various oil physical/chemical properties were highly variable.

A simple continuous-flow toxicity test system for microscopic life stages of aquatic organisms

Abstract This paper describes a flow-through toxicity testing system utilizing a new exposure chamber designed for microscopic organisms. Typically, flow-through testing is conducted with either a serial or proportional diluting system. While generally relying on gravity to drive water flow, as different amounts of toxicant and diluent are combined in glass or plexiglass mixing cells, they are almost always open to the surrounding atmosphere. In contrast, the system described here is based on a simple exposure design utilizing premixed stocks representing each exposure concentration. While the system is entirely closed to the surrounding atmosphere, for testing of volatile organic mixtures in addition to nonvolatile inorganic toxicants, the delivery manifold may be aerated for toxicants of low volatility and high BOD. The system incorporates flexible Teflon gas sampling bags for stock preparation and storage (thus avoiding need for a headspace), and digital unified-drive peristaltic pumps for controlled toxicant delivery. To reduce surface partitioning of toxicants, all system components are constructed of chemically inert materials (Teflon, glass and silicone).

Relationship of some physical properties of oil dispersants and their toxicity to marine organisms

Oil spill dispersants contain one or more surface-active agents. The surfactant properties that allow dispersants to work are nonspecific and can also affect the lipid-bilayer membranes of living cells. One important parameter used to characterize the physical behavior of surfactants is the concentration at which dissolved surfactant monomers begin to aggregate—the critical micelle concentration (CMC). The CMC can be toxicologically relevant because toxic effects are generally linked to monomers rather than micelles. The CMCs of four different oil dispersants (Corexit® 9527, Corexit® 7664, Nokomis® 3, and Slik-A-Way®) in seawater were measured using surface tension as the indicative metric. From these data, predicted surface tensions were calculated for NOEC and median-effect concentration estimates obtained with the same dispersants for the early life stages of four marine species. In three of the four agents, toxicity to all four species occurred below the CMC; however, in the fourth, toxicity to three of the species occurred well above the CMC. No biologically significant relationship between surface tension and toxicity was noted.

ACUTE EFFECTS OF FRESH VERSUS WEATHERED OIL TO MARINE ORGANISMS: CALIFORNIA FINDINGS

ABSTRACT Early experiences with dispersants led to a widely accepted paradigm in the United States that chemically dispersing oil led to increased ecological damage. Since then, dispersant formulations have evolved significantly, leading many in the oil spill response community to revisit the question of whether or not dispersing oil can help achieve an overall net ecological benefit. Spill response must necessarily involve weighing the costs and benefits of both dispersant use and non-use to resources potentially at risk. The majority of comparative data on the toxicity of dispersed and undispersed oil in the literature to date is based on fresh oil. In most circumstances, however, mounting of dispersant operations requires hours to days, making the use of data based on fresh oil problematic. Laboratory-weathered oil has been used in the evaluation of dispersant effectiveness, but its use in toxicological investigations has been limited. Using standardized methods, the authors have compared the acute aqu...

Comparative toxicity of Corexit® 7664 to the early life stages of four marine species

The toxicity of the oil dispersing agent Corexit® 7664 was evaluated using the early life stages of four California marine species: the red abalone (Haliotis rufescens), the topsmelt (Atherinops affinis), a mysid (Holmesimysis costata), and the giant kelp (Macrocystis pyrifera). Spiked-exposure, continuous-flow toxicity tests of 48–96 h were performed in triplicate in closed test chambers. Dispersant concentrations were measured by UV spectrophotometry. In terms of median-effect concentration, the order of test sensitivity was Haliotis>Atherinops>Holmesimysis>Macrocystis. NOEC data also showed Haliotis tests to be the most sensitive, with Macrocystis tests having similar values, followed by Atherinops and Holmesimysis tests, respectively. Toxicity of Corexit® 7664 was compared to that of Corexit® 9527, and the latter was found to be more toxic to all four species; interspecific rankings were similar for the two agents.

A modified swirling flask efficacy test for oil spill dispersants

Abstract The state of California has recently implemented the Swirling Flask Test (SFT) as the standard method for evaluating the comparative effectiveness of oil spill cleanup agents on petroleum products transported through state waters. Use of this ‘standard ruler’ will provide an aid in spill response decision-making. This implementation has involved modifications undertaken to address problems encountered with the existing SFT procedure as specified by the U.S. Environmental Protection Agency (EPA). These modifications involve the actual laboratory procedures, chemical analysis, and data reduction techniques. Primary differences between the California (CAL) and EPA SFT techniques include use of a closed test vessel, chemical analysis by gas chromatography (GC) and correction for dispersant contribution when estimating effectiveness. These new procedures have been used to evaluate the relative efficacy of two surfactant-based dispersants, Corexits® 9500 and 9527, with Prudhoe Bay crude oil.

ACUTE AQUATIC EFFECTS OF CHEMICALLY DISPERSED AND UNDISPERSED CRUDE OIL

ABSTRACT The acute aquatic toxicity of untreated and chemically dispersed Prudhoe Bay crude oil has been investigated using spiked-exposure toxicity tests. Testing was accomplished under closed, flow-through conditions using the sensitive early life stages of three coastal California marine species. Water-accommodated fractions of untreated oil were prepared using low-energy, equilibrium methods, whereas chemical dispersions were prepared at somewhat higher energies. Results showed substantial differences in toxicity both among species and between dispersed and undispersed oil.

Acute Toxicological Consequences of Oil Dispersal To Marine Organisms

ABSTRACT The acute effects of untreated and chemically dispersed Prudhoe Bay crude oil was investigated using modeledexposure toxicity tests. Testing was accomplished under closed, flow-through con...

EVALUATION OF DISPERSANT TOXICITY USING A STANDARDIZED MODELED-EXPOSURE APPROACH

ABSTRACT A spiked-exposure toxicity test procedure has been developed, in which initial dispersant concentrations are diluted at a standardized rate to provide a simple model of exposure experience...