Accumulation and depuration of the cyanobacterial toxin

cylindrospermopsin in the freshwater mussel Anodonta cygnea

Martin L. Sakera,b,*, James S. Metcalfc, Geoffrey A. Coddc, Vitor M. Vasconcelosa,b

aCentro Interdisciplinar de Investigacao Marinha e Ambiental, Rua dos Bragas 177, Porto 4050-123, PortugalbDepartamento de Zoologia e Antropologia, Faculdade de Ciencias, Praca Gomes Teixeira, 4050 Porto, Portugal

cDivision of Environmental and Applied Biology, School of Life Sciences, University of Dundee, Dundee DD1 4HN, UK

Received 30 September 2003; accepted 17 November 2003

Abstract

Cylindrospermopsin (CYN) is a toxic alkaloid produced by several genera of freshwater cyanobacteria. This compound has

been implicated in outbreaks of human sickness and the death of domestic and wild animals. Given that several of the

cyanobacterial genera known to produce CYN are common components of the phytoplankton of freshwaters including

aquaculture facilities, we studied the accumulation of CYN in the freshwater mussel (swan mussel) Anodonta cygnea.

Anodonta were exposed to CYN-producing cultures of the cyanobacterium Cylindrospermopsis raciborskii for 16 days and

were found to accumulate the toxin to concentrations up to 2.52 mg g tissue dry weight21. There was considerable variation in

the concentrations of CYN detected in different parts of the body. At the end of a 2-week accumulation period the distribution of

CYN in the body of Anodonta was as follows: haemolymph (68.1%), viscera (23.3%), foot and gonad (7.7%) and mantle

(0.9%). No CYN was detected in the gills or adductor muscle of any animals. Following a 2-week depuration period,

approximately 50% of the toxin remained in the tissues. Based on the recently derived guideline value for CYN in human

drinking water (1 mg l21) and the concentrations of this compound in animal tissues reported here, there is a clear need for the

increased monitoring of this compound in organisms grown for human and animal consumption.

q 2003 Elsevier Ltd. All rights reserved.

Keywords: Cyanobacteria; Cylindrospermopsis; Cylindrospermopsin; Bioaccumulation; Depuration

1. Introduction

Cylindrospermopsin (CYN) is an alkaloid toxin pro-

duced by several genera of freshwater cyanobacteria

including Anabaena (Schembri et al., 2001), Aphanizome-

non (Banker et al., 1997; Shaw et al., 1999), Cylindros-

permopsis (Hawkins et al., 1997; Griffiths and Saker, 2003),

Raphidiopsis (Li et al., 2001) and Umezakia (Harada et al.,

1994). Studies of the toxicological properties of this

compound have shown that it is a general cytotoxin with

a similar level of toxicity in the mouse bioassay to some

other cyanobacterial totoxins including microcystins and

nodularin (Kuiper-Goodman et al., 1999). The LD50 of pure

CYN to mice (intra-peritoneal administration) is

2100 mg kg21 at 24 h and 200 mg kg21 at 5–6 days.

Histopathological studies have shown that the liver is the

primary target organ although damage to kidneys, thymus

and heart have also been reported (Harada et al., 1994;

Falconer et al., 1999). It is a general inhibitor of protein

synthesis (Terao et al., 1994) and studies by Humpage et al.

(2000) and Shen et al. (2002) have shown that CYN causes

DNA strand breakage which might indicate an increased

risk of carcinogenic effects by this compound.

Incidents of human poisoning and cattle mortality have

been attributed to the presence of CYN in potable supplies

and farm dams (Byth, 1980; Hawkins et al., 1985; Saker

0041-0101/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/j.toxicon.2003.11.022

Toxicon 43 (2004) 185–194

www.elsevier.com/locate/toxicon

* Corresponding author. Address: Centro Interdisciplinar de

Investigacao Marinha e Ambiental, Rua dos Bragas 177, Porto

4050-123, Portugal. Tel.: þ351-22-340-1813; fax: þ351-22-339-

0608.

E-mail address: martinsaker@hotmail.com (M.L. Saker).

et al., 1999; Griffiths and Saker, 2003). Given that several of

the species known to produce CYN are common com-

ponents of the phytoplankton of freshwater aquaculture

facilities, there is a clear need to investigate the potential for

bioaccumulation of this compound within the tissues of

cultured organisms. For another freshwater hepatotoxin,

microcystin-LR, concentrations ranging from 10 to

130 mg g tissue dry weight21 are frequently reported for

freshwater clams and mussels exposed to microcystin-

producing cyanobacterial blooms and laboratory-grown

cultures (e.g. Eriksson et al., 1989; Vasconcelos, 1995;

Prepas et al., 1997; Yokoyama and Park, 2003). Such

concentrations are considered to represent a potential health

risk to consumers (Van Buynder et al., 2001). Saker and

Eaglesham (1999) detected CYN within the tissues of

commercially cultured crayfish (Cherax quadricarinatus)

collected from a pond containing a bloom of Cylindros-

permopsis raciborskii. The highest tissue concentration

encountered in that study was 4.3 mg CYN g dry weight21,

similar to the concentration of microcystin-LR found in a

closely related crayfish species (Vasconcelos et al., 2001).

In this study, we investigated the accumulation and

depuration of CYN in the swan mussel, Anodonta cygnea.

Given the recently derived guideline value for the presence

of CYN in human potable water supplies (1 mg l21), and the

reported ‘No Observed Adverse Effect Level’ (NOAEL) of

30 mg kg21 day21 (Humpage and Falconer, 2003), we have

also taken the opportunity to investigate the potential for

human health problems resulting from the consumption of

food contaminated with this toxin.

2. Materials and methods

2.1. Experimental setup

Thirty six A. cygnea were collected from Lake Mira, in

the north of Portugal (88440W, 408260N) in November 2002.

Phytoplankton monitoring over the last 5 years has shown

that Lake Mira is not contaminated by Cylindrospermopsis

or any other known CYN-producing cyanobacteria.

Blooms of Microcystis aeruginosa are a seasonal feature

of the lake.

The animals had a shell length of 11.9 ^ 0.8 cm

(average ^ 1SD) and a weight (including shell) of

225 ^ 35 g. After collection from the lake, animals were

transported to the laboratory, cleaned externally to remove

epiphytes and placed in a tank containing 10 l of non-sterile

Z8 medium (Kotai, 1972). The Anodonta were maintained

at constant temperature (20 8C), with aeration, under dim

light for 7 days. Medium was replaced daily to allow for

acclimation to the laboratory conditions and to facilitate the

expulsion of material from their alimentary tracts. After this

initial incubation period, the animals were exposed to the

experimental conditions described below.

Initially, two randomly selected animals were removed

from their shells. One of the animals was homogenised in a

blender, weighed, frozen, lyophilised and re-weighed. The

other animal was divided into the following six body parts;

haemolymph, gills, mantle, viscera, adductor muscle and

foot (containing the gonad). The wet weight of each of these

samples was recorded before being frozen, lyophilised and

re-weighed.

The remaining 34 animals were exposed to a CYN-

producing culture of C. raciborskii (CR3) that had

previously been isolated from an aquaculture pond in

Townsville, Australia (Saker and Eaglesham, 1999; Saker

and Neilan, 2001). Bulk cultures of this strain were grown

under the conditions described in Saker et al. (2003) and

were supplied to the Anodonta over eight consecutive two-

day intervals. At the beginning and end of each of the

successive two-day incubations, samples of media were

taken. The concentration of C. raciborskii cells was

determined using a Sedgwick-rafter cavity slide (to measure

trichomes ml21) in combination with high power micro-

scopic measurement of average trichome and cell lengths.

Concentrations of intra- and extra-cellular CYN were

determined by filtering 100 ml of media through a GF/C

filter paper. Filter papers and filtered media were frozen and

lyophilised for the measurement of CYN concentrations. At

the end of each two-day incubation, two randomly chosen

Anodonta were sacrificed as described above.

After 16 days (eight successive two-day incubations) of

exposure to cultures of C. raciborskii, the remaining animals

were placed in CYN-free Z8 medium and maintained for a

further 16 days. The medium was replaced at two-day

intervals. At the end of each two-day incubation, samples of

medium were taken for the measurement of intra- and extra-

cellular CYN concentrations and two of the animals

sacrificed as described.

2.2. Analysis of CYN from Anodonta tissues

and cyanobacteria culture media

Lyophilised Anodonta tissues (0.3–1.0 g dry weight)

and samples for the analysis of intra- and extra-cellular

CYN were extracted in 100% methanol with ultrasonication

on ice (60 s, 50 Hz). Tissue and cell debris were removed by

centrifugation and the supernatant dried at 50 8C under

nitrogen and re-suspended in 300–1000 ml of sterile milliQ

water. The samples were centrifuged again to remove

insoluble material and placed in HPLC vials for the analysis

of CYN.

Analytical detection of CYN was performed using a

Waters 2690 separations module and a 996 photodiode array

detector. Separation was achieved using a method modified

from that of Harada et al. (1994) employing a Cosmoil C18

column (Phenomex; 5 mm, 150 £ 4.6 mm i.d.) with a linear

gradient of 1–12% (v/v) methanol/water over 24 min at

40 8C (Metcalf et al., 2002). Chromatograms were mon-

itored at 262 nm with spectra from 200 to 300 nm.

M.L. Saker et al. / Toxicon 43 (2004) 185–194186

Quantification was achieved by comparison to a CYN

standard purified using Waters equipment including a 510

pumping system, 471 WISP, 484 UV detector and a Waters

fraction collector employing a Phenomenex Luna semi-prep

column (C18, 5 mm, 150 £ 10 mm i.d.; Metcalf et al.,

2002).

3. Results

The Anodonta were apparently healthy and filtered

actively during the experiment. No mortality occurred

during the study. Over the 16-day accumulation period,

animals were exposed to concentrations of C. raciborskii

ranging from 265,000 to 1,900,000 cells ml21 (Fig. 1a).

Concentrations of total CYN in the culture medium

(calculated by the addition of intra- and extra-cellular

fractions) ranged from 14 to 90 mg l21 during the accumu-

lation phase (Fig. 1b). In each of the successive two-day

incubations, there was a reduction in the total CYN content

of the media, with the exception of the first incubation where

total CYN increased from 14 to 38 mg l21. This result is

difficult to explain. However, in general, the reduction in

total CYN could be related to the removal of C. raciborskii

cells by Anodonta filtering activity (Fig. 1b).

The ratio of intra- to extra-cellular CYN concentration

varied from 0.5 to 4.5 over successive incubations (Fig. 1c).

The reduction in the concentration of C. raciborskii cells

(Fig. 1a) lead to a decrease in the ratio of intra- to extra-

cellular CYN in each of the successive two-day incubations,

due to the removal of the intra-cellular component of the

total media CYN concentration and therefore, to a relative

increase in the extra-cellular CYN content (Fig. 1c).

The intra-cellular CYN content of the medium correlated

strongly with the cell concentrations of C. raciborskii in the

medium (R2 ¼ 0:968; p ¼ 6:78 £ 10212; n ¼ 16) indicating

that the toxin quota per cell of the C. raciborskii cells

remained approximately constant during the 16-day

accumulation period. Based on these data, the C. raciborskii

strain used in this study was found to have a CYN content of

3.026 £ 1028 ^ 1.07 £ 1028 mg CYN cell21 (n ¼ 16;

mean ^ 1SD (N)).

Fig. 1. Variation in C. raciborskii cell concentrations in eight successive two-day incubations (a). Changes in the concentration of total CYN

(calculated by the addition of intra- and extra-cellular fractions) (b) and changes in the ratio of intra- to extra-cellular CYN over the 16-day

accumulation period (c).

M.L. Saker et al. / Toxicon 43 (2004) 185–194 187

Fig. 2. HPLC analysis of extracts of Anodonta exposed to a CYN-producing strain C. raciborskii. Chromatograms are shown for purified CYN

(a), an extract from the whole body of Anodonta (b), viscera (c), and haemolymph (d). CYN peaks identified in the extracts are represented by

asterisks, and the spectra of cylindrospermopsin from each tissue and for the purified toxin are inset into each chromatogram.

M.L. Saker et al. / Toxicon 43 (2004) 185–194188

The HPLC method was found to be useful for the

detection of CYN within the tissues of Anodonta exposed to

a CYN-producing culture of C. raciborskii. Fig. 2 shows

typical chromatograms for standard CYN (a), haemolymph

(b), viscera tissues (c) and a whole-body extract (d) from

Anodonta after 16 days of exposure to CYN-producing

cultures of C. raciborskii. Under the analytical conditions

used in this study, CYN had a retention time of

approximately 6.00 min. The retention times of CYN

extracted from the tissue samples varied by up to ^10%

compared with the standard. This variation did not interfere

with the positive identification of CYN, because peaks were

analysed for their characteristic absorbance spectra at

262 nm. The UV absorbance spectra are shown for standard

CYN, haemoymph, viscera and a whole-body extract from

Anodonta (Fig. 2(a)–(d)).

Anodonta were found to progressively accumulate CYN

over the eight successive incubations. CYN was detectable in

the samples after the first 2 days of exposure. The

concentrations of CYN in the haemolymph, viscera and

whole-body extracts of the Anodonta increased up to day 10

of exposure and were variable until day 16 (Fig. 3). The

maximum concentrations of CYN recorded for haemolymph,

viscera and whole-body extracts were 61.5, 5.9 and 2.9 mg g

dry weight21, respectively, with the highest values recorded

over days 10–16 of the accumulation phase. Small amounts

of CYN were detected in the mantle on days 10, 12 and 16

(maximum concentration 0.13 mg g dry weight21) and in the

foot plus gonad tissues on days 10 and 16 (maximum

concentration 0.75 mg g dry weight21). Thereafter, during

the depuration period, the Anodonta contained high concen-

trations of CYN, even after 16 days when they contained ca.

50% of the amount present at the end of the accumulation

phase. The pattern of accumulation/depuration appeared to

be bi-phasic with a peak of accumulation at days 10–16,

followed by a decrease at the beginning of the depuration

period and a subsequent rise in CYN concentration at days

22–28 (Fig. 3). This trend was evident for haemolymph,

viscera and whole-body extracts. Control animals were free

of CYN at the commencement of the exposures.

There was considerable variation in the quantity of CYN

present in different organs. The haemolymph and viscera

Fig. 3. Concentrations of CYN detected in the haemolymph (a), viscera (b), and whole-body (c) of Anodonta during exposure to 32 days. Data

show the mean of triplicate measurements with associated SD. Figure shows data trend line (broken line).

M.L. Saker et al. / Toxicon 43 (2004) 185–194 189

together accounted for over 90% of the total detectable CYN

content, although the distribution of CYN between these

two body parts varied versus time (Fig. 4a). At the end of the

accumulation period (day 16) the amounts of toxin

expressed as a percentage of the total toxin content of the

Anodonta were as follows; haemolymph (68.1%), viscera

(23.3%), foot/gonad (7.7%), mantle (0.9%) (Fig. 4a).

Within the haemolymph at the end of the accumulation

period, the concentration of CYN, expressed on a volume

basis was found to be 193 mg l21 (average from three

animals), much higher than the concentration of CYN in the

surrounding culture media at that time (46 mg l21). The

maximum concentration of CYN detected in the haemo-

lymph was 408 mg l21 on day 14 of the accumulation

period, when the medium contained 34 mg l21 (Fig. 4b).

The concentration of CYN within the whole-body tissues

correlated positively with the cumulative number of C.

raciborskii cells consumed by the Anodonta over the

preceding period (R2 ¼ 0:75; p ¼ 0:005; n ¼ 8) (Fig. 5).

4. Discussion

4.1. Accumulation of CYN within tissues of Anodonta

Previous studies investigating the accumulation of

cyanobacterial toxins in freshwater/marine mussels and

clams have investigated either the microcystins produced by

Microcystis and Oscillatora (Eriksson et al., 1989; Vascon-

celos, 1995; Prepas et al., 1997; Amorim and Vasconcelos,

1999) or the PSPs produced by Anabaena and marine

dinoflagellates (Chen and Chou, 2001; Negri and Jones,

1995). Among these reports there is a general agreement

that bivalves are quite resistant to cyanobacterial toxins

although it has been noted that there are differences in the

accumulation characteristics of different bivalve species

(Yokoyama and Park, 2002). In this study, following the 16-

day exposure of A. cygnea to CYN-producing cultures of C.

raciborskii there was no evidence of any adverse effects on

the animals, suggesting that as with other cyanobacterial

toxins, bivalves are resistant to high concentrations of CYN.

Studies of the distribution of cyanobacterial toxins in

bivalve tissues have shown that the majority of toxin is

present in the visceral mass, resulting from the consumption

of toxin-containing cells and the presence of cyanobacterial

toxins in the alimentary tract. Vasconcelos (1995) reported

that in Mytilus galloprovincialis, 95% of the detected toxin

was contained within the digestive gland. Similarly, for a

study of PSP distribution within the freshwater mussel

Alathyria condola 96% of the total toxin was detected in the

viscera (Negri and Jones, 1995). However, for the genus

Anodonta, the results appear to be more variable. Eriksson

et al. (1989) reported that for A. cygnea, ca. 90% of the toxin

was present in the hepatopancreas and viscera while Prepas

Fig. 4. Changes in the percentage distribution of CYN in the haemolymph (X), viscera (W) and other tissues (P) of Anodonta over a 16-day

accumulation period and a 16-day depuration period (a). Concentration of CYN detected in the haemolymph of Anodonta exposed to a CYN-

producing culture of C. raciborskii (W) and concentration of total CYN in the surrounding medium (X). Days 1–16 represent the accumulation

phase and days 16–32, the depuration phase. Results are expressed as mg CYN l21 ^ SD ðn ¼ 3Þ (b).

M.L. Saker et al. / Toxicon 43 (2004) 185–194190

et al. (1997) reported that for A. grandis simpsoniana, the

total toxin content was divided evenly between visceral

mass, gills and muscle tissue. No studies to date have

reported the concentrations of cyanobacterial toxins present

in the haemolymph, which is surprising considering that this

fluid comprises ca. 50% of the animal wet weight.

In this study, the haemolypmph was found to contain the

highest concentrations of CYN. The maximum concen-

tration of CYN detected in the haemolymph (and expressed

on a volume basis) was 408 mg l21 (equivalent to

61.5 mg g dw21), a value much higher than the total CYN

content (addition of intra- and extra-cellular CYN pools) of

the surrounding media which contained a maximum CYN

content during the accumulation period of 90 mg l21. This

demonstrates that Anodonta accumulated CYN rather than

reflecting only the ambient toxin content of the surrounding

medium. The ability of Anodonta to accumulate CYN over

time was also demonstrated by the relationship between the

concentration of CYN in the whole-body extracts and the

calculated accumulative number of C. raciborskii cells

consumed per gram of mussel wet weight (Fig. 5). This

relationship suggests that exposure times and exposure

concentrations can be used to predict the amount of CYN

present in A. cygnea.

However, the rate of clearance varied versus time. Over

days 1–10 of the accumulation period, the mussels cleared

ca. 80–90% of the C. raciborskii cells from the medium.

Thereafter, over days 10–16, the clearance rate was much

lower (ca. 20–30%). In our investigations there was no non-

toxic control of C. raciborskii cells, so we cannot speculate

on whether the reduction in the clearance rate over the

accumulation period was in response to avoiding the

consumption of toxin-containing cells. However, the ability

of some mussel species to cease feeding when in the

presence of high concentrations of toxic cyanobacteria has

been discussed by Negri and Jones (1995).

After the first 2 days of depuration, the amount of toxin

in the tissues was reduced by ca. 50% and then interestingly

increased from days 22 to 28 (Fig. 3). This bi-phasic pattern

has also been noted in a study of the accumulation of

microcystin in Mytilus by Amorim and Vasconcelos (1999).

Clearly, the toxin could not have been derived from the

medium as tests showed that no CYN was present (Fig. 1b).

In studies investigating the accumulation of microcystins in

Mytilus, this bi-phasic pattern has been attributed to the re-

release of tissue-bound microcystin-LR, which was not

detected by the HPLC method used in that study.

Microcystins are known to undergo a further fate, namely

glutathione S-transferase-catalysed detoxication. This

occurs in a wide range of aquatic organisms, including

mussels (Pflugmacher et al., 1998). Whether CYN can also

be detoxified in mussels is not known.

4.2. Risk assessment for the consumption of aquaculture

products contaminated with CYN

Assessment of the risks to human health arising from the

consumption of water contaminated with toxic cyanobac-

teria is usually based on data obtained from bioassays (i.p. or

oral mouse). A recent study by Humpage and Falconer

Fig. 5. Relationship between the concentration of CYN in whole-body tissues (mg CYN g dw21) and the cumulative quantity of C. raciborskii

cells consumed by Anodonta over eight successive two-day incubations. R2 ¼ 0:75; p ¼ 0:005; n ¼ 8:

M.L. Saker et al. / Toxicon 43 (2004) 185–194 191

(2003) determined a NOAEL for CYN to mice (oral

administration) based on a 14-day trial of 30 mg kg21 -

day21. As standard practice, NOAEL values are used to

calculate water quality guideline values, by incorporating

uncertainty factors (UF) for intra- and inter-specific

variation and less-than-lifetime exposure. Assuming a

human body weight of 60 kg and water consumption of

2 l day21, a guideline value of 0.81 mg l21 was obtained

(Humpage and Falconer, 2003).

Similar calculations can be applied to evaluate the

potential risk to consumers of the consumption of food

contaminated with CYN. Using the NOAEL value (30 mg

kg21 day21) from Humpage and Falconer (2003) and

incorporating UF’s for intra- and inter-species variation and

less-than-lifetime exposure of 10, 10 and 10, respectively, the

Tolerable Daily Intake (TDI) is calculated as follows

TDI ¼ NOAEL=UF

¼ 30=ð10 £ 10 £ 10Þ

¼ 0:03 mg kg21 day21

Using the TDI value of 0.03 mg kg21 day21, calculated over a

trial time period ðDÞ of 14 days (Humpage and Falconer,

2003), for an average adult of body weight (bw) of 60 kg and

allowing for an additional chronic/sub-chronic uncertainty

factor ðFÞ of 10 over a 2-week period, the maximum allowable

intake is calculated as follows

Maximum allowable intake ¼ ðTDI £ F £ bw £ DÞ

¼ ð0:03 £ 10 £ 60 £ 14Þ

¼ 252 mg CYN

Using fortnightly seafood intake of fish, prawns and mussels

obtained from food surveys of 1600, 350 and 270 g,

respectively (Van Buynder et al., 2001), the derived health

alert level for CYN in seafood are as follows

Fish ¼ 158 mg kg wet wt21

Prawns ¼ 720 mg kg wet wt21

Mussels ¼ 933 mg kg wet wt21

Table 1 shows a summary of the maximum tissue

concentrations of CYN recorded for the freshwater crayfish

C. quadricarinatus (Saker and Eaglesham, 1999) and

A. cygnea (results from this study). C. quadricarinatus is

cultured commercially for human consumption. A. cygnea

is not cultured commercially, although it is known to be

consumed by people living around the margin of Lake Mira

and other lakes in Portugal where this bivalve occurs. The

concentrations of CYN within crayfish hepatopancreas and

swan muscle viscera are above the calculated maximum

allowable concentrations for prawns (proxy for crayfish)

and mussels, respectively, indicating a potential human

health risk. For crayfish, only muscle tissue is usually

consumed by humans and for mussels, the viscera only

represent a small proportion of the total body mass (ca. 6–

9% of the wet weight) which might limit the risk to humans.

It should be noted, however, that freshwater organisms in

natural environments can be exposed for much longer

periods than are usually employed in laboratory-based

experiments, and based on the results of this study, longer

exposure times and higher exposure concentrations could

potentially lead to much higher tissue concentrations

(Fig. 5). Furthermore, there is a much higher risk to

animals that consume the whole body.

The concentrations of C. raciborskii used in this study

(200–2000 £ 103 cells ml21) are within the range reported

for natural lakes and reservoirs (Bouvy et al., 2000;

McGregor and Fabbro, 2000; Saker and Griffiths, 2001;

Griffiths and Saker, 2003). The concentrations of toxins

used in the accumulation experiments (ca. 10–90 mg l21)

are also frequently encountered in natural lakes and

reservoirs, although much higher concentrations (up to

589 mg l21) have been reported from aquaculture ponds

(Saker and Eaglesham, 1999). Further studies are required

to investigate the potential transfer of CYN to higher

trophic levels.

Acknowledgements

This study was funded by a post-doctoral scholarship to

M.L. Saker provided by the Fundacao para a Ciencia e a

Tecnologia (SFRH/BPD/8059/2002). G.A. Codd and J.S.

Metcalf acknowledge financial support from the European

commission (EVKI-CT-2002-00107, TOXIC).

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Table 1

Maximum recorded concentrations of CYN in the tissues of

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blooms

Organism/tissue Maximum recorded

concentrations

(mg kg wet wt21)

Reference

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Crayfish hepatopancreasa 2312 Saker and

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Swan mussel viscera 1099 This study

Swan mussel whole-body 247 This study

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