Effects of freshly neutralized aluminum on oxygen consumption by freshwater invertebrates

The hypothesis tested in this study was if a pulse of precipitating aluminum (Al) at circumneutral pH covers the body of an invertebrate and, therefore, reduces the surface area available for respiration, organisms exposed to precipitating Al in an experimental system should consume less oxygen than organisms not exposed to aluminum. To test this hypothesis, experiments were conducted in the laboratory placing test organisms in biochemical oxygen demand (BOD) bottles containing a recently neutralized acidic, Al-enriched solution; conditions were meant to loosely mimic those of an acidic, Al-rich stream flowing into a larger, neutralizing receiving stream. The experiments suggested that freshly neutralized Al, i.e., Al in transition from ionic species in acidic waters to polymers or precipitating hydroxides after a rapid increase to pH > or = 6.8, impaired oxygen consumption by D. magna in a repeatable, dose-dependent fashion. Precipitating Al also impaired oxygen consumption by the perlid stoneflies Perlesta lagoi and Acroneuria abnormis, at the lower concentrations used, but higher concentrations resulted in oxygen consumption similar to that of controls. An ionoregulatory impairment response may explain this trend. Aluminum did not affect oxygen consumption by the larger, detritivorous stonefly, Pteronarcys pictetii.