Pollution-induced community tolerance (PICT) in marine periphyton in a gradient of tri- n-butyltin (TBT) contamination

Abstract

Before the ban of tri- n-butyl tin (TBT) compounds as antifouling agents, yacht marinas were important sources of TBT contamination in coastal waters. The impact of TBT on marine periphyton communities were investigated around a small marina on the Swedish west-coast, using the PICT (pollution-induced community tolerance) methodology. The increase in community tolerance due to elimination of TBT-sensitive algae, is an indicator of damage to the algal community. Periphyton was sampled on artificial substrata in temporal and spatial gradients of TBT exposure during the boating season 1988, i.e. before the ban. The community tolerance was quantified as EC50-values for TBTCl, TBTO and the reference compound DCMU based on short-term inhibition of periphyton photosynthesis. Photosynthesis was measured as the incorporation of 14CO 2 into acid-stable organic compounds. Ratios between EC50-values for the monomer TBTCl and the dimer TBTO suggests that the toxic effect is exerted by the same dissociation product, most likely the TBT cation. Water samples for chemical analyses were taken to characterise TBT exposure during the colonization period. Periphyton communities showed elevated tolerances to TBTCl and TBTO, but not to DCMU, both in the spatial and temporal gradient, provided that the TBT exposure exceeded 0.5 nM. This is the same effect threshold as estimated earlier in controlled microcosm experiments. We have demonstrated that the PICT methodology is sensitive, specific and robust enough to detect minor effects of TBT on marine periphyton in a complex field situation. The estimated NEC value is 0.5 nM TBT, above which damage to algal communities should be expected.