Use of microbenthic algal communities in ecotoxicological tests for the assessment of water quality: the Ter river case study

The tolerance of microbenthic algal communities to two model toxicants,atrazine and copper, was studied in the Ter river during spring and summer.Artificial substrata were colonised at 9 sites and used to perform short-term(1–4 h) toxicity tests in the laboratory and to obtain photon yield as theecotoxicological endpoint. The tolerance was lower in spring than insummer for both toxic substances and varied according to the site studied.Copper toxicity was associated with physico-chemical conditions (totalsuspended solids and water pH) and, especially, with severalbiomass-related parameters, whereas atrazine toxicity was related to algalabundance and species composition. Temporal and spatial changes innutrient concentration may alter the biomass and species composition ofthe communities and thus affect their tolerance to toxic substances. It hasto be therefore considered that the environmental characteristics of theriver system may determine relevant direct and indirect effects on the algalcommunities, then affecting their specific ecotoxicological responses. Oncethis is assumed, the empirical expressions obtained on calculatingEC₅₀ and EC₁₀ can be used to predict the community-leveltransient effects of toxic exposures.