BIOSORPTION OF TRIBUTYLTIN AND OTHER ORGANOTIN COMPOUNDS BY CYANOBACTERIA AND MICROALGAE

Biosorption of triorganotin compounds by the cyanobacteria Synechocyst is PCC 6803 and Plectonema boryanum and the microalga Chlorella emerso nii, incubated in 2-(N-morpholino)ethanesulphonic acid (MES) buffer, p H 5.5, in the presence of 0.5 mm organotin (supplied as chlorides), in creased with molecular mass of the organotins, the order being triphen yltin > tributyltin (Bu3SnCl) > tripropyltin greater-than-or-equal-to trimethyltin greater-than-or-equal-to triethyltin. In the butyltin ser ies, monobutyltin biosorption was lowest, although levels of dibutylti n uptake were greater than for Bu3SnCl. Cyanobacterial Bu3SnCl biosorp tion was complete in 5 min with no subsequent accumulation. In contras t, a second phase of uptake in C. emersonii resulted in an approximate 2.4-fold increase in cellular Bu3SnCl between 5 min and 2 h. The exte rnal pH had a marked influence on biosorption of Bu3SnCl by Synechocys tis PCC 6803 and P. boryanum, with maximal uptake at pH 5.5 and 6.5, r espectively. Effects of pH were less evident in C. emersonii. In all t he organisms examined, no inhibition of Bu3SnCl biosorption was observ ed between 0.05 and 50 mm NaCl. However, an increase in the external N aCl concentration from 50 to 500 mm resulted in an approximate 55-65% reduction in Bu3SnCl uptake. Biosorption increased at increasing Bu3Sn Cl concentrations (0.25-3.0 mm). Saturation of Bu3SnCl biosorption at the higher concentrations was most evident in the cyanobacteria, altho ugh uptake levels were greater in these organisms at less-than-or-equa l-to 2 mm Bu3SnCl. Theoretical maximum biosorption levels at complete cell saturation, derived from reciprocal Langmuir plots, were approxim ately 565, 525 and 1050 nmol Bu3SnCl mg dry weight, for Synechocystis PCC 6803, P. boryanum and C. emersonii, respectively.