Not to be cited without prior reference to the author

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1 ICES CM 2007/J:14 Not to be cited without prior reference to the author DOES TENAX EXTRACTION BASED DESORPTION MEASURE (BIO)AVAILABILITY OF SEDIMENT-ASSOCIATED CONTAMINANTS? Jarkko Akkanen, Arto Sormunen, Merja Lyytikäinen, Matti Leppänen, Sari Pehkonen and Jussi V.K. Kukkonen University of Joensuu, Faculty of Biosciences, P.O.Box 111, FI-80101, Joensuu, Finland [tel: , fax: , Abstract Tenax -resin has been originally developed for grabbing volatile organic compounds from gases. The resin is a porous polymer (2,6-diphenyl-p-phenylene oxide) and it has low affinity for water (floats on the surface). It has high affinity for hydrophobic organic contaminants (HOCs), thus capturing them efficiently from water. On the other hand, the HOCs can be quite easily be extracted from Tenax. Due to these properties Tenax has been applied to measure desorption of HOCs in sediment- (and soil-) water systems. The Tenax extraction has indicated that HOCs sorbed to sediments can be modeled to belong to 2 or more compartments on the basis of rate of desorption (for example rapid, slow and very slow fractions). Following this it has been anticipated that mainly the rapidly desorbing fraction, obviously containing also the freely dissolved fraction, would be bioavailable. Several studies have been conducted to determine if Tenax extraction based desorption could be used to predict bioavailable fraction in sediments. In many cases the laboratory studies indicated that there is a relationship between the size of rapidly desorbing fraction or rate constant for the rapid fraction and bioavailability. However, there are some issues that we must be aware when using Tenax extraction. For example, it appears that ecological factors, such as species life and feeding habits affect the bioavailability in ways that cannot be detected by Tenax extraction. Introduction Sediments are both sinks and sources of hydrophobic organic contaminants (HOCs). The availability of HOCs, however, varies site specifically and total HOC concentration in sediment does not provide very accurate estimate of the availability and risks posed by the chemicals. Therefore we need means to measure availability of HOCs in sediments. Bioassays provide, of course, the best estimates but easier and less time consuming methods have been developed. Recent studies have indicated hysteresis in association of HOCs with sediments and soils. This means that sorption of chemicals can be fast whereas desorption is slower. In consequence of these findings the number of studies on release i.e. desorption of sediment sorbed HOCs has increased rapidly. These studies have shown that HOCs are fragmented to fractions desorbing at different rates. On this basis it has been anticipated that the rapidly desorbing fraction would contribute to the bioavailable fraction (Kraaij et al. 2001; ten Hulscher et al. 2003).

2 Tenax extraction has been applied to study the availability of HOCs in sediments, soils and natural water (Akkanen et al. 2005; Cornelissen et al. 1997; Pignatello 1990). Tenax -TA (Figure 1) is a porous polymer (2,6-diphenyl-p-phenylene oxide) and it has low affinity for water (floats on the surface). It has high affinity for HOCs, thus capturing efficiently freely dissolved HOCs. On the other hand, the HOCs can be quite easily be extracted from Tenax for analysis. Figure 1. Tenax -TA resin used to study desorption of sediment sorbeb contaminants. The purpose of this presentation is to introduce the use of the Tenax extraction method for evaluation of availability of HOCs for benthic invertebrates in sediments. Tenax extraction The Tenax extraction is conducted by adding sediment (or soil), water and a portion of the resin into an experimental vessel. The vessel is shaken and the resin is replaced with a clean portion of resin at predetermined intervals (Figure 2). The resin samples are then extracted to determine the amount of chemical removed by the resin. The values are usually fitted with two or three phase nonlinear model to give the proportions and rate constants for fraction desorbing at different rates. The division to different phases or fractions is operational, but it indicates that there are different mechanisms in interaction between HOCs and sediments. The decision to use either two or three phase model is usually made on the basis of better fitness of one of the models. The model usually used to fit the experimental data is the following: S t / S 0 = F rapid e -k rapid t + F slow e -k slow t + F very slow e -k very slow t (Cornelissen et al. 1997), where S t and S 0 indicate the amount of the studied compound in sediment at time t and in the beginning. F and k represent the proportions of the desorbing fractions and their rate constants (Figure 3).

3 F rap F slow St/S F vs 0.2 Figure 2. Tenax extraction in test tubes Time, h Figure 3. A theoretical desorption curve. Results and discussion Perhaps the first condition for Tenax extraction to work is that the resin really removes efficiently HOCs from the aqueous phase. This has been shown to be true (Akkanen et al. 2005; Zhao and Pignatello 2004). In addition, water chemistry parameters, such as salinity, have been shown to have only a minor influence on the performance of the resin (Zhao and Pignatello 2004). This way the method provides an estimate of maximum desorption. In sediments, the HOCs are generally assumed to be distributed among freely dissolved, dissolved organic matter (DOM) and particulate sorbed phases. Proportions of HOCs in these different phases are controlled by the properties of sediments and HOCs as well as other environmental conditions. Surprisingly; it was found that the interaction between HOCs and DOM resembled the interaction between HOCs and bulk sediment. In natural lake water the desorption experiment showed that there was loosely sorbed (rapidly desopbing) and strongly sorbed (desorption resistant) phase (Figure 4), indicating differences in availability of the chemicals between the two DOM sorbed phases. 1.1 Fraction remaining in water FREE 0.05 Frap 0.35 Fslow TIME (h) Figure 4. Desorption of BaP from lake water. Free = the proportion of freely dissolved compound. Frap = the proportion of rapidly desorbing compound. Fslow = the proportion of slowly desorbing compound. Data from Akkanen et al. (Akkanen et al. 2005).

4 Table 1 shows differences in desorption of benzo[a]pyrene spiked into five freshwater sediments with differing characteristics. Parameters indicate differences in the sizes of different fractions, but also differences in the rate constants of particular fraction. Overall, the amount (and quality) of organic carbon appears to be the main factor controlling desorption. Table 1. Desorption parameters for benzo[a]pyrene spiked in laboratory to five freshwater sediments (unpublished data). Sediment F rap k rap F slow k slow F very slow k very slow Kuorinka Höytiäinen Mekrijärvi Varparanta Ketelmeer Comparison of desorption from laboratory spiked and field-contaminated sediments shows that the rapidly desorbing fraction is far smaller in the field-contaminated sediments ((Kraaij et al. 2001), Figure 5). Figure 5 shows the clear difference between sediment contaminated by pyrogenic PAHs and clean sediment spiked in laboratory. In the field contaminated sediment the desorption is really low, whereas laboratory spiked pyrene exhibits far higher availability (Figure 5). However, Kraaij et al. (Kraaij et al. 2001) have shown that rapidly desorbing fraction can be used to predict bioavailability to marine amphipod in both lab- and field contaminated sediments. It was also shown that the rapidly desorbing fraction correlates with bioavailability at variable HOC concentrations (Sormunen et al. unpublished). In addition, 6 h Tenax extraction has been successfully used to predict bioavailability in soils and sediments (ten Hulscher et al. 2003). Pyr Pyr A 100 B % desorbed % desorbed h h Figure 5. Examples of desorption curves for pyrene (polycyclic aromatic hydrocarbon, PAH) from laboratory spiked (A) and field-contaminated (B) sediments. (Unpublished data). The size of the rapidly desorbing fraction is not the sole parameter correlating with bioavailability. For example Leppänen et al. (Leppänen et al. 2003) showed that Tenax extraction overestimated bioavailable fraction. Another study indicated that rate constants of the desorbing fractions gave better correlation with bioavailability than sizes of the fractions (Leppänen and Kukkonen 2006). Sormunen et al. (unpublished) found that influx of chemical to experimental organisms correlated strongly with the outflux of chemical from the rapidly desorbing fraction.

5 In addition, we have found in a laboratory study that adding black carbon (charcoal of wood origin) to sediment decreased availability of HOCs as measured with Tenax extraction, but effect on bioavailability were negligible (Pehkonen et al. 2006). Interestingly, it was found that feeding of the experimental organisms (oligochaete worm, Lumbriculus variegatus) increased with the black carbon addition. This could have masked the reduced chemical availability because the worms ingested increased amounts of the contaminated sediment leading to increased exposure. Conclusions Tenax extraction is a useful tool for evaluation of the overall physical availability of contaminants, but also for estimations of bioavailability of HOCs in sediments. However, some aspects have to be taken into account when measuring desorption. The size of the rapidly desorbing fraction is not necessarily the only factor contributing to the bioavailability, but desorption rates may play a role too. In addition, ecological factors, such as organisms feeding habits, may affect bioavailability in a way that is not detectable by the Tenax extraction method. To answers the question Does Tenax extraction based desorption measure (bio)availability of sediment-associated contaminants? stated in the topic: yes, it does, but few things mentioned above should be noted to ensure accuracy in bioavailability estimations. References Akkanen, J., Tuikka, A., and Kukkonen, J.V.K Comparative sorption and desorption of benzo[a]pyrene nad 3,4,3',4'-tetrachlorobiphenyl in natural lake water containing dissolved organic matter. Environmental Science and Technology 39: Cornelissen, G., Van Noort, P.C.M., and Govers, H.A.J Desorption kinetics of chlorobenzenes, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls: sediment extraction with tenax and effects of contact time and solute hydrophobicity. Env.toxic.and chem. 16 (7): Kraaij, R.H., Ciarell, S., Tolls, J., Kater, B.J., and Belfroid, A Bioavailability of labcontaminated and native polycyclic aromatic hydrocarbons to the amphpod Corophium volutator relates to chemical desorption. Environmental Toxicology and Chemistry 20: Leppänen, M.T. and Kukkonen, J.V.K Evaluating the role of desorption in bioavailability of sediment associated contaminants using oligochaetes, semipermeable membrane devices and Tenax extraction. Environmental Pollution 140: Leppänen, M.T., Landrum, P.F., Kukkonen, J.V.K., Greenberg, M.S., Burton, G.A.Jr., Robinson, S.D., and Gossiaux, D.C Investigating the role of desorption on the bioavailability of sediment associated 3,4,3',4'-tetrachlorobiphenyl in benthic invertebrates. Environmental Toxicology and Chemistry 22: Pehkonen, S., Kukkonen, J.V.K., and Akkanen, J Bioavailability of PBDE 99 and pyrene in sediments: the effect of sediment characteristics and black carbon (BC)

6 addition and spiking method. Abstracts SETAC Europe 16th Annual Meeting in Hague 129. Pignatello, J.J Slowly reversible sorption of aliphatic halocarbons in soils. I. formation of residual fractions. Environmental Toxicology and Chemistry 9: ten Hulscher, T.E.M., Postma, J., den Besten, P.J., Stroomberg, G.J., Belfroid, A., Wegener, J.W., Faber, J.H., van der Pol, J.J.C., Hendriks, A.J., and Van Noort, P.C.M Tenax extraction mimics benthic and terrestrial bioavailability of organic compounds. Environmental Toxicology and Chemistry 22: Zhao, D. and Pignatello, J.J Model-aided characterization of Tenax -TA for aromatic compound uptake from water. Environmental Toxicology and Chemistry 23: