The Applications of Chemical Analyses of Sediments and Soils in ...

operation. Wastewater is a major source of heavy metal contamination (Helz et al,1975). Rapid decrease in concentration of Zn, Cu, Pb, and Cd below the outfall intoBlack River, Maryland was attributed to processes other than dilution, such asadsorption, precipitation, colloidal flocculation or biological uptake scavenging themetals from the water and depositing them in the sediments. Intense algae bloomswere noted with day time pH often above 9.0 compared with average effluent pH of 6.9leading to rapid deposition of trace metal hydroxides, carbonates or phosphates, andpossibly increased sorption on organic and inorganic particles.Algae have also been found to concentrate heavy metals and as they die andsink carry the heavy metals into the sediments (Martin and Knauer, 1973). Cadmiumappears to remobilize from the sediment possibly by cation exchange, or aging anddecay of organic material, or solubilization as aqueous complexes (Helz et al, 1975).Acidity and colloid content, both inorganic (clays) and organic (humic material),are important factors governing metal solubility, exchange and mobility.Total soluble metals in soil (and sediment) are made up of simple ions,hydrolysis species, complexes and chelated species (Lindsay, 1975). For metals withmore than one valence state, solubility and mineral transformations are affected byredox state. Measurement of ion activities can be useful.Initial contact of water soluble metals with soil or sediment, particularly underbasic conditions, normally results in precipitation, first highly amorphous with large7