Copper accumulation and toxicity in fluvial periphyton: the influence of exposure history.

Periphyton communities have a good bioaccumulation capacity and can be used to monitor metal pollution in fluvial ecosystems. Depending on the dose and exposure time, metals may produce changes in the structure and function of these communities, thus it is expected that the kinetics of metal accumulation and metal sensitivity will also be influenced by the exposure history. In this study, the effects of pulsed and continuous Cu exposures during the colonization of the communities were investigated under controlled conditions. This investigation includes the study of metal accumulation kinetics and the evaluation of community tolerance. Pulsed copper exposure did not affect the community structure but influenced the accumulation kinetics (decreasing intracellular copper uptake). On the other hand, continuous copper exposure caused a huge increase in metal content (both total and intracellular) and modified the structure of the community (increasing the percentage of cyanobacteria and diatom diversity). Both pulsed and continuous periphyton metal exposure may have negative repercussions for the fluvial ecosystem. While Cu pulsed exposure may be toxic to periphyton communities, continuous exposures may lead to community adaptation, which is often related to changes in species composition and higher metal contents being transferred to higher trophic levels of the stream food chain.