The influence of mucus on copper speciation in the gill microenvironment of carp (Cyprinus carpio)

pH and mucus (as total organic carbon) in the gill microenvironment of carp , Cyprinus carpio,exposed to various concentrations of total copper were me asured in an exposure experiment using Playle's apparatus. The activities o f free copper ions in both inspired and expired waters were determined usin g a copper ion selective electrode. A trial-and-error procedure of coupling species distribution calculations (MINEQA2) with single-site complexation modeling (mucus-copper) Was proposed for computation of both copper speciat ion and complexation capacity of gill mucus for copper in an interactive lo op. The method was demonstrated to be valid in calculating the metal specia tion in this study. It was found that pH and alkalinity in the gill microen vironment were slightly higher than in the surrounding water of pH 6.7. The Fates of excretion of CO2, HCO3-, and mucus at the gills increased, either linearly or nonlinearly with increases in the total copper concentration i n the surrounding water. The conditional complexation stability constant of the mucus was;calculated as log k = 5.32, while the complexation stability equivalent concentration of the mucus was derived as 0.95 mmol Cu/mg C. As a consequence of changes in pH and alkalinity, in conjunction with occurre nce of mucus, copper speciation in the gill microenvironment:is significant ly different from that in the surrounding water, with 3-20% of the copper c omplexed by the gill mucus. The sequence of species domination also shifted from CuCO30, Cu2+, CuHCO3+, and Cu(OH)(2)(0) in the surrounding water to C uCO30, Cu2+, Cu(OH)(2)(0), CuHCO3+, and mucus-Cu,in the gill microenvironme nt. (C) 2000 Academic Press.