Environmental Pollution 85 (1994) 3-13 EFFECTS OF PULP MILL CHLORATE ON BALTIC SEA ALGAE Arno Rosemarin,* Karl-Johan Lehtinen,~/Mats Notini & Jan Mattsson § MFG Swedish Environmental Research Group, Fryksta 665 O0 Kil, Sweden (Received 27 April 1989; accepted 3 May 1993) Abstract The long-term effects of pulp mill chlorate on different algal species of the Baltic Sea were studied in land-based model ecosystems simulating the littoral zone. Brown algae (Phaeophyta) exhibited an extraordinarily high sensitivity to chlorate and pulp mill effluents containing chlorate. All brown algal species ceased growth or showed major signs of toxicity at all concentrations tested, down to microgram per litre levels. ECso levels for growth of Fucus vesiculosus were about 80-100 t~g CIO; litre-I. Blue-green algae (Cyanophyta) were not deleteriously affected nor were green algae (Chloro- phyta). The perennial and annual species of red algae ( Rhodophyta) were also unaffected by the effluents. Di- atoms did not show any sensitivity and phytoplankton (fresh- and brackish water) were particularly insensitive. A phanerogam, Zostera marina was also unaffected by the treatments. INTRODUCTION Chlorate is toxic to plants, algae, bacteria and fungi, and was used extensively as a weed killer during the 1930s to 1950s (Crafts & Robbins, 1962). Aberg (1947) proposed that chlorate itself was not toxic but rather as an analogue of nitrate, it was rendered toxic by conver- sion to chlorite via reduction by nitrate reductase. This was confirmed by Goksoyr (1952) for Escherichia coli and more recently by Hofstra (1977) for tomato plants, and Solomonsson & Vennesland (1972) for Chlorella. In algae it is well known that nitrogen starvation enhances both nitrate uptake and reduction (Hipkin et al., 1980). It therefore follows that in nitrogen-limited systems, such as the Baltic Sea where algae such as Fucus vesiculosus are nitrogen-limited, chlorate, if introduced, would be readily taken up and reduced to chlorite. The concentrations at which significant nitrate (and chlorate) * To whom correspondence should be addressed at" Stock- holm Environment Institute, Box 2142, S-103 14 Stockholm, Sweden. Fax +46 8 723 0348; Tel +46 8 723 0260; E-mail seihg @ nordnet-se. ~: Present address: Finnish Environmental Research Group, Teknikvagen 12, SF-02150 Esbo, Finland. §Present address: Water and Sewage Administration of Gothenburg, Box 1514, S-401 05 Gothenburg, Sweden Environ. Pollut. 0269,7491/94/$07.00 © 1993 Elsevier Science Limited, England. Printed in Great Britain uptake should occur, conform to Michaelis-Menton second order kinetics (Chapman et al., 1978). Chlorate plus nitrate interact such that cells do not discriminate between the two (Rosemarin et al., 1986) although the relative specific affinities appear to vary between algal groups (Balch, 1987). Chlorate is one of the substances often found in the effluents emanating from pulp mills due to the use of chlorine dioxide in the bleaching process (Germg~rd et al., 1981). In one case, in the mid-1980s at M6nster~ts pulp mill in the Baltic Sea, it occurred in effluent at mg litre m levels (mean value 53 mg CIO3- litre-t). Here Fucus vesiculosus disappeared from an area of about 12 km 2 (Lindvall, 1984) as a result of the presence of chlorate in the effluent. Field transplant experiments and short-term uptake tests confirmed these findings (Rosemarin et al., 1986; Lehtinen et al., 1988; Rosemarin et al., 1990a). Removal of chlorate from these effluents has in fact allowed Fucus to begin to recolonise this area (Notini, 1991). Inhibition of primary productivity by pulp mill effluents via light limitation due to colour and turbidity and via chemical toxicity and BOD-loading have been studied in phytoplankton and periphyton from marine and freshwater systems (Stockner & Cliff, 1976; Landner & Larsson, 1977; Moore & Love, 1977; Bothwell & Stockner, 1980). Toxicity of pulp mill chlorate has been studied only in this single case from the Baltic Sea. Controlled phytotoxicity experiments over the long- term at relatively low concentrations of treated or partially treated pulp mill effluents are rare. The long- term effect of low levels of chlorate on aquatic algae and plants has also never been examined prior to this study. By using model ecosystems in land-based pools this work investigated the effects of low levels of chlorate and pulp mill effluents containing chlorate on the littoral algae of the Baltic Sea over a 6-month exposure period. In addition, the short-term effects of chlorate on phyto- plankton productivity both in seawater and freshwater were investigated. Model ecosystems have proven to be a practical link between laboratory and field studies. As reviewed by Lundgren (1985) and Grice & Reeve (1982), a host of substances such as metals, oil and nutrients have been tested on various systems such as the CEPEX plankton columns, the MERL plankton-sediment tanks, limno- corrals and the Fucus-based ecosystems used here. The 3