Effects of the fungicide metiram in outdoor freshwater microcosms: responses of invertebrates, primary producers and microbes

Abstract

The ecological impact of the dithiocarbamate fungicide metiram was studied in outdoor freshwater microcosms, consisting of 14 enclosures placed in an experimental ditch. The microcosms were treated three times (interval 7 days) with the formulated product BAS 222 28F (Polyram®). Intended metiram concentrations in the overlying water were 0, 4, 12, 36, 108 and 324 μg a.i./L. Responses of zooplankton, macroinvertebrates, phytoplankton, macrophytes, microbes and community metabolism endpoints were investigated. Dissipation half-life (DT₅₀) of metiram was approximately 1-6 h in the water column of the microcosm test system and the metabolites formed were not persistent. Multivariate analysis indicated treatment-related effects on the zooplankton (NOEC(community) = 36 μg a.i./L). Consistent treatment-related effects on the phytoplankton and macroinvertebrate communities and on the sediment microbial community could not be demonstrated or were minor. There was no evidence that metiram affected the biomass, abundance or functioning of aquatic hyphomycetes on decomposing alder leaves. The most sensitive populations in the microcosms comprised representatives of Rotifera with a NOEC of 12 μg a.i./L on isolated sampling days and a NOEC of 36 μg a.i./L on consecutive samplings. At the highest treatment-level populations of Copepoda (zooplankton) and the blue-green alga Anabaena (phytoplankton) also showed a short-term decline on consecutive sampling days (NOEC = 108 μg a.i./L). Indirect effects in the form of short-term increases in the abundance of a few macroinvertebrate and several phytoplankton taxa were also observed. The overall community and population level no-observed-effect concentration (NOEC(microcosm)) was 12-36 μg a.i./L. At higher treatment levels, including the test systems that received the highest dose, ecological recovery of affected measurement endpoints was fast (effect period < 8 weeks).

Fig. 1

Dynamics in taxa richness of zooplankton (a), macroinvertebrates (b), phytoplankton (c) and chlorophyll a biomass of phytoplankton (d) in the different treatments of the metiram enclosure experiment. The shaded area shows the range observed in control enclosures and the geometric mean values are presented per treatment. The vertical dotted lines indicate days of metiram application. The NOECs for treatment-related responses are presented in Tables 4, 5 and 6

Fig. 2

Principal response curve diagram for the zooplankton dataset (a), the sediment bacteria DGGE band intensity dataset (b) and sediment bacteria OTUs dataset based on presence of DGGE bands (c) of the metiram enclosure study (for further explanation see description in text). The vertical dotted lines indicate days of metiram application. C _dt canonical coefficient showing the difference between treatments and control in time, b _k species weight that indicates the affinity of the taxon (a) or specific DGGE bands on the gels (b, c) with the PRC. The NOECs for treatment-related responses are presented in Tables 4 and 7. a 33 % of all variance could be attributed to sampling date (horizontal axis) and 31 % to treatment level, 34 % of which is displayed on the vertical axis. b 39 % of all variance could be attributed to sampling date and 21 % to treatment level, 17 % of which is displayed on the vertical axis. c 35 % of all variance could be attributed to sampling date and 23 % to treatment level, 17 % of which is displayed on the vertical axis

Fig. 3

Dynamics in population abundance of zooplankton taxa (a–g) and of the phytoplankton taxon Anabaena sp. (h) in the different treatments of the metiram enclosure experiment. The shaded area shows the range observed in control enclosures and the geometric mean values are presented per treatment. a Total Rotifera, b A. fissa (Rotifera), c P. remata (Rotifera), d T. gr. similis (Rotifera), e total Copepoda, f Cyclopoida (Copepoda), g nauplii (Copepoda), h Anabaena sp. (Cyanophyta). The NOECs for treatment-related responses are presented in Tables 4 (zooplankton) and 6 (Anabaena sp.)

Fig. 4

Dynamics in conidia abundance scores of aquatic hyphomycetes, and alder leaf decomposition. The shaded area shows the range observed in control enclosures and the mean values are presented per treatment. a Conidia abundance score A. longissima, b conidia abundance score T. setigerum, c mass loss (g dry weight) of alder leaves in coarse mesh bags, d mass loss (g dry weight) of alder leaves in fine mesh bags, e fungal biomass (μg/mg) in decomposing alder leaves. The NOECs for treatment-related responses are presented in Table 7