Metal flux and dynamic speciation at (bio)interfaces. Part VI: The roles of simple, fulvic and aggregate complexes on computed metal flux in-freshwater ligand mixtures; comparison of Pb, Zn and Ni at planar and microspherical interfaces

摘要

The computations of metal flux in aquatic systems, at consuming interfaces like microorganism surfaces are of major importance in ecotoxicology and dynamic risk assessment. In this paper, the flux of Z_n(II) and Ni(II), at a planar consuming interface in a typical natural freshwater, are studied. The system includes (a) simple ligands (ОН~_, СО_3~2 ); (b) fulvics; (c) aggregates, as complexants, i.e., those which play the major roles in controlling the metal distribution and/or metal flux in aquatic media. The above two metals are chosen because they participate, respectively, to intermediate and very slow chem_ical reactions with complexing sites, and are thus complementary to Pb(II) and C_u(II) (two metals with very fast reactions) studied in Parts III_V of this series. The effects of the various physico-chemical factors, in particular, the diffusion layer thick_ness, the stability constants and complexing site distribution of fulvics and the size distribution of aggregates, are studied in details. The contribution to the flux, of each complex type, is computed. This paper also compares the dynamic behaviour of Pb(II), Z_n(II) and Ni(II) as well as the labilities and flux contributions of their various complexes at planar and microspherical interfaces. This enables to make predictions on biouptake by microorganisms.