Kirsti Lahti

Persistence of cyanobacterial hepatotoxin, microcystin-LR in particulate material and dissolved in lake water

Abstract The persistence of cyanobacterial hepatotoxin, microcystin-LR, was investigated in Lake Tuusulanjarvi in southern Finland from August to October, 1993 and 1994. The amount of toxin in particulate material and dissolved in water were determined by HPLC from samples collected from mesocosm enclosures and from the surrounding lake water. In the beginning of the experiments over 80% of the phytoplankton biomass consisted of cyanobacteria. The main species were Microcystis wesenbergii (Chroococcales, Cyanobacteria), M. viridis and M. aeruginosa. The microcystin-LR concentration in particulate material varied from 2.7 to 3.2 μg l−1 and the corresponding concentration of microcystin LR dissolved in water from 0.06 to 0.21 μg l−1. The cyanobacterial biomass decreased towards the middle of September and simultaneously the microcystin concentration in freeze dried particulate material decreased below the detection limit of 10 μg g−1, corresponding 0.01 μg l−1. Dissolved microcystin-LR was detected in a concentration range of 1 to 5 ng l−1 even at the end of the experiments in October, when the cyanobacterial biomass was less than 1 mg l−1. Thus, dissolved microcystin was more persistent compared to microcystin in particulate material: the decimal reduction time for dissolved toxin was 30 d and for toxin in particulate material about 15 d.

Biodegradability and adsorption on lake sediments of cyanobacterial hepatotoxins and anatoxin‐a

Cyanobacterial hepatotoxins and anatoxin‐a, a neurotoxin, were shown to be degraded when crude extracts of lysed toxic laboratory strains of cyanobacteria were exposed to natural populations of micro‐organisms from lakes. While anatoxin‐a decayed equally fast with all the inocula from lake sediment and water, the degradation rate of hepatotoxins was higher with inocula from places at which cyanobacterial water blooms had occurred than with inocula from places with no known mass occurrences of cyanobacteria. Degradation was slowest when an inoculum from a humic lake was used. A part of the loss of the toxins was shown to be due to adsorption on lake sediments.

Endotoxins associated with cyanobacteria and their removal during drinking water treatment

The aim of this study was to investigate endotoxin concentrations in cyanobacterial water blooms and strains, and to assess the removal of endotoxins during drinking water treatment. Endotoxin concentrations were measured from 151 hepatotoxic, neurotoxic and non-toxic cyanobacterial water blooms by using Limulus amebocyte lysate (LAL) assay, and the results were compared to bacterial data. Endotoxin activities ranged from 20 to 3.8 x 10(4) endotoxin units (EU) per ml. Endotoxicity of the samples correlated with phycobiliprotein concentration that was used to assess cyanobacterial abundance, heterotrophic plate count, and Aeromonas spp. but it did not correlate with the number of coliforms or streptococci. The high endotoxin concentrations occasionally detected in the water bloom samples were probably due to Gram negative bacteria that existed together with cyanobacteria since the 26 axenic cyanobacterial strains from different genera that were studied showed very low endotoxin activity. No differences in endotoxin activity were detected between hepatotoxic, neurotoxic and non-toxic strains. Removal of endotoxins during drinking water treatment was studied at nine waterworks that previously had been associated with high numbers of cyanobacteria and that used different processes for water purification. Endotoxin concentration in raw waters ranged from 18 to 356 EU ml(-1). The treatment processes reduced 59-97% of the endotoxin activity; in the treated water the concentration ranged from 3 to 15 EU ml(-1). The most significant reduction occurred at the early stages of water treatment, during coagulation, settling and sand filtration. Activated carbon filtration either increased or had no effect on endotoxin concentration. Ozonation and chlorination had little effect on the endotoxin concentrations.

Assessment of rapid bioassays for detecting cyanobacterial toxicity

Simple and easy‐to‐use bioassays with Artemia salina (brine shrimp) larvae, luminescent bacteria and Pseudomonas putida were evaluated for the detection of toxicity due to cyanobacterial hepato‐and neurotoxins. The hepatotoxins and a neurotoxin, anatoxin‐a, were extracted from laboratory‐grown cultures and natural bloom samples by the solid phase fractionation method and dissolved in diluent for different bioassays. The toxin concentration of cyanobacterial extracts was determined with HPLC. The Artemia biotest appeared to be quite sensitive to cyanobacterial hepatotoxins, with LC 50 values of 3–17 mg l‐1. The Artemia test was also shown to be of value for the detection of toxicity caused by anatoxin‐a. The fractionated extract of anatoxin‐a was not lethal to Artemia but it disturbed the ability of the larvae to move forwards. Filtered cyanobacterial cultures with anatoxin‐a, on the other hand, caused mortality of Artemia larvae at concentrations of 2–14 mg l‐1. With the solid phase fractionation of cyanobacterial samples, no non‐specific toxicity due to compounds other than hepato‐ and neurotoxins was observed. In the luminescent bacteria test, the inhibition of luminescence did not correlate with the abundance of hepatotoxins or anatoxin‐a. The growth of Ps. putida was enhanced, rather than inhibited by cyanobacterial toxin fractions.

Screening for cyanobacterial hepatotoxins in herring and salmon from the Baltic Sea

Nodularin, a cyclic pentapeptide hepatotoxin closely related to microcystins, is produced by the toxic brackish water cyanobacterium Nodularia spumigena which regularly forms blooms in the Baltic Sea. Baltic herring ( Clupea harengus membras L.) and salmon ( Salmo salar L.) were caught in the Baltic Sea during 1997 to assess levels of nodularin and microcystins resulting from the blooms. The total toxin content in herring muscle and salmon liver was measured with an enzyme-linked immunosorbent assay. Despite exceptionally heavy blooms of toxic Nodularia in the Baltic Sea during the summer of 1997, Baltic herring and salmon contained very low quantities of nodularin and microcystins (2.5-6.5 ng g -1 dry weight, not corrected for recovery, [30%]). These concentrations do not pose a health threat to humans, based on the World Health Organization value of tolerable daily intake. Moreover, the concentrations we found in salmon and herring were much lower than those reported for livers of European flounder ( Platichthys flesus L.) or Atlantic cod ( Gadus morhua L.) from the Baltic Sea during 1996-1999. We suspect that cyanobacterial hepatotoxins do not effectively accumulate in herring and salmon.

Effects of fish removal on cyanobacteria and their toxicity in Lake Tuusulanjärvi, Southern Finland

lntroduction Lake Tuusulanjãrvi ( 5.95 km2, mean depth 3 .2 m) underwent eutrophication as a result o f sewage loading. Symptoms of eutrophication include high phytoplankton biomass, cyanobacterial water blooms, and increase of other organisms, such as zooplanktivorous fish ( e.g. JEPPESEN et al. 1991 ). High nutrient concentrations may increase the intracellular toxin concentrations in cyanobacteria (RAPALA et al. 1997, VEZIE et al. 2002). Since sewage diversion in 1979 several efforts have been made to restore the lake, but responses have been insignificant due to remaining high external and interna! phosphorus loading (LEPISTÕ et al. 1999, JOENSUU & PEKKARINEN 2005). Since the end o f the 1990s various additional measures have been used in an attempt to restore the lake, including a further reduction of external phosphorus loading, prevention of interna! loading by intensive mechanical mixing of the water colurnn, and food web manipulation by selective removal of zooplanktivorous fish (SAMMALKORPI 2000, JOENSUU & PEKKARlNEN 2005, SAARIJÃRVI & LAPPALAINEN 2005). Following intensive mixing of the water colurnn since 1998 the relative importance of diatoms has increased with their average biomass remaining constant (LEPISTõ et al. 2003). The aim o f this investigation was (l) to study effects of fish removal on cyanobacterial biomass and species composition by comparing the three-year pre-management period 1995-1997 with seven management years, 1997-2003, and (2) to investigate variation in cyanobacterial hepatotoxin concentrations during the studied years. Tbe environmental variables examined were phosphorus and nitrogen concentrations, water temperature, and removal of fish.