Sodium Lauryl Sulphate

Sodium Lauryl Sulphate photo by: Newly Natural

Sodium Lauryl Sulphate

Identification of Petitioned Substance

Chemical Names: Sodium lauryl sulfate (SLS)

Other Names: dodecyl sodium sulfate; dodecyl sulfate; sodium dodecyl sulfate (SDS); sodium n-dodecyl sulfate; Chemfinder (2006) lists many additional names

for SLS

CAS Number: 14 151-21-3

Other Codes: X1001083-4 (ACX number); 1315 (HSDB number); SS110 (IMS number); WT1050000 (RTECS number); 079011 (USEPA PC Code)

Trade Names: Aquarex ME; Dupanol WAQE; CT-535 (petition); Richonol AF; Stepanol ME; HSDB (2002a) and RTECS (2005) list over a hundred; additional trade names for SLS and mixtures containing SLS

Characterization of Petitioned Substance

Composition of the Substance: 

SLS has the chemical formula C12H25NaO4S or CH3-(CH2)11-O-SO3-Na+ and its structure is presented in. Figure 1. SLS is a high production volume chemical (i.e., annual production and/or importation volumes above 1 million pounds in the United States). In solution, the sodium cation (Na+) dissociates from the anionic part of the compound (lauryl or dodecyl sulfate), and this anionic compound is the active chemical.

Properties of the Substance:

SLS is an anionic surfactant, which is a class of chemicals used for their detergent properties. One end of the molecule is charged and therefore has an affinity for water, and the other end is nonpolar and soluble in fats/oils. SLS has a negatively charged sulfonate group as its “hydrophilic” end and a saturated 12-carbon chain for its “lipophilic” end. SLS has a faint odor of fatty substances and at room temperature, occurs as white or cream-colored crystals, flakes, or powder (Chemfinder 2006), or a clear to yellowish thick fluid. SLS is stable under ordinary conditions of use and storage but is incompatible with strong acids or strong oxidizing agents (PTCL 2005). When heated to decomposition, SLS emits toxic fumes (sulfur oxides and sodium oxides) (HSDB 2002a).

Specific Uses of the Substance:

SLS is a “soap” type of herbicide and pesticide (PAN 2005). The petitioner is requesting that SLS be included on the National List as a synthetic substance allowed for use in organic crop production as an herbicide with no restrictions. More specifically, the petitioned use would be as a non-selective herbicide to be applied (sprayed) on weeds in the proximity of crops for organic production. NOP §205.601(b)(1) allows “As herbicides, weed barriers, as applicable: (1) Herbicides, soap-based - for use in farmstead maintenance (roadways, ditches, right of ways, building perimeters) and ornamental crops” provided that use does not contribute to contamination of crops, soil, or water. NOP §205.601(e)(7) allows “Soaps, insecticidal” for use as insecticides with the same restriction described for herbicidal soaps.

In general, the major use of SLS is as a synthetic chemical surfactant1 for emulsion2 polymerization (HSDB 2002). Other major uses include the following: in the electroplating industry as an emulsifier; as a wetting agent and adjuvant in insecticides; as an emulsifier and penetrant in varnish and paint remover; in the formulation of injection-molded explosives; as a model surfactant and reference toxicant in aquatic and mammalian toxicological testing; as a whipping agent and surfactant in foods; and as a cleaning agent in a wide variety of personal care products, such as toothpastes, shampoos, bubble baths, shaving creams—any product that requires a thickening effect and the ability to create a lather. HPD (2004) lists household products that include SLS.

Approved Legal Uses of the Substance:

SLS is included as one of 31 “Active Ingredients Which May Be in Minimum Risk Pesticide Products” which are exempt to Section 25(b) of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) (EPA 2000, 2004). SLS is included as one of more than 3,000 total substances that together comprise an inventory often referred to as “Everything Added to Food in the United States (EAFUS)” determined by the U.S. Food and Drug Administration (FDA) Center for Food Safety and Applied Nutrition (CFSAN). The list of substances are ingredients that may be added directly to food which FDA has either approved as food additives or listed or affirmed as “Generally Recognized As Safe” (GRAS) substances (FDA 2005). 

More specifically, FDA allows SLS to be used as a direct food additive (emulsifier) in or with egg whites; as a whipping agent in the preparation of marshmallows; as a surfactant in fumaric acid-acidulated dry beverage base and fruit juice drinks; and as a wetting agent in the partition of crude vegetable oils and animal fats (HSDB 2002). SLS is also an FDA-approved indirect food additive for use as a component of resinous and polymeric coatings and as a component of resinous and polymeric coatings for polyolefin films. 

Action of the Substance:

No specific information was located regarding the mode of action of SLS as an herbicide. In general, the principle value of soap-based herbicides (like SLS) is in their capacity to penetrate green plant tissue and disrupt cellular structure, leading to dehydration and eventual death (Whitacre and Ware 2004). Herbicidal soaps can effectively kill plant parts with which they come in contact within hours; however, they do not affect underground portions of the plant such as roots (Lanier 1998). 

The most effective fatty acid3 salts are those near the carbon chain length of lauric acid (12 carbons). Similarly, insecticidal soaps work on contact only and kill susceptible insects by washing away the protective coating on the surface of the insect and by disrupting normal membrane functions inside the insect, causing cell contents to leak and resulting in the rapid death of sprayed insects (IMP-Alaska 2005). For both soap-based herbicides and insecticides, the organisms must come into direct contact with the spray droplets for the material to be effective.

Status

Sodium lauryl sulfate is not specifically listed for the petitioned use or other uses in the following international organic standards:

• Canadian General Standards Board

• CODEX Alimentarius Commission

• European Economic Community (EEC) Council Regulation 2092/91

• International Federation of Organic Agriculture Movements

• Japan Agricultural Standard for Organic Production