| dc.description.abstract | Lead, cadmium, selenium and arsenic were the selected indicators of toxic heavy metals
which were determined using atomic absorption spectroscopy (AAS) in sewage being
reused for irrigation in Athi River town of Kenya. Coliform counts and Escherichia coli
were also determined in the same sewage as indicators of pathogenic bacterial agents.
Lead and cadmium were further detected in soils and in a selected number of food crops
under sewage irrigation. The pH of both soils and sewage was also tested as the main
factor that determine the availability of these toxic heavy metals to the crops. Similarly,
the activities of the pathogenic microbiological agents were deduced with respect to the
temperatures of the sewage.
In general, an average of twenty samples per parameter were taken. The levels of toxic
heavy metals were found as follows: lead (0.17 ppm), cadmium (0.04 ppm), selenium
(0.009 ppm) and arsenic (0.008 ppm) in sewage. But in soils the average levels oflead and
cadmium were 0.44 /-ig/g and O.13/-ig/g respectively, the crops analysed were selected as
root crops (cassava, sweet potato & arrowroots), leaf crops (kale & spinach) and fiuit (or
seed) crops (beans, tomatoes & maize). These analyses were done on dry weight basis on
their edible parts only.
The average levels oflead found in these crops were 0.061lg/g, O.lllg/g and 0.051lg/g for
root, leaf and fruit crops respectively. Similarly, the mean levels of cadmium in root, leaf
and fruit crops were 0.016/-ig/g. O.03J1.g/gand 0.02J1.g/grespectively. Coliform counts was
> 300 counts per 100 ml. in all sewage samples.. Thes.e samples. also gave positive
indication of the presence of Escherichia coli.
These levels of toxic heavy metals found in sewage were not significantly different (at 95%
C.1.)from those of World Health Organisation/Food and Agricultural Organisation health
guidelinesconsidering the fact that the sewage on reuse had not been given any preliminary
treatment. Levels in soils and crops found were within the natural environmental levels
and therefore expected to pose little or no health problems.
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But the levels of pathogenic bacterial indicators were found to be quite high. These levels
coincide with those found in places where incidence of water related epidemic outbreak
of diseases had been recorded. It was therefore, in order to relate any pathogen-related
diseaseoutbreak in the area to such levels. But in contrast, the past public health records
in this Athi River town do not show any significant diseases outbreak related to sewage
farming:a fact that seems to agree with the fanners claims that they do not have any health
problems related to the irrigation activities reusing the sewage. Yet, observations
madeindicated that even basic recommendations for sound health practices are not being
followed. Therefore, conclusive explanation of these contrasting results calls for further
research in relationship to the pathogenic micro-organisms and the conditions that make
them endemic in a society. However, for this research, it should be sufficient to say that
the less intensive reuse of sewage for farming, the currently low population density in the
region and the high temperatures with less rainfall might account for low occurrence of
expected diseases outbreak.
But with the now increasing population and the need for an alternative source for water
supply,reuse of sewage (which is about 1 million litres per day in Athi River) should not
be disregarded entirely during this environmental awareness age on the basis of the menace
of pathogenic microbiological agents. Moreover, a spectrum of technical solution are
available. Further research is required on adaptation of a synthesized low cost and
acceptable technology for the treatment of sewage for reuse in farming in developing
nations | en_US |
