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I <br />TOXIC SUBSTANCES 27 <br />Table 4.3. Influence of the addition of acidic or alkaline materials on the pH of receiving waters of various <br />hardnesses. <br />Total hardness Resultant pH <br />(as CaC03) of <br />receiving water <br />Extremely soft <br />0-9 ppm <br />3.0-5.0 5.0-6.0 <br />A pH of <5.0 Aluminum is <br />may be toxic, most toxic to <br />depending fish; other <br />on species toxic metals <br /> are Cd, Cu, <br /> and Zn <br />Very soft Indicates acid Normal or <br />10-39 ppm input limited acid <br /> input <br />Soft Indicates acid Indicates acid <br />40-159 ppm input and input <br /> possibility of <br /> C02 toxicity <br />Harda Indicates acid Indicates acid <br />160-279 ppm input and input <br /> possibility of <br /> C02 toxicity <br />Very hardy Indicates strong Indicates acid <br />280-399 ppm acid input input <br />Extremely hardy Indicates strong Indicates acid <br />>400 ppm acid input input <br />aAs hardness increases, the toxicity of metals decreases <br />Fish kills due to insecticides <br />may destroy all fish and in- <br />vertebrates but have no ef- <br />fect on plants (as shown <br />here by the thriving duck- <br />weed among the dead fish). <br />6.0-9.0 <br />At pH 8 and <br />above, sug- <br />gests algal <br />bloom or <br />alkali input <br />Normal pH <br />Normal pH <br />Normal pH <br />9.0-11.0 >11.0 <br />Indicates strong Indicates strong <br />alkali input alkali input <br />Indicates alkali <br />input <br />Indicates alkali <br />input <br />Indicates alkali <br />input <br />Indicates strong <br />alkali input <br />Indicates strong <br />alkali input <br />Indicates strong <br />alkali input <br />Normal pH Indicates alkali Indicates strong <br />input alkali input <br />Normal pH Normal in alka- Indicates strong <br />line waters alkali input <br />A