Agriculture Reference
In-Depth Information
Table 6.3 Mean numbers of helminth eggs in irrigation water from
different sources
Irrigation water source
1
Helminth eggs (l
1
) (arithmetic mean)
City
Accra
Drain
8
Stream
15
Kumasi
Shallow well
2
Stream
27
1
Piped water was not included because no helminth eggs were observed during the study
period (n ΒΌ 15 for each irrigation water source).
streams and wells in Accra and Kumasi also exceeded the WHO
recommended level of one or less eggs per litre for unrestricted irrigation
(Table 6.3). The main species of helminth eggs isolated in water and on
lettuce included those of Ascaris lumbricoides (most predominant species in
all samples), Hymenolepis diminuta, Fasciola hepatica, T. trichura and
Strogyloides larvae. The results from Kumasi showed a higher helminth
population in stream water than in shallow wells, probably due to run-off.
The results of the microbiological quality of irrigation water confirm
earlier reports (Cornish et al, 1999; Mensah et al, 2001; Keraita et al, 2002)
that low-quality water is being used for urban vegetable production in most
Ghanaian cities. Shallow wells or dugouts might be expected to meet the
WHO recommended standard due to the natural filtering of aquifer materials
and long underground retention times. However, those used in this study were
often not protected against surface inflow.
The significant differences recorded in FC levels between the two sources
in Kumasi may suggest that shallow well water may pose relatively less risk to
farmers and consumers, although the coliform levels still exceed 1000 counts
per 100ml. Similar results have been reported from Kenya (Hide et al, 2001).
However, the situation can also change. For example, Cornish et al (1999)
recorded in Kumasi temporarily higher FC population in shallow wells than in
nearby streams. This may be due to the fact that probably the wells used were
shallower and got more easily contaminated through surface run-off on the
field (Drechsel et al, 2000).
Microbiological quality of lettuce at different entry points along the
production consumption pathway
Irrespective of the irrigation water source, mean FC levels on produce
exceeded recommended standards. Figure 6.3 shows FC populations on lettuce
samples collected in Kumasi at the farm gate, wholesale market and retail
outlets over a 12-month period and for three irrigation water sources. There
were no significant differences in average lettuce contamination levels at
different entry points (farm, wholesale market and retail outlet). Similar
contamination levels were recorded for the three irrigation water sources in
Accra (Amoah et al, 2007). High levels of FC counts (usually above the
