Method for Determining the Bioconcentration Factor of Linear Alcohol Ethoxylates

Abstract

Abstract Determination of the potential of surfactants to bioaccumulate in marine species has long been problematic in the chemical hazard and environmental impact assessments performed for offshore operations. Recently, this issue has become increasingly significant as regulators have invoked the precautionary principle and assume that all surfactants with molecular weight of less than 700 will bioaccumulate, leading to an increased number of oilfield chemical products labeled as environmentally unacceptable. The relationship between the bioconcentration factor (BCF) of nonsurfactant substances and their corresponding octanol-water partition coefficient (Pow) value is well studied, and many relationships have been developed. Log Pow is generally, therefore, used as a surrogate for the BCF of nonsurfactant substances. This methodology cannot be applied directly to surfactants because the formal log Pow of such substances is difficult, if not impossible, to determine accurately. By their very nature, surfactants tend to form emulsions or accumulate at interfaces; therefore, the standard OECD 107 or OECD 117 protocols cannot be used. This paper describes a simple method for accurately determining the bioconcentration factor of linear alcohol ethoxylates (LAEs), an important group of nonionic surfactants that are commonly used in the oil industry. Quantitative Structure-Activity Relationship (QSAR) software built on fragment contributions averaged over a large number of mostly nonsurfactant substances is initially used to calculate a pseudo-log Pow. This hydrophobic parameter is then correlated to BCF values determined in flow-through experiments, with excellent agreement (R2 > 0.99). The method involves no animal testing; is cheap to set up and perform, accessible to all, quick, easy to use and verify; and gives clear output. Introduction In areas such as the North Sea, the hazard assessments conducted on chemical products that are intended for use offshore rely heavily on the ecotoxicological properties of toxicity, biodegradation, and bioaccumulation or bioconcentration. To perform a truly meaningful assessment, information on all three properties must be developed. The bioconcentration factor of a chemical substance is the concentration of the substance in or on an aquatic organism (e.g., fish) relative to that in the surrounding medium (e.g., seawater). The substance is thought to partition between the lipids/fats/oils of the organism and the surrounding aqueous phase (Meylan et al., 1999). In general terms, hydrophobic substances will, therefore, have a greater affinity for the lipids/fats/oils and a higher BCF, and hydrophilic substances will remain in the aqueous compartment, leading to a lower BCF. The BCF is the most reliable and accurate indicator of the tendency of a substance to accumulate in aquatic organisms, but it is not commonly determined in the laboratory because the test is expensive and involves the destruction of the test organism.