The adsorption of cyanobacterial hepatotoxins from water onto soil during batch experiments

Public health concerns associated with cyanobacteria, both chronic and acut e, arise from their ability to produce toxins. Rural communities within Aus tralia and those in developing countries require an inexpensive and low-cos t method for removing toxins from drinking water. A candidate technology is bank filtration. Adsorption of cyanobacterial hepatotoxins was measured in batch studies to determine the applicability of bank filtration as an effi cient removal strategy. Five soils with different physicochemical propertie s were collected from regions around South Australia. The soils were mixed with either nodularin or microcystin-LR in distilled water and buffered sol utions (pH 4.8, 6.9 and 9.1). Additionally, nodularin was mixed in unbuffer ed solutions (pH 4.8 and 8.9). The three soils with the high clay and/or or ganic carbon contents (Paringa A, McLaren Flat and Lakes Plains) had the hi gher nodularin adsorption coefficients, ranging from 0.2 to 16.59 L kg(-1). Soil suspensions in acetate buffer (pH 4.8) generally produced significant ly higher nodularin adsorption coefficients, when compared to the other buf fer systems. The background interference from the ionic strength of the buf fers, however, made interpretation of the effect of pH on toxin sorption di fficult. Increases in solution ionic strength, from freshwater to seawater, resulted in corresponding increases in the nodularin adsorption coefficien ts for all sites, except the sandy Hallett Cove site. The implications for bank filtration are that higher water pH values and lower salinities will e nhance the in situ mobility of the toxins, resulting in an increased distan ce of filtration through the river bank before toxin free water could be ab stracted for human consumption. (C) 2001 Elsevier Science Ltd. All rights r eserved.