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Treatment options for microcystin toxins: similarities and differences between variants

G Newcombe1, D Cook, S Brooke

  • 1Australian Water Quality Centre, a partner in the CRC for Water Quality and Treatment, PMB 3, Salisbury, South Australia 5108, Australia.

Environmental Technology
|April 22, 2003
PubMed

Insights

Microcystin variants LR and LA behave similarly in water treatment, except for activated carbon adsorption. Microcystin-LR adsorbs more readily than microcystin-LA, contrary to expectations.

Area of Science:

  • Environmental Science
  • Toxicology
  • Water Treatment

Background:

  • Over sixty variants of the blue-green algal toxin microcystin exist.
  • Microcystin-LR and microcystin-LA differ by a single amino acid (arginine vs. alanine).
  • Previous research suggested similar behavior of microcystin variants in water treatment.

Purpose of the Study:

  • To investigate the adsorption behavior of microcystin variants on activated carbon.
  • To understand the factors influencing the differential adsorption of microcystin variants.
  • To challenge the consensus of similar responses of microcystin variants to water treatment.

Main Methods:

  • Comparative adsorption experiments of microcystin-LR and microcystin-LA on activated carbon.
  • Testing adsorption on both negatively and positively charged carbons.
  • Electrostatic shielding experiments.

Main Results:

  • Microcystin-LR adsorption onto activated carbon is significantly higher than microcystin-LA.
  • This adsorption trend was also observed for microcystin-RR and microcystin-YR.
  • The difference in adsorption is not due to electrostatic interactions with the carbon surface.
  • Electrostatic repulsion between adsorbed microcystin-LA molecules (net charge -2) may explain its lower adsorption.

Conclusions:

  • Microcystin variants exhibit differential adsorption onto activated carbon, contrary to expectations.
  • Intermolecular electrostatic repulsion is a likely cause for reduced adsorption of variants with higher net charges.
  • This finding has implications for optimizing water treatment processes for microcystin removal.

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