DETECTION OF POLLUTION-INDUCED COMMUNITY TOLERANCE (PICT) IN MARINE PERIPHYTON COMMUNITIES ESTABLISHED UNDER DIURON EXPOSURE

In the present work an effort aiming at a partial validation of the pollution-induced community tolerance (PICT) methodology is reported. Periphyton communities were established on artificial substrata in a marine microcosm system for 3 to 4 weeks. The communities were exposed to concentrations of the herbicide diuron (DCMU, 3-(3,4-dichlorophenyl)-1.1-dimethyl urea) ranging from 1.6 nM to 1-mu-M. A short-term test on periphyton photosynthesis was used to quantify the tolerances of the different communities, and an increase in the tolerance (PICT) was detected at concentrations above 40 nM. The results are discussed in terms of a 'comparison triad' where comparisons are made between the short-term effects on photosynthesis of control communities, the PICT of diuron-exposed communities, and other long-term effects such as cholorophyll a content, specific photosynthetic activity (P) and diatom species richness. The first effect of diuron on periphyton photosynthesis in short-term tests was recorded at about 3.2 nM, while effects after long-term exposure, reflected by the various long-term parameters, were detectable only at higher concentrations, about 20 to 40 nM.