Dialysis investigations of atrazine-organic matter interactions

Erin C. Devitt and Mark R. Wiesner

Contamination of surface and ground waters by atrazine is a problem for water utilities in the United States and Europe. Though not removed by traditional liquid-solid separation, it is removed by nanofiltration. Retention of atrazine by a series of dialysis membranes was investigated over a range of solution chemistries with the goal of better understanding how the solution matrix may influence atrazine retention by membranes. Atrazine was significantly retained by membranes with molecular weight cut-offs less than 500 daltons in the presence of natural organic matter (NOM), presumably by association with NOM.

Atrazine retention was independent of the initial concentration. Solution chemistry was important in determining the extent of atrazine retention. Where NOM aggregation and hence NOM retention increased, atrazine retention decreased, and vice versa. Atrazine retention tended to decrease at higher ionic strengths. This effect was significantly stronger with divalent calcium than with monovalent sodium.

Partitioning coefficients calculated here are much higher than values reported from experiments of atrazine retention by soil organic matter. It is speculated that the most likely mechanism of atrazine retention by NOM is through association of atrazine with interior adsorption sites on the NOM molecule by transitory hydrogen bonding and subsequent physical entrapment.