Biological contamination of barley and carrots by pathogens in soil fertilised with anthropogenic nutrients

Abstract

The aim of this study was to find out if the use of septic tank sludge, urine and composted
faeces as fertilizer for barley and carrot crops would pose a health risk due to pathogen
transfer,
This study was accomplished as a greenhouse experiment in the premises of the TAM K
University of Applied Sciences, Tampere. The study concentrated on the qualitative detection
of Salmonella and a quantitative detection of coliform bacteria in the growing medium - and
more importantly, in the plant products. Methods used were based on instructions given on
the compact salmonella (SL) detection plates and the Compact coliform (CF) detection plates
with a modified method of standards SFS 3950 and SFS 4447. The results were compared
among others to the European Commission regulation 2073/2005 on microbiological criteria
for foodstuff
Salmonella was absent in the fertilizers, and thus its presence would be impossible in the plant
products. Coliform bacteria were initially detected in the growing medium, but generally the
amount decreased significantly within time. At the end of the experiment barley grains from
the first urine duplicate and first composted faeces duplicate were totally free of coliform
bacteria. Also, the amount of coliform bacteria in barley grains of other treatments was
acceptable in hygienic terms, being less than I cfu/g. The amount of coliform bacteria in
carrots grown in commercial fertilizer and composted faeces treatments were within the
satisfactory limits. The small size of carrots from urine and septic tank sludge treatments did
not allow complete handling, nevertheless, the amount of colony forming units was
considered to be within the acceptable limit of 100-IO00 cfu/g. Results from this study
indicate that the use of composted excreta and source separated human urine as fertilizer is
not posing a health risk in terms of coliform bacteria. More thorough research, however, is
needed in order to define the risk of other disease causing microbes, like enterococci and
viruses.