Occurrence and risk assessment of mycotoxins in subsistence farmed maize from Zimbabwe

Maize is the staple food of Zimbabweans and is consumed daily in the majority of households, particularly subsistence farming households. The objectives of this study were first, to determine the occurrence of mycotoxins in maize produced and consumed by subsistence farmers in Zimbabwe and second, to determine mycotoxin exposure through maize consumption and subsequently the human health risk. A total of 95 maize meal samples were collected from the household stores of randomly selected subsistence farming households. Maize intake data and agronomic practices of these households were investigated A multi-mycotoxin LC-MS/MS method was used to analyze and quantify mycotoxin contamination in the maize samples. Mycotoxin contamination was compared across agro-ecological zones in order to determine differences in mycotoxin contamination levels and presented. Of the toxicologically relevant mycotoxins, aflatoxin B1 (AFB1), fumonisin B1 (FB1), FB2, deoxynivalenol (DON) and zearalenone (ZEN) were detected in 1, 95, 31, 24 and 15 % of the samples at mean levels of 11, 242, 120, 217 and 110 μg/kg respectively. Other mycotoxins detected in the maize were 15-acetyl-deoxynivalenol (15-ADON), nivalenol (NIV), FB3, alternariol-methylether (AME), AFB2, AFG1 and diacetoxyscirpenol (DAS) and the percentage contamination ranged between 1 and 4 % in the maize samples. Contamination of the maize by the mycotoxins was observed at minimum levels below limit of detection for each mycotoxin and maximum levels of 105, 530, 67, 108, 3, 4 and 14 μg/kg for 15-ADON, NIV, FB3, AME, AFB2, AFG1 and DAS respectively. The median levels of each mycotoxin were reported below the limit of detection, with the exception of FB1 (median, 146 μg/kg), which was further considered in the exposure and risk assessment. Dietary exposure was derived from combining mean maize intake data and median FB1 contamination. Mean maize intake was estimated to be 26.8, 37.2, 30.1, 15.8 and 15.0 g/kg bodyweight (bw)/day for under 5s, children, adolescents, adults and the elderly respectively. Subsequently FB1 exposure from maize was calculated, to be 3.91, 5.40, 4.40, 2.30 and 2.20 μg/kg bw/day for these populations. Exposure to FB1 through maize intake was observed to equate to 196, 272, 220, 115 and 110 % of the provisional maximum tolerable daily intake (2 μg/kg bw/day) for under 5s, children, adolescents, adults and the elderly respectively. Subsistence farming communities in Zimbabwe are at risk of high exposure to FB1 and the risk was highest for under 5s, children and adolescents respectively.     

Co-occurrence and evaluation of mycotoxins in organic and conventional rye grain and products

A study on the co-occurrence of Fusarium toxins in conventional and organic grain and derived products was carried out. A total of 117 samples were collected during the period 2009–2012. Eight mycotoxins were determined using the LC-MS/MS method. Among the investigated mycotoxins, four were of major importance: DON, ZEN, T-2 and HT-2. DON was present at the highest concentration in both the agricultural systems, with its maximum level of 254 ± 23 μg kg⁻¹ being present in conventional rye grain. The co-occurrence of two or more mycotoxins was observed in more than 50% of samples, with the most frequent combination being DON + ZEN. The correlation between the concentrations of T-2 and HT-2, DON and ZEN, as well as T-2 and ZEN was confirmed statistically. The concentration of DON, HT-2 and T-2 was significantly higher in conventional products. Also the higher level of ZEN in organic grain in comparison to derived products was significant. None of the samples contained DAS, while NlV, MAS and 3ADON concentrations were close to the detection limits.     

Statistical comparison of Fusarium mycotoxins content in oat grain and related products from two agricultural systems

A total of 98 samples of oat grain and products from two farming systems were collected during the period of 2009–2011 and analyzed for the presence of trichothecenes (deoxynivalenol, nivalenol, 3-acetyldeoxynivalenol, T-2 toxin, HT-2 toxin, monoacetoxyscirpenol, diacetoxyscirpenol) and zearalenone using liquid chromatography–tandem mass spectrometry method. All mycotoxins were found at different frequency and levels in the tested oat samples; however, a higher intensity of distribution of DON, T-2 and HT-2 toxins was found in the conventional system of farming than in organic. The highest concentration in both systems (up to 655 μg kg⁻¹) was that of the mycotoxin NIV.     

Non-destructive detection of mycotoxins in maize kernels using diffuse reflectance spectroscopy

Deoxynivalenol is one of the most abundant contaminants in crops worldwide. Its presence in food and feed products causes health risks and induces economic losses. To date, deoxynivalenol is mostly detected by sample-based, time-consuming chemical analyses. To obtain a non-destructive detection of deoxynivalenol in unprocessed, solid maize kernels, we investigate UV–Vis–NIR diffuse reflection spectroscopy. Specifically, we propose a two-stage spectroscopic measurement procedure, allowing the characterization and identification of deoxynivalenol in ungrounded maize kernels. The first stage focuses on the characterization of the optimum illumination and detection wavelengths, by the measurement of the mean contamination of a collection of maize kernels, using a 250 mm-reflection integrating sphere. The second measurement stage enables an accurate classification of contaminated maize grains, by the measurement of the local contamination on individual kernels, using a 30 mm-reflection integrating sphere. We first characterized and compared the reflection spectra of low (150 ppb) and high (1388 ppb) natural deoxynivalenol-contaminated maize kernels. Moreover, we validated these measurement results by the characterization of a reference deoxynivalenol-contaminated maize powder (1840 ± 30 ppb). A spectral contrast between the low and high contaminated samples could be observed between 700 nm and 1400 nm. Furthermore, a detection criterion could be defined, allowing us to successfully classify a contaminated maize batch into a high (18184 ppb) and low (654 ppb) contaminated subsample. As a result, this verifies the two-stage measurement approach and illustrates the use of diffuse reflection spectroscopy as a valuable tool for the measurement of deoxynivalenol concentrations in maize, paving the way for real-time non-destructive industrial scanning-based detection.     

Impact of local pre-harvest management practices in maize on the occurrence of Fusarium species and associated mycotoxins in two agro-ecosystems in Tanzania

Knowledge on the presence of mycotoxins in Africa is fragmentary, although it can be assumed that both concentrations and prevalence in food commodities is high. The present study focuses on the presence of Fusarium species and their associated mycotoxins in maize from two geographically distant agro ecological systems in Tanzania. In a two-year survey, both Fusarium species and concomitant mycotoxins were surveyed in the Northern highlands (Hanang district) and the Eastern lowlands (Kilosa district). Parallel with this, a questionnaire on agricultural practices in both agro-ecosystems was included in this study. This allowed us to put the presence of the toxigenic Fusarium species and their mycotoxins within a relevant agricultural framework.Fusarium verticillioides, Fusarium graminearum and Fusarium poae were the predominant species in both locations although the population in the Eastern lowlands was slightly more complex comprising also Fusarium culmorum, Fusarium avenaceum and Fusarium sporotrichioides. The predominant presence of F. verticillioides resulted in a high prevalence of fumonisins in both regions. The importance of F. graminearum in the population was reflected by the presence of deoxynivalenol in the mycotoxin analysis. Although the agricultural practices differed significantly amongst both locations, only few significant correlations were detected between mycotoxin presence and crop rotation, storage conditions, and insect control measures.     

Fast and sensitive aflatoxin B1 and total aflatoxins ELISAs for analysis of peanuts,maize and feed ingredients

Aflatoxins are a group of carcinogenic compounds produced by Aspergillus fungi that can grow on different agricultural crops. Both acute and chronic exposure to these mycotoxins can cause serious illness. Due to the high occurrence of aflatoxins in crops worldwide fast and cost-effective analytical methods are required for the identification of contaminated agricultural commodities before they are processed into final products and placed on the market. In order to provide new tools for aflatoxin screening two prototype fast ELISA methods: one for the detection of aflatoxin B₁ and the other for total aflatoxins were developed. Seven monoclonal antibodies with unique high sensitivity and at the same time good cross-reactivity profiles were produced. The monoclonal antibodies were characterized and two antibodies showing IC₅₀ of 0.037 ng/mL and 0.031 ng/mL for aflatoxin B₁ were applied in simple and fast direct competitive ELISA tests. The methods were validated for peanut matrix as this crop is one of the most affected by aflatoxin contamination. The detection capabilities of aflatoxin B₁ and total aflatoxins ELISAs were 0.4 μg/kg and 0.3 μg/kg for aflatoxin B₁, respectively, which are one of the lowest reported values. Total aflatoxins ELISA was also validated for the detection of aflatoxins B₂, G₁ and G₂. The application of the developed tests was demonstrated by screening 32 peanut samples collected from the UK retailers. Total aflatoxins ELISA was further applied to analyse naturally contaminated maize porridge and distiller's dried grain with solubles samples and the results were correlated with these obtained by UHPLC-MS/MS method.     

Storage stability of maize-groundnut composite flours and an assessment of aflatoxin B1 and ochratoxin A contamination in flours and porridges

Defatting of groundnut flour used for composite development can not only improve nutritional quality of its products but also the storage stability. Maize, groundnut and their composite (full fat and defatted) flours were prepared and stored at room temperature over a period of 3 months. Storage stability of these products was assessed based on changes in water activity, peroxide value (PV), free fatty acids (FFA), thiobarbituric acid (TBA), microbiological profiling and levels of mycotoxins that included aflatoxin B₁ (AFB₁) and ochratoxin A (OTA). Overall results revealed that the rate of change of PV, FFA and TBA significantly (p ≤ 0.05) increased with increasing storage time, which was highest for full fat flours than in the defatted flours. For example, PV of the FFG and DFG were respectively, 0.88 and 0.40 mEq/kg, meanwhile TBA was 4.53 and 2.71 mg malonaldehyde/kg. There was a much higher rate of increase in FFA (%) with increasing storage time in full fat and composite flours when compared to that of their defatted counterparts. Generally, microbiological data demonstrated an increase in total microbial counts during storage in these foods possibly resulting in mycotoxins, AFB₁ (range: 9.08–38.48 μg/kg) and OTA (range: 0.33–19.50 μg/kg) in all samples with groundnut and maize having the highest contamination levels. A 127.8% increase in OTA level was noted when maize flour inclusion level in the full fat composite increased from 55 to 85%, but only a 24.7% increase in OTA level was noted in defatted composites during storage. Reducing the inclusion level of groundnut flour, the main source of AFB₁ as found, resulted in a drastic reduction in AFB₁ level in full fat and defatted composite flours by 54.1 and 76.4%, respectively, during storage. The findings highlight that shelf life stability of composites can be maintained upon defatting during the fortification process. It can therefore, be inferred that monitoring quality and safety of the raw materials as well as that of the final products during storage is crucial.     

Inactivation of aflatoxigenic fungi (Aspergillus spp.) on granular food model,maize, in an atmospheric pressure fluidized bed plasma system

Atmospheric plasma provides the advantages of high microbial inactivation that can be performed under ambient conditions; therefore, it is regarded as a potential alternative to traditional food preservation methods. The present work presents the results of a critical study conducted on the efficiency of a non-thermal atmospheric pressure fluidized bed plasma (APFBP) system used for decontamination of maize. Maize grains that were artificially contaminated with Aspergillus flavus and Aspergillus parasiticus spores were treated in APFBP system for 1–5 min at two differently designed fluidized bed reactors with air and nitrogen. Results indicate maximum significant reductions of 5.48 and 5.20 log (cfu/g) in Aspergillus flavus and A. parasiticus after 5 min air plasma treatment. The native microbial flora of the maize grains decreased to more than 3 log after 3 min APFBP treatment, and no viable cells were counted. During the storage of plasma treated maize samples at 25 °C for 30 days, the Aspergillus spp. spores log reduction was maintained with no occurrence of re-growth. Overall, this study shows that plasma treatment has a fungicidal effect on A. flavus and A. parasiticus spores associated with alterations in spore surface morphology and loss of spore integrity. APFBP can inactivate aflatoxigenic spores on maize grains and could be optimized to improve the safety and quality of produce.     

Aflatoxin B1 occurrence in maize sampled from Croatian farms and feed factories during 2013

The aim of the study was to determine the level of aflatoxin B₁ (AFB₁) in maize sampled from farms and feed factories situated in Northern, Central and Eastern Croatia during 2013, following the occurrence of cow milk AFM₁ contamination. Maize samples (n = 633) were analysed using Enzyme-Linked Immunosorbent Assay (ELISA) as a screening method and High Performance Liquid Chromatography Tandem Mass Spectrometry (LC–MS/MS) as a confirmatory method. Mean AFB₁ value found in maize coming from all investigated regions equalled to 81 μg/kg, with the maximal value of 2072 μg/kg found in maize obtained from Eastern Croatia. The observed contamination might have arisen on the grounds of extremely hot (>98%) and dry (<2%) weather witnessed from May to September 2012 during the maize growth and harvesting period, which might have favoured AFB₁ production and consequently the contamination of dairy cattle feeds. In order to prevent the adverse effects of AFB₁ on humans and animals, and also to reduce losses in agricultural production, systematic monitoring and further investigations of AFB₁ contamination are necessary.     

Multi-class determination of pesticides and mycotoxins in isoflavones supplements obtained from soy by liquid chromatography coupled to Orbitrap high resolution mass spectrometry

A methodology has been developed to identify and quantify 257 toxic substances (including pesticides and mycotoxins) in diverse isoflavones supplements obtained from soy. Two different extraction procedures were compared, QuEChERS and “dilute and shoot”. The best results were observed when the “dilute and shoot” methodology was applied using acetonitrile acidified with formic acid (1% v/v) as extraction solvent followed by a clean-up step with Florisil cartridges. Validation of the method was carried out evaluating trueness, repeatability and intermediate precision, obtaining recoveries between 70 and 120% with relative standard deviation (RSD) values lower than 20%. Limits of detection and quantification were below 5 and 10 μg kg⁻¹ respectively. The validated methodology was applied to the analysis of real samples, finding pesticides such as flutolanil (12.2 μg kg⁻¹) and etofenprox (48.2 μg kg⁻¹). Regarding mycotoxins, aflatoxin B1 (8.2–17.1 μg kg⁻¹) and aflatoxin G2 (6.4 μg kg⁻¹) were detected.     

北海盆地大油气田形成条件及分布特征

北海盆地为典型的中生代裂谷盆地,其油气的形成与分布具有较明显的特征,了解它们的形成与分布可以指导其他裂谷型盆地的勘探。根据IHS及C&C提供的相关数据,结合生油层、储层、盖层及圈闭特征方面的研究,对北海盆地及邻区已发现的57个大油气田进行分析,得出南北海盆地气源岩为上石炭统威斯特伐利亚阶煤系地层,北北海盆地主要油源岩为上侏罗统到下白垩统沉积的KimmeridgeClay组(英国)、Mandal组、Draupne组(挪威)和Farsund组(丹麦)泥页岩;主力储层分别为南北海盆地的赤底统砂岩,北北海盆地维京地堑内中侏罗统Brent群砂岩及中央地堑内的上白垩统白垩;南部区域盖层为上二叠统盐岩,北部区域盖层以泥灰岩为主。北海大油气田形成与分布的主要受控因素为:有效烃源岩分布及其成熟度;优质储集体的发育及其分布;盐运动及同裂谷期断裂作用产生的相关盐构造和断块背斜、掀斜断块圈闭的发育;区域性盐岩及泥灰岩盖层的有效封盖。这些有利条件共同作用下,北海大油气田在整个区域上具南部产气、北部以油为主的特点;局部上,受有利储层Brent群分布位置和中央地堑区域盐构造运动影响,大油田集中富集于维京地堑西北部与中央地堑中部挪威区域。     

准噶尔盆地彩南地区天然气干燥系数异常高原因分析

为明确准噶尔盆地彩南地区天然气干燥系数普遍偏高的原因,厘清天然气运移成藏规律,开展了天然气组分和碳同位素、储层中岩石矿物组成、方解石全岩碳氧同位素分析以及实验室烃类氧化模拟实验。该区侏罗系天然气以甲烷为主,干燥系数普遍大于0.95,δ¹³C₁值基本大于-32‰,C₇轻烃中以甲基环己烷占优势,甲基环己烷指数大于50%,指示来源于高—过成熟石炭系烃源岩。从天然气运移判识指标ln（C₁/C₂）与δ¹³C₁-δ¹³C₂图版来看,从彩47井区—彩31井区—彩003井,ln（C₁/C₂）值逐渐增大,但δ¹³C₁-δ¹³C₂值并未呈现变小或变大趋势,说明运移或成熟度并不是研究区天然气组分与碳同位素变化的主控因素。烃类热氧化模拟实验显示,油气中醇类在125℃时会被MnO₂氧化生成甲烷和二氧化碳,当温度达到200℃时才能氧化甲烷生成CO₂,从而改变油气的组成,造成天然气中甲烷含量增高。运用背散射电子探针技术,发现研究区侏罗系干气层段具有两类方解石,其中一类方解石中Mn含量较高,Mn含量可高达3%,在阴极发光下呈现亮橘红色、橘黄色特征,且方解石全岩碳同位素负偏,较正常方解石全岩碳同位素负偏5‰~10‰,随着方解石Mn含量越高,其全岩碳同位素越负,证实该区侏罗系干气层段存在普遍的弱烃类氧化作用。彩南地区侏罗系天然气干燥系数异常高的原因是腐植型烃源岩经过高成熟—过成熟演化后,在富含氧化性矿物的侏罗系储层中聚集成藏,后遭受烃类氧化作用,甲烷含量进一步增加,造成天然气干燥系数普遍偏高。     

华北地区东部下古生界烃源岩特征及其影响因素

华北地区下古生界烃源岩研究对前古近系油气战略资源选区具有重要意义。从沉积学角度出发,通过对研究区有机碳含量、生烃潜力和氯仿沥青“A”等参数的统计分析和平面制图,划分了烃源岩类型,并对影响烃源岩发育因素进行分析。研究认为:华北东部奥陶系上、下马家沟组及峰峰组为较好的烃源岩。影响烃源岩发育的必要因素是海洋生物生产力,影响烃源岩发育的主要因素包括古气候、古沉积环境、古构造及沉积作用。此成果可以为华北东部油气资源战略选区提供有效的地质依据。     

北美含油气域大油气田形成条件和分布规律

北美地区油气资源丰富,全球有近1/5的大油气田分布其中。研究区限于落基山褶皱冲断带、马拉松—沃希托褶皱冲断带、阿巴拉契亚褶皱冲断带和因努伊特褶皱带所围限的北美克拉通以及北大西洋被动大陆边缘地区北美部分,称之为北美含油气域。根据北美地区构造沉积特征,结合盆地分布及其地质结构特征,将北美含油气域划分为5个构造区带。通过深入剖析研究区大油气田的成藏要素和作用,结合含油气系统的思想,探讨大油气田的形成条件和分布规律。研究表明,研究区的构造沉积演化有泥盆纪、二叠纪和白垩纪3个重要时期,对区内大油气田的分布有着重要的控制作用。大油气田分布在落基山前陆地区、马拉松—沃希托前陆地区和中陆地区、内克拉通地区以及北大西洋被动大陆边缘地区,其中,在前陆地区最为集中。区内大油气田的烃源岩、储层和盖层主要位于泥盆系、二叠系和白垩系,圈闭类型主要是背斜圈闭、岩性圈闭和礁型圈闭以及构造和地层的复合圈闭。大油气田的产层深度主要在3km以上,其中泥盆系以大油田为主,二叠系大油田和大气田都较多,白垩系则以大气田为主。     

柴达木盆地北部块断带圈闭特征与油气分布的有序性

柴达木盆地北部块断带圈闭的发育受构造与沉积的控制,古近纪只在隆起背景上继承性产生构造圈闭,而晚侏罗世-白垩纪、新近纪-第四纪大面积形成构造圈闹;同时,构造与沉积还控制圈闭的分布,表现为平面上分区成带,垂向上不同时期或同一时期不同类型的圈闭叠加。油气资源类型、成藏组合、保存及富集程度等方面与圈闭时空展布存在耦合,呈现出“断褶区聚气,山前、潜伏区聚油,凸起顶、凸起斜坡区油气并存”的基本卡占局和油气富集程度依次变好的序列。     

中国大中型油气田的主力烃源岩分布特征

中国大中型油气田主力烃源岩的分布在时代、盆地类型、岩性和沉积环境方面都具有多样性。在地质时代上 ,从中元古代到新生代 (泥盆系除外 )均有烃源岩分布 ,最重要的是在中、新生代。在盆地类型上 ,有中、新生代的裂谷盆地、古生代早期的克拉通盆地和晚期的前陆盆地、以及中生代的前陆盆地。不同类型盆地的烃源岩的分布、地质地化特征和生烃潜力差别较大。源岩类型有海相碳酸盐岩、泥岩以及海陆过渡相和陆相泥岩、煤系及碳酸盐岩 ,其中以湖相碎屑岩为主。     

华北地区煤层气储集与产出性能

对华北地区9个典型煤田（盆地）共144件煤岩样品进行块煤光片法显微裂隙测试、低温氮比表面及孔径测试和压汞孔隙结构测试。测试结果表明，华北地区煤的显微裂隙以宽度小于5μm、长度小于300μm的裂隙为主，裂隙密度约20～200条／9cm^2，孔隙度为2．38％～10．3％，孔隙类型以孔径小于100nm的吸附孔为主，有利于煤层气储集而不利于其产出。煤层的储集性能以焦作煤田和荥巩煤田最好，平顶山煤田、大同煤田和沁水盆地南部次之，其他地区较差。煤层气产出性能以淮北煤田、淮南煤田、平顶山煤田和安鹤煤田最好，永夏煤田和大同煤田最差。焦作煤田显微裂隙不甚发育，荣巩煤田孔隙连通性差，沁水盆地煤的微孔、小孔比例过大，分别成为制约各区煤层气产出的“瓶颈”问题。图1表4参17     

Paleozoic Composite Petroleum System of North Africa： Hydrocarbon Distribution and Main Controlling Factors

North Africa,which is one of the main oil and gas producing regions in the world,is best known for its sub-salt Paleozoic-Triassic reservoirs and Paleozoic source rocks.Hydrocarbon abundance varies greatly from one structural domain to another areally and from one stratigraphic interval to another vertically.Analyses of the essential elements and geological processes of the Paleozoic petroleum system indicate that the distribution of the Lower Silurian shale source rocks,the development of a thick Mesozoic overburden,the presence of the Upper Triassic-Lower Jurassic evaporite seal are the most important factors governing the distribution of the Paleozoic-sourced hydrocarbons in North Africa.The Mesozoic sequence plays a critical role for hydrocarbons to accumulate by enabling the maturation of the Paleozoic source rocks during the Mesozoic-Paleogene times and preserving the accumulated hydrocarbons.Basins and surrounding uplifts,particularly the latter,with a thick Mesozoic sequence and a regional evaporite seal generally have abundant hydrocarbons.Basins where only a thin Mesozoic overburden was developed tend to have a very poor to moderate hydrocarbon prospectivity.     

华北-东北地区海相层系烃源特征与战略选区

摘要：通过大量露头、钻井样品的测试分析,初步落实了冀北中-新元古界、华北南缘下寒武统、鄂尔多斯盆地西南缘中奥陶统优质烃源岩的分布。冀北中-新元古界优质烃源岩主要分布在蓟县系洪水庄组下部,华北南缘下寒武统优质烃源岩主要发育在辛集组（或雨台山组）底部,鄂西南中奥陶统较好烃源岩主要发育在平凉组下部,它们均以黑色泥页岩为主要特点。同时指出,华北台内奥陶系马家沟组碳酸盐岩是一套总体较差的烃源岩;上古生界石炭-二叠系煤系烃源岩以南华北地区发育条件最为优越,比鄂尔多斯、渤海湾盆地多发育了上、下石盒子组含煤层系。综合运用多种分析测试技术,对东北地区上古生界进行了变质相区划,初步认为二连盆地中西部、松辽盆地东南部是上古生界发育未变质潜在烃源岩的主要地区。综合评价认为,鄂尔多斯盆地西南缘是古生界油气突破的有利地区,华北南部是进一步探索上古生界煤成油气的有利地区,冀北中-新元古界、东北上古生界是值得进一步研究探索的新领域。