Surrogate parameter for the baseline toxicity content of contaminated water: simulating the bioconcentration of mixtures of pollutants and counting molecules.


A large part of all environmental pollutants can be classified as narcosis-type chemicals with regard to acute aquatic toxicity. This baseline, or narcosistype, toxicity is generally assumed to be brought about through one and the same mechanism. The effects of these chemicals are directly related to their (equilibrium) body burden. This implies that the 'total baseline toxicity content' of an aquatic sample is dependent only on the cumulative body burden of these compounds and that this could be made into an important parameter in risk assessment for the aquatic ecosystem. A simple procedure to simulate the biotic body burden of a mixture of pollutants, by using Cia-Empore disks and to subsequently quantify this cumulative body burden on the basis of molar concentrations by means of vapor pressure osmometry is described. This procedure fulfils the requirements of a true surrogate parameter for the estimation of the total baseline toxicity content of environmental water samples by obviating the need of identifying and quantifying individual compounds and by enabling an estimation of the contribution of baseline toxicity to the overall toxicity of surface waters and effluents. Introduction Approaches in Risk Assessment of Complex Mixtures of Pollutants. The pollution of surface water, wastewater effluents, and groundwater is one of the major problems of our time. In most cases, water pollution encompasses complex mixtures of organic and inorganic contaminants, which normally have to be (qualitatively) identified and (semi)quantitatively analyzed in order to be able to accurately assess the associated risk. Moreover, the risk assessment of contamination with mixtures is confounded by the fact that the combined effect of mixtures may be either antagonistic, additive, synergistic, or anythmg in between. Our insight into these processes of joint toxicity in the environment has been furthered by the distinction into different types ofmixtures as pointed out by Konemann ( 1 ) or Broderius and Kahl (Z), who showed that for mixtures of compounds with the same (or a similar) mode of action effects are completely concentration additive. The (semi)quantitative analyses needed for risk assessment can be performed using a number of basically different approaches: (1) Identification and quantification of all individual pollutant components from an environmental sample and subsequent assessment of the toxic potency of the sample using known or estimated aqueous toxicities for each component (2) Quantitative determination of a so-called 'surrogate' parameter for groups of (known, organic) pollutants. Examples of surrogate parameters are total organic chlorine (TOCl) or extractable organic chlorine (EOC1) as an indication of the amount of organochlorine contaminants or an in-vitro acetylcholinesterase (AChE) inhibition assay as an indication of the amount of organophosphorus andlor carbamate pesticides. (3) Direct determination of the toxicity of an environmental water sample or a concentrate of the sample, in any of a number of types of (simple) toxicity tests such as the Microtox assay (Photobacterium phosphoreum) or a Daphnia test. All mentioned approaches have inherent drawbacks that will, sometimes severely, limit their usefulness in actual risk assessment procedures. Analysis of individual components presupposes the availability of methods of complete and nonselective extraction of all xenobiotics from water-something which is not normally achieved-and the possibility of positive identification of all extracted compounds. Noordsij et al. (3) concluded that, in 1983, not even 5% of all extracted organic compounds could be identified by GUMS techniques. By 1994, this situation had not improved considerably (4) . Moreover, for only a small percentage of actual identified pollutants, pertinent toxicity data are available, and even less is known on how to arrive at a measure of the toxicity of a complex mixture from individual toxicity data and concentration data. Another problem with this approach is that no information is available on what fraction of extracted compounds is actually bioavailable for aquatic lifeforms and what fraction

DOI: 10.1021/es00003a021

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@article{Verhaar1995SurrogatePF, title={Surrogate parameter for the baseline toxicity content of contaminated water: simulating the bioconcentration of mixtures of pollutants and counting molecules.}, author={Harald J. J. Verhaar and Frans J M Busser and Joop L. M. Hermens}, journal={Environmental science & technology}, year={1995}, volume={29 3}, pages={726-34} }