Optimization and in-house validation of TDA-AAS method for mercury control in water and wastewater treatment plants sludges

The thermal decomposition, amalgamation, and atomic absorption spectrometry (TDA-AAS) method was validated for mercury (Hg) determination in sludge samples. A linear range was obtained from 30 to 200 ng. TDA-AAS method provides a limit of quantification (LOQ) well below the legal maximum admitted concentration of Hg in sludge samples, which makes it suitable to measure its concentrations at the imposed legal limits, and for monitoring studies of Hg trace levels in sludge samples. Repeatability and within-laboratory reproducibility of the method were good with relative standard deviations lower than 6%. Expanded uncertainty, estimated using a top-down approach with the data obtained from accuracy and precision studies, was 18% for a coverage factor k= 2. Mercury concentration in sludge samples from water treatment plants was below LOQ (0.33 mg Hg/kg dw) and in wastewater treatment plants was well below the legal limit for their reuse in agriculture (16 mg Hg/kg dw).