No abstract

No abstract

The kinetics of Cu(II) interactions with Susquehanna River (mid-Atlantic, USA) particle suspensions using the copper ion selective electrode (Cu-ISE) method indicated that the concentration of Cu2+ in both the suspension and filtrate was kinetically controlled; the reaction of Cu(II) in the suspension was faster than that in the filtrate. Bioassay tests were performed in continuous flow-through bioassay systems to examine the effect of kinetics of Cu(II) interactions with suspended solids on the toxicity of Cu to Ceriodaphnia dubia. The toxicity curves were displaced to higher total Cu concentration as the reaction time increased, indicating that such interaction of Cu with solids was time dependent. Further, the toxicity curves overlapped for reaction times of 6 and 24 h, indicating that the reaction was relatively rapid and that equilibrium was achieved within 6 h. The survival of organisms was related to the free Cu2+ concentration but deviated from the result for bioassays in which dissolved organic matter (DOM) rather than particles reacted with the added Cu(II) to affect the free Cu2+ concentration. It may be interpreted that, besides the toxic effect of Cu2+, particles exert adverse influences on the organisms.

The kinetics of trichloroethene (TCE) reductive dechlorination mediated by humic-Ni complexes in homogeneous aqueous solution using titanium(III) citrate as the bulk reductant was examined under various environmental conditions (e.g., pH and ionic compositions). Using Ca2+, Zn2+, and Hg2+ ions to vary Aldrich humic acid (HA)-Ni complex concentrations, pseudo-first-order rate constants for TCE reduction were observed to be proportional to HA-Ni levels (as calculated by speciation modeling), confirming HA-Ni complexes as the probable active mediator species. TCE reduction by HA-Ni was observed to be strongly pH dependent and could be due to both the variations of HA-Ni concentration and Eh with pH. Evidence is presented which suggests that quinone moieties may not be crucial for the humic-Ni mediated reduction of TCE. A variety of natural soil and aqueous humic material and Ni systems were examined, and some showed reactivity toward TCE. Humic-metal complexes may be important electron-transfer mediators in natural systems.

No abstract