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Dernière mise à jour : Mai 2018

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Pathogen levels in soils

The micro-organisms detected in the soils are essentially enterococci and C. perfringens, but there is no visible effect from the input of OWPs. Helminth eggs are detected at times, but there is no link with spreadings. Other micro-organisms (salmonella, L. monocytogenes and E.coli) are not detected in the soils, except sporadically. Pathogens from OWPs have not survived in the soils.

The micro-organisms detected in the soils are essentially enterococci and C. perfringens, but there is no visible effect from the input of OWPs. Helminth eggs are detected at times, but there is no link with spreadings. Other micro-organisms (Salmonella, L. monocytogenes and E.coli) are not detected in the soils, except sporadically. Pathogens from OWPs have not survived in the soils.

Monitoring in the soils has been carried out every year since 2005 at harvest time in order to evaluate the possible link between the presence of micro-organisms in the soils and plants. In addition to this regular monitoring, in 2004 and 2006 monitoring was carried out before and after spreading to evaluate the survival of pathogens in the soils. Monitoring was performed on plots in the section of the system receiving mineral fertilisation. In 2005 and 2006, three of the four plots for each treatment were monitored. In 2007, the four plots for each treatment were studied.

The pathogenic micro-organisms L. monocytogenes and salmonella were not detected in the soils, with the exception of a soil sample from one of the three BIO plots. The quantities of E. coli were below the detection threshold of 10 or 100 CFU/g DM in all of the soil samples.Helminth eggs are rarely detected (Table 1). They were not detected before spreading (To), or 12 or 22 months after spreading. Certain samples taken 1, 2 and 6 months after spreading tested positive for no apparent reason. Helminth eggs were not detected in the distributed ROPs and the control plot was positive after 1 month, even though no ROPs were spread. In 2006 and 2007 they were no longer detected, except in a GWS plot.

Tableau 1. Détection des oeufs d'helminthes dans les sols.

oeufs-d-helminthes

Enterococci population levels were fairly stable in the soil, at between 100 and 1,000 MPN/g fresh soil (Figure 1). However, 2, 3 and 6 months after spreading during the 2004/2005 campaign, the plots conditioned with manure had slightly higher levels compared with other plots, although this difference was not significant (less than a factor of 10).
C. perfringens was also detected in the soil, but with no significant effect from the input of OWPs (Figure 1). Before spreading, as well as 1 and 2 months after spreading, concentrations in the soil ranged from 10 to 100 CFU/g fresh soil. 6 months after spreading, the concentration falls below the detection threshold (10 CFU/g DM). This decrease could be due to weather conditions. This is because the sample was taken after a cold winter period, during which C. perfringens can be found in spore form, which is not detected by the analytical method used. The rise in temperature may explain the increase in C. perfringens (germination of spores) up to a level of 100 CFU/g fresh soil 13 months after the spreading, which is comparable to the initial level measured in September 2004. This value is subsequently repeated in July 2006 and July 2007.

population-enterocoque
Figure 1. Change in enterococci and C. perfingens population levels over time in the soil from September 2004 to September 2007.