Phthalates and Nonylphenols in Roskilde Fjord

Different standard methods can be used to define the vertical transport ofmatter through the water phase. The sedimentary fraction can be foundfrom standing in e.g. 2 hours (DS/R 233 1973) and the suspended fractionfrom filtering (DS/R 233 1973). The remaining amount is either dissolved(molecular) or colloid. No standardised methods exist that canidentify the transition between these last two groups.The total sedimentary fraction is obtained through centrifugation wherethe sedimentary fraction, suspended fraction and some of the colloidalmatter is comprised. If the particulate matter is defined as particles withdiameters larger than 1 µm the following materials are the predominantcontributors in the sedimentation process.Table 23 Properties for suspended particulate matter (Harremoës etal., 1990).Diameter[µm]Density[g ⋅ cm -3 ]Inorganic: Clay particles 1 - 2 2.5 - 2.7Silt, fine 2 - 6 2.5 - 2.7Silt, medium 6 - 20 2.5 - 2.7Silt, coarse 20 - 60 2.5 - 2.7Organic: Algae 1 - approx. 50 1.01 - 1.03The sedimentation process can be described by a pseudo 1 st order removalof particulate matter from the water phase. Thus, the removal ofadsorbed xenobiotics isdCdtw⋅ Xw⋅ Kdw=- k1sed⋅Cw⋅Xw⋅Kdw⎡⎢⎣mglitre⎤⋅ sec. ⎥⎦(3)wherek1sedv=hsedm1≈hour3 m= 0.331hours= 81daysis the sedimentation constant and v sed is the sedimentation velocity suggestedby Harremoës et al., (1990), h is the water depth. X w is the concentrationof particulate matter in the water. In the following a sedimentationconstant fitted for the present data is found.Extraction is a process whereby the non-sedimentary organic matter canbe transported to the sediment. It comprises adsorption of colloids to thesediment and absorption of molecular substances in micro-organismspresent in the sediment. The resulting concentration gradient across theboundary layer is followed by a vertical diffusive transport from the totallymixed water to the sediment.59