1. Prevalence of aflatoxin along the maize
value chain in Kenya.
George Mahuku (CIMMYT) & Henry
(H. Sila) Nzioki (KARI)

2. Mycotoxin producing fungi
• Weak parasite
• Very susceptible
to ecological F. graminierum A. Flavus F. verticillioides
conditions
• Optimum DON FB
AF
conditions differ
for growth &
toxin production
• Mycotoxins
production Temp 25° 35° 30°
elicited by stress aw 0.98 0.78 0.96

3. Mycotoxins in Maize and effect on
human health
Fungus Mycotoxin International Health Effects
limits (vary)
Aspergillus Aflatoxin B1 (0 – 50 ppb) Carcinogen, affecting the liver,
flavus and A. reduced efficiency of the
parasiticus Kenya (10 ppb) immunological system, retards
growth and development of
children
Fusarium Fumonisin B1 4 ppb Asociated with esophageal cancer,
verticillioides and neural tube defects leading to
abortion
Fusarium Zearalenone Not established Properties of estrogen hormones
graminearum
F. Deoxynivalenol 1 ppm Reduced efficiency of the
graminearum immune system
Penicillium Ochratoxin A Not established Chronical renal diseases
verrucosum

4. Variation in acceptable aflatoxin
levels

5. Aflatoxin
• are naturally occurring mycotoxins
produced by the fungi Aspergillus
flavus and A. parasiticus.
• not all A. flavus strains are toxigenic
• grow on maize, peanuts ,wheat, beans
and rice.
• are a problem particularly in warm and
humid, tropical countries.
• drought conditions are ideal for growth
and proliferation of fungi.

6. Aflatoxin affected major crops
• Cereals: Maize, Sorghum, Pearl millet
• Oil seeds: Groundnuts, Soybean, Sunflower
• Spices: Chillies, Black pepper, Turmeric
• Tree nuts: Pistachio, Almonds, coconut

7. Aspergillus and aflatoxin
• Aspergillus flavus – opportunistic pathogen
• Superior adaptability
– Survives in a wide range of environments: soil, plant debris, dead insects
and seeds
• Fungus does not need a live host to survive
• Complex environmental and ecological factors affect A. flavus
infection and aflatoxin contamination.
• Aflatoxin contamination is:
– unavoidable under the present production, processing and storage of
crops & commodities.
• Infection and aflatoxin contamination can occur at pre-harvest,
harvest, post-harvest, process, storages, transit stages

8. Factors affecting Aflatoxin contamination
of Maize
Environmental Factors Harvesting
Biological Factors
-Temperature - Crop maturity
-Susceptible crop - Moisture availability - Temperature
- Compatible toxigenic fungi - Mechanical injury - Moisture
-Insect/ bird damage -Handling
Processing &
Humans
Storage Animals
-Structure;
-Moisture; -Temperature
Distribution
Detection/diversion
Animal Products

9. Aflatoxin in the Food Chain
FEED

10. Response to different concentrations of
aflatoxin
zero
Increasing concentration of aflatoxin

11. Objectives
• Understand the incidence and prevalence of aflatoxin
along the maize value chain in selected study areas.
• Identify critical points where intervention
technologies are mostly likely to be more effective

12. Maize Sampling Sites
• Lower Eastern
– Machakos County: Machakos, Kathiani Kangundo and
Matungulu Districts
– Makueni County: Mbooni East and Makueni Districts
• Upper Eastern
– Embu County: Mbeere North, Embu North and Embu
West Districts
• South Western Kenya
– Homabay County: Homabay and Rongo Districts
– Kisii County: Kisii Central District

13. Methodology
• Along identified critical points along the market
chains, samples were collected:
• Pre-harvest – physiological maturity while in the field
• Harvest, handling and processing for storage
• Storage by farmers (30 day interval)
• Markets (30 day interval)
• Assemblers
• Wholesalers
• Retailers
• Consumers of products

14. Information / Data collected
• Farmer / Actor name
• GPS coordinates
• Maize variety
• Source of maize
• Moisture content
• I kg maize sample for analysis (following a
standard protocol: Aflacontrol website)

15. Maize samples collected from farmer
fields (pre-harvest)
Year
Region 2009 2010 2011 Total
Lower Eastern (LE) 30 167 143 340
Upper Eastern (UE) 10 41 40 91
South Western - 153 99 252
(Homabay/Rongo [HR})
South Western (Kisii - 78 41 119
Central [KC])
Total 40 439 323 802

16. Maize samples collected from farmer
stores (post-harvest / storage)
Year
Region 2009 2010 2011 Total
Lower Eastern 87 276 156 519
Upper Eastern 59 253 44 356
South Western - 368 101 469
(Homabay/Rongo)
South Western (Kisii Central) 30 214 39 283
Total 176 1111 340 1627

17. Maize samples collected from
markets
Year
District 2009 2010 2011 Total
Lower Eastern 152 535 219 906
Upper Eastern 126 232 38 396
South Western - 345 92 437
(Homabay/Rongo)
South Western (Kisii 52 154 40 246
Central)
Total 330 1266 389 1985
Total Samples analyzed = 4,414

18. Maize samples from farmer fields & Stores with
aflatoxin levels above and below 10ppb (2009)
120
#Samples <10 (μg/kg)
100
% Samples >10 (μg/kg)
80
Region Range
60 (μg/kg) STDev
Upper Eastern (UE) 0 - 9091.8 2874.9
40 FF
Lower Eastern (LE) 0 - 273.8 68.9
20
Upper Eastern (UE) 0 - 27393.7 4188
0 FS
UE LE UE LE (N= KC Lower Eastern (LE) 0 - 3180.7 422
(N=10) (N=30) (N=58) 87) (N=30)
Kisii Central (KC) 0 - 5.4 1.6
Farmer Fields Farmer Stores

19. Maize samples from market with aflatoxin
levels above and below 10ppb (2009)
60
% Samples <10 (μg/kg)
50
% Samples >10 (μg/kg)
40
30
Region Range (μg/kg) STDev
20
Upper Eastern (UE) 0 - 12000 2160
10
Lower Eastern (LE) 0 - 9302 166.4
0 Kisii Central (KC) 0 – 3442.2 2160
KC (N=52) LE (N=152) UE (N=126)

20. Proportion of Maize samples from the
farmer stores with aflatoxin levels
above 10 ppb (2009)
90
80
70
60
50 1 month PH
40 2 months PH
3 months PH
30
20
10
0
Makueni Embu Mbeere Kisii
North

21. Proportion of Maize samples from the market
with aflatoxin levels above 10 ppb (2009)
100
90
80
70
60
1 month PH
50
2 months PH
40 3 months PH
30
20
10
0
Makueni Embu Mbeere Kisii
North

22. Maize samples from farmer fields & Stores with
aflatoxin levels above and below 10ppb (2010)
90
% Samples <10 (μg/kg)
80
% Samples >10 (μg/kg)
70
60
50
Region
Range (μg/kg) STDev
40 Upper Eastern (UE)
0 - 252 52.7
30
Lower Eastern (LE)
20 0 – 1454.8 139.1
FF
10 Hbay/Rongo (HB)
0 – 722.2 66
0 Kisii Central (KC)
0 – 558.7 77.5
Upper Eastern (UE)
0 – 22641.7 253.5
Farmer Fields Farmer Stores Lower Eastern (LE)
0 – 1978.3 234.5
FS
Hbay/Rongo (HB)
0 – 1511.2 123.6
Kisii Central (KC)
0 – 611.8 77.2

23. Maize samples from the first and second
seasons with aflatoxin levels above 10ppb
(2010)
50
45
40
35
30
25
October-November
20 March - May
15
10
5
0
Lower Eastern Upper Eastern Hbay/Rongo Kisii Central
(N=149) (N=41) (N=153) (N=79)

24. Proportion of samples collected from
farmer stores with aflatoxin levels above
10 μg/kg (2010)
February – March harvest July - August harvest
80
80
70
70
60 60
50 KisiiCentral 50
40 Homabay / Rongo 40
30 Lower Eastern 30
20 Upper Eastern 20
10 10
0 0
1 month 2 months 3 months 1 month 2 months

25. Maize samples from markets with aflatoxin levels
above and below 10ppb, (2010)
90
80
% Samples <10 (μg/kg)
70
% Samples >10 (μg/kg)
60
50
40
30
20
Region Range (μg/kg) STDev
Upper Eastern (UE) 0 – 1632.9 184.7
10
Lower Eastern (LE) 0 – 2076.7 188.4
0
Lower Upper Hbay/Rongo Kisii Central Hbay/Rongo (HB) 0 – 379.5 42
Eastern Eastern (N=345) (N=154)
(N=535) (N=232) Kisii Central (KC) 0 – 1308.8 148.9

26. Maize samples from farmer fields & Stores with
aflatoxin levels above and below 10ppb (Jan – May
2011)
120
% samples < 10ppb
100 % samples >10 ppb
80 Region Range
(μg/kg) STDev
Upper Eastern (UE)
60 0 – 581.5 94.4
Lower Eastern (LE)
0 – 354.6 49.8
40 FF
Hbay/Rongo (HB)
0 – 20.2 3.6
20
Kisii Central (KC)
0 – 63.1 9.8
0
Upper Eastern (UE)
0 – 248.5 49.1
Lower Eastern (LE)
0 – 685.6 92.9
FS
Hbay/Rongo (HB)
0 – 41.6 5.6
Farmer Fields Farmer Stores Kisii Central (KC)
0 – 357.2 57

27. Maize samples from markets with aflatoxin levels
above and below 10ppb, (Jan – May, 2011)
100
90 % samples < 10ppb
80 % samples >10 ppb
70
60
50
40
Region Range
30
(μg/kg) STDev
20 Upper Eastern (UE) 0 – 1679.6 286.2
10 Lower Eastern (LE) 0 – 3568.3 335.9
0 Hbay/Rongo (HB)
H/R (N=92) KC (N=40) LE (N=219) UE (N=38) 0 – 36.8 5.9
Kisii Central (KC) 0 – 60.7 9.7

28. Conclusion
• Occurrence of aflatoxins in maize is a complex series of interaction
between G x E x Pathogen x Farmers practices. This complexity
poses difficulties in achieving control.
• We did not find differences in aflatoxin levels among varieties /
hybrids grown by farmers.
• Contamination starts from the field
– Need to factor in environmental conditions
• Aflatoxin is not homogeneously distributed in contaminated lots.
Sampling poses a major challenge, hence the fluctuations between
sampling times.
• Aflatoxin contaminated maize samples were found from both South
western and Eastern Kenya regions
• This is the first systematic study looking at aflatoxin contamination
along the maize value chain

29. Acknowledgements
• Partners: Ministry of Agriculture extension
staff, Farmers, Traders, KARI – Katumani
staff: Centre Director, crop protection and
support staff
• ICRISAT for aflatoxin analysis
• ACDI/VOCA
• Financial support
– Bill and Melinda Gates Foundation