Surfactants environmental assessment

Fig. 2 Environmental assessment of surfactants is based on values of biodegradation and aquatic toxicity. A surfactant must lie within the shaded areas in order to meet the OECD regulatory directives...

Routledge, E.J. and Sumpter, J.P. (1996). Estrogenic activity of surfactants and some of their degradation products assessed using a recombinant yeast screen. Environmental Toxicology and Chemistry 15, 241-248. 

Roy, D. and M. Liu. 1997. Anthracene removal from soil columns by surfactant. Pages 263-288 in P.N. Cheremisinoff (ed.). Ecological Issues and Environmental Impact Assessment. Gulf Publishing, Houston, TX. 

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The assessment of whether a substance presents a risk to the receiving environmental compartment is based on a comparison of the measured or predicted environmental concentration (PEC) of the chemical of concern with the predicted no effect concentration (PNEC) to organisms in the ecosystem. This is briefly discussed in Chapter 7.4. Studies carried out so far, e.g. by Vandepitte and Feijtel [91], show that the risk of anionic surfactants such as LAS, AE and AES for the aquatic environment is low, since the PECs are always lower than the maximum permissible concentrations. 

The major part of the biosphere is aerobic and consequently priority has been given to the study and assessment of biodegradability under aerobic conditions. Nevertheless, there are environmental compartments that can be permanently (e.g. anaerobic digesters) or temporarily anaerobic (e.g. river sediments and soils) and surfactants do reach these. The majority of surfactants entering the environment is exposed to and degraded under aerobic conditions. This is the predominant mechanism of removal even in cases of absence of wastewater treatment practices (direct discharge) and it is estimated that less than 20% of the total surfactant mass will potentially reach anaerobic environmental compartments [1]. Only in a few cases, however, will the presence of surfactants in these compartments be permanent. The presence of surfactants in anaerobic zones is not exclusively due to the lack of anaerobic degradation. Physico-chemical factors such as adsorption or precipitation play an important role as well as the poor bioavailability of surfactant derivatives (chemical speciation) in these situations. 

Surfactants and their biotransformation products enter surface waters primarily through discharges from wastewater treatment plants (WWTPs). Depending on their physicochemical properties, surface-active substances may partition between the dissolved phase and the solid phase through adsorption onto suspended particles and sediments [1,2]. Several environmental studies have been dedicated to the assessment of the contribution of surfactant residues in effluents to the total load of surfactants in receiving waters. This contribution reviews the relevant literature describing the presence of linear alkylbenzene sulfonates (LASs) and in particular of their degradation products in surface waters and sediments (Table 6.3.1). 

The sustainable management of sediments, in addition to water, soil and sludge environmental matrices, in relation to surfactant regulations, is also an important and relevant issue. The US EPA has recently shown concern regarding the levels of surfactants in sediments and has thus released a Draft Contaminated Sediment Science Plan. In this draft, recommendations for the development of analytical methods and evaluations of the toxicity and risk assessment of Emerging endocrine disrupters like APEOs and their metabolites in sediment samples are outlined. 

Figure 1. Factors considered in determination of environmental hazard assessment for anionic surfactants.

Exposure of an organism to a surfactant in surface water will depend on the amount of material used, disposal practice, removal rate during sewage treatment, dilution in the receiving stream, and sorption on particles or aquatic dissolved organic carbon. The exposure component of an environmental hazard assessment utilizes information from the fate studies described in the previous section, mathematical modeling to predict environmental concentrations, and environmental monitoring to verify model predictions. 

Risk assessments for anionic surfactants are obtained by comparing environmental exposure concentrations to effect levels (the quotient method). A protection factor that reflects the environmental safety of the material is calculated by dividing the exposure level by the effect concentration. If the protection factor is greater than 1, the material is deemed safe. Although this approach to assessing risk yields a numerical value that could be interpreted as the relative safety of a compound, comparisons of protection factors for different compounds should be avoided. The risk assessment for each material must be considered separately because of differences in chemical properties and differences in the database used to obtain the protection factor. In addition, the degree of uncertainty in the exposure and effect... 

Lewis MA (1990) Chronic toxicides of surfactants and detergent builders to algae A review and risk assessment. Ecotoxicology and Environmental Safety 20 123-140. 

Environmental risk assessment has to address all compartments of the environment like air, water, sediment and soil. The partition of a substance between the various compartments is controlled by the physico-chemical parameters of a substance. Water-soluble or dispersible surfactants and emulsifiers will predominantly affect the water and sediments. As surfactants are widely used not only in manifold industrial applications but also in consumer products the pollution is widely dispersed. The contribution of surfactants used in polymer production is comparably rather small but has nevertheless to be controlled and monitored. 

Another extremely useful method for cac determination, especially in the light of high sensitivity, is fluorescence emission spectroscopy [15]. Some aromatic water-insoluble dyes that are present in trace amounts in mixed polyelectrolyte-surfactant solutions have an ability to solubilize within the self-assembled surfactant aggregates and to change their photophysical properties because of the change of environmental polarity. Through this, they offer a very sensitive method for the determination of cac values. A typical and lately frequently used compound is pyrene, which is used as a fluorescence probe to assess various micellar properties. Pyrene exhibits a polarity dependent fluorescence spectrum with the ratio /,//3 (the ratio of the intensity... 

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