Determination of alkylphenols and alkylphenol ethoxylates in sewage sludge: effect of sample pre-treatment.

A complete characterization of sewage sludge collected from five biological waste water treatment plants was done to determine physico-chemical parameters, heavy metals and alkylphenols, making special emphasis on sampling, homogenization, and sample pre-treatment. Ultrasonic extraction followed by gas chromatrography coupled with mass spectrometry was used to evaluate the effect of sample pre-treatment (untreated sample, freeze-drying, drying at 40 degrees C or drying at 100 degrees C) on the concentration of octylphenol (OP), nonylphenol (NP) and nonylphenol ethoxylates (NP1EO, NP2EO). Untreated samples and samples dried at 100 degrees C gave concentration levels up to 62% and 89% lower, respectively, than freeze-dried samples. In 50% of cases, freeze-dried samples led to significantly higher concentrations than those obtained by drying at 40 degrees C. Thus, freeze-drying is the recommended sample pre-treatment to prevent possible losses of OP, NP, and NP1EO. Using this methodology, concentrations detected were from 3.2 to 199 mg kg(-1) being NP followed by NP1EO found in highest concentration. The total concentration of NP and NP1EO exceeded the limit of 50 mg kg(-1) proposed by the draft European directive on sewage sludge in three out of five samples studied. Contrarily, heavy metals were below the legislated values.