Synergistic cytotoxicity between pentachlorophenol and copper in a bacterial model Ben-Zhan Zhu * , Svetlana Shechtman, Mordechai Chevion Department of Cellular Biochemistry, Hebrew University ± Hadassah Schools of Medicine and Dental Medicine, Jerusalem 91120, Israel Received 23 October 2000; accepted 31 October 2000 Abstract Both pentachlorophenol PCP) and copper compounds have been widely used as wood preservatives, and are commonly found not only in the area near wood-preserving facilities, but also in body ¯uids and tissues of people who are not occupationally exposed to them. In this study, we found that exposing bacteria to a combination of PCP and copper at non- or sub-toxic concentrations resulted in enhanced cytotoxic eect in a synergistic mode as indicated by both the inhibition of growth and the lowering of the colony-forming ability. The toxicity of the combination PCP/ CuII) was relieved by hydrophilic chelating agents, thiol compounds and adventitious proteins, but was markedly potentiated by low levels of the lipophilic metal chelating agents. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Pentachlorophenol; Copper; Synergistic cytotoxicity; Chelating agents 1. Introduction Since its introduction as a preservative for wood and wood products, pentachlorophenol PCP) has gained worldwide recognition as an agent to control mold, mildew, and termites on wood IARC, 1986, 1991; Rao, 1987). Because of its eciency, broad spectrum, and low cost, PCP and its salts have been used also as bacteri- cides, fungicides, herbicides, insecticides, and mollusci- cides with a variety of applications in industrial, agricultural, and domestic ®elds Rao, 1987; IARC, 1991). Althoughmostdevelopedcountrieshaverestrictedthe use of PCP in recent years, after more than 60 years of extensive uses, PCP and other polychlorinated phenols are considered to be ubiquitously present in the envi- ronment and are even found in body ¯uids and tissues of people who are not occupationally exposed to it Rao, 1987; IARC, 1991; Seiler, 1991). PCP has been listed as a priority pollutant by the US EPA, and classi®ed as a group 2B environmental carcinogen IARC, 1991). Several possible mechanisms have been proposed to explain the toxicity of PCP, including i) uncoupling of oxidative phosphorylation Weinbach and Garbus, 1969); ii) metabolic activation by microsomal enzymes resulting in the formation of highly reactive metabolites Seiler, 1991); and iii) transition metal-mediated redox reactions leading to the formation of reactive oxygen species ROS). Among these, the ®rst two have been extensively studied, while the third has been little studied Weinbach and Garbus, 1969; IARC, 1986, 1991; Rao, 1987; Seiler, 1991). In this study, we will focus on the latter mechanism, with special emphasis on the role of copper in PCP-induced toxicity. Copper is a redox-active transition metal forming the essential redox-active center in a wide variety of metal- loenzymes Linder, 1991). Copper has been found in chromosomes, and is closely associated with DNA bases, particularly near G-C sites Geierstanger et al., 1991; Karlin, 1993; Wacker and Vallee, 1995). The Chemosphere 45 2001) 463±470 www.elsevier.com/locate/chemosphere * Corresponding author. Present address: Linus Pauling Institute, Oregon State University, 559 Weniger Hall, Corvallis, OR 97331, USA. Tel.: +1-541-737-5085; fax: +1-541-737-5077. E-mail address: benzhan.zhu@orst.edu B.-Z. Zhu). 0045-6535/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII:S0045-653500)00582-8