Study On Sorption Behavior Of Diazinon On Marine Sediments

Pesticides are toxic organic pollutants, which are ubiquitous in the environment .Agricultural and outdoor residential use of pesticides are of increasing environmental concerns because these chemicals are recognized as nonpoint and point pollution sources of potential adverse environmental impacts, and their presence in seawater and sediments has grown considerably. The sorption of pesticides on sediments is a major factor which affects their environmental behaviors, since the sorption can further affect their diffusivity and mobility, volatility and other processes such as chemical and biological degradations as well as their bioavailability. Changes in these properties and processes are critical to the environmental fates of these organic pollutants. It is therefore of great importance to assess the sorption behavior of pesticides on marine sediments in order to have a deeper insight to their transformation in marine environment and the consequent ecological effects.In this thesis, the sorption behavior of Diazinon on Jiaozhou Bay sediment was systematically investigated. The effects of some environmental parameters, such as temperature, salinity, acidity, sediment granularity, and concomitant organic contaminants, on its sorption behavior were examined. The possible sorption mechanism was discussed based on data obtained in the thesis, combined with existing literatures. Major results and conclusions are shown as follows:1. The sorption equilibrium time of Diazinon on Jiaozhou Bay sediment was approximately 6 hours at an initial concentration of 20 mg/L .2. The sorption isotherms of Diazinon on sediment samples are of L-type and can be described by Langmuir or Freundlich isotherms very well, with Freundlich isotherm giving a better fitting result.3. The sorption capacity of Diazinon decreased with increasing the temperature and sediment granularity,while it increased with increasing salinity.4. The higher sorption capacity of Diazinon appeared at a lower pH value..The apparent amount of sorption would increase at a lower pH value because of hydrolysis of Diazinon, while it would decrease at a higher pH owing to the increased mobility of Diazinon.5. Coexisting sodium dodecyl sulphate (SDS) greatly affects the sorption of Diazinon. The sorption capacity of Diazinon increased with SDS at a lower concentration, while it decreased significantly with SDS at a higher concentration.6. Concomitant tetradecyltrimethylammonium bromide (TDTMA) has a pronounced effect on the sorption of Diazinon. The sorption capacity of Diazinon increased with increasing the concentration of TDTMA.