The Influence of Mucus on Copper Speciation in the Gill Microenvironment of Carp (Cyprinus carpio)

Abstract

pH and mucus (as total organic carbon) in the gill microenvironment of carp, Cyprinus carpio, exposed to various concentrations of total copper were measured in an exposure experiment using Playle's apparatus. The activities of free copper ions in both inspired and expired waters were determined using 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 speciation and complexation capacity of gill mucus for copper in an interactive loop. The method was demonstrated to be valid in calculating the metal speciation in this study. It was found that pH and alkalinity in the gill microenvironment were slightly higher than in the surrounding water of pH 6.7. The rates of excretion of CO2, HCO−3, and mucus at the gills increased, either linearly or nonlinearly with increases in the total copper concentration in 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 mmolCu/mgC. As a consequence of changes in pH and alkalinity, in conjunction with occurrence of mucus, copper speciation in the gill microenvironment is significantly different from that in the surrounding water, with 3–20% of the copper complexed by the gill mucus. The sequence of species domination also shifted from CuCO03, Cu2+, CuHCO+3, and Cu(OH)02 in the surrounding water to CuCO03, Cu2+, Cu(OH)02, CuHCO+3, and mucus–Cu in the gill microenvironment.