In studies of heavy metals in sediments, there is a need for standardization of the procedures for sample collection and preservation, chemical analyses and presentation of results. The method and depth of sampling depend on the aim of the investigation and on local sediment conditions, such as consistency of the sediment, rate of sedimentation, diagnetic processes and bioturbation. Therefore no general recommendations can be given in this respect. During collection and preservation, contamination and loss of constituents must be avoided. In sediments, the best means for estimating total contents of metals is digestion with HF, in combination with strong acids. Other methods include X-ray fluorescence and neutron activation analyses. The use of HF is considered objectionable by some laboratories. A reasonable alternative is aqua regia. Because variations in granular composition affect metal contents, it is advisable to use the fraction < 63 /Um for the analysis.Chemical partition of sediments provides an insight into the source of metallic constituents, and their pathways to deposition areas. A three-step extraction procedure, in the sequence 0. M hydroxylamine-HC1, H 2 0 2 30% and HF, is proposed.Finally, attention is paid to the anthropogenic enrichment of metals in sediments. The establishment of base-line levels is discussed.

During periods of high water discharge, dyke-protected floodplains of the river Rhine in the Netherlands become inundated and suspended matter from the river settles out. In the last 30 years, floodplain top layers have been sampled several times just after deposition; samples were dried and stored in a specimen bank. The samples were used to assess the development of sediment contamination with heavy metals and organic micropollutants during the past decades. Heavy metals studied include Zn, Cu, Cr, Pb, Cd, Ni, Hg and As. Different groups of chemically persistent organic micropollutants were studied: polycyclic aromatic hydrocarbons, polychlorobiphenyls, hexachlorobenzene, DDT and DDT-metabolites. The levels of most contaminants decreased substantially between 1958 and 1981. The variation among the different floodplain locations is due to differences in hydrodynamic characteristics of the location. A comparison was made between the concentrations found and the levels considered acceptable if the floodplain area is used for cattle grazing; a comparison was also made with estimated natural background levels and with reference values defined by the Dutch government. (Abstract retrieved from CAB Abstracts by CABI’s permission)