In the Rhine-Delta, accumulation of microcontaminants in floodplain foodwebs has received little attention in comparison with aquatic communities. Here, soil and cattle milk samples were taken from three floodplains and analyzed for polychlorinated biphenyls (PCBs), dibenzodioxins (PCDDs) and dibenzofurans (PCDFs). Based on 2,3,7, 8-tetrachlorodibenzodioxin equivalents, total PCDD and PCDF residues in milk did not exceed the quality standard of 0.006 microg/kg fat weight. This was still the case if non- and mono-ortho PCBs were added to the total. Yet, the floodplains investigated were only moderately polluted according to previous studies and one cannot exclude higher levels in milk from other floodplains. Bioconcentration ratios of milk fat vs soil organic matter were about 0.01 to 0.1 for persistent PCBs. These values are in accordance with a few literature data found for other persistent compounds. Yet, ratios are lower than expected from equilibrium partitioning. Ratios for PCDDs and PCDFs were even lower, possibly due to biotransformation.
Ecotoxicological management and research have several instruments at their disposal. A discriminatory is made between monitoring of chemical, biochemical, toxicological and ecological parameters, and modeling at a simple, intermediate, and complex level. Their usefulness is discussed and illustrated by examples from the Rhine-Meuse delta.Each type of instrument has its own benefits. In simple cases, application of one instrument will do. More often, however, the objectives set, the compounds concerned, and the species involved require a combination of tools to be used. Chemical and biochemical parameters are oriented around sources and concentrations of well-known priority substances. Toxicological and ecological variables, on the other hand, are directed toward species and the impact of these compounds and other factors as well. In the Rhine-Meuse delta, contamination decreases and more refined instruments are needed to pick out the compounds and species that should get our attention most. An intermediate level of modeling is considered the next logical step after application of simple rules of thumb.
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