Toxicity measurements in concentrated water samples - Rivm

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Environmental parameters As discussed, several parameters have a bearing on extraction, which are summarized in Table 3-2. So far, no experimental concessions have been made to reduce the influence of environmental parameters during extraction. Temperature Adsorption of hydrophobic substances increases as the temperature rises. Adsorption of hydrophilic substances such as nonionogenic surfactants decreases. Therefore we chose to carry out the extractions at ambient temperature. Light Surface water samples usually contain different forms of life, e.g. algae. In light, algae continue primary production, resulting in an increase in pH, which in turn can change the effectiveness of the adsorption of chemicals. Photodegradation of components may also occur. For this reason, extractions were carried out under reduced light conditions. In addition to the parameters mentioned in Table 3-2, it was also checked if the concentration of organic solvents in the water could disturb the extraction. It was found that only above a solvent concentration of 20 % (!) extraction efficiency decreased. Such values are far above values found in surface waters. Table 3-2. Summary of the influence of some parameters on the extraction efficiency. For more detailed information see Struijs and Van Buren (1995). extraction Parameter Substance group efficiency when parameter value increases pH Ionic strength, NaCl Temperature Water solubility acids - bases + nitrosamines + nonionogenic detergents + hydrophobic + hydrophilic - extremely hydrophobic - weakly hydrophobic + weakly hydrophilic + extremely hydrophilic - RIVM Report 607013010 33
3.3.2 Elution from XAD Solvent selection In order to be extracted from the XAD, a substance must be desorbed from the resins. The choice of solvent, or combination of solvents, is a key factor in the effectiveness of elution. The choice of solvent for the purpose of substances concentration was based on solvent capacity, boiling point, vapour pressure, toxicity in bioassays and health safety procedures. In principle, several solvents are suitable for elution of XAD, including liquid carbon dioxide, using supercritical fluid extraction (Struijs et al., 1998). For several reasons, acetone proved to be most suitable for the purpose (Struijs and Van de Kamp, 2001). It was selected because of its general properties as a solvent – a wide range of chemicals are soluble in acetone – its volatility and its low boiling point (56 °C), which make it easy to remove (see textbox on solvent properties). The solvent must be free of impurities to avoid addition of unintentional toxicity. Solvent properties For desorption from XAD, the substance must be soluble in the solvent that is used to elute the XAD. Preferably, the substance should have more affinity for the solvent than for XAD. The affinity can be characterised by the Hildebrand solubility parameter δ, which is related to the polarity of a substance. The higher δ, the more polar a substance. For good desorption, δ of the substance should be closer to δ of the solvent than to δ of the XAD. Generally, compatibility between two materials can be expected when their solubility parameters are close in value. Table 3-3. The affinity of several substances expressed as the Hildebrand solubility parameter δ (From Burke, 1984). Substance δ (J 1/2 /m 3/2 ) Methanol 29.7 Ethanol 26.2 DMSO 26.4 Water 23.5 Dichloromethane 20.2 Acetone 19.7 XAD-8 19.3 XAD-4 18.6 Hexane 14.9 Acetone concentrates (25 ml) are stored at -20 °C to minimise loss of substances. Samples may be stored for several months before analysis. Methodical influences The duration of the drying of XAD, the acetone volume used for elution and the flow rate during elution can influence recovery of substances. 34 RIVM Report 607013010
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Page 9 and 10: 4 Toxicity testing 51 4.1 Choice of
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Lobith and Eijsden, where these riv
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20 16-20 11-15 6-10 2-5 Nieuwe Wate
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In a second sampling campaign the i
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Figure 7-6. Maximum effect values s
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Preliminary experiments suggest tha
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In planning monitoring activities u
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their natural environment. However,
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98 RIVM Report 607013010
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Dekker T, Greve GD, Ter Laak TL, Bo
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Peeters ETHM (2001) Benthic macroin
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Willemsen A, Vaal MA, De Zwart D (1
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Substance type Substance CAS nr mol
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approach is that it ignores the pre
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RIVM National Institute for Public
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Toxicity measurements in concentrated water samples - Rivm

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