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A subchronic toxicity study was performed by exposing organisms to two surfactants in a continuous flow-through system for 120 h, followed by a depuration phase of 48 h. The bivalve mollusc Ruditapes philippinarum, widely distributed in intertidal zones and of high commercial value, was used. The main anionic and non-ionic surfactants employed were linear alkylbenzene sulphonate (LAS) and nonylphenol ethoxylate (NPEO2.8), respectively. The organisms were exposed to three environmental levels (µg L–1), and the concentrations of C11-LAS measured in the tissues were 2.4, 6.7 and 12.8 µg g–1 for the low, intermediate and high exposure levels, while those of NPEO2.8 were 13.4, 14.8 and 31.7 µg g–1, respectively. The responses used as "end point" of subcellular toxicity were the enzymatic activity of catalase (CAT), acid phosphatase (AcP) and alkaline phosphatase (ALP). No significant differences were observed in CAT activity at the end of the exposure phase; however, at the end of the depuration phase there was an increase in CAT activity in the organisms exposed to the low concentration of C11-LAS (P < 0.05) and a significant decrease in the individuals exposed to the high concentration of NPEO2.8, which is related to the largest accumulation of the compound inside the organism. The organisms exposed to the intermediate and high concentrations (P < 0.05) of C11-LAS showed inhibition for AcP and activation for ALP at the end of the experiment (day 7). In the organisms exposed to the high concentration of NPEO2.8 there was an increase in the specific activity at the end of the depuration stage.
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