Organic contaminants in an agricultural soil with a known history of sewage sludge amendments: polynuclear aromatic hydrocarbons

Abstract

The PAH content of soils from a long-term agricultural experiment that received 25 separate sewage sludge applications from 1942 to 1961 is presented along with data from an untreated control plot and a plot that received repeated applications of farmyard manure. Archived plough layer (0-23 cm) soil samples were collected, stored, and processed in the same manner between 1942 and 1984 (i.e., before, during, and after sludge amendments) and samples of the applied sludges were available for analysis. Soil {Sigma} PAH concentrations increased between 1942 and 1960 on the sludge-amended plot and subsequently showed a steady decline. By 1984 the sludge-amended plot still contained over 3 times more {Sigma} PAH than the corresponding control soil. By 1960 {approximately} 70% of the {Sigma} PAH load added in the sludge was unaccounted for; this had increased to nearly 85% by 1984. Some compound-specific trends are apparent in the data; generally, the higher molecular weight PAHs have been more persistent. It is argued that biodegradation and transboundary transfers due to ploughing are the two main loss mechanisms.