Impact of the biocide Irgarol on the phytoplankton community in freshwater pond mesocosms

Feibicke, M., Mohr, S., Berghahn, R., Schmidt, R.

Federal Environment Agency, Schichauweg 58, D-12307 BerlinCorrespondence: michael.feibicke@uba.de

Introduction

Biological establisingPond bottom: Sand, natural fine sediment, littoral zone (Fig. 1)

Macrophytes: Potamogeton nodosus and Myriophyllum verticillatum (Fig. 1) (

).

Stocking: Plankton and macro-invertebrates from nearby mesotrophic lakes and ponds

effects on macrophytes see: Berghahn et al. 2006 - SETAC

Materials & Methods

Experimental design l Single application of Irgarol (11-04-05) by spraying a

methanolic stock solution on the water surface.

Homogenisation by use of a battery driven outboard

motor and air ventilation on the water surface.

Spiking with 6 different nominal concentrations:

0.04 (1 pond), 0.2 (2 ponds), 1 (1 pond), and 5 µg/L

(2 ponds). Two ponds served as controls.

Sampling & analysisl Water samples for the detection of Irgarol and

selected metabolites were taken at first in three-hour

intervals after dosage, gradually extended to a

fortnightly sampling interval (details see: Fig. 3,

)

l Integrated phyto- and zooplankton samples (10 sites

per pond) were taken fortnightly. Phytoplankton

samples were preserved by adding Lugol-solution.

l Phytoplankton analysis followed standard procedures

by use of Utermoehl-technique. Abundance as well as

biovolume were detected.

Data evaluationl EC50 calculation by Probit analysis (SPSS 11) and

analysis of phytoplankton community response using

principle response curve (PRC) (CANOCO V 4.5).

fate

of Irgarol see: Meinecke et al. 2006 - SETAC

Pond designSize: length 690 x width 325 x height 250 cm

3Water volume: c. 15 m

Artificial light: mean 13,000 lx

Nutrient regime: Tot-P >0.02 mg/L; Tot-N >0.7 mg/L

As photosystem II inhibitor, the commonly used antifouling component Irgarol is highly toxic to algae (e.g. 5-d-EC50 for Navicula pelliculosa: 0.1 µg/L). Although many studies on environmental concentrations of Irgarol have been reported mainly from marine sites, there are only data from single species toxicity tests and 1 microcosm studies on the effects of Irgarol available. Up to now, there are no data on the effects of Irgarol on freshwater phytoplankton communities at the mesocosm scale. Therefore, effects of Irgarol on phytoplankton communities were investigated by the German Federal Environment Agency in the framework of an indoor pond mesocosm study.

ResultsPhytoplankton compositionlCryptomonads and diatoms were dominating in all systems during the study, whereas green algae, chrysophytes, and blue-greens

appeared temporarily (Fig. 4).

lAbove the 0.2 µg/L-concentration level, strong adverse effects were observed on both dominating groups - the cryptophytes

(Cryptomonas spp.) and diatoms (Fragilaria ulna) - 8 and 21 d after treatment, resp. (Fig. 4) as well as on macrophytes (Fig. 2).

lIn the 0.2, 1.0 and 5.0 µg/L-ponds, reduction of abundance and biomass followed an effect-concentration relationship, whereas

in the 0.040 µg/L-pond, phytoplankton biomass increased directly after application (Fig. 5).

lRecovery of higher taxa occurred even on the highest treatment level, at first by small centric diatoms, partly followed by

cryptophytes and green algae. However, differences in species composition between the treatments were obvious (Fig. 4-6).

ConclusionslMost EC50 data from laboratory testing (Fig. 7) are below the 2

µg/L level (data set from 5 publication: micro- and macro-algae

and vascular plants, freshwater and marine species).

lAdverse effects on the mesocosm level (this study) were found

in the lower EC50-range between 0.04 and 1.0 µg/L 8 and 21 days

after application (higher taxa: only by range indication, 8-d-EC50

for Cryptomonas spp.:0.069 µg/L by probit analysis) (Fig. 7),

confirming the high herbicidal toxicity of Irgarol.

lAlthough recovery appeared to some extent - even on the

highest treatment level (see: Solomon et al. 1996 - atrazine) -

significant differences at the community level were observed on

almost all sampling days, indicating a relevant shift in species

composition and abundance after application.

Principal Response CurvelThe treatment regime as a whole (sum of all

canonical eigenvalues) represented c. 53 % of

the variance of the data set (P: 0.004) (Fig. 6).

lBy use of Monte Carlo permutation testing

(all can. axes) all sampling dates >= 8 d after

treatment indicated significant differences (P <

0.05) between the treated ponds (as a whole

group) and the control ponds.

lAccording to bk-values, the benthic algae

species Cocconeis spp., Ankyra lanceolata,

Amphora pediculus, and Oedogonioum sp.

decreased in this study, whereas planktonic taxa

like centric diatoms and the cryptomonad

Rhodomonas minuta were promoted by Irgarol

application (

) .

effects on periphyton see: Mohr

et al. 2006 - SETAC

Analytics

Fig. 1: Schematic overview of the mesocosm pond incl. littoral zone and macrophytes

Control 5 µg/LControl 5 µg/L

Fig. 2: Control pond and treated pond contami-nated with 5 µg/L Irgarol (14-06-05)

Fig. 3: Irgarol concentration in the water column of the 6 treated mesocosm ponds.

Fig. 4: Cumulative biomass of main phytoplankton groups (higher taxa).

Fig. 5: Abundance of main phytoplankton groups (higher taxa) 8 days after application.

Fig. 7: Species distribution of EC50-values of algae and vascular plants from published lab tests compared with effects of phytoplankton groups from this mesocosm study (8 and 21 d after application).

Fig. 6: PRC-analysis of the phytoplankton community. Bk value = spe-cies weight (only range > or < 0,2 units is given).

OEDOGONZ Amph ped Anky lan

Cocc ped

Cocc pla

MALLOMOZ CRYPTOMZ

NITZSCHZ

Rhod min CENTRALES

Scen acu

CHLORELLZ

Kirc sub

Mono con Gymn lan Chro min Coel mic

Scen qua

-3

-2,5

-2

-1,5

-1

-0,5

0

0,5

1

1,5

2

2,5

3

-30000 -25000 -20000 -15000 -10000 -5000 0 5000 10000

bk

-3-2,5

-2

-1,5-1

-0,50

0,51

1,52

2,53

01. 03. 31. 03. 01. 05. 31. 05. 01. 07. 31. 07. 31. 08.

Control 0.04 µg/L 0.20 µg/L 1 µg/L 5 µg/L

Treatment

Legend:M. verticillatumP. nodosus

N

N

N

S

NN

Control 0,04 µg/L 0,2 µg/L 1,0 µg/L 5,0 µg/L

0,1

1

10

100

1000

Ind/m

L Phytoplankton (Sum) Cryptomonads Diatoms

M A M J J A

0,01

0,1

1

10

M A M J J A

0,01

0,1

1

10

M A M J J A

0,01

0,1

1

10

M A M J J A

0,01

0,1

1

10

M A M J J A

0,01

0,1

1

10

M A M J J A

0,01

0,1

1

10

M A M J J A

0,01

0,1

1

10

M A M J J A

0,01

0,1

1

10

bio

vol.

(mm

3/L

)

Higher taxa: Bacillariophyceae Chlorophyceae Chrysophyceae Cryptophyceae Cyanophyceae Dinophyceae

control 1

Application

bio

vol.

(mm

3/L)

control 2

bio

vol.

(mm

3/L

) 0,04 µg/L

bio

vol.

(mm

3/L

)

0,2 µg/L - 1

bio

vol.

(mm

3/L

)

0,2 µg/L - 2

bio

vol.

(mm

3/L

)

1,0 µg/L

bio

vol.

(mm

3/L

)

5,0 µg/L - 1

bio

vol.

(mm

3/L

)

5,0 µg/L - 2

A M J J A S0,001

0,01

0,1

1

10

5,0 µg/L (2 ponds)

1,0 µg/L (1 pond)

Irgar

ol(µ

g/L

)

0,04 µg/L (1 pond)

0,2 µg/L (2 ponds)

0 3 6 9 12 150

25

50

75

100

rela

tive

freq

uen

cysu

m

EC50 (µg*L-1)

0,01 0,1 10

10

20

30

40

50

EC50 (µg*L-1)

EC50-ranges (this study):

PhytoplanktonCommunity

Cryptomonads

Diatoms

References: Bérard et al. 2003, Chesworth et al. (2003), Jones

& Kerswell (2003), Readman et al. (2004), Okamura et al.

(2000a), Solomon et al. (1996), US EPA (2000)