Degradation and environmental risk of surfactants after the application of compost sludge to the soil

In this work, the degradation of anionic and non-ionic surfactants in agricultural soil amended with sewage sludge is reported. The compounds analysed were: linear alkylbenzene sulphonates (LAS) with a 10-13 carbon alkylic chain, and nonylphenolic compounds (NPE), including nonylphenol (NP) and nonylphenol ethoxylates with one and two ethoxy groups (NP1EO and NP2EO). The degradation studies were carried out under winter (12.7°C) and summer (22.4°C) conditions in Andalusia region. The concentration of LAS was reduced to 2% of the initial concentration 100 day after sludge-application to the soil. The half-life time measured for LAS homologues were ranged between 4 and 14days at 12.7°C and between 4 and 7 days at 22.4°C. With regard to NPE compounds, after 8 and 4days from the beginning of the experiment at 12.7 and 22.4°C, respectively, their concentration levels were increased to 6.5 and 13.5mg/kgdm (dry matter) as consequence of the degradation of nonylphenol polyethoxylates. These concentration levels were reduced to 5% after 63 and 70 days for 12.7°C and 22.4°C, respectively. The half-life times measured for NPEs were from 8 to 16 days at 12.7°C and from 8 to 18 days at 22.4°C. Environmental risk assessment revealed that for LAS homologues no environment risk could be expected after 7 and 8 days of sludge application to the soil for 22.4 and 12.7°C, respectively; however, potential toxic effects could be observed for the nonylphenolic compounds during the first 56 days after sludge application to the soil.