Adsorption Of Ionic Surfactants On The Soils And Their Effects On The Properties Of Soils

Due to its broad application, surfactant can be charged into soil through various ways and have some direct and potential effects on the soils. In order to sysmetically estimate the safety of soil ecology of the surfactants, one cationic surfactant cety trimethyl ammonium bromide(CTAB), and one anionic surfactant sodium dodecyl sulfate(SDS) were used, with methods of adsorption, sieving of soil aggregates, soil water infiltration, soil column leaching and pot experiment, to investigate their adsorptive affinity on soils, effects on the stability of soil aggregates, soil water repellency, soil nutrient ions transport, soil enzymes activities and grownth of plant. Our finds are fellowed:(1) CTAB reached the adsorptive equibibrium at a higher rate while SDS reached the adsorptive equilibrium at a slower rate. The pseudo-second-order(PSO) rate equation described the adsorptive kinetics of CTAB and SDS better than the pseudo-first-order(PFO) rate equation. With the enhancement of equilibrium concentration, the adsorptive capacity of CTAB and SDS increased and tended to the maximum. The adsorption isotherm can be fitted well by Langmuir and Freundlich equation. The optimal equation to fit the the adsorption isotherm was dependent on the soil type and surfactant kind. When the experimental temperature increased, the adsorption of CTAB and SDS on the soil decreased. The adsorptive affinity of CTAB and SDS varied with the different soils and adsorptive capacity of CTAB was higher than SDS on the same soil.(2) After interacting with soils for 0.5 h, CTAB and SDS had similar effects on the amount of the soil aggregates. Both of them made the quantity of 2~0.25 mm and <0.053 mm size aggregates increase while the amount of 0.25~0.053 mm aggregate decrease. Meanwhile, with the enhancement of the surfactant concentrations, the mean weight diameter(MWD) of the soil aggregates increased, which indicated that the structure of the soil improved. Compared to the control treatment, except 200 mg L-1, all the other CTAB treatment had a faster soil water infiltration rate. And to some extent, it showed the trendency that the higher concentration of CTAB, the faster rate it was. Conversely, all SDS treatment had a slower soil water infiltration than the control treatment. Soil repellency factor(R) of the control treatment was 1.22, lower than the critical value of 1.95, which implied that soil of blank treatment was free soil water repellency. For CTAB, only 200 and 400 mg L-1 treatment's R were higher than 1.95 while all SDS treatment's R were higher than 1.95.(3) Surfactants had certain effects on the tansport of some substance in soil. CTAB inhibited the transport of soil colloids, promoted the transport of K+, and had on significant effect on the transport of phosphate ion. SDS promoted the transport of K+ and inhibited the transport of phosphate ion. The effect of SDS on the transport of soil colloids was dependent on the concentration of SDS. At the low concentration, SDS inhibited the transport of soil colloids and at the high concentration, SDS promoted the transport of soil colloids.(4) The results indicated that both CTAB and SDS promoted spinach's growth at the lower concentrations and inhibited at the higher concentrations. The thresholds for the inhibitory effect of CTAB and SDS on spinach's growth were 500 and 1000 mg kg-1, respectively. Regardless of CTAB and SDS treatments, activities of superoxide dismutase(SOD) increased significantly depending on the enhancement of surfactant concentration. Except for particular cases, the activity of catalase(CAT) was promoted by CTAB and SDS. Oppositely, despite lack of the regular pattern, the activity of peroxidase(POD) was inhibited by CTAB or SDS under most-common situations. Besides, the activities of soil dehydrogenase, soil urease, soil sucrase and neutral phosphatase were almost reduced or restrained by CTAB. However, SDS had the different effects on them. The activities of soil dehydrogenase and soil surcase were prompted by SDS and the activities of soil urease and soil neutral phosphatase were almost inhibited by SDS except several particular cases.To sum up, the adsorption of surfactant on the soil depended on the kind of surfactants and the type of soils. The cationic surfactant had a higher adsorptive capacity and faster adsorptive rate than the anionic surfactant. The ionic surfactant had an effect on the stability of the soil aggregate, the infiltration of the soil water, the transport of soil substance and some other soil physicochemical properties. Meanwhile, after its cumulative concentration in the soil being up to certain magnitude, the ionic surfactant would inhibit the spinach's growth and change the activity of soil enzyme. To some extent, these findings indicated the interactive law between ionic surfactants and soils were crucial to understanding the environmental behavior of the ionic surfactant and provide some reference for their assessing and managing the soil ecological security.