TOXICITY ASSESSMENT BY POLLUTION-INDUCED COMMUNITY TOLERANCE (PICT), AND IDENTIFICATION OF METABOLITES IN PERIPHYTON COMMUNITIES AFTER EXPOSURE TO 4,5,6-TRICHLOROGUAIACOL

Periphyton communities established on artificial substrates in a brackish-water mesocosm test system and in a marine microcosm test system were exposed to 4,5,6-trichloroguaiacol (456TCG) and monitored for effects on biomass, species composition and short-term tolerance of CO2-incorporation. In the brackish-water mesocosms no effects on biomass or species composition were correlated to the 456TCG exposures in the range of 1.7 to 50 nM. EC20 of 456TCG for short-term effects on periphyton CO2-incorporation were in all cases, including periphyton from a field reference station, between 1 and 12-mu-M. Periphyton from the marine microcosm system showed the same short-term tolerance of CO2-incorporation as periphyton from the brackish-water experiments and the marine field reference station, except at the pre-exposure level of 32-mu-M, where a marked increase occured. The pre-exposure of 32-mu-M is higher than the short-term EC20 of all periphyton communities exposed to lower pre-exposure concentrations. This is in accordance with the concept of Pollution Induced Community Tolerance (PICT) (Blanck et al., 1988), which states that a toxicant acting as a selection pressure on a community causes a tolerance increase due to exclosure of sensitive species and/or individuals from the community. The periphyton community exposed to 32-mu-M showed both an increased short-term tolerance, a decreased species number, and a decreased concentration of chlorophyll a. Two metabolites were identified in the periphyton of the microcosm test system, 3,4,5-trichlorocatechol (345TCC) and 3-bromo-4,5,6-trichlorocatechol (BTCC). A dimeric biotransformation product was also found in the periphyton. Acid hydrolysis of both water and periphyton samples gave an increase in the amounts of 456TCG and metabolites, indicating a large proportion of the compounds being bound or conjugated.