Method for testing for bioaccumulation

Abstract

For use in estimating or predicting bioaccumulation of a chemical analyte, even a surfactant, log P ow values for the analyte may be determined by calculating the log of the ratio of the concentrations of the analyte in n-octanol and in water, equilibrated using a slow-stir method. In this method, samples of the analyte are prepared and stirred in n-octanol and water (or other largely immiscible solvents) at a rate sufficiently low to avoid emulsions over time at a constant temperature. After stirring, the n-octanol layer and the water layer are sampled and the quantity of analyte in each measured.

1. A method for obtaining a log P value of a chemical for use in chemical bioaccumulation analysis, said method comprising:
 providing a sample of said chemical in two largely immiscible solvents;  
 allowing said sample to equilibrate at constant temperature over time;  
 determining the concentration of the chemical in each of the solvents; and  
 calculating the partition coefficient.  
 
   
   
     2. The method of  claim 1  further comprising stirring said sample to expedite said equilibration at a rate sufficiently slow that emulsions do not occur. 
   
   
     3. The method of  claim 1  wherein said chemical is a surfactant. 
   
   
     4. The method of  claim 1  wherein said solvents are water and n-octanol. 
   
   
     5. The method of  claim 4  wherein said temperature is in the range of about 20° C. to about 22° C. 
   
   
     6. The method of  claim 1  wherein said temperature is below the boiling point of said solvents and said chemical. 
   
   
     7. The method of  claim 1  wherein said time extends over several days or weeks. 
   
   
     8. The method of  claim 4  wherein said calculation is made using the equation: 
         P   ow     =         c     n   ⁢     -     ⁢   octanol         c   water       .         
 
   
   
     9. A method for obtaining a log P value of a surfactant for use in surfactant bioaccumulation analysis, said method comprising:
 providing a sample of said surfactant in two largely immiscible solvents,  
 stirring said sample at constant temperature and at a rate sufficiently slow that emulsions do not occur over time while allowing equilibration of said sample;  
 determining the concentration of the surfactant in each solvent, and calculating the partition coefficient of the surfactant.  
 
   
   
     10. The method of  claim 9  wherein said rate of stirring provides a vortex in said sample such that the ratio of the length of the fluid column of said sample to the vortex height ranges from about 1 to about ∞. 
   
   
     11. The method of  claim 9  wherein said rate of stirring provides a vortex in said sample such that the ratio of the length of the fluid column of said sample to the vortex height ranges from about 4 to 5. 
   
   
     12. The method of  claim 9  wherein said partition coefficient is calculated using the following formula: 
       P   =         c     (     lighter   ⁢           ⁢   solvent     )         c     (     heavier   ⁢           ⁢   solvent     )         .         
 
   
   
     13. The method of  claim 9  wherein the solvents are water and n-octanol and the following equation is used in calculating said partition coefficient: 
         P   ow     =         c     n   ⁢     -     ⁢   octanol         c   water       .         
 
   
   
     14. The method of  claim 13  wherein said temperature is in the range of about 20° C. to about 22° C. 
   
   
     15. The method of  claim 9  wherein said temperature is below the boiling point of said solvents and said surfactants. 
   
   
     16. A method for obtaining the partition coefficient of a surfactant analyte dissolved in a two-phase system consisting of two largely immiscible solvents wherein said analyte is allowed to reach equilibrium in said system while avoiding the formation of emulsions. 
   
   
     17. The method of  claim 16  wherein said equilibrium is reached through slow stirring. 
   
   
     18. The method of  claim 17  wherein said stirring causes a vortex in said system such that the ratio of the length of the fluid column of said system to the vortex height ranges from about 1 to ∞. 
   
   
     19. The method of  claim 17  wherein said stirring causes a vortex in said system such that the ratio of the length of the fluid column of said system to the vortex height ranges from about 4 to 5. 
   
   
     20. The method of  claim 16  wherein said partition coefficient is calculated using the formula: 
       P   =         c     lighter   ⁢           ⁢   phase         c     heavier   ⁢           ⁢     phase   .           .         
 
   
   
     21. The method of  claim 16  wherein said equilibrium is reached while maintaining the surfactant analyte and solvents at constant temperature. 
   
   
     22. The method of  claim 21  wherein said temperature is below the boiling point of said system. 
   
   
     23. The method of  claim 21  wherein the two-phase system is n-octanol and water and said partition coefficient is calculated using the formula: 
         P   ow     =         c     n   ⁢     -     ⁢   octanol         c     water   .         .         
 
   
   
     24. The method of  claim 23  wherein said temperature is in the range of about 20° C. to about 25° C. 
   
   
     25. The method of  claim 16  comprising calculating the logarithm in base 10 of said partition coefficient for use in bioacculation analysis.