Blue-green Algal Toxin (Microcystin)

Levels in Minnesota Lakes

By M. J. Lindon and S.A. Heiskary July 2008

No. 11

Abstract!Recent interest in blue-green algal toxins has led to increased monitoring to assess occurrence

and levels of toxins in Minnesota lakes. Microcystin (MC), a hepatotoxin, is one of the primary toxins studied

in Minnesota and elsewhere in North America. The MPCA has measured MC in numerous lakes across

Minnesota as a part of three separate, but related, efforts: 1) A targeted survey conducted in 2006 to assess

MC levels in 12 eutrophic lakes in two south-central Minnesota counties to determine the prevalence and

seasonal trends in MC and to assess environmental variables associated with elevated MC; 2) A stratifiedrandom survey of 50 lakes in Minnesota as a part of the National Lake Assessment Project (NLAP); and 3)

Incident-based samples from various lakes during 2004-2007 with reports of severe nuisance algal blooms,

potential for human health risk and/or documented dog deaths as a result of algal toxins. This article will

focus on the 2006 study and links between MC and other chemical, physical and biological measures. Data

from the other two efforts are used to place the 2006 results in perspective and provide a good representation of MC concentrations that may be encountered in MinnesotaUs lakes. Better understanding of this toxin

and its relationship and linkages to other water quality parameters will allow for better risk management and

public awareness.

Introduction

Cyanobacteria, often referred to as blue-green algae, are

a common component of the algal community in lakes and

rivers in Minnesota and elsewhere in the world. It has been

long known that certain forms of blue-greens have the

ability to produce toxins and these toxins have been implicated in animal deaths and human-health problems. These

toxins, which include anatoxin, saxitoxin, microcystin and a

more recently described toxin, cylindrospermopsin, vary in

their toxicity. Of these, microcystin (MC) is the most commonly measured in most studies. MC is an acute hepatotoxin (liver-affecting toxin) produced by several genera of

blue-green algae including: Anabaena, Coelosphaerium,

Lyngbya, Microcystis, Oscillatoria, Nostoc, Hapalosiphon

and Anabnaenopsis. MC has also shown to be carcinogenic

(Chorus and Bartram 1999).

While there has long been concern regarding blue-greens

and the production of toxins (Carmichael and Gorham

1977), recent literature shows numerous efforts in countries

such as Australia (Brookes and Bruch 2004), Germany

(Chorus et al. 2001), and the United States (Graham et al.

2005) intended to improve understanding of this issue, the

factors that lead to toxicity and the ability to manage the

blooms that cause the toxicity.

Blue-green algae have several properties that contribute

to their success in lake communities. Perhaps the most

significant is the ability to control their buoyancy to optimize

light and nutrient conditions. This property also allows for

the buildup of scums under the right conditions. Algae at

the surface water interface can take advantage of abundant

light, as well as atmospheric carbon and nitrogen. The

buildup of algal scums is not only related to nutrient concentration and buoyancy, but is also influenced by climatic

factors such as wind, sunlight and other chemical and

physical factors.

Blue-green algal toxicity is not a new issue in Minnesota.

Olson (1949, 1954, and 1960) documents several incidences

of blue-green algal blooms in Minnesota that have led to

animal deaths, including cattle, horses and dogs. Some of

these accounts date back to the late 1800s with animal deaths

attributed to contact with blue-green blooms on Lake

Elysian, near Waterville. Documented incidences were also

noted in the Fergus Falls area in 1900 and various other

incidents from 1918 to 1934. Studies conducted at that time

associated the toxicity with the blue-green genera: Anabaena,

Aphanizomenon, Coelosphaerium, Lyngbya, and Microcystis.

Toxic blue-green blooms were noted on Lake of the Isles

Lagoon and Kenilworth Lagoon in 1918 (Buell 1938).

tdr-eb08-11
ENVIRONMENTAL BULLETIN - No. 11 -2- Minnesota Pollution Control Agency

In the mid 1980s, isolated reports of animal deaths

(typically dogs), presumably caused by blue-green algal

toxins, prompted renewed interest in this subject and some

work was conducted by the MPCA and collaborators to

take a closer look at this issue. In recent years (2004 I 2007),

several dog deaths, potential human health impacts and

reports of very severe nuisance blooms have been reported.

MC and supporting water quality data are typically collected

in the course of these MincidentN investigations.

In 2005 MPCA joined with the Minnesota Department

of Natural Resources (MDNR), Minnesota Department of

Health (MDH) and the Minnesota Veterinary Medicine

Association to form the Minnesota Blue-green Algal Toxicity

Workgroup to share information on blue-green algal toxicity,

increase awareness within agencies and the veterinarian

community and develop a public information campaign to

raise awareness among the public. This resulted in development of a poster that was displayed in public places and

veterinarian offices, several news releases and fact sheets, and

an updated web site for further information and links to

other states. These discussions also led the workgroup to the

opinion that Minnesota had minimal information on magnitude and frequency of occurrence of MC in MinnesotaXs

lakes.

In summer 2006 a study was conducted to characterize

the magnitude and variability of MC concentrations in a set

of eutrophic to hypereutrophic lakes. For this purpose, 12

lakes in south central Minnesota were selected with six each

in the counties of Blue Earth and McLeod. The questions

we sought to answer from this study include:

z What is the likelihood of encountering measurable MC

at a pelagic (also referred to as mid-lake or index) site

in a eutrophic to hypereutrophic lakes?

z What is the likelihood of the same when measuring

MC at a near-shore site?

z What is the distribution of MC values for both midlake and near-shore sites? Are these distributions

significantly different?

z How do values from this study compare to levels

found elsewhere? How do they compare to World

Health Organization guideline levels?

z Is there some seasonality to MC levels in these lakes?

z As bloom intensity (chlorophyll-a) increases, is there a

greater likelihood of encountering high MC values?

z What limnological and physical factors appear to be

associated with high MC concentrations?

z How can these findings be used to communicate risk

to lake users?

Two additional MC data sets will be compared with the

2006 data. In 2007 MC samples were collected as a part of

the National Lakes Assessment Project (NLAP). In contrast

to the 2006 study, the NLAP lakes were randomly selected

as a part of this nationwide, statistically based sampling

effort. Details on NLAP may be found at http://

www.pca.state.mn.us/water/nlap.html. A second data set is

derived from MPCA incident-based monitoring in response

to citizen concerns regarding severe nuisance blooms, dog

deaths and/or potential human-health problems for the

period 2004-2007.

Background

Study Area

The 2006 study focused on south central Minnesota near

the North Central Hardwood Forest (CHF) and Western

Corn Belt Plains (WCP) ecoregion transition (Figure 1)btwo

ecoregions with numerous eutrophic to hypereutrophic lakes.

Figure 1: 2006 study lake locations and ecoregion map
ENVIRONMENTAL BULLETIN - No. 11 -3- Minnesota Pollution Control Agency

To the best of our knowledge, MC data was not collected

previously for any of the study lakes. The 2007 NLAP lakes

were distributed statewide (Figure 2) consistent with the

stratified random study design. In addition to these two

studies, Hincident-basedJ MC samples were collected as a

part of investigations on select lakes in 2004-2007. The

majority of these lakes were located in central or southern

Minnesota.

Climate

Summer 2006 was characterized by droughty conditions

throughout much of central Minnesota. In general, May

through August temperatures were above normal while

September was below the long-term norm in both areas.

Precipitation was generally below normal for the May

through August period and returned to normal to above

normal in September. The northern portion of the study

area experienced five one-inch or greater events from May

through September, while the southern portion was somewhat drier. Summer 2007 was characterized by warm and

dry conditions as well with May and June being particularly

warm relative to the long-term records.

Figure 2: 2007 NLAP study lake locations
ENVIRONMENTAL BULLETIN - No.11 -4- Minnesota Pollution Control Agency

Materials and Methods

Sample location, collection and laboratory

analysis

In the 2006 study, pelagic sites were selected based on

established sampling sites whenever possible, and were

typically located near the site of maximum depth. Nearshore sites were often located near a downwind shoreline

area that allowed for accumulation of algae and often

resulted in a distinct algal scum on the surface of the water.

While pelagic sites were constant among sample events, the

near-shore sites varied depending on the wind direction and

intensity and presence of an algal bloom.

Samples were collected monthly from May through

September. Standard water quality parameters were collected at the pelagic site using a two-meter integrated

sampler. Near-shore water quality and all MC samples were

collected as surface grab samples. When scums were present,

near-shore samples were collected in the midst of the scum.

Water chemistry samples and field measurements were taken

near the MC sample.

Several field observations were made at each sample

event. Dissolved oxygen (DO), temperature, pH, and

conductivity profiles (at one-meter intervals) were made at

each pelagic site and surface measures were typically taken at

the near-shore site. Secchi transparency was taken at all

pelagic sites. Other observations included our standard

subjective assessment of the physical condition and recreational suitability of the lake (Heiskary and Walker 1988) and

basic observation on wind intensity and direction and

percent cloud cover.

 Chlorophyll-a (Chl-a) samples were filtered on the day

of collection, filters placed in Petri dishes and wrapped in

foil. Samples were chilled on ice or frozen prior to shipment to the MDH for analysis. Samples for qualitative

assessment of the algae were subset at the time of filtering

and preserved in Lugols. These samples were later identified

to family or genera in most cases by Dr. Howard Markus

of the MPCA using the Minnesota Rapid Algal Analysis

Procedure. This technique provides a semi-quantitative

estimate of the relative biomass of the phytoplankton

community and focuses on the dominant forms in the

sample. This allowed for an estimate of the relative amount

of MC-producing genera in the sample.

All water quality samples, with the exception of phytoplankton, were analyzed by the Minnesota Department of

Health (MDH) lab in St. Paul. Method numbers, associated

quality assurance information and all raw data are available

in the detailed report (Lindon and Heiskary 2007).

Lakes in the 2007 NLAP study were sampled once in

either July or August 2007. A majority of the water quality

samples (including MC) were collected from a mid-lake

(index) site. MC was also collected from a random nearshore site on each lake in conjunction with other near-shore

measurements. The random sites were established in the

office prior to going into the field so there was no subjectivity in their selection. Full details on NLAP parameters

measured and sampling procedures may be found at:

http://www.pca.state.mn.us/water/nlap.html

MC analysis and data management

Analysis was done by MDH using a bench-top Abraxis

ELISA method, with a method detection limit of 0.15 μg/L

total MC (for purposes of statistical analysis a non-detect

substitution of 0.075 μg/L was used). MC samples underwent a triple freezing cell lysis procedure. The MC analysis

conducted for this study is considered as a quantification of

MC congeners including nodularins and is intended to

represent total MC. It has an assay method maximum

quantifiable range of 5 μg/L that requires dilution of

samples when concentrations are above this range. This can

result in reduced accuracy depending on the amount of

dilution. A summary of MC quality assurance, based on

samples from the summer of 2006, is as follows:

z Percent recovery within 90-110% - 67%

z Percent recovery within 75-125% - 100%

z Coefficient of variation (CV) between

sample and replicate <15% - 56%

z CV between sample and replicate <25% - 100%

World Health Organization (WHO) risk guidelines,

established for recreational waters and drinking water,

provide a basis for placing the MC data in perspective and

describing relative risk. Though the guidelines are based on

the congener LR as described in Guidelines for Safe Recreational Water Environments (WHO 2003), they are often

used as a basis to evaluate total MC data. MC LR is considered the most frequently occurring form of MC (Chorus

and Bartram 1999). The categories used are as follows:

z <1 μg/L very low risk

z 1- 10 μg/L low risk

z 10 - 20 μg/L moderate risk

z 20 c 2000 μg/L high risk

z > 2,000 μg/L very high risk

The four categories from 1 to >2,000 μg/L were drawn

directly from the WHO guidelines. The very low risk

category was added to include those measurements that were

very near the method detection limit for MC and below the

1 μg/L drinking water guideline for MC LR.
ENVIRONMENTAL BULLETIN - No. 11 -5 Minnesota Pollution Control Agency

Results and Discussion

2006 seasonal patterns in chemical, physical and

biological measures

Surface water temperatures ranged from about 14-16 C

in May to peak temperatures on the order of 26-30 C in late

August. Surface temperatures peaked in the northern

(McLeod County) lakes in July, while the southern (Blue

Earth County) lakes peaked in early August. A rapid cooling

in most lakes was evident in September, consistent with a

rapid decline in air temperature. Temperatures were conducive for blue-green algal growth (in excess of 22 C) from

June through late August on most lakes.

All lakes were eutrophic to hypereutrophic based on TP,

Chl-a and Secchi. TP ranged from less than 40 μg/L (StahlPs

and Ballantyne) to over 300 μg/L (Otter and Silver). Based

on previously-defined levels (Heiskary and Walker 1988) of

Chl-a, Vsevere nuisanceW (Chl-a > 30 μg/L) and Vvery severe

nuisanceW (Chl-a >60 μg/L) conditions were common

throughout the summer at the pelagic sites on these lakes

(Figure 3a). Chl-a was frequently higher at the near-shore

sites (expected given the subjective nature of the near-shore

sample collections) as compared to the pelagic sites

(Figure 3b.)

MC was highly variable within and among lakes (Figures

4a & b). Over 25% of the data is between 0.9 μg/L and

the non-detect substitution of 0.075 μg/L (Figures 5a & b).

One μg/L and greater results were unevenly distributed up

to 8,400 μg/L. Since MC maxima are of the most concern

they were not considered as outliers. Six percent of MC

results were below the detection limit. Near-shore and

pelagic sites exhibited different distributions and have

statistically different means based on a log normalized t-test

and 95% confidence intervals; however, near-shore and

pelagic medians were not significantly different.

About 85 percent of the pelagic samples were considered very low to low risk (Figure 5a). Likewise, a high

percentage of the near-shore samples were in these categories as well. Distributions for the moderate- to high-risk

categories were not substantially different among the pelagic

and near-shore sites; however, the only very high risk measures were found at the near-shore sites (Figure 5a).

Toxic incidents involving MC or other blue-green algal

toxins are most frequently associated with large surfacebloom-forming genera (Chorus and Bartram 1999; Chorus

et al. 2001). Though it was common for the pelagic sites to

have distinct green coloration and high Chl-a, surface scums

were limited to the near-shore sites. Even at the near-shore

sites distinct surface scums were not that common (Figure

5b). In a comparison of sites with and without surface

scums, it was evident that the sites with surface scums

exhibited higher and more variable MC concentrations

compared to sites without scums (Figure 5b). Also, the

likelihood of moderate to very high risk MC concentrations

was found to be greater at sites with a distinct surface scum.

These results are consistent with observations by Graham et

al. (2004) when they note that MC in scums may be much

greater than at pelagic locations.

MC exhibited no consistent seasonal pattern at either the

pelagic or near-shore sites (Figures 4a & b). Silver and Hook

lakes exhibited the highest pelagic concentrations and had the

only concentrations that fell in the moderate risk level

(Figure 4a). In contrast, seven of 12 lakes were below the

low risk threshold (10 μg/L) for the entire summer at the

pelagic site. High- to very high-risk concentrations were

noted at near-shore sites on three lakes: Madison, Hook and

George (Figure 4b). Some of the highest concentrations

were from samples collected in May and June, which was

not expected.

2006 MC and other environmental factors

Field and laboratory studies have demonstrated that the

relationship between cyanobacteria, MC concentration and

environmental factors is invariably complex (Graham et al.

2004). Some work indicates that variations in strains among

toxin-producing species have more impact on MC production than environmental factors (Chorus and Bartram 1999).

Thus without getting to this level of analysis, isolating key

environmental factors affecting MC is often difficult.

Associations among MC and several chemical, biological,

and physical parameters were evaluated using the nonparametric SpearmanPs rank correlation coefficient (Rs

). These

comparisons resulted in four moderate and three high

correlations with MC (Figure 6). Parameters exhibiting

strong positive Rs with MC included: pH, Chl-a of MC

producers, % Chl-a of MC producers, total suspended

volatile solids (TSV), Chl-a, and subjective measures of

physical condition. Negative relationships were found with

alkalinity, Secchi depth and specific conductance.

Chl-a concentrations and trends were highly variable

among the study lakes (Figure 3) and no significant linear

relationship was evident between MC and Chl-a. Several

lakes had extremely high Chl-a through the majority of the

summer. Pelagic-site Chl-a concentrations from Silver and

Hook lakes (Figure 4a) were among the highest in the study

as was the case for MC (Figure 3a). In contrast, Chl-a for

Loon and Otter lakes was also very high but MC was very

low (Figures 3 and 4). MC had a moderate relationship with

TSV (Rs

=0.51; Figure 6); however, this relationship is likely a

function of the high collinearity with Chl-a, since algae

comprise much of the TSV in these lakes.
Near-shore sites

0 20 40 60 80 100 120 140 160 180 200

Ballantyne

Cedar

Duck

Eagle

George

Hook

Loon

Madison

Marion

Otter

Silver

Stahls

Chl-a μg/L

ENVIRONMENTAL BULLETIN - No. 11 -6- Minnesota Pollution Control Agency

Figure 3a: 2006 pelagic (mid-lake) chlorophyll-a

concentrations by lake and date

Figure 3b: 2006 near-shore chlorophyll-a

concentrations by lake and date

Pelagic Chlorophyll-a values that exceed 200 μ/L

Lake Value Month

Silver July 218

Silver Early August 365

Silver Late August 284

Silver Mid-August 289

Near-shore Chlorophyll-a values that exceed 200 μg/L

Lake Month Value

Silver Early August 357

Silver Late August 293

Marion Early August 284

George July 238

Pelagic sites

0 20 40 60 80 100 120 140 160 180 200

Ballantyne

Cedar

Duck

Eagle

George

Hook

Loon

Madison

Marion

Otter

Silver

Stahls

Chl-a μg/L

May

June

July

Early August 

Late August 

September
Figure 4a: 2006 pelagic (mid-lake) microcystin (MC)

concentrations by lake and date

Figure 4b: 2006 near-shore microcystin (MC)

concentrations by lake and date

ENVIRONMENTAL BULLETIN - No. 11 -7- Minnesota Pollution Control Agency

Near-shore sites

0 20 40 60 80 100

Ballantyne

Cedar

Duck

Eagle

George

Hook

Loon

Madison

Marion

Otter

Silver

Stahls

μg/L MC

May

June

July

August Early

August Late

September

99

2,200

140

Pelagic sites

0 20 40 60 80 100

Ballantyne

Cedar

Duck

Eagle

George

Hook

Loon

Madison

Marion

Otter

Silver

Stahls

μg/L MC

May

June

July

August Early

August Late

September

8250
MC distribution by site and risk category 

11

33

5

8

2

25

37

6 6

0

5

10

15

20

25

30

35

40

0.075-1 >1-10 >10-20 20-2000 >2000

Low Risk Low Risk Moderate High Risk Very High

MC distribution within WHO risk categories (ug/L)

Frequency

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Cumulative

Near shore Sites

Pelagic Sites

Near shore Site Cumulative %

Pelagic Site Cumulative %

Near-shore MC as a function of scum occurence

2

8

3 2 2

9

24

1

3

0

5

10

15

20

25

30

0.075-1 >1-10 10-20 20-2000 >2000

Low Risk Low Risk Moderate Risk High Risk Very High risk

MC distribution within WHO risk categories (ug/L) 

Frequency

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Cumulative

Bloom site w/ scum

Bloom site w/o scum

Cumulative % w/ scum

Cumulative % w/o scum

Figure 5a: 2006 MC frequency distribution comparison for mid-lake (pelagic) and near-shore sites

Figure 5b: 2006 near-shore MC frequency distribution comparisons for sites with scum vs. no scum

ENVIRONMENTAL BULLETIN - No. 11 - 8- Minnesota Pollution Control Agency
ENVIRONMENTAL BULLETIN - No. 11 -9- Minnesota Pollution Control Agency

Combining MC and bloom intensity provides a basis for

describing the 7risk9 of encountering specified levels of MC as

a function of bloom intensity. Based on Figure 7a, moderaterisk MC concentrations were not encountered until blooms

exceeded 30 μg/L (7severe nuisance9). As blooms exceeded

30 μg/L, the frequency of moderate- to high-risk MC increased to 12 percent and above 50 μg/L the likelihood of

encountering moderate to high risk MC increased to 28

percent. All high risk MC concentrations were associated with

Chl-a > 30 μg/L.

A strong inverse relationship between Secchi and algal

biomass (Chl-a) has long been noted. Secchi depth also

exhibits an inverse relationship with MC (Figure 6). Similar to

the relationship between MC and bloom intensity, there is

somewhat of a threshold effect; as Secchi declines below

0.5 m, there is an increased frequency (risk) of moderate- to

high-risk MC (Figure 7b). Dense blooms of MC-producing

blue-greens, such as Anabaena and Microcystis, routinely result

in very low transparency.

The variable with the strongest relationship with MC was

pH (Rs

=0.73; Figure 6), which is consistent with correlations

observed by Paerl and Ustach (1982). In the 2006 study, high

correlation with pH is likely a reflection of algal productivity

(Chl-a Rs=0.58). Wetzel (2001) notes 7rapid photosynthesis can

rapidly reduce total dissolved inorganic carbon (DIC) and

increase pH.9 Further, cyanobacteria prefer a high pH

environment (Shapiro 1973). Over 90% of the pH values

>9.0 was associated with severe nuisance bloom levels

(Chl-a >30 μg/L). All high-risk MC concentrations

corresponded to pH levels >9.0 (Figure 7c). As a matter

of perspective, the state water quality standard for pH is

9.0 and a typical pH range for WCP ecoregion lakes is 8.2

a 9.0.

Conversely, alkalinity exhibited a moderate negative

relationship (Rs = 0.61). It is unlikely that alkalinity is a

direct driver of MC production; rather it may reflect the

superior competitive advantage that blue-greens have at

low DIC concentrations, which are most likely to occur in

eutrophic, low alkalinity systems at high pH. In the 2006

study all pH values of 9.0 or greater were associated with

alkalinities of 150 mg/L or less.

MC comparison among studies

A comparison of the 2006 study of 12 eutrophic

lakes with the NLAP and incident-based samples provide

further perspective on MC concentrations in Minnesota

lakes (Figure 8). Based on this comparison, it is evident

that the distributions of these three data sets are

Figure 6: 2006 Spearman correlation coefficients (R) for various parameters relative to MC.

Parameters sorted by R value. Negative (-) implies inverse relationship between parameter

and MC.

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Alkalinity

Secchi 

Spec. Cond.

Temp.

Cl

Color

Pheo.

TSS

TP

% BG

Suit. Rec.

TKN

Phys. Cond.

Chl a

% MC Producers

TSV

Chl-a of MC P.

pH

R

6SHDUPDQ5

High 

Moderate

Very High
ENVIRONMENTAL BULLETIN - No. 11 -10- Minnesota Pollution Control Agency

Figure. 7a,b, c: Microcystin (MC) as a function of a) bloom intensity (chl-a concentration); b) Secchi; and c) pH

0 1

5 5

2

2 2

32

22

18 18

0000

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

<30 30-50 50-80 > 80

Chl-a Range (μg/L) and Bloom Intensity

< 1 ug/L MC

>1-10 

>10-20 

>20-2000 

>2000 

2

4

1

2

3

6

10

12

18

5 6

0

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

 < 0.3 0.3 - 0.4 0.5 - 0.7 >0.7

Secchi range (meters) 

< 1 ug/L MC

>1-10 

>10-20 

>20-2000 

8

2 1

4

4

11

21

11

17

10

2

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

 < 8.6 8.6-8.8 8.8-9.0 > 9.0

pH range 

< 1 ug/L MC

>1-10 

>10-20 

>20-2000 

>2000 

a.

b.

c.
ENVIRONMENTAL BULLETIN - No. 11 -11- Minnesota Pollution Control Agency

significantly different, which comes as no surprise given the

population of lakes sampled and focus of each study. As

expected, the 2006 eutrophic lakes exhibit a larger range

and more extreme MC concentrations as compared with

the NLAP data (Figure 8). Both of these data sets reveal

higher MC concentrations at near-shore sites as compared

to mid-lake index sites. The incident-based sampling

yielded some extremely high event-based values, which

again is not too surprising given the intensity (magnitude)

of the blue-green blooms sampled.

Figure 8: Comparison of frequency distributions for:

2006 study (index and near-shore), 2007

NLAP study (index and near-shore), and

complaint-based data.

Summary

Cyanobacteria have the ability to produce several

different toxins, which may be acutely and chronically

toxic. There has been extensive study worldwide on this

issue. Numerous articles in the literature document toxic

events attributed to cyanobacteria, describe the toxicity and

action of the various toxins, and describe development of

action levels and thresholds that express the relative risk of

these toxins. Other studies such as Graham et al. (2004)

describe the distribution of particular toxins (e.g., MC) and

some environmental factors that may contribute to production of the toxin.

The 2006 study focused on one of the toxins, MC, in

eutrophic to hypereutrophic lakes in south-central Minnesota. Several questions intended to advance knowledge on

the extent, magnitude and frequency of MC in Minnesota

lakes were posed. The questions listed in the Introduction

provide a basis for organizing the following summary

comments:

z MC was above the MDL (>0.15 μg/L) in over 94% of

the 133 samples collected from May \ September at both

near-shore and pelagic sites. Over 60% of the pelagic MC

samples were 1 μg/L or less as compared to 25% of the

near-shore samples. The near-shore samples exhibited a

much larger range (Figure 4b) and much higher maximum

value (8,400 μg/L) as compared to the pelagic samples

(77 μg/L). Likewise near-shore mean and median MC

was higher than the pelagic samples.

z WHO guidelines provided a basis for evaluating the

relative risk of the MC levels measured in this study. 80%

of all MC values were in the WHO low risk category for

recreational waters (82% pelagic and 72% near-shore). The

remainder of the pelagic samples was in the moderate to

high risk category (Figure 4a). Only two near-shore

samples were in the very high risk category (Figure 4b).

z It was anticipated there would be some seasonality to the

MC concentrations, perhaps consistent with patterns often

observed for Chl-a and nuisance algal blooms \ whereby

late summer is often characterized by elevated Chl-a and

severe nuisance blue-green algal blooms. However, based

on the 2006 study, there was no distinct seasonality to MC

concentrations. This was due in part to a couple of lakes

that exhibited very high MC in May and June at near-shore

sites. The incident-based sampling and dog deaths (2004-

2007) also indicate that elevated MC may occur at any

time in the summer.

z A relatively distinct relationship was observed among MC

and algal bloom intensity. When Chl-a remained < 30 μg/

L, MC was in the very low to low risk categories (Figure

7a). As Chl-a increased to the 30-50 μg/L range, MC was

in the moderate- to high-risk range in about 12% of the

samples and as Chl-a increased to > 50 μg/L, the moderate to high MC risk increased to approximately 30%.

High and very high risk MC were found only when Chl-a

was > 30 μg/L.

z Several limnological and physical factors were tested for

their association with MC. Because of extreme values and

a non-normal distribution, nonparametric Rs

 was used for

this purpose. Based on Rs strong positive relationships

with MC were noted (in order of Rs) for pH, Chl-a of

MC producers, TSV, %MC producers, Chl-a and physical

condition rating. Strong negative relationships were found

for alkalinity, Secchi and specific conductivity. This

suggests that as the relative abundance of MC-producing

genera increases, MC increases as well. The correlations

with pH and alkalinity are to some degree an expression

of algal productivity and buffering capacity of the lakes.

With the exception of one sample, all lakes with high MC

risk had a pH of 9.3 or greater. The negative correlation

0.1 1.0 10.0 100.0 1000.0 10000.0

Log MC μg/L

07 NLAP Index

07 NLAP Near-shore

Index 06 study

Near-shore 06 study

04-07 Response
ENVIRONMENTAL BULLETIN - No. 11 -12- Minnesota Pollution Control Agency

with Secchi is a function of the overall abundance of .

algae (Chl-a) and that several of the MC-producing

genera have small cells that form dense colonies that

limit light. In this study moderate- to high-risk MC was

found only when Secchi was 0.5 m or less.

The 2006 study, as is the case with most studies on MC,

does not allow for precise prediction as to which blue-green

algal blooms will produce MC in the moderate to very high

risk range. However, it does suggest that MinnesotaGs

current recommendations to the public to avoid contact

with severe nuisance blooms is sound advice. Severe and

very severe nuisance blooms are readily recognizable to staff

and public in general. Further, it was found that moderate

to high MC was often associated with high pH ( > 9.3) and

low Secchi (<0.5 m), two parameters that are easy to

measure. Further, three independent data sets indicate that

MC is measurable across a wide range of Minnesota lakes

and collectively, they provide a good basis for evaluating

MC results from future monitoring efforts

Risk communication

Minnesota does not have widely accepted thresholds

(nor do most states) for assessing MC risk for aquatic

recreational use. Hence WHO thresholds were used as a

basis to assess risk; however, no attempt was made to assess

their validity for assessing risk in MinnesotaGs waters. Further

review of WHO and related MC thresholds should be

conducted among resource management agencies. This

review would ideally result in mutually agreed upon thresholds for assessing and communicating MC risk to humans

and animals. Also from a risk communication standpoint, it

is important to remember that several other toxins (e.g.

saxitoxin and anatoxin) may be produced by Cyanobacteria

as well as other algae. It may be of value to determine their

relative concentrations and how they vary relative to MC,

Chl-a and other factors in future studies.

References

Brookes, J. and M. Bruch. 2004. Toxic Cyanobacteria

Management in Australian Waters. LakeLine 24(4):29-32

Buell, H. 1938. A Community of Blue-Green Algae in a

Minnesota Pond. State College, Raleigh, North Carolina

Eco. 19:224-232

Carmichael, W and P. Gorham. 1977. Factors Influencing

the Toxicity and Animal Susceptibility of Anabaena flosaquae (Cyanophyta) Blooms. J. Phycol. 13:97-101

Chorus, I., and J. Bartram. Editors. 1999. Toxic

Cyanobacteria in Water. WHO, E & FN Spon, London.

Chorus, I., V. Niesel, J. Fastner, C Wiedner, B Nixdorf, and

K.-E. Lindenschidt. 2001 Environmental factors and

microcystin levels in water bodies, In: I. Chorus, editor.

Cyanotoxin: occurrence, causes, consequences. Springer,

Berlin pp.159-177.

Heiskary, S.A. and W.W. Walker. 1988. Developing Phosphorus Criteria for Minnesota Lakes. Lake and Reservoir

Management 4(1):1-10.

Graham J. L. et al. 2004. Environmental Factors Influencing

Microcystin Distribution and Concentration in Midwestern

United States. Water Res. 38:4395-4404.

Lindon. M. and Heiskary, S. A. 2007. fMicrocystin Levels in

Eutrophic South Central Minnesota Lakes.g Part of a series

on Minnesota Lake Water Quality Assessment. MPCA St.

Paul MN 53 pp.

Olson, T. A. 1949. History of Toxic Plankton and Associated Phenomena. 1949. Sewage Works Engineering and

Municipal Sanitation 20:71

Olson, T. A. 1954. United States Bureau of Sport Fisheries

and Wildlife, Fish and Wildlife Service US. GPO, 1954+

Waterfowl Tomorrow.

Olson, T.A. 1960. Water poisoning j a study of poisonous

algae blooms in MN. Amer. J. Pub. Health 50: 883-884.

Paerl H. W. and J. F. Ustach. J. F. 1982. Blue-green algal

scums: An Exploration for Their Occurrence During Fresh

Water Blooms. Limnol. and Oceanogr. 27(2): 1982 212-217

Shapiro, J. 1973. Blue-green Algae: Why They Become

Dominant. Science 179:382-384

Wetzel, Robert G. 2001. Limnology. Lake and River

Ecosystems. 3rd edition. Academic Press

World Health Organization. 2003. Guidelines for Safe

Recreational Water Environments. Coastal and Fresh Waters.

Volume 1. Geneva, Switzerland

The MPCAGs Environmental Bulletin Series is designed to

highlight environmental outcomes and results of scientific

studies the MPCA conducts in air, water and waste

management. This issue and archived copies of previous

bulletins are available electronically on the MPCAGs web site

at http://www.pca.state.mn.us/publications/

environmentalbulletin/index.html

Correspondence about this bulletin can be directed to

Matthew Lindon at 651-297-8218 or

matthew.lindon@pca.state.mn.us For more information

about the Environmental Bulletin Series, contact either of

the following MPCA staff of the Environmental

Reporting and Special Studies Unit.

Patricia Engelking 651-297-3847

Tom Clark 651-296-8580