Surfactants bioconcentration

Tolls J, Kloeppersams P, Sijm D (1994) Surfactant bioconcentration - a critical-review. Chemosphere 29 693-717... 

The first-order one-compartment model [43,58], which considers the organism as one homogeneous compartment surrounded by a homogeneous medium, provides an acceptable estimation of surfactants bioconcentration, and has been adopted by the OECD and EPA in their guidelines [3-5]. The BCF can be determined as a ratio of the concentrations of the chemical in the organism (Ca) and the medium (Cw) under equilibrium state or as a ratio of the uptake and elimination constants (ki and, respectively). 

Although the marine environment is the final compartment receiving surfactants, few reports have considered seawater species. To the best of our knowledge, surfactants bioconcentration has been determined in marine algae [8], shrimp [51], mussel [51,66,69] and the stickleback [51]. Although experiments are increasingly being focused on the marine and coastal environments, further work is necessary to measure bioconcentration in these ecosystems. 

The surfactant bioconcentration data available in the literature show considerable variability, due mainly to the different compounds, species, environmental characteristics and analytical procedures used to determine the BCF. Physicochemical properties of surfactants, such as molecular structure, molecular weight, partitioning coefficients (Kom Kqc), water solubility and sorption rate constants all influence their BCF [47]. 

The majority of the bioconcentration data is based on experiments with radiolabelled surfactants. Since the measurements of radioactivity were performed without prior separation of metabolites, the data are not specific for the parent surfactants and therefore not a quantitative measure of surfactant bioconcentration (Tolls et al., 1994). The general trend observed in these data is that bioconcentration of surfactant increases with decreasing values of the CMC, indicating that a relationship between surfactant bioconcentration and hydrophobicity exists (Tolls and Sijm, 1995). This trend has been confirmed with parent compound-specific data measured for LAS (Tolls et al., 1997). 

Tolls, J., P. Kloepper-Sams, D. T. H. M. Sijm, Surfactant bioconcentration—critical review, Chemosphere, 1994,29, 693-717. 

Bioconcentration may occur as a result of continuous exposure to a certain compound, even at concentrations sufficiently low for no toxic effect to be observed. This process is very relevant in the case of surfactants, due with their affinity for interfaces, since they tend to associate with biological membranes (i.e. the interfaces between organisms and their medium). 

Experiments with various species simultaneously carried out in ponds, streams or mesocosms have been reported for non-ionic, anionic and cationic surfactants. NP bioconcentration has been studied in the shrimp Crangon crangon, the mussel M. edulis and the fish... 

Organisms can accumulate chemicals via either ingestion of food or directly from the environmental medium. The overall process is referred to as bioaccumulation. If accumulation from food results in a higher concentration in the exposed organism on a weight basis than in its food, this is called biomagnification. In the environment, surfactants are present mainly in water rather than in air or soil. Therefore, bioconcentration from the water is the most important process leading to bioaccumulation of surfactants. 

Bioconcentration experiments (Tolls, unpublished results Tolls and Sijm, 1999 Tolls et al., accepted for publication) as well as literature data for indicate that LAS and CnEOms are extensively biotransformed by fish (v. Egmond et al., 1995). Therefore, correlations of the bioconcentration behavior with physical-chemical parameters can be expected only if a) biotransformation occurs at the same rate for all CnEOms, or b) it depends on physical-chemical properties of the surfactants. 

Kimerle, R.A., R.D. Swisher, and R.M. Schroeder-Comotto. 1975. Surfactant structure and aquatic toxicity. In Proc. IJC Symposium on Structure Activity Correlations in Studies on Toxicity and Bioconcentration with Aquatic Organisms, pp. 22-25, March 11-13, 1975. 

Tolls,J., R Kloepper-Sams, and D.T.H.M. Sijm. 1994. Bioconcentration of Surfactants a critical review, Chemosphere 29, 693-717. 

The octanol-water partition coefficient for surfactants can not be determined using the shake-flask or slow stirring method because of the formation of emulsions. In addition, the surfactant molecules will exist in the water phase almost exclusively as ions, whereas they will have to pair with a counter-ion in order to be dissolved in octanol. Therefore, experimental determination of K w does not characterize the partition of ionic surfactants (Tolls, 1998). On the other hand, it has been shown that the bioconcentration of anionic and non-ionic surfactants increases with increasing lipophilicity (Tolls, 1998). Tolls (1998) showed that for some surfactants, an estimated log Kow value using LOGKOW could represent the bioaccumulation potential however, for other surfactants some correction to the estimated log Kow value using the method of Roberts (1989) was required. These results illustrate that the quality of the relationship between log Kow estimates and bioconcentration depends on the class and specific type of surfactants involved. Therefore, the classification of the bioconcentration potential based on log Kow values should be used with caution. 

Tolls, J. 1998. Bioconcentration of surfactants. Ph.D. Thesis. Utrecht University, Utrecht, The Netherlands... 

With such a variety of available structures, how does one choose the proper surfactant for a particular purpose Alternatively, why are only certain surfactants used for a particular purpose and not other surfactants Economic factors are often of major importance—unless the cost of using the surfactant is trivial compared to other costs, one usually chooses the most inexpensive surfactant that will do the job. In addition, such considerations as environmental effects (biodegradability, toxicity to and bioconcentration in aquatic organisms) and, for personal care products, skin irritation are important considerations. The selection of the best surfactants or... 

The toxicity of surfactants to marine organisms and their concentration in them depends upon their tendency to adsorb onto them and their ability to penetrate their cell membranes (Rosen, 1999). The parameter AG0ad/a, where AG°a(j is the standard free energy of adsorption of the surfactant at the aqueous solution-air interface (Chapter 2, Section IIIF) and am is the minimum cross-sectional area of the surfactant at that interface (Chapter 2, Section IIIB), was found to correlate well for several anionic and nonionic surfactants with rotifer toxicity. The same parameter was found to correlate well for a series of cationic surfactants with rotifer and green algae toxicity and, for a series of linear alkylbenzenesulfonates, with bioconcentration in fish (Rosen, 2001). 

Consequently, from the data in this section and in Section IIA above, it appears that some chemical structures in the surfactant molecule that promote biodegradability (such as increased length and linearity of the hydrophobic group or decreased oxyethylene content) increase its toxicity to or bioconcentration in marine organisms. 

Relationships have been found between the adsorption properties described above of surfactants and their environmental effects (toxicity, bioconcentration) on aquatic organisms (algae, fish, rotifers). The log of the EC 50 (the surfactant molar concentration in the water at which the organism population is reduced by 50% relative to a no-dose control) and the log of the BCF (the ratio of surfactant concentration in the fish relative to that in the water) have both been shown (Rosen, 1999, 2001c) to be linearly related to the parameter AG°d/u for a series of anionic, cationic, and nonionic surfactants. The values of asm and AG°d were obtained by the methods described above in Sections IIIB and IIIF, respectively. 

With regard to bioconcentration, it is important that surfactants are characterized by combining a lipophilic and a hydrophilic moiety in the same molecule. This is true for all four classes, namely anionic, nonionic, cationic and amphoteric surfactants. Although these classes possess quite different hydrophilic groups, the lipophilic part usually consists of an alkyl chain or alkyl chains of different lengths. There is some evidence that the lipophilic groups of surfactants are metabolized after uptake by aquatic invertebrate species (Daphnia and Chironomus) and fish. 

Water chemistry hardness, ionic strength, etc. are determinant especially for the bioconcentration of surfactants. 

Degradation and metabolic transformation often result in reduced apparent bioconcentration (Spacie, Landrum and Leversee, 1983 Gobas and Schrap, 1990), due not only to the reduction in the concentration of the parent compound but also to the increased polarity of the metabolites formed. The bioconcentration of surfactants as well as, for example, organophosphates (Bruijn and Hermens, 1991a,b) and aromatic amines (Wolf et ai, 1992a) is significantly influenced by the (bio)transformation of the parent compounds. 

As expected, aU these methods (HLB, CPP and Kow) are connected to each other (Cheng, 2003 Cheng et al, 2005). These cited references also showed that Kg can be used to correlate toxicity and the bioconcentration factor of various small alcohol ethoxylate surfactants. HLB is also linked to CMC, as shown for one surfactant family in Figure 5.16. 

Vails, M., P. Fernandez, J. M. Bayona, Fate of cationic surfactants in the marine environment. I Bioconcentration of long-chain alkylnitriles and trialkylamines, Chemosphere, 1989, 19, 1819-1827. 

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