Geochemistry Process Of Anionic Surfactants In Shuangtaizi River Estuary

Linear alkylbenzene sulfonates （LAS）, which is an anionic surfactant widelyused in household detergents and other industrial applications, has been largelyintroduced into environment via sewage discharge. With the rapid development of theeconomy and urbanization in China, the production and consumption of LAS isincreasing due to high demand of,daily chemical articles. However, it may threatenthe health of ecology and human beings. Based on the establishment of determinationmethod on total LAS in soil/sediment, a laboratory modeling experiment, in whichsalinity, water temperature and concentration of suspended particles were controlled,was developed to research on the distribution, transportation and transformation inShuangtaizi estuary. Moreover, environmental risk of LAS was evaluated in studiedarea. The research had practical significance in discovery of biogeochemical cycle oforganic pollutants as well as environmental quality evaluation in Shuangtaizi estuary.Determination method on total LAS in soil was firstly established, matching withthe water quality-determination of anionic surfactants by the methylene bluespectrometric method （GB7494-87）. Soil samples was first extracted in20mL ethanolwater solvent （70%） under the condition of shaking for2h at a45°C water bath, andthen centrifuged for20min at4000r/min. The supernant reacted with methylene blueand measured in at652nm. The method precision was1.89%, recovery was locatedat91-97%and detection limit was0.020mg/kg.Two predominant factors as LAS transported into the estuary were significantlystudied in the modeling experiment. As a result, LAS was clearly conservative andtended to decrease when the salinity increases under control, with two theoreticaldilution lines V海/V=-5.989C_LAS+1.0897（r=0.9995），V海/V=-0.2005C_LAS+0.9947（r=0.9982）at0.20mg/L and5.00mg/L in fresh water end respectively. Under different conditions, adsorption of LAS on suspended particles/sediment could entirely be described byFreundlich sorption isotherm with Log Kfof3.11-3.77, and it was concluded that theamount of adsorption increased with decreasing water temperature and increasingsalinity and organic carbon content.Determination of field samples showed dissolved LAS decreased with thetransportation process in the estuary. Annual concentration ranged from0.009to0.070mg/L with0.032mg/L on average. Concentration of dissolved LAS was higherin surface water than that in bottom water. LAS associated with particulate mattersacted similarity as dissolved LAS and concentration ranged from10to44mg/kg dwwith24mg/kg dw on average.Linear regression coefficients between LAS and salinity are below-0.30underin-site conditions, which shows dissolved LAS is not controlled by dilution. However,it is different from modeling experiment that dissolved LAS is obviouslynon-conservative due to the interaction of biodegradation, adsorption of LAS andsewage discharge. Nearly90%sites indicate LAS is removed from dissolved LASwith removal rates at-18.19--52.64%and the effect is more distinct influenced byincreasing water temperature. Log Kdand adsorption percentage between dissolvedand particulate LAS decrease while salinity increases, with the value of2.48-3.37and2.07-19.87%separately, because decreased dissolved LAS restricts the amountdistributed to particulate matters in the open water so that the in-site concentrations ofparticulate LAS were all below the modeling values.The annual concentration of surface sediment samples ranges from0.000-4.095mg/kg dw with1.943mg/kg on average and has strong relationship with bottom water（r=0.623） and particulate matter （r=0.655）. Log KdBetween sediment and bottomwater are below modeling values ranging from1.34to2.38, but the reason isuncertain. Agreed with modeling experiment, the concentration of LAS in sediment isinfluenced by salinity and organic carbon content. However, water temperatureimpacts little.The vertical variation of LAS in tidal area is different from that in reed wetland.LAS content in reed wet land decreased quickly from19.277mg/kg dw in the surface to0.840mg/kg dw in the bottom because of biodegradation being main factor, whileit fluctuates vertically in tidal area with content0.755-3.712mg/kg dw on account ofrunoff being the most influential factor.On the basis of geochemical process of LAS in Shuangtaizi estuary, Massbalance equation is established with dissolved LAS as research object. Appropriatevalues or expressions for fractions of the process are expected to be formulated toestimate the LAS fluxes in the estuary.