Quick Dips

Beating Roving Bugs

The farmer is spraying cowshed waste onto the paddocks as liquid manure -- are you breathing in any of it? Probably.

"In some weather conditions it's probably inevitable that at least a small amount of the sewage waste spray, in the form of tiny droplets or aerosols, will travel outside the target area. And that's frequently been the basis of public concern for people who live near disposal sites for waste from agricultural or related operations," says Dr Mike Noonan.

The Lincoln University microbiologist hopes that a mathematical model and an air sampling device designed to mimic the human lungs will help provide some answers.

Noonan and scientists from the Meat Industry Research Institute of New Zealand (MIRINZ), together with mathematical modellers from NIWA (the National Institute of Water and Atmospheric Research), are undertaking a thorough investigation of the dispersal of microbial aerosols and how to address public concerns.

"At the moment it is difficult to reassure the public over microbial aerosols as there is no satisfactory scientific information available to predict dispersal patterns or plan effective barriers which would stop aerosols from reaching neighbouring properties," says team leader Dr Andrea Donnison of MIRINZ.

To come up with that information, the team has set up an experimental site on a flat, treeless paddock and has been spraying a fine mist of bacteria-laced water onto it. Making a close record of weather conditions at spraying time, the scientists have put all the relevant data into a computer model, and they can now predict the maximum number of microbes you could be breathing in for a given set of weather conditions. The next step is to repeat their experiments with real manure sprayers and perhaps some extra factors such as trees.

"Eventually we hope to be able to accurately predict the extent of spray dispersals under various regimes so that farmers and others can better manage this activity and put effective barriers in place to stop aerosols reaching neighbouring properties," says team member Dr Gavin Fisher of NIWA.

The challenge of the research team over the next couple of years is to extend investigations to large-scale spray equipment and to produce mathematical models that can be used at real sites.

"The results have a wider interest too," says Fisher, "and the team hopes to look at microbe emissions from conventional sewage schemes, other parts of the wastewater stream, and also agricultural pesticide overspray which is recognised as a major problem in New Zealand."