CHLOROBENZENES IN-FIELD SOIL WITH A HISTORY OF MULTIPLE SEWAGE-SLUDGE APPLICATIONS

The chlorobenzene (CB) content of soil from a longterm agricultural experiment that received 25 separate sewage sludge applications from 1942 to 1961 is reported, together with data from an untreated control plot. Archived plough layer (0-23 cm) soil samples were collected, stored, and processed in a similar manner between 1942 and 1991 (i.e., before, during, and after sludge applications), and samples of the applied sludges were available for analysis. The total concentration of CB compounds (Sigma CBs) in soil increased in the sludge-amended plot. About 10% of the applied Sigma CBs became recalcitrant and remained in the soil up to the present time, while most of the Sigma CBs disappeared very rapidly following the amendment. Volatilization is regarded as the main loss mechanism for CBs from the soils. Hexachlorobenzene (HCB) was the most persistent CB: the loss of this compound from sludge-amended soil continued for over a decade longer than the other CBs. The 1,4-dichlorobenzene (DCB) content in both the sludge-amended and the control soils increased remarkably during the 1960s; trace level impurities in pesticides and/or atmospheric deposition are possible sources.