Reduction of diffuse losses
Diffuse losses of pesticides after use in the field can occur by several different routes, e.g. as
volatilization, surface transport and leaching through the soil profile to drainage pipes or ground water. The magnitude of losses emanating from these processes depends on for instance how long the pesticide is exposed to the environment. The risk for contamination from diffuse sources therefore significantly can be reduced if pesticide residues are degraded as fast as possible after the intended effect has been obtained. One way to obtain this could be to add at the spraying microorganisms that can degrade the pesticide as soon as it is deposited on places where it will not have the intended function.

Results obtained
Some results obtained so far in studies of the concept of simultaneous addition of a pesticide and degrading microorganisms or enzymes are:

Development of a test system for experiments with plants and effect of inoculation with MCPA-degraders on the degradation of MCPA. A test system with a mini-greenhouse placed in a cultivation chamber for experiments with plants sensitive and insensitive to phenoxyalkanoic acids (white mustard and wheat) and inoculation with pesticide degraders has been developed. One week after sowing, the soil and the plants were sprayed with MCPA to give approximately 4 mg of MCPA/kg dw of soil. In one treatment an inoculum (2 x 105 cells/g of soil) of an enriched MCPA-degrading culture was applied simultaneously with the herbicide. The results show that the hypothesis works in systems with plants present (Figs. 1A and 1B). The results also show that the herbicidal effect of the MCPA was not eliminated or changed, since no herbicidal effect was evident in the treatment with the insensitive winter wheat, while all white mustard plants had died 7 days after spraying.

Degradation of glyphosate in solution by Mn-peroxidase and laccase.

Glyphosate degradation by Mn-peroxidase and laccase produced by different fungi was tested (Pizzul et al., 2009). All the different enzymes tested degrade glyphosate (Fig 2).

Degradation of a pesticdes in a mixture by Mn-peroxidase.

The ability of Mn-peroxidase to degrade different pesticides was studied (Pizzul et al., 2009). In a mixture of 22 different pesticides, all were degraded (20-100%) by Mn-peroxidase (Fig. 2).

Useable products require isolation, identification, cultivation, formulation and risk assessment
After isolation and identification of pesticide degrading microorganisms or enzymes, they must be produced on a large scale. For the practical use in the field, appropriate formulations of the degrading microorganisms or enzymes then will be required, so they can be handled and mixed into the spraying tank in order to be distributed together with the pesticide but not being activated until the pesticide has had its intended effect. In addition, risk assessments of all interesting candidate microorganisms must be made, in order to avoid unwanted effects from their use.

References

Castillo, MdP, Torstensson, L. & Stenström, J. 2008. Biobeds for environmental protection from pesticide use - A review. J. Agric. Food Chem. 56(15), 6206–6219. DOI: 10.1021/jf800844x.

Pizzul, L., Castillo, MdP & Stenström, J. 2009. Degradation of glyphosate and other pesticides by ligninolytic enzymes. Biodegradation DOI: 10.1007/s10532-009-9263-1.

Personnel

The project group consists of Professor Anders Jonsson (project leader), Professor John Stenström, Dr. Leticia Pizzul and technician Maria Eriksson. PhD student Karin Önneby closely cooperates with the project and the DOM programme researchers Dr. Thomas Eberhard (fermentation), Dr. Sebastian Håkansson (formulation) and Professor Ingvar Sundh (safety assessment) also are involved in the project.