Mineralization of organic contaminants in sludge-soil mixtures

The mineralization of 14C-labeled linear alkylbenzene sulfonate (LAS), nonylphenol (NP), nonylphenol-di-ethoxylate (NP2EO), di-(2-ethylhexyl)phthalate (DEHP), pyrene, and 1,4-dichlorobenzene (DCB) was investigated in different sludge-soil mixtures and soils. Under aerobic conditions, the mineralization of LAS, NP, and NP2EO was between 50 and 81% of the added amounts after two months, while DEHP and pyrene were mineralized more slowly. The mineralization of the model chemicals was indirectly affected by the amount of sludge in the test mixtures. A higher content of sludge in the mixtures reduced the overall concentration of oxygen, which resulted in a decrease of the mineralization of several of the model chemicals. In sludge-soil mixtures with predominantly anaerobic conditions, the mineralization was slower for all of the chemicals with the exception of DEHP and DCB. The mineralization of DCB was enhanced in mixtures with a high sludge content. No pronounced difference in the mineralization of the model chemicals (except DEHP) was observed when the sludge was mixed with three different agricultural soils.