PARENT SESSION
4B Site-specific ecological risk assessment
9:00 AM to 7:00 PM, Tuesday, 08 May 2001
Session Chair:

(T/MF174) Spatial heterogeneity of trace metals and AVS in Dutch flood plain lake sediment.

van Griethuysen, Corine¹, Meijboom, Erwin¹, Koelmans, Albert¹, ¹

ABSTRACT- In ecological risk assessment of trace metal polluted sediments, it is important to know whether spatial heterogeneity of sediment properties and contaminants occurs. Total trace metal concentrations are often related to sediment texture and sediment organic matter. In flood plain sediments also redox conditions play a large role in determining the bio-availability and mobility of these metals. In risk assessment of reduced sediments much attention is paid to the immobilizing effect of sulfide (AVS) on trace metals. Following this approach, metals that are simultaneously extracted during AVS analysis (SEM) are potentially bio-available when exceeding AVS concentrations. However, not much is known about the spatial distribution of SEM and AVS. We studied the spatial variability of sediment properties (texture, organic matter content, bulk chemistry), redox-related conditions (redox potential, AVS content) and contaminant concentrations in a Dutch floodplain lake, in order to assess magnitude and range of the variation of environmental availability of trace metals. Sampling of the top five centimeter of sediment was done in January 2000 on 40 locations on a predetermined regular triangular grid. Spatial dependency of the analyzed variables was determined using kriging techniques. Statistical (co-)variation was interpreted by correlation, regression and factor analysis. Variation was approximately 10 % for total trace metal contents, texture and bulk chemistry. AVS concentrations showed a strong spatial dependence due to differences in lake depth and total sulfur pools. However, factor analysis revealed that AVS was not the only variable controlling trace metal availability, because SEM was strongly related to oxides. In conclusion, in this case of diffuse contamination in rather homogeneous clayey sediments and low AVS concentrations, spatial variation is of minor importance in risk assessment. However, if AVS concentrations are higher, the observed spatial variation in redox conditions may become important for the availability of trace metals.

Key words: trace metals, spatial heterogeneity, acid volatile sulfide, flood plain lake