Gatobu, Ken

Harvey, Jagger

Hoffmann, Vivian

Milgroom, Michael

Mutiga, Samuel

Nelson, Rebecca

English

Research Papers in Economics

Aflatoxin Contamination and Consumer Valuation of Maize  
in Western Kenya 
 
Vivian Hoffmann 
University of Maryland, College Park 
vhoffmann@arec.umd.edu 
 
Samuel Mutiga 
Cornell University 
skm88@cornell.edu 
 
Rebecca Nelson 
Cornell University 
rjn7@cornell.edu 
 
Ken Gatobu 
Innovations for Poverty Action, Kenya 
kgatobu@poverty-action.org  
 
Michael Milgroom 
Cornell University 
mgm5@cornell.edu 
 
Jagger Harvey 
Biosciences east and central Africa (ILRI-BecA Hub) 
J.Harvey@cgiar.org 
 
 
 
 
 
Poster prepared for presentation at the Agricultural & Applied Economics Association 2010 
AAEA,CAES, & WAEA Joint Annual Meeting, Denver, Colorado, July 25-27, 2010 
 
 
Copyright 2010 by Hoffmann, Mutiga, Nelson, Gatobu, Milgroom and Harvey. All rights 
reserved. Readers may make verbatim copies of this 
document for non-commercial purposes by any means, provided that this copyright notice 
appears on all such copies. • Consumers were willing to pay the most for their own, maize 
they could taste before bidding was next, and then maize 
produced by fellow farmers for their own consumption.
• Maize purchased from traders in a local market was valued 
35% less than own-produced maize.
• Part of the difference is visual quality; removing rotten and 
broken grains reduces the difference to 21%
• Certification as below the legal acceptable level of aflatoxin
contamination has approximately the same effect as visual 
sorting, and combining these reduces the discrepancy still 
further.
Aflatoxin Contamination and Consumer Valuation of Maize in Western Kenya
Research Questions
• What are the relative levels of aflatoxin contamination in own-
produced and marketed maize?
• Does consumer valuation of maize categories correspond to average 
aflatoxin content?
•Are consumers willing to pay more for higher quality, less 
contaminated maize?
Acknowledgements
We are grateful to a large field team for survey data and sample collection, and 
to colleagues at Biosciences east and central Africa for their assistance with the 
laboratory analysis.
Consumer Valuation of Maize Quality
155 participants across 8 villages around Bungoma Town were invited to a session in which 
they could purchase maize of different qualities and origins through a second-price auction.
So as not to overwhelm participants, each session involved only four of the above types of 
maize.  Both the composition of maize types offered, and the order in which they were 
offered, was varied across sessions to avoid order and comparison effects.
Conclusions and Policy Implications
•Aflatoxin levels in maize samples taken were relatively low 
compared to previous studies in Kenya.
•Maize received as gifts had the highest level of contamination, 
suggesting that the poor are particularly at risk; awareness of the 
dangers of eating contaminated maize may be important for 
reducing exposure.
• Maize purchased from informal traders has significantly higher 
aflatoxin levels than maize grown for own consumption by 
farmers, suggesting that information asymmetry is leading to a 
market for lemons.
• Consumers’ valuation of their own maize is significantly higher 
than for maize of typical quality purchased in a local market. 
Certification and differentiation by quality and taste have the 
potential to narrow this gap.
• Regulation of the commercial maize market could improve the 
safety of food consumed by households and allow smallholder 
farmers to diversify their production away from maize.
Design Effects
Background: Aflatoxin and Maize in Kenya
• The fungus that produces aflatoxin is present in many tropical 
soils. Contamination of crops is exacerbated by  drought stress, pest 
damage before and after harvest, and inadequate drying prior to 
storage.
• Populations in many developing countries are chronically exposed 
to high levels of aflatoxin (Wild et al., 1993) 
• Chronic exposure interferes with immune system function, retards 
child growth, and leads to cancer (Strosnider et al., 2006). 
• Maize, the main dietary staple in Kenya, is one of the crops most 
susceptible to aflatoxin contamination
• Occasional epidemics of aflatoxicosis receive media attention in 
Kenya, but awareness of the probability and effects of chronic 
exposure are low.
Hammer Mill Survey
• Samples of maize were taken from 649 customers at village hammer mills around 23 market 
cetners in Western, Nyanza and Rift Valley provinces and matched to a questionnaire about the 
source of the maize, drying and storage practices
•A brief questionnaire about the source of the maize, drying and storage practices  was 
administered
•Highest aflatoxin levels were found in maize that had been received as a gift (n=30; p<0.001) . 
Own-produced maize had slightly higher aflatoxin content than purchased maize (n= 375; 
n=216; p<0.1)
2.26
2.98
5.76
own farm purchased gift
Mean Aflatoxin Content (ppb)
5%
11%
27%
own farm purchased gift
Proportion of Samples Above 
Legal  Limit of Aflatoxin (10 ppb)
Before the second-price auction, quantities of one or two KG 
of maize were purchased from farmers.  Both the quantity, and 
the mechanism used to purchase the maize were varied 
randomly in order to test for robustness of results to design 
effects.  No significant difference was found between the price 
charged under the BDM vs. posted-offer mechanism, nor for 
one vs. two KG of maize.
Maize Valuation Results
0.57
0.37
0.42
0.45
0.49 0.50 0.51
2nd Price Auction Bids (USD / KG Maize )
References
• Strosnider, H., E. Azziz-Baumgartner, M. Banziger, and R.V.
Bhat. 2006. “Workgroup Report: Public Health Strategies
for Reducing Aflatoxin Exposure in Developing Countries.”
Environmental Health Perspectives 114(12): 1898–
1903.
Wild, C.P., L.A. Jansen, L. Cova, and R. Montesano. 1993.
“Molecular Dosimetry of Aflatoxin Exposure: Contribution
to Understanding the Multifactorial Etiopathogenesis of
Primary Hepatocellular Carcinoma with Particular Reference
to Hepatitis B Virus.” Environmental Health Perspectives
99: 115–122.
Economists:
Vivian Hoffmann, University of Maryland
Ken Gatobu, Innovations for Poverty Action
Plant Scientists:
Samuel Mutiga, Cornell University
Rebecca Nelson, Cornell University
Michael Milgroom, Cornell University
Jagger Harvey, Biosciences east and 
central Africa (ILRI-BecAHub)
Research Team

Aflatoxin Contamination and Consumer Valuation of Maize in Western Kenya

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