Science - April 6, 2006

Pesticides help blue algae

Reports from all over the world suggest that freshwater areas are being taken over by the poisonous blue algae. Biologists regard global warming and increasingly high concentrations of fertilisers in water as the cause. According to Dr Miquel Lurling, however, they are forgetting another important factor: pesticides.

‘In Brazil in 1996 scores of people died when blue algae got into their kidney dialysis equipment,’ says Dr Miquel Lurling, who is associated with the Aquatic Ecology and Water Quality Management Group. ‘There are reports from China of liver tumours in areas where blue algae are found in the water. And in the Netherlands, recreational swimming areas are being shut more often because of blue algae. They are definitely on the rise.’
Blue algae produce poisonous substances which, if they come into contact with the eyes or skin, cause irritation. If you ingest the substances, for instance by swallowing water while swimming, you can become nauseous, feverish or even develop liver damage.’

In scientific terms the name ‘blue algae’ is incorrect. ‘They are officially called cyanobacteria,’ says Lurling. ‘They get their name from a pigment that gives them their blue colour. The bacteria are among the oldest organisms found on earth, but they are referred to commonly as blue algae.’
Cyanobacteria are found almost everywhere. ‘The problems arise when they start to dominate,’ says Lurling. ‘We wanted to find out under laboratory conditions if herbicides played a role in the process.’ Lurling and his colleague Ivo Roessink from Alterra have published an article in the journal Chemosphere describing how the cyanobacteria microcystis has no problem displacing the harmless green algae scenedesmus in the presence of the herbicide metribuzin, a permitted pesticide in the Netherlands.

‘Without the pesticide, the cyanobacteria would not have stood a chance in our experiment,’ says Lurling. ‘If you start an experiment in an aquarium with cyanobacteria in the majority, the green algae would dominate in the end. But the situation changes if you introduce the pesticide: then the cyanobacteria wins, even if it was in the minority to start with.’
The researchers used high concentrations of the pesticide, but say that this reflects field conditions. ‘We think that in late spring and early summer a ‘window for dominance’ occurs,’ says Lurling. ‘During that period the ecosystem in ponds and ditches is especially vulnerable to the impact of pesticides. If farmers spray and a shower of rain comes along that drives the pesticide into areas of water, you have the ideal conditions for cyanobacteria.’
Lurling is taking his research further. The next step is to examine the effect of pesticides on the micro-organisms that algae eat. ‘Less green algae means less animal plankton,’ says Lurling. ‘Biodiversity might be decreasing as a result of pesticides.’ / WK