ABSTRACT
Every year thousands of tons of sludge are produced in sewage treatment plants. Application to agricultural land and disposal in sanitary landfills are the most popular sludge disposal practices in Europe (Brunner and
Lichtensteiger, 1987). Chemicals contained in the sludge have the potential to directly enter the biogeochemical cycle after application to land or indirectly through emissions (gas, leachates and erosion) of the sanitary landfill. Here, we consider the polychlorinated biphenyls (PCBs) and the detergent-derived chemicals: linear alkylbenzenesulphonates (LAS), nonylphenol mono-(NPlEO) and diethoxylates (NP2EO), and nonylphenol (NP). PCBs are ubiquitous, persistent organic pollutants, which are very hydrophobic and occur in wastewater at concentrations of µg/L (Petrasek et al., 1983; de Alencastro and Taradellas, 1988). NP, NP1EO, and NP2EO are refractory biointermediates derived from nonylphenol polyethoxylates (NPnEO, n=1-20) by cleavage of the ethoxy chain. NPnEO are by far the most used alkylphenol polyethoxylates (APnEO). The LAS and APnEO are the most commonly employed aromatic surfactants in detergent cleaning products (Greek, 1988), where they are used as characteristically complex mixtures of homologs, oligomers and isomers (Marcomini et al., 1988a). Their common structural feature is a hydrophobic group (i.e. linear and highly branched alkyl chains attached to a benzene ring for LAS and APnEO, respectively) and a hydrophilic group (i.e. the sulphonate group for LAS and the polyethoxy chain for APnEO). The usage of these surfactants leads to concentrations at mg/L levels in the influent water of sewage treatment plants (Giger et al., 1987a,1987b). Biodegradation and sorption are the major processes that affect LAS and APnEO during sewage treatment (Marcomini et al., 1988b; Giger et al., 1987a). Due to their amphiphilic character, LAS, NP2EO, NP1EO, and NP can adsorb to particles, which are subsequently incorporated into the sewage sludge. Particularly under anaerobic conditions, NP2EO and NP1EO act as precursors to NP. Remarkably high concentrations of LAS and NP, compared with those of ubiquitous pollutants like PAHs and PCBs, were found in anaerobically digested sludge (average of 5 and 1 g/kg, dry weight (d.w.), respectively) (McEvoy and Giger, 1986; Giger et al., 1987b; Brunner et al., 1988). Despite these high concentrations and the common disposal of sludge to agricultural land and/or sanitary landfills, no investigations have been carried out so far on the ultimate fate of these detergent-derived chemicals. The main reason for such a lack of information was the nonavailability of a suitable analytical procedure for the determination of LAS, NP, NP1EO and NP2EO in soil. Once procedures based on high-performance liquid chromatography (HPLC) requiring minimum manipulation of the sample were available (Marcomini and Giger, 1987), investigations into the fate and behavior of these compounds in the soil environment became feasible. A few data on LAS occurrence in sludge amended soil were recently reported (Matthi js and De Henau, 1987). German and U.K. sludge amended soils had LAS concentrations of 0.9-2.2 mg/kg (d.w.). By semispecific infrared spectroscopy, Holtzclaw and Sposito (1978) found 1% LAS in the fulvic acid fraction of sludge amended soil and suggested that LAS can build up in this fraction of soil organic matter and eventually affect soil fertility.
