Toxicological interactions of ibuprofen and triclosan on biological activity of activated sludge

The growing use of pharmaceutical and personal care products increases their concentrations in the wastewater entering treatment plants and their levels into biological reactors. The most extended biological wastewater treatment is the activated sludge process. The toxicity of ibuprofen and triclosan, individually and combined, was studied by tracking the biological activity of the activated sludge measuring oxygen uptake rate and the inhibition of the esterase activity. Short-term exposure produced significant inhibition in oxygen uptake, with lower damage to enzymatic activity. Median effect values for oxygen uptake inhibition were 64 ± 13 mg L−1 and 0.32 ± 0.07 mg L−1 for ibuprofen and triclosan respectively using 125 mg L−1 activated sludge. For the inhibition of enzymatic activity values were 633 ± 63 mg L−1 for ibuprofen and 1.94 ± 0.32 mg L−1 for triclosan. Results indicated that oxygen uptake, related to primary activity of microorganisms, was more strongly affected than the enzymatic activity associated to energy consumption. Toxicity interactions were determined using the Combination Index-isobologram method. Results showed antagonism at lower values of affected population, after which the mixtures tended to additivity and synergism. For the case of enzymatic activity, the antagonism was less marked and the additivity range was higher.