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54g

aLow means 10% percentile.

bHigh means 90% percentile.

cKOW values as collected by Booij et al. [25]

dOnly data twice the detection limit were used.

eLess than 60 datapoints generally means that other data are below twice DL. fAlso data lower than twice DL were used to calculate the BAF for DBahA. gCB 49, CB 170 and CB 187 were not always analysed.

aLow means 10% percentile.

bHigh means 90% percentile.

cKOW values as collected by Booij et al. [25]

dOnly data twice the detection limit were used.

eLess than 60 datapoints generally means that other data are below twice DL. fAlso data lower than twice DL were used to calculate the BAF for DBahA. gCB 49, CB 170 and CB 187 were not always analysed.

Fig. 19.7. Seasonal variability of freshwater fraction and pyrene concentrations in mussel (mgkg_1) and water (pgL_1). Freshwater fraction is calculated as (1_salinity/34). Data points are connected by lines to make profiles more clearly visible but do not necessarily represent the concentration between sampling.

Fig. 19.7. Seasonal variability of freshwater fraction and pyrene concentrations in mussel (mgkg_1) and water (pgL_1). Freshwater fraction is calculated as (1_salinity/34). Data points are connected by lines to make profiles more clearly visible but do not necessarily represent the concentration between sampling.

phenanthrene where the relative range for CW is over three times larger than that of the equivalent range for mussels. Over the set of compounds investigated there is a strong decrease in freely dissolved concentration as hydrophobicity increases.

A simple comparison of mussel and water phase concentrations illustrated in Fig. 19.7 shows that the seasonal variation observed for pyrene in the water phase also occurs in mussels. A first glance suggests that the seasonal profile is related to the salinity, i.e., the freshwater fraction. However, the variation also occurs where there is little variation in salinity. Note that it is not a log scale and that the relative abundance for lower concentrations is of the same order of magnitude as the higher concentrations. A profile similar to that observed for salinity is seen for temperature across all stations. Furthermore the sampling rate tends to have, with some scatter, a similar profile. However, the sampling rate would not affect the pyrene concentration as pyrene almost reached equilibrium for all stations except station 6. In this work no corrections were made for temperature. A correction would imply that a higher KSW should apply at lower temperature, leading to lower concentrations in the aqueous phase for winter periods and would indeed flatten the profile.

19.5.2 Equilibrium or uptake phase

Passive sampling monitoring was introduced to measure the pollution as experienced by organisms, in this case mussels. The reasoning was that it would be possible to predict uptake by or concentrations in mussels (CM) from PS data. Passive sampling results are expressed as freely dissolved aqueous phase concentrations; the driving force for uptake by mussels. On this basis just as PS does not reach equilibrium for the more hydrophobic compounds it is also possible that the mussels are still in the uptake phase for these compounds when sampled after 6 weeks. Though equilibrium is more likely than for PS since when the mussels are in good shape, they actively pump water over the respiratory surface, and also take up pollutants through the food [11]. Moreover mussels do not start from zero concentration but already contain contaminants at the start of deployment. A factor that works against the achievement of equilibrium is the growth of mussels during deployment. In order to assess contaminant levels in mussel in relation to PS results it is important to know whether the mussel was in the uptake phase or whether approached equilibrium or steady state. When both mussels and samplers are in the uptake phase this would mean that the uptake of mussels may be related to the uptake of the PS. Where equilibrium is achieved the final concentration is a function of the concentration in the water phase. To explore this, the uptake by mussels is plotted versus the uptake of the PS for the winter and autumn samplings of 2003 (left-hand graphs in Fig. 19.8). These samplings were selected because of the large variation in growth and include a situation with only 28% survival. A non-equilibrium situation will be more prominently visible for hydrophobic compounds and therefore CB 153 was selected for illustration. For the PS this compound is far from equilibrium and clearly still in the linear uptake phase. The measured (uncorrected) PS concentrations were used as a measure of the PS uptake. The uptake for mussels is calculated as the difference between the final concentrations minus the start concentration, i.e., the concentration the mussel would have had without uptake but corrected for growth. This is essentially a measure for the difference in body burden before and after exposure. In the graphs the bubble size represents the growth factor in relation to the initial size which is also indicated. The left-graphs of Fig. 19.8 shows that the amount taken up by the mussels correlates well with uptake by the PS, with the exception of station 5. For this station only 28% of the mussels survived and the remaining mussels had lost 25% weight. In this condition the uptake is limited. However, in the right-hand graph the same sample fits well when CM is plotted versus the CW. Another observation in the left graph is that there is a slight tendency for mussels that grow strongly to also have a higher than average uptake; especially visible in autumn data. This, however, does not lead to larger concentrations as

ng taken up by mussel of 1g dry weight o

Initial size

Only 28% survival

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