Update on mycotoxin contamination of maize and peanuts in East African Community Countries

The East African Community (EAC) is a regional Inter-Governmental body comprising of Uganda, Kenya, Tanzania, Rwanda, Burundi, and South Sudan. This region produces and extensively consumes maize and peanuts as staple foods. Maize and peanuts are susceptible to fungal growth and mycotoxin contamination and this is favored by high temperatures, high humidity as well as other factors such as grain damage by birds or insects, poor postharvest handling, and storage. Mycotoxins are toxic secondary metabolites of fungi that contaminate food with far-reaching consequences on human and animal health in addition to causing huge economic losses. Major mycotoxins of concern in maize and peanuts are Afl atoxins, Fumonisins, Zearalenone, and Deoxynivalenol. Among the East African Community countries afl atoxins and fumonisins are the most detected and researched mycotoxins in maize and peanuts. The highest reported afl atoxin contamination levels in maize and peanuts among the East African Community countries were 48,000μg/kg and 7,525μg/kg respectively both of which were recorded in products from Kenya while the highest fumonisin contamination in maize was 18,184 μg/kg which was reported in products from Tanzania. Human beings are exposed to mycotoxins mainly through the consumption of contaminated foods or their products. The East African Community through the East African Bureau of Standards set regulatory limits for afl atoxins and fumonisins in maize and peanuts at 5 ppb for afl atoxin B1, 10 ppb for total afl atoxins, and 2000 ppb for fumonisins. This paper reviews the current literature on mycotoxin contamination of Maize and Peanuts in the East African Community region, current regulations, their negative consequences on health and trade as well as factors contributing to their high prevalence in the region.


Introduction
The East African Community (EAC) is a regional block  Table   1 [1].
Maize and peanuts are susceptible to fungal attack and mycotoxin contamination [2]. According to the East African Community Facts and Figures, 2019 the region in 2018 recorded the highest maximum rainfall of 953mm while the average minimum and maximum temperatures were 20°C and 29°C respectively. These conditions are conducive for fungal growth and mycotoxin production [3]. Mycotoxins are secondary toxic metabolites of fungi that contaminate food in many different parts of the world with far-reaching consequences on human and animal health in addition to causing enormous economic losses [4][5][6][7][8]. Several studies have reported high mycotoxin levels in maize and peanuts from the East African community region [9][10][11][12][13][14][15]. Major mycotoxins of concern in maize and peanuts are Afl atoxins (AFT), Fumonisins (FBs), Zearalenone (ZEN), and Deoxynivalenol (DON) which are mainly produced by Aspergillus sp and Fusarium sp as shown in Table 2 [2,[16][17][18][19]. Fungal growth and subsequent mycotoxin production Citation: Ankwasa  can occur when the crops are still in the fi eld as well as after harvesting, during processing, handling, transportation, and storage [13,20,21]. Other factors such as grain damage by birds or insects and poor postharvest handling and storage also greatly contribute to high mycotoxin occurrence in food [22][23][24][25][26][27] Table 2. who consume contaminated maize and yet go unconsidered [2]. Most of the previous studies have targeted one mycotoxin but currently, research is now targeting multiple mycotoxins because of their co-occurrence in agricultural products [5].
There is a need to evaluate the collective toxicity as a result of multiple occurrences or co-occurrence of mycotoxins in food on human health [31,32]. This paper reviews current literature on mycotoxin contamination in Maize and Peanuts in the East African community region, their negative health and economic effects as well factors contributing to their high prevalence in the region.

Occurrence and Exposure to mycotoxins in the East African Community Countries
Afl atoxins and Fumonisins are the most widely spread, detected, and researched mycotoxins occurring in maize and peanuts in the East Africa community region and Africa generally [2,3,12,23]. Afl atoxins B 1 has the highest toxicity among the afl atoxins and accounts for 75% of the total food contamination related to afl atoxins however there is Scanty information available on the prevalence of other mycotoxins like DON, and ZEN in maize and peanuts for human consumption in East Africa though some studies have been undertaken in animal feeds [2,6,18,19,[33][34][35][36][37][38][39][40]. Deoxynivalenol is detected more frequently in animal feeds than in food [6,8,41]. Human beings are exposed to mycotoxins mainly through eating contaminated plant-based foods but can also be exposed to carry-over mycotoxins and their metabolites through animal-based products such as milk, meat, and eggs [4,9,23,42]. According to the Food and Agricultural Organization of the United Nations, approximately 25% of food crops all over the world are contaminated with mycotoxins [3]. Many people in East Africa are continuously exposed to high afl atoxin levels mainly through the consumption of contaminated maize and peanuts which are stapled foods in their daily diets. Many developing countries including East African Community countries export high-quality grains leaving behind low-quality ones which have increased consumption of contaminated and low-quality foods by the local population thus greatly increasing their exposure to mycotoxins [3,43,44]. It is important to note that in many instances checking for mycotoxins in food is mainly done on food products intended for the export market while the locally traded food products are not tested which exposes many East Africans to mycotoxins through their diets [45].
Babies can be exposed to afl atoxin M 1 through breast milk from their mothers who consume food contaminated with afl atoxins. A study that was undertaken in Northern Tanzania involving 143 breastfeeding mothers indicated that their breast milk contained 0.01 to 0.55ng/ml afl atoxin M 1 (AFM I ) a hydroxylated product of AFB 1 [2]. Afl atoxin M 1 occurrence in animal milk has been strongly associated with afl atoxin B 1 content in feeds given to animals [38,46]. Workers who handle and process afl atoxin-contaminated grains and feeds are also at risk of exposure to afl atoxins through inhalation of dust produced during the processing of such agricultural products [27,47]. A report from Kenya indicated that a local brew made from fermented maize was highly contaminated with afl atoxins, Fumonisin, and DON, and consumption of such a  Good grain handling and storage practices such as cleaning to remove dirt and debris, sorting to remove damaged grains, proper aeration of the warehouses or stores to avoid dampness and proper grain drying to a moisture content of 12% or below before storage greatly improve grain quality and prevent or retard growth of fungi and production of mycotoxins [29]. Multiple mycotoxins can occur in one food item and this co-occurrence results in multi-toxin exposure to humans. Many health guidelines focus mainly on the toxicity of individual mycotoxins while paying less attention to the combined effects of multiple toxin interactions [6,12,30]. The problem of multiple mycotoxin occurrence in food has been attributed to the production of more than one mycotoxin by some fungal species, as well as combining raw materials contaminated with several mycotoxins during food production.
It is signifi cant to mention that DON, ZEN, and FB are all produced by the Fusarium species and therefore can co-occur with each other in food but may go undetected. Afl atoxins and fumonisins have been reported to co-occur in Maize and afl atoxicosis could co-occur with Fumonisin toxicity in humans Citation: Ankwasa  brew could serve as an exposure route to these mycotoxins [2].
Another report from Uganda reported that farmers use fungicontaminated maize to make local brew which can also be a direct source of mycotoxin contamination [48].

Mycotoxin prevalence in maize and peanuts in East Africa Community Countries
Maize and peanuts are staple foods extensively produced and consumed in the East African community region and these two crops and their products are very susceptible to fungal growth and mycotoxin contamination [2,12,14,15,49,50] ppb respectively which are higher than the 10 ppb limit for afl atoxins in EAC countries. The rest of the districts had mean contamination levels below the 10 ppb limit and the lowest contamination of 3.8 ppb was registered in samples from Mpigi [14]. A study on the occurrence of Fumonisin contamination in maize samples from three agro-ecological zones (High attitude, mid-altitude moist, and mid-latitude dry) revealed that the high altitude areas registered the highest total Fumonisin content ranging from 0.85 ppm (850 ppb) to 10 ppm (10,000 ppb) with an average of 4.93 ppm (4930 ppb) which is higher than 2 ppm (2000 ppb) limit for fumonisins in EAC countries [51]. Peanuts provide a rich source of proteins and are widely consumed in Uganda and the East African region however they are very susceptible to mycotoxins [18,52,57].
A study conducted on peanut samples from four districts in Uganda (Mayuge, Iganga and Mubende, and Kampala) revealed that 60% of all samples collected at farm level in different villages were contaminated with afl atoxins and two villages of Kiboyo and Bugodi recorded average contamination levels of 12.4 ppb and 10.5 ppb respectively which were higher than the 10 ppb limit for afl atoxins in EAC countries. Among the market segment samples, it was observed that unsorted peanut seeds and milled peanut fl our had higher afl atoxin contamination levels of 65.4 ppb and 59.4 ppb respectively compared to sorted and roasted peanut seeds which had lower contamination levels of 8.3 ppb and 12.7 ppb respectively. The study recommended that consumers should eat roasted peanut paste which had lower contamination levels compared to white milled peanut fl our [53]. Another study involving peanuts, cassava, millet, sorghum fl our, and eshabwe sauce samples from fi ve districts in western Uganda (Mbarara, Ntungamo, Rukungiri, Kasese, and Kabale) revealed that peanut fl our samples were contaminated with afl atoxins with average total afl atoxin contamination levels of 11.5 ppb which are higher than 10 ppb limit for afl atoxins [10]. Another study involving maize, peanuts, cassava fl our, and peanut paste samples from markets in Kampala revealed that peanuts and peanut paste sold in different markets in the country were contaminated with afl atoxins and the contamination levels reached 940 ppb in peanuts and 720 ppb in peanut paste which is higher than 10 ppb limit for afl atoxins [58]. Another study conducted by Muzoora [26], on peanut samples collected from eight districts in four regions revealed that 62% of the samples were contaminated with afl atoxins and more specifi cally 26% of the samples tested positive for AFB 1. This study showed that 52% of the samples had afl atoxins levels higher than the 10 ppb limit for EAC countries and the total afl atoxin content in milled samples ranged from 0.31 ppb to 11,732 ppb while in seed samples the range was from 1.6 ppb to 516 ppb. It was observed in this study that milled peanut fl our samples had high contamination than peanut seeds and this was suspected to be caused by traders who mill contaminated peanuts to conceal proof of spoilage. It was also observed that urban samples were more contaminated than rural samples and this was attributed to the possible long transportation and storage of peanuts from rural areas to urban areas since mycotoxin contamination has been known to occur during poor transportation and storage conditions. Another study conducted by Baluka, et al. [ reported afl atoxin contamination levels as high as 2687.6 ppb in Busia District and 7525 ppb in Homabay District [62].
Another study conducted by [63] in Nairobi and Nyanza provinces in Kenya on afl atoxin contamination of peanuts and peanut butter revealed that peanut butter from the cottage industry had afl atoxin levels as high as 2377.1 ppb while raw peanuts had contamination levels reaching 364 ppb. The high incidence of afl atoxins in peanut butter was attributed to using defective ground nuts contaminated with afl atoxins to make peanut butter but could have also increased due to bad processing habits such as poor hygiene at the grinding mills,

Tanzania
Maize is also widely grown and consumed in Tanzania but is also susceptible to fungal growth and mycotoxin  kg [40]. Another study carried out on maize fl our for human consumption from markets in Rwanda also reported high AFB 1 contamination levels with the highest average of 24.7± 23.7μg/ kg which was reported in samples from Nyarugenge in round one of assessment and 25.9± 25.9μg/kg which was reported in samples from Nyamirambo in round two. In both scenarios, the average contamination levels were above the 5 ppb limit for AFB 1 in EAC member countries [68].

Burundi
A study conducted on maize, cassava, beans, soybeans, sorghum, and groundnut samples collected from markets in Burundi and Eastern DRC revealed that all the samples were contaminated with afl atoxins. The samples from Burundi had an average total afl atoxin contamination level of 117.0μg/kg which is higher than the 10 ppb limit for EAC countries [17].

South Sudan
South Sudan is the youngest country in the world and the newest member of the East African Community having joined on 15 th August 2016 and the available information on mycotoxins relates to former Sudan before it was split into Sudan and South Sudan and therefore cannot be accurately reported for South Sudan.

Regulation of mycotoxins in East African Community Countries
Regulatory limits offer a guarantee to consumers that the food will not contain toxins in concentrations that are harmful to their health [3]. The fi rst mycotoxin regulations were set in the late 1960s and by 1981, 33 countries in the world had mycotoxin regulations. By 1987 the number of countries regulating mycotoxins had increased from 33 to 66 countries and by 2003 this number had increased to 99 countries representing approximately 87% of the world population. Out of 99 countries, only 15 countries were from Africa [69][70][71]. The increase in the number of countries with mycotoxin regulations demonstrates the commitment of Governments to reduce the negative effects of mycotoxins on humans health and as well as their impact on trade. It is also signifi cant to note that the number of mycotoxins covered under the regulation limits increased from 1 mycotoxin (mainly afl atoxin) in 1981 to currently 13 [69]. The East African Community formed the East African Bureau of Standards which was mandated to harmonize standards for goods and services in the region and put in place regulatory limits for mycotoxins in food and feeds which has greatly improved the quality and safety of food products in the region. The regulation limits for mycotoxins in maize and peanuts cover afl atoxins and Fumonisins [72]. It is important to note that such harmonized regional standards mostly improve trade relations among countries but may fail to offer the desired protection to health due to differences in food consumption patterns as well as mycotoxin occurrence and exposure rates among countries [73]. There is a lot of informal trade among the EAC countries which makes it diffi cult to effectively enforce mycotoxin regulations within the region and this means that poor quality foods are being consumed which poses negative health effects Table 3.

Health and Economic impact of mycotoxins
Mycotoxin contamination of food has direct and indirect Citation: Ankwasa  economic consequences as well as severe health effects to humans and animals as a result of acute toxicity or chronic exposure [5,17,80]. The health consequences resulting from exposures to mycotoxins in humans range from acute to chronic effects such as afl atoxicosis, organ toxicity, neurotoxicity, Mutagenicity, Carcinogenicity, cytotoxicity, Growth retardation, diarrhea and vomiting, Immunosuppression, reproductive disorders, and death [4,17,27,35,42,43,52]. In Kenya, several cases of afl atoxicosis and death resulting from consumption of afl atoxin-contaminated maize have been reported with the most severe outbreak reported in 2004 [2,3,61,81]. Consumption of afl atoxin-contaminated food for a long time has been strongly linked to Hepatocellular carcinoma, retarded growth, and underweight in children [2,3,61]. In East Africa, several reports have indicated a correlation between afl atoxin exposure and high incidences of Hepatocellular carcinoma (HCC) in humans and it is estimated that there are 29 cases and 33.1 cases per 100,000 people in rural-Kenya and Tanzania respectively [2]. Among the East African Community countries liver cancer is the 5 th ranked type of cancer occurring in men and women and in 2007 approximately 290,052 new cases of liver cancer were registered [10]. In Uganda, it is reported that the country loses $577 million per annum due to hepatocellular carcinoma treatment, and an extra 910,000 US dollars are spent on treating sicknesses and medical conditions related to afl atoxins [52]. Research by numerous scientists has shown a correlation between chronic exposure to mycotoxins (such as afl atoxins and Fumonisins) and impaired growth rate in children as was reported in a study conducted in Haydom Tanzania [82]. Growth impairment in children is reported to increase as the children grow and this is because as they grow they stop exclusive breastfeeding and start taking weaning foods (complementary foods) many of which are cereal-based (maize and peanut) which are suspected to be contaminated with afl atoxins and fumonisins [83]. Chronic exposure to fumonisins through consumption of contaminated maize has also been linked to regular occurrences of oesophageal cancer in Kenya although more studies are needed to confi rm this pattern in other high maize consuming countries in East Africa [2,51]. A study conducted on the incidence of oesophageal cancer in Eastern Africa revealed that this region is a high incidence area for oesophageal cancer and that this presents a hefty burden on the health service systems in the region. It is reported that in East Africa oesophageal cancer is the second most frequently detected cancer among men with an estimated 10,500 new detected cases in 2008 which is strongly linked to consumption of maize-based diets [2]. The agricultural and economic consequences of mycotoxin contamination of food include low crop yield and livestock productivity, reduced value of contaminated products and low profi ts, rejection of food and feeds in international markets, high human medical and animal veterinary care costs, and death of humans and animals [17,41,54,84]. There are other high implied and indirect costs related to mycotoxin contamination of food and feeds such as the enforcement of regulation, continuous monitoring, and research on occurrence levels, toxic effects, and detoxifi cation strategies to avert the negative effects of these mycotoxins [47,85]. The high mycotoxin limits used by the European Union hinder trade between the European Union and countries in Sub-Saharan Africa [17]. Sub-Saharan Africa which includes East African Countries loses approximately $670 million in exports every year because of high EU regulation ) [80]. Uganda experiences a 43.5% reduction in agriculture exports due to afl atoxins contamination of agriculture products including maize and peanuts and the country loses approximately 38 million dollars every year as a result of export rejects related to afl atoxin contamination [52]. Acute or chronic exposure to mycotoxins causes several health problems in humans including death (Table 4).

Factors contributing to prevalence and exposure to mycotoxins in East Africa
In the East Africa Community region, several factors contribute to fungal growth and the high prevalence of mycotoxins in food. These factors are environmental (soil contamination by fungi, water stress, warm and humid conditions) political (regulations, laws, policies, enforcement), and economic as well as related to food production, handling,   [88][89][90]. There is also a problem of weak enforcement of mycotoxin regulations in some countries while in others the existing regulations cover a limited number of mycotoxins which has greatly contributed to the high prevalence of mycotoxins in the region [10,12,17,52] . Illiteracy among farmers and consumers in East Africa and limited access to information about mycotoxins have also greatly contributed to their high occurrence in food in the region [3,16,17,30].
Limited funding for mycotoxin research, limitations in terms of expertise, limited up to date mycotoxin data as well as limited research facilities have also greatly contributed to the high prevalence of mycotoxins in the region [3,17,52]. Most of the East African countries experience warm and humid weather conditions which are very favorable for fungi growth and mycotoxin production. There is an argument that climate change will make East Africa warmer and more humid which will greatly increase mycotoxins in the region [27,62]. The above factors coupled with low technological applications in food production, processing, and handling systems contribute to the high prevalence of mycotoxins in this region of Africa. production in food at pre-harvest, during harvest, during post-harvest storage, transport, and processing stages because they are diffi cult to eliminate from food once contamination occurs. East African Community Countries should continue to prioritize, design, and support programs aimed at mitigating health and economic threats posed by mycotoxin contamination of food. The creation of the East African Bureau of Standards has greatly improved the quality of food products in the region as well as boosted cross-border trade. The East African Bureau of Standards currently has put in place regulatory limits for afl atoxins and fumonisins in maize and peanuts but there is a need to widen the regulations to cover other potential mycotoxins such as Deoxynivalenol, Zearalenone among others. Regional governments should ensure that existing regulations are enforced to effectively control mycotoxin occurrence and contamination in food. Farmers and traders should be sensitized and trained on the dangers of mycotoxin occurrence and contamination in food, prevention, and possible control methods to fi ll the knowledge gap currently existing. All the different stakeholders such as Government, Academia, food manufacturers' and traders within the region should continue to work together, share expertise, experience, knowledge as well as resources and facilities to effectively detect, monitor, and control mycotoxins in susceptible foods along the whole value chain.