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

摘要

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 eth-oxylates with one and two ethoxy groups (NP1E0 and NP2E0). The degradation studies were carried out under winter (12.7 ℃) and summer (22.4 ℃) 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 14 days at 12.7 ℃ and between 4 and 7 days at 22.4 ℃. With regard to NPE compounds, after 8 and 4 days from the beginning of the experiment at 12.7 and 22.4 ℃, respectively, their concentration levels were increased to 6.5 and 13.5 mg/kg dm (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 ℃ and 22.4 ℃, respectively. The half-life times measured for NPEs were from 8 to 16 days at 12.7 ℃ and from 8 to 18 days at 22.4 ℃. 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 ℃, respectively; however, potential toxic effects could be observed for the nonylphenolic compounds during the first 56 days after sludge application to the soil.