Agriculture Reference
In-Depth Information
Table 8.6 Mean concentrations of heavy metals in the irrigation water during
the rainy (dry) season, 2005
Pb
2
þ
(g/l)
Cd
2
þ
(g/l)
Cr
2
þ
(mg/l)
Co
2
þ
(mg/l)
Ni
2
þ
(mg/l)
Cu
2
þ
(mg/l)
Sampling site
ENDA
264
(239)
122
(132)
0.33
(0.26)
0.09
(0.07)
0.22
(0.31)
1.8
(1.6)
ENDM
347
(162)
184
(108)
0.26
(0.24)
0.10
(0.06)
0.29
(0.27)
1.5
(1.7)
EPP
517
(191)
155
(117)
0.24
(0.25)
0.03
(0.03)
0.32
(0.29)
2.0
(1.3)
EET
261
(243)
157
(143)
0.22
(0.25)
0.08
(0.04)
0.303
(0.32)
1.9
(1.6)
EMA
532
(265)
256
(168)
0.26
(0.25)
0.09
(0.12)
0.35
(0.41)
1.7
(1.7)
EPA
279
(182)
276
(109)
0.21
(0.26)
0.04
(0.04)
0.30
(0.43)
2.3
(1.7)
EPNA
411
(182)
387
(103)
0.24
(0.25)
0.09
(0.08)
0.32
(0.32)
2.2
(1.6)
ERO
418
(200)
317
(163)
0.23
(0.25)
0.04
(0.05)
0.28
(0.33)
1.6
(1.5)
EJE
631
286
0.25
0.05
0.49
1.5
ED
473
(217)
209
(118)
0.33
(0.28)
0.07
(0.07)
0.31
(0.27)
1.5
(1.5)
FAO standards
5000-10,000
10-50
0.1-1.0
0.05-5.0
NA
0.2-5.0
the maximum authorized value for long-term use of irrigation water (FAO,
2003); whereas the concentrations of Cd
2
þ
were, in most cases, more than ten
times higher than the allowable limit. In about half the samples,
concentrations of Co were less than 0.05mg/l, allowable for long-term use. Ni
values were higher than the allowable value of 0.2mg/l. In a couple of
sampling locations, Cu values were higher than the allowable value of
2.0mg/l. Heavy metals can be a significant risk for humans and animals
(FAO, 2003); moreover, the bioaccumulation of cadmium can be toxic in
humans (FAO, 2003), and high levels of Zn, Cu and Ni can kill plants.
Bacteriological quality of irrigation water and potential risk of human
contamination. Contaminated wastewater used for irrigation poses a risk to
vegetables, farmers and consumers (Mara and Cairncross, 1991; Niang, 1996).
This risk was evaluated by sampling the irrigation water for total coliform,
fecal coliform, fecal streptococci and E. coli (Table 8.7). In the majority of
cases, the water was found to be contaminated by micro-organisms, whose
concentrations were higher than acceptable standards.
Farmers working in market gardens are exposed to several risks, most
notably exposure to E. coli and Salmonella dysenteriae in the water; insects
such as mosquitoes, tsetse flies and bees; and metallic objects in household
garbage. The majority of market gardeners do not use protection such as
