Uptake and toxicity of brominated flame retardants and pesticides : Studies on littoral organisms and model communities

Abstract: In this thesis, brackish and freshwater littoral model communities (microcosms) of varying size and complexity were used to study the effects of brominated flame retardants (BFRs) and pesticides. The brackish water microcosms consisted of natural water, sediment and associated organisms, while the larger freshwater microcosms also contained submersed macrophytes (Elodea canadensis). Both the BFR hexabromocyclododecane (HBCDD) (Paper II) and the strobilurin fungicide azoxystrobin (Paper III) were found to dramatically reduce the abundance of the dominating crustacean zooplankton, calanoid copepods, in brackish water microcosms. For the fungicide, these effects were observed at concentrations more than an order of magnitude lower than reported no-effect concentrations for crustaceans in standard toxicity tests. The direct toxic effects on the copepods reduced their grazing pressure on phytoplankton. Indirect effects on the phytoplankton community were observed as increased abundance and biomass and altered community structure. Heterotrophic flagellates (Paper II) and rotifers (Paper III) increased in exposed microcosms, apparently also an indirect response to the reduced copepod grazing. In Papers IV-V, indoor freshwater microcosms dominated by the vascular macrophyte Elodea canadensis, were monitored following exposure to the sulfonylurea herbicide metsulfuron-methyl. The macrophytes were directly susceptible to the substance, and growth and biomass declined. The reduced competition from the macrophytes induced secondary indirect effects on the algal community, for example an increased phytoplankton primary production and altered community structure. The zooplankton community was also indirectly affected by the herbicide treatment. The community structure was altered and the total zooplankton biomass increased in exposed microcosms towards the end of the study. The need for increased knowledge on the uptake and bioaccumulation potential of chemical compounds in biota is often stressed. In one of the studies (Paper I) we investigated the uptake and bioaccumulation of BFR polybrominated diphenyl ethers (PBDE) in blue mussels. High bioaccumulation but also high depuration rates were found, especially for the tetra- and penta-BDE congeners. These results indicate that blue mussel may provide a source of PBDEs for other organisms in the Baltic Sea. It can be concluded from the effect studies that apart from direct toxic effects on sensitive organisms, the tested substances induced secondary, indirect effects on organisms not themselves susceptible to the toxicants. These indirect effects resulted from changes in interactions between organisms, and would not have been detected in single species test systems where no inter-specific interactions take place. Unanticipated community level responses can occur at considerably lower concentrations than the direct toxicity suggested from existing single species toxicity data, and in natural shallow aquatic ecosystems, the ecological consequences might be severe.