**2.2.3 QC/QA**

A strict Quality Control/Quality Assurance (QC/QA) measurement was followed throughout the process of analysis.

The recovery of the analytic procedure was determined by measuring the amounts of surrogate compounds added prior to sample extraction. The recoveries range from 44.2% to 118.3% (except Nap-d8 volatile even at room temperature), within the restrictive range of US EPA 610 method Therefore, except Nap whose values can only serve as reference, other data satisfy the demand for quantitative analysis. All data have not been revised and all concentration values are according to the instrumental recoveries. All the PAH concentrations were reported on a dry weight sediment basis.

The relative standard derivation for duplicate samples ranged from 0 to 15%.

A method blank experiment was carried out for every 12 samples.

The solvent blanks were checked and none of the investigated substances were found in the blanks.

<sup>1</sup> ppm (parts per million)
