Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in sewage sludge: congener patterns, toxic equivalency and comparison with effluent concentrations and toxic equivalency

Domestic and industrial wastewater treatment plants, and petrochemical industries within the Houston Ship Channel (HSC) located in Houston, Texas, USA, were sampled for sewage sludge and analysed for polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). The United States Environmental Protection Agency (USEPA) method 1613B which employs high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) was used to quantify the PCDD/Fs in the sludge samples. The measured toxic equivalency (TEQ) across all samples ranged between 0.73 pg/g and 7348.40 pg/g dry weight, and the mean TEQ in the industrial sludge was higher than that in the sewage sludge by a factor of 40. Industrial samples exhibited higher PCDD homolog concentrations and among the PCDF homologs, different congeners exhibited maximum concentrations among the industrial and wastewater sludge samples. It was deduced that both the effluent and sludge from industries exhibited higher furan concentrations, and contributed the most toxicity to receiving waters, due to the high percent contribution of 2,3,7,8-Tetrachlorodibenzodioxin (2,3,7,8TCDD) and 2,3,7,8-Tetrachlorodibenzofuran (2,3,7,8-TCDF) towards total TEQ. Comparing sludge samples with the effluent samples led to the observation that the total TEQ in sludge samples was significantly higher than that in effluent samples obtained from the same facility, thereby indicating the difference in source of PCDD/Fs between industries and sewerage systems.