pH-dependent hydrophobicity of the cyanobacteria toxin microcystin-LR

Although the presence of hepatotoxins in surface and drinking water is rega rded as an ecotoxicological and human health problem, limited knowledge exi sts on the fate of these compounds. Therefore the n-octanol/water distribut ion ratio (D-ow) of the hepatotoxin microcystin-la (MC-LR) was determined i n order to enable the prediction of the fate of this compound in the aquati c environment. The presence of two free ionizable carboxyl groups and one f ree ionizable amino group in MC-LR suggest that its speciation and partitio ning between octanol and water is pH dependent. This was experimentally stu died and confirmed in the present study. The log D-ow of MC-LR decreased fr om 2.18 at pH = I to -1.76 at pH = 10. From the low log D-ow values, especi ally at the basic pH region at which the toxin producing cyanobacteria flou rish, a low tendency to bioconcentrate from water in biota can be expected. (C) 1998 Elsevier Science Ltd. Ail rights reserved.