SUITABILITY OF THE PH BUFFERS -N-BIS(HYDROXETHYL)AMINO]-2-HYDROXYPROPANESULFONIC ACID AND N-2-HYDROXYETHYLPIPERAZINE-N'-2-ETHANESULFONIC ACID FOR IN-VITRO COPPER TOXICITY STUDIES

The influence of the zwitterionic (ampholytic) pH buffers, N-bis(hydro xyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO, 10 mM) and N-2-hy droxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES, 25 mM), on the t oxicity of copper(II) to the marine dinoflagellate, Amphidinium carter ae, was investigated. For this purpose, DIPSO or HEPES buffered comple te ESAW (enrichment solution artificial seawater) growth media as well as simplified (enrichment solution deficient) buffered media were ass ayed in the toxicity tests, at pH 8.0. Similar assays were performed i n unbuffered ESAW medium. Toxicity evaluation was based on growth chan ges, EC(50) (effective concentration of labile copper that reduces gro wth rate by 50%) and esterase activity. In addition to biological para meters, electrochemical behavior of the buffers in the presence of cop per(II) was used to interpret the results. Neither of the buffers were toxic to A. carterae. HEPES increased copper toxicity (synergistic ef fect) while DIPSO diminished it (strong antagonistic effect). HEPES do es not significantly complex copper(II) and this effect was possibly d ue to change in kinetics of metal binding to the organisms due to its surfactant properties at 25 mM. DIPSO is a strong copper(II) complexin g agent (average conditional stability constant, log K = 7.3, pH 8.0, 25 degrees C). These results suggest that DIPSO may substitute EDTA in culture media with the advantage of simultaneously buffering changes in pH and metallic cations.