Agriculture Reference
In-Depth Information
300,000 (GSS, 2002). In contrast to Accra and Kumasi, Tamale Municipality
has few bodies of water and only a few seasonal streams.
Phase I: Sampling of vegetables at the markets
The purpose of this phase was to determine pathogens and pesticide
contamination of vegetables produced at UA sites. From October to
December 2002, a total of 180 vegetable samples (lettuce, cabbage and spring
onion) were collected from nine major markets and 12 specialized, individual
vegetable and fruit sellers (i.e. sellers with permanent stalls outside of
designated markets) in Accra, Kumasi and Tamale (see Figure 6.1). At each
market, samples were collected under normal purchase conditions from three
randomly selected sellers. A minimum of three composite samples - each
containing two whole lettuce heads, three bunches of spring onions (each
containing two bulbs) and three cabbages - were collected from the upper,
middle and lower shelves of each seller, put in sterile polythene bags and
transported on ice to the laboratory, where they were analysed immediately or
stored at 48C until analysis could occur within 24 hours.
These and all other samples collected (see below) were analysed for
coliform and helminth egg populations using the most probable number
(MPN) method (APHA/AWWA/WEF, 2001) and the floatation and
sedimentation method following a modified US Environmental Protection
Agency (US-EPA) method (Schwartzbrod, 1998), respectively. Gas
Chromatography (Flame Ionization Detector; Hewlett-Packard 5890 series II)
was used for pesticide residues on lettuce following the method adopted by
Ntow (2001). Sample peaks were identified by their retention times compared
with those of the corresponding pesticide standard obtained from the
International Atomic Energy Agency. The ability of the laboratory to identify
these substances has been verified by cross-tests of river sediments in Ghana.
Phase II: Contamination pathway study
This study was undertaken to determine the microbiological contamination
levels at various entry points along the production-marketing chain. In Accra
and Kumasi, two major irrigated vegetable production sites were selected
based upon the source of irrigation water and the type of vegetables grown,
with emphasis on exotic vegetables such as lettuce that were probably going to
be consumed raw. Both sites in Accra used water from drains and streams,
while shallow wells and streams provided the sources in Kumasi. Farmers in at
least one of the two sites in each city used irrigated, piped water as their source
over a period of at least three years. All sites had a similar history of land use.
For instance, all were under vegetable cultivation for periods of not less than
five years, and all farmers used poultry manure as a source of fertilizer.
Irrigation water
This study monitored the microbiological quality of irrigation water from
different urban sources. One composite sample per week was collected from
