Hazardous Wastes in the Hydrosphere

Hazardous waste substances can enter the hydrosphere as leachate from waste landfills, drainage from waste ponds, seepage from sewer lines, or runoff from soil. Deliberate release into waterways also occurs and is a particnlar problem in countries with lax environmental enforcement. There are, therefore, nnmerons ways by which hazardous materials may enter the hydrosphere. 

For the most part, the hydrosphere is a dynamic, moving system, so that it provides, perhaps, the most important variety of pathways for moving hazardous waste species in the environment. Once in the hydrosphere, hazardons waste species can nndergo a number of processes by which they are degraded, retained, and transformed. These include the common chemical processes of precipitation-dissolntion, acid-base reactions, hydrolysis, and oxidation-reduction reactions. Also inclnded is a wide variety of biochemical processes that, in most cases, reduce hazards, but in some cases, snch as the biomethylation of mercnry, they greatly increase the risks posed by hazardons wastes. 

Fignre 15.6 shows some of the pertinent aspects of hazardous waste materials in bodies of water, with emphasis on the strong role played by sediments. An interesting kind of hazardous waste material that may accumulate in sediments consists of dense, water-immiscible liquids that can sink to the bottoms of bodies of water or aquifers and remain there as blobs of liquid as was the case with the PCB wastes dumped into the Fludson River, noted in Section 15.9. 

Hazardous waste species undergo a number of physical, chemical, and biochemical processes in the hydrosphere that strongly influence their effects and fates. The major ones are listed as follows  

FIGURE 15.6 Aspects of hazardous wastes in surface water in the hydrosphere. The deep unstirred sediments are anoxic, and the site of hydrolysis reactions and reductive processes that may act on hazardous waste constituents is sorbed to the sediment. 

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