Agriculture Reference
In-Depth Information
Table 6.2 Pesticide residue detection and concentrations on lettuce (n
ΒΌ
60)
MRL
1
(mg/kg)
lettuce
Pesticide
Lettuce with
detected
pesticide
residues
(%)
Range of
concentrations
(mg/kg) on
lettuce with
residues
Mean
value
(mg/kg)
lettuce
Lindane
31
0.03-0.9
0.3
0.01
Endosulphan
36
0.04-1.3
0.4
0.05/0.5
Lambda-cyhalothrin
11
0.01-1.4
0.5
1.0/0.1
Chlorpyrifos
78
0.4-6.0
1.6
0.05/0.5
DDT
33
0.02-0.9
0.4
0.05
1
MRL, maximum residue limit (Pesticide Safety Directorate, 2005).
14 per cent of samples had no detectable pesticide residues. More than 60 per
cent of the lettuce samples had two or more pesticide residues, with 78 per
cent of samples showing chlorpyrifos, an organophosphate of moderately
acute hazard (WHO, 2005). Chlorpyrifos was the only pesticide with higher
levels in one city, Kumasi. In most cases, pesticide residue levels observed
exceeded the MRL.
The results of tests for pesticide residue indicate that several pesticides
(particularly chlorpyrifos) are widely used by vegetable producers in Ghana,
in keeping with other studies (Okorley and Kwarteng, 2002). As also
described by Danso et al (2002), farmers mix cocktails of various pesticides to
increase their potency. Vegetables are often eaten raw so it is not surprising to
read about evidence of chlorpyrifos contamination such as can be found in
waakye, a popular Ghanaian dish (Johnson, 2002). Lindane and endosulphan
are restricted for the control of capsids on cacao trees, stem borers in maize
and for pests on coffee plants, while DDT is banned in Ghana. However, the
data show clearly that these potent agrochemicals are used irrespective of
whether approved for vegetable production or not. It has been reported that
in several African countries the legislation on importation and regulation of
pesticides is sketchy, nonexistent or imbedded in bodies of legislation
indirectly related to pesticides (Tallaki, 2005). Because of the lack of proper
regulations, organochloride pesticides banned in industrialized countries for
their retention in the environment or their high toxicity are still commonly
used.
This widespread pesticide contamination, often exceeding the MRL,
indicates potential health risks to consumers. Washing vegetables before
consumption is highly recommended, but the majority of pesticides cannot
just be washed away and may still pose health risks (Volpi, 2005). A rough
calculation helps to elucidate this potential: The acceptable daily intake
(ADI)
3
of chlorpyrifos, for example, is 0.01mg kg
1
body weight (WHO,
1997). To exceed the ADI, a child weighing 30 kg would have to consume
at
least 0.3mg of chlorpyrifos per day. With a residue level of 1.6mg
