The concentrations and fate of linear alkylbenzene sulphonate in sludge amended soils

Abstract

A programme of monitoring work to determine the fate of linear alkylbenzene sulphonates (LAS) in sludge amended soil is described. The concentration of LAS in soils are given for a large number of locations (24 farms and 51 fields) in the Thames Water Authority (TWA), U.K. The sites selected provide a range of soil types, frequency and concentration of sludge applications and agricultural uses (pasture/arable). In addition, the disappearance of LAS from soil with time is shown at three selected sites following different sludge application practices. A solid phase extraction-HPLC method, employing a Soxhlet extraction technique to recover LAS from soil matrices, is described for these determinations which gave an average recovery of LAS (2–15 μgg − spikes) of 97%. In fields (42) not recently spread with sludge (prior to 1987) the concentrations of LAS found in the sludge amended soil are generally less than 1 p g LAS/g soil. When this data is compared with the estimated total cumulative load based on known sludge applications the majority of the sites show losses of LAS > 98%. In fields (9) recently spread (during 1987) the concentrations of LAS in soil are in the range <0.2–20 Mg g −1 representing losses of LAS between 70 and 99% of the estimated total cumulative load. The time course studies confirm the rapid removal of LAS from sludge amended soils at three locations (5 fields) and for three different methods of application. The calculated half-lives for LAS in soil range from 7 to 22 days and agree with laboratory test results and other monitoring studies. The homologue distributions determined for LAS in soil suggest that microbial breakdown rather than leaching is the prime mechanism for its removal. Overall, the data indicate that an adequate safety margin exists between the concentrations of LAS in sludge amended soils and those likely to affect the growth of crop plants.