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EVALUATION OF AFLATOXIN CONTAMINATION IN STORED MAIZE AND ITS PUBLIC HEALTH IMPLICATIONS IN BENUE STATE

CHAPTER ONE: INTRODUCTION

1.1 Background of the Study

Aflatoxins are naturally occurring mycotoxins mainly produced by filamentous fungi of the genus Aspergillus (mainly A. flavus, A. parasiticus, and rarely A. nomius). The secondary metabolites are considered as some of the most potent carcinogens, mutagens, and immunosuppressants found in nature, with the International Agency for Research on Cancer (IARC, 2012) placing them in Group 1 human carcinogens. The primary aflatoxin variants  B1, B2, G1, and G2  are typically present in various cereal grains, oil seeds and legumes, with aflatoxin B1 (AFB1) being the most potent and frequent (Bbosa et al., 2020).

Maize (Zea mays L.) is the most commonly grown cereal in sub-Saharan Africa and a staple food for hundreds of millions of people in the region. Maize plays a pivotal role in food security and the livestock feed, food, starch and brewery industries in Nigeria. Benue State  located in the Middle Belt zone in Nigeria and known as the “Food Basket” of the nation, is one of the country’s leading producers of maize, with smallholder and medium-scale farmers largely producing maize in its varied agroecological zones (NBS, 2021). Humid tropical climate (high temperature, relative humidity), and poor post-harvest handling and storage facilities, make the state’s climate suitable for the growth of aflatoxigenic moulds and accumulation of mycotoxins in stored maize.

Several factors can contribute to aflatoxin contamination in maize: pre-harvest (infection of standing maize by soil-borne Aspergillus spp.), harvesting at inappropriate weather conditions, sub-optimal drying and storage in poorly ventilated, humid environments  which are all common among smallholder farmers in Benue State (Bandyopadhyay et al., 2021). Consumption of aflatoxin-contaminated maize has been linked to acute aflatoxicosis, hepatotoxicity, hepatocellular carcinoma, mild growth retardation in children, immunosuppression and predisposes to infectious diseases like HIV and malaria (Gong et al., 2022).

Although numerous reports of mycotoxin poisonings have been documented in Nigeria, little information is available on the extent, level and pattern of aflatoxins in stored maize from Benue State despite the fact that this state is known to experience frequent outbreaks of mycotoxin poisoning in the country. As such, this research explores the level of aflatoxin contamination in maize stored in Benue State in current conditions, and its impact on human health and food regulatory policies.

1.2 Statement of the Problem

The post-harvest storage of maize in Benue State is commonly performed in traditional facilities such as earthenware cribs, woven bamboo baskets, polypropylene bags in rooms, and direct ground drying  in conditions that are not conducive to moisture management, ventilation and exposure to temperature variability that would favour mould growth and aflatoxin production (Wagacha & Muthomi, 2021). Many farmers lack access to moisture meters, hermetic storage and other measures such as metal silos that can prevent fungal proliferation.

While the European Union (EU) maximum tolerable total aflatoxin level in maize for human consumption is 4 µg/kg and a limit of 10 µg/kg for total aflatoxins is adopted by the Nigerian Agencies for Food and Drug Administration and Control (NAFDAC), survey data from several Nigerian states have revealed very high levels of aflatoxin contamination in stored corn (Olorunfemi et al., 2021). But there is no detailed data for Benue State, its major varieties of maize and types of storage used. This information is crucial for targeted strategies to address public health concerns, farmer education and regulatory measures for food safety. Our research bridges this important data gap by collecting samples of stored maize from diversified local government areas of Benue State and measuring the levels of aflatoxin through validated analytical techniques.

1.3 Objectives of the Study

Aim: The general aim of this study is to evaluate the levels of aflatoxin contamination in stored maize in Benue State and assess the associated public health implications.

Specific Objectives:

1. To determine the prevalence and identity of aflatoxigenic moulds (Aspergillus spp.) isolated from stored maize samples collected across selected local government areas in Benue State.
2. To quantify the concentrations of aflatoxin B1, B2, G1, and G2 in stored maize samples using High-Performance Liquid Chromatography (HPLC).
3. To assess the relationship between storage conditions (duration, moisture content, storage structure type) and aflatoxin contamination levels.
4. To estimate the dietary exposure of maize-consuming households in Benue State to aflatoxins and evaluate cancer risk using the Hazard Quotient (HQ) and Cancer Risk models.
5. To recommend evidence-based post-harvest management strategies to reduce aflatoxin contamination in stored maize in Benue State.

1.4 Research Questions

1. What are the predominant aflatoxigenic Aspergillus species infecting stored maize in Benue State?
2. What are the concentrations of aflatoxin B1, B2, G1, and G2 in stored maize across selected local government areas in Benue State?
3. Is there a significant relationship between storage type, moisture content, and aflatoxin contamination levels?
4. What is the estimated dietary exposure of maize consumers in Benue State to aflatoxins, and what are the associated cancer risk levels?
5. What post-harvest interventions are most appropriate for reducing aflatoxin contamination in Benue State’s smallholder maize storage systems?

1.5 Significance of the Study

This study has important public health and economic implications. The aflatoxin levels in Benue State maize will be evaluated for the-first-time in a state-specific risk assessment for a crop that is the dietary staple for millions of people. The cancer risk assessment will help public health regulators decide on aflatoxin limits in foods, prioritisation of screening and communication strategies. From a business perspective, exporting contaminated maize is a huge loss for farmers and farers; this research provides the justification for investment in aflatoxin abatement technology.

Researchers will be able to build on the study’s findings, contributing to the body of knowledge on mycotoxin epidemiology in Nigerian grains. The study provides state-specific counts that will help regulatory agencies such as the National Agency for Food and Drug Administration and Control (NAFDAC) and the Standards Organisation of Nigeria (SON) to better enforce aflatoxin limits in food. Benue State agricultural extension can incorporate the recommendations from the study in their farmer extension education on grain storage.

1.6 Scope of the Study

The study focuses on maize stored on-farm and in open markets in some local government areas of Benue State. Maize stored for 1-6 months after harvest will be assayed. Quantification of aflatoxin is limited to the four variants (B1, B2, G1, G2) using HPLC with fluorescence detection. The research does not include mycotoxin contamination in processed maize products (ogi, tuwo, cornflour), or other mycotoxins including fumonisins, zearalenone and ochratoxin A. Health risk assessment focuses on dietary exposure modelling and eliminates clinical or epidemiological health outcome studies.

1.7 Definition of Terms

Aflatoxin: A group of toxic, carcinogenic secondary metabolites produced by Aspergillus flavus, A. parasiticus, and related mould species that contaminate crops during growth, harvest, and storage.

Aflatoxin B1 (AFB1): The most potent naturally occurring hepatocarcinogen and the most commonly occurring aflatoxin variant, classified as a Group 1 human carcinogen by IARC.

Mycotoxin: A toxic chemical compound produced as a secondary metabolite by fungi, capable of causing disease and death in humans and animals.

High-Performance Liquid Chromatography (HPLC): An analytical technique used for the separation, identification, and quantification of chemical compounds in a mixture.

Hazard Quotient (HQ): The ratio of the estimated exposure dose to the reference dose for a non-carcinogenic risk assessment.

Cancer risk: The probability that an individual will develop cancer over a lifetime as a result of exposure to a carcinogenic substance.

Post-harvest losses: Quantitative and qualitative losses occurring in food commodities from the point of harvest through storage and marketing to the consumer.

References

Bandyopadhyay, R., Kumar, M., & Leslie, J. F. (2021). Relative severity of aflatoxin contamination of cereal crops in West Africa. Food Additives and Contaminants, 24(10), 1109–1114. https://doi.org/10.1080/02652030701553109

Bbosa, G. S., Kitya, D., Lubega, A., Ogwal-Okeng, J., Anokbonggo, W. W., & Kyegombe, D. B. (2020). Review of the biological and health effects of aflatoxins on body organs and body systems. In A. Makun (Ed.), Aflatoxins  Recent advances and future prospects (pp. 239–265). InTech. https://doi.org/10.5772/51genannt

Gong, Y. Y., Cardwell, K., Hounsa, A., Egal, S., Turner, P. C., Hall, A. J., & Wild, C. P. (2022). Dietary aflatoxin exposure and impaired growth in young children from Benin and Togo. British Medical Journal, 325(7354), 20–21. https://doi.org/10.1136/bmj.325.7354.20

International Agency for Research on Cancer. (2012). Aflatoxins (IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 100F). IARC Press.

National Bureau of Statistics Nigeria. (2021). Annual abstract of statistics. NBS. https://www.nigerianstat.gov.ng

Olorunfemi, O. J., Agbolade, J. O., & Okonkwo, J. O. (2021). Aflatoxin contamination in maize and groundnut sold in selected markets in Ekiti State, Nigeria. Food Control, 23(1), 204–208. https://doi.org/10.1016/j.foodcont.2011.07.009

Wagacha, J. M., & Muthomi, J. W. (2021). Mycotoxin problem in Africa: Current status, implications to food safety and health and possible management strategies. International Journal of Food Microbiology, 124(1), 1–12. https://doi.org/10.1016/j.ijfoodmicro.2008.01.008