Agriculture Reference
In-Depth Information
larger surface area exposed. Cabbage and spring onion showed geometric
mean counts of 3
:
3
10
6
g
1
and 1
:
1
10
6
g
1
wet weight, respectively. No
sample had less than 4000 FC per gram wet weight.
The mean FC levels of all the three crops exceed the International
Commission on Microbiological Specifications for Food (ICSMF, 1974)
recommended level of 10
3
fecal coliforms per gram fresh weight. Several
factors may account for the high levels recorded in most of the analysed
vegetables. Among these is the use of polluted irrigation water and fresh
poultry manure, both of which are applied on top of the crops. Significantly
high FC contamination levels (between 4
:
8
10
3
and 2
:
8
10
6
100ml
1
)
which usually exceed common standards have been recorded in irrigation
water (Cornish et al, 1999; Drechsel et al, 2000; Mensah et al, 2001; Keraita
et al, 2002). High FC populations (between 3
:
6
10
4
and 1
:
1
10
7
) were also
reported in poultry manure in the same study areas.
Another potential source of contamination is market-related handling,
especially where provision for better sanitary standards (e.g. clean water for
crop washing and refreshing) is lacking. A relatively high total and FC
population recorded on some vegetables was also reported by Johnson (2002)
and Armar-Klemesu et al (1998) analysing street food and market crops in
Accra, respectively.
Mean helminth egg population on vegetables
About 30 per cent of vegetables had no helminth eggs. Lettuce, cabbage and
spring onion carried mean helminth egg populations of 1.1 g
1
, 0.4 g
1
and
2.7 g
1
wet weight, respectively. No significant difference was observed in the
mean helminth egg populations recorded in lettuce and cabbage; however, the
difference between spring onion and both lettuce and cabbage was significant
(P
<
0
:
05). If distributions skewed, the mean separations were compared using
one-way ANOVA. The eggs identified included Ascaris lumbricoides,
Ancylostoma duodenale, Schistosoma heamatobium and Trichuris trichiura,
with Ascaris lumbricoides eggs being the predominant contaminant (60 per
cent of lettuce, 55 per cent of cabbage and 65 per cent of spring onions
showed Ascaris lumbricoides eggs).
Biologically, the highest health risk from pathogens is infections due to
helminth contamination. Because helminths persist for longer periods than
pathogens in the environment, host immunity is usually low to non-existent
and the infective dose is small (Gaspard et al, 1997). Such microbial and
parasitic contamination probably contributes to the high number of food-
borne and water-related diseases in Accra such as diarrhoea (sometimes
caused by typhoid or cholera), as well as intestinal worm infections. However,
these also have to be seen in the context of generally sub-optimal sanitary
conditions in parts of the metropolis (Arde-Acquah, 2002).
Pesticide residues on lettuce leaves
Table 6.2 shows pesticide detection prevalence and residues recorded on
lettuce leaves, with maximum residue limits (MRL) as comparators. Only
