POLLUTION-INDUCED COMMUNITY TOLERANCE (PICT) IN MARINE PERIPHYTON IN A GRADIENT OF TRI-N-BUTYLTIN (TBT) CONTAMINATION

Before the ban of tri-n-butyl tin (TBT) compounds as antifouling agent s, yacht marinas were important sources of TBT contamination in coasta l waters. The impact of TBT on marine periphyton communities were inve stigated around a small marina on the Swedish west-coast, using the PI CT (pollution-induced community tolerance) methodology. The increase i n 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 exposur e during the boating season 1988, i.e. before the ban. The community t olerance was quantified as EC50-values for TBTCl, TBTO and the referen ce compound DCMU based on short-term inhibition of periphyton photosyn thesis. Photosynthesis was measured as the incorporation of (CO2)-C-14 into acid-stable organic compounds. Ratios between EC50-values for th e monomer TBTCl and the dimer TBTO suggests that the toxic effect is e xerted by the same dissociation product, most likely the TBT cation. W ater samples for chemical analyses were taken to characterise TBT expo sure during the colonization period. Periphyton communities showed ele vated tolerances to TBTCl and TBTO, but not to DCMU, both in the spati al and temporal gradient, provided that the TBT exposure exceeded 0.5 nM. This is the same effect threshold as estimated earlier in controll ed microcosm experiments. We have demonstrated that the PICT methodolo gy 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 shoul d be expected.