Method for Determining the Bioconcentration Factor of Linear Alcohol Ethoxylates

Abstract

Summary 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 because 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 [Test No. 107: Partition Coefficient (n-octanol /water): Shake Flask Method 1995] or OECD 117 [Test No. 117: Partition Coefficient (n-octanol /water), HPLC Method 2004] protocols cannot be used. This paper describes a simple method for accurately determining the BCF 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 "log pseudoPow" value. 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 inexpensive to set up and perform, is accessible to all, is quick and easy to use and verify, and gives clear output.