Lethality of trace metal mixtures to American flagfish in neutralized acid water

Acute lethality of H+ alone to fry of American flagfish (Jordanella floridae) produced a 96 hr LC50 at pH 4.82 in very soft water (5.5 mg/L as CaCO3). At pH 5.3, the combined lethality of Al, Zn, Cu, and H+ produced an LC50 corresponding to 17, 2.8, and 1.4 micrograms/L, of Al, Zn, and Cu, respectively, acting as a mixture. Raising exposure pH from 5.3 to 6.9 in the same soft water reduced apparent Al/Zn/Cu lethality by a factor of 2.6. Decreased mixture lethality was attributed more to reduced H+ lethality at higher pH than to the modifying effects of pH on metal lethality. Neutralization acidic, metals-enriched, soft water with dolomite raised pH from 5.84 to 6.84, total hardness from 5.1 to 17.2 mg/L (as CaCO3) and reduced metal lethality by a factor of 2.4. Reduced lethality was attributed equally to elevated pH and to elevated hardness and alkalinity. Neutralization of culturally acidified waters will reduce the acute lethality of H+ and metals to biota.