978 Environmental Toxicology and Chemistry, Vol. 20, No. 5, pp. 978–984, 2001  2001 SETAC Printed in the USA 0730-7268/01 $9.00 + .00 VARIATIONS IN HEAVY METAL CONCENTRATIONS AND SPECIATION IN TWO MINING-POLLUTED STREAMS IN CENTRAL NORWAY PA ˚ L GUNDERSEN,*² P A ˚ L A. OLSVIK,‡ and E. STEINNES² ²Department of Chemistry, ‡Department of Zoology Norwegian University of Science and Technology, N-7491 Trondheim, Norway ( Received 24 April 2000; Accepted 13 October 2000) Abstract—The dissolved (dialysis in situ), colloidal (filtered minus dissolved), and total concentrations of Cu, Zn, Cd, and Al were determined and compared with pH, Ca concentrations, and alkalinities through seasonal variations in water levels in two streams, Rugla and Naustebekken, in the Røros area of central Norway. The main objective was to monitor the dissolved fraction of the metals during the seasons and to establish the extent to which chemical parameters influencing metal toxicity were unfavorable during episodes of high total metal concentrations. The average dissolved fractions of Cu, Zn, Cd, and Al were lower in Rugla (55, 69, 64, and 17%, respectively) compared with Naustebekken (59, 82, 82, and 30%, respectively). This is probably due to sedimentation of metal particles in a small lake located in the path of Naustebekken. Alkalinity and Ca concentrations were generally low during the flood episodes, when the highest metal concentrations occurred. This is unfavorable since these parameters are assumed to counteract toxic effects of metals. On the other hand, the results indicate that toxic stress during metal concentration peaks was moderated by adsorption of dissolved metal species on colloids and/or particles. Keywords—Metals Speciation Dialysis River Aquatic INTRODUCTION During mining activity, deep reservoirs of rocks are crushed and brought to the surface. Residuals are stored in a more or less environmentally acceptable manner, and huge surface ar- eas of unextracted metal sulfides in the residuals may be ac- cessed by water and oxygen. Sulfides in the residuals can thereby be oxidized and release metals to aquatic environments [1]. Mine tailings may weather and leach metals for several hundreds of years after the mining activity has ceased. Many aquatic organisms are sensitive to metal pollution, and also toxic effects on humans are reported, e.g., from Cu in drinking water [2]. It is well known that different metal species are absorbed by biota at different rates, and dissolved species, in particular free metal ions and metal hydroxides, are known to penetrate biological membranes easily and lead to toxic responses [3,4]. The Ca concentration, alkalinity, pH, and ligands and particles present may influence the metal speciation, bioavailability and toxicity of metals in aquatic systems, and total concentrations are therefore not considered very reliable as measures for metal stress [4–6]. Most previous investigations dealing with metal pollution in aquatic environments were based on analysis of water samples either without any pretreatment or that were filtered through 0.45-m pore-size filters. In the present study, concentrations of truly dissolved metal species (diameter smaller than 2.5–5 nm) are considered in addition. The dis- solved species are fractionated by dialysis in situ [7]. In this method, bags of membrane material are filled with deionized water and placed in a river. After equilibration, the interior water of the dialysis bags can be analyzed directly for the dissolved metal concentration of the river water. In the present * To whom correspondence may be addressed (pal.gundersen@chembio.ntnu.no). study, the dissolved concentrations are used as first approxi- mations to the biologically available fractions of the metals. The metals selected for this study (Cu, Zn, Cd, and Al) are the ones most likely to reach toxic levels toward aquatic life in fresh waters of the area. An important aim of the study was to assess the influence of the river water level on the fraction of metals occurring as dissolved species. Additionally, the tem- poral variations in main water chemical parameters influencing metal toxicity were compared with the metal variations. These are pH, Ca, alkalinity, and, in a few cases, total organic carbon (TOC). During dry periods in summer and autumn or during the winter season when the precipitation is mainly snow, weath- ering products may accumulate in mine tailings. During early stages of storm floods, these accumulated compounds may be released and lead to increased metal concentrations in rivers [8]. A high runoff peak would normally lead to more particles and colloids in the water. This could lower the fraction of the metals occurring as dissolved since these particles would offer additional binding sites to metal ions. On the other hand, the fraction of the high alkalinity groundwater reaching rivers is normally low during flood episodes, leading to decreased pH levels [9]. In mining areas, pH in downstream rivers may also decrease due to rainwater flushing through oxidized residuals. Either way, a pH decrease occurring during a flood episode could lead to desorption of metals from colloids and particles. Evaluation of the overall effects of these partly counteracting and partly additive influences on metal toxicity during flood episodes is attempted for the two rivers. Very few internationally published studies have dealt with size fractionation at such small pore sizes in freshwater, and studies describing temporal variations in the metal speciation are particularly scarce. SITE DESCRIPTION Both sampling sites are highland mine polluted streams in the Røros area, central Norway (Fig. 1). The area is dominated