Print This PageMycotoxins
Environmental Stress
Plants are exposed to numerous biotic and abiotic stress factors. These factors contribute to significant yield losses in crops, preventing crop from delivering their full yield potential. Biotic stress factors include disease causing organisms such as fungi, bacteria and viruses, and insect pests and weeds. The first generation of biotech crops expressed traits to protect against biotic stress factors. For example, Bt crops provide protection from key insect pests and RR crops are tolerant to the Roundup family of herbicides. The next generation of stacked-trait crops is designed to help crops tolerate abiotic stress factors such as drought, heat, cold, and soil salinity.
What is a mycotoxin?
Mycotoxins refer to substances produced by some fungi that are toxic to both humans and animals. Historically, mycotoxins have most affected the agricultural, food, poultry and cattle industries. Some molds produce mycotoxins in the field prior to harvest or during storage, if the grain storage conditions favor mold and mycotoxin development.
Aflatoxins and Fumonisins
Some of the most prevalent mycotoxins produced by fungi are the aflatoxins and fumonisins. Aflatoxin, a known human carcinogen, is a potential threat to food safety in the developing world and a periodic concern to producers in developed countries. In the US, mycotoxins are carefully monitored to limit their presence in the food supply, but their presence in feed grain can cause hundreds of millions of dollars of losses to animal producers. Fumonisins, identified in 1988 by a group of South African scientists, are a likely cause of some human disorders and have been shown to be toxic to certain animals; horses are most susceptible but poultry, swine and cattle also are affected.
Health Effects on both Humans and Animals
Exposure to mycotoxins can occur through contact or inhalation of airborne particulates and ingestion. Mycotoxin exposure in both farm animals and humans can impact the immune system and specific organs. Pulmonary hemorrhage, dermatitis, recurring cold and flulike symptoms, burning/sore throat and diarrhea are some of the acute symptoms while chronic effects include carcinogenicity, mutagenicity, central nervous system and immune system damage. Mycotoxins found in indoor environments can cause coughs, irritation of eye, skin and respiratory tract, joint ache, headache and fatigue.
Specific effects of mycotoxin exposure in animals include reduced productivity (lower milk production in dairy cows and egg production in chickens), increased incidence of disease due to immune-suppression and damage to vital organs. Additional symptoms are decreased feed utilization and efficiency, jaundice and anemia, decreased reproductive performance and embryonic death (North Carolina State Univ #AG-523, 1994).
Control Procedures Used in the US
The FDA has set "Action Levels" for aflatoxins and "Advisory Levels" for fumonisins. The term "action levels" refers to levels at which the FDA requires specific regulatory action. Since high levels of mycotoxins may be in some kernels and none in others, sampling is very important when testing for their presence. The larger the sample, the more kernels there are and the better the chance there is of getting a truly representative sample. There are established procedures for grinding and sizing the samples set by the Federal Grain Inspection Service (FGIS).
Food and feed companies have relied on numerous tests to determine potential toxin contamination, but some are either imprecise or take too long. There is a newer device that uses planar waveguide technology and can provide analysis in about 20 minutes. Keeping corn kernels dry during storage is important for maintaining mycotoxins at allowable levels. Mechanical and chemical drying methods have been employed on the farm, at storage facilities, and by food and feed companies.
Mycotoxins and Bt Corn
Bt corn introduced by Monsanto in 1997 utilized a gene from Bacillus thuringiensis, a soil microbe that produces proteins that are toxic to certain corn pests, such as the European corn borer, but do not affect unrelated non-target species, including humans, animals, and beneficial insects. Bt proteins are the active ingredients found in many microbial pesticides used in conventional and organic agricultural systems for more than fifty years.
Corn borer feeding on conventional corn ears creates cavities where fungus (mold) can grow and produce fumonisins. Fumonisin levels are reduced significantly in grain from Bt corn because corn borer pests feeding on ears are killed, eliminating damage to kernels, and dramatically reducing fungus growth and mycotoxin levels. When present at high levels, certain insects are only suppressed by the first generation Bt corn products. The cumulative effect from the increased pesticide pressure can cause enough damage to ears to allow fungus growth and production of fumonisins and aflatoxins.
The second generation of Bt corn contains other Bt proteins that protect against a broader variety of insect pests, including corn borers and fall armyworms and corn earworms. These products should reduce both fumonisin and aflatoxin levels in corn grain because of their broader control of ear-feeding caterpillar pests.
References
2008. Fungus Fight: Researchers Battle Against Dangerous Corn Toxin. Science Daily.
2008. Blandino, M., Reyneri, A., Vanara, F. 2008. Effect of Plant Density on Toxigenic Fungal Infection and Mycotoxin Contamination of Maize Kernals. Field Crops Research. IN PRESS: 8 pages. doi: 10.1016/j.fcr.2007.12.004.
2006. New Approaches to Problems in the Fields of Mycotoxin and Stress Tolerance Research. Bayer Crop Science. 7 pages.
1994. Understanding and Coping with Efects of Mycotoxins in Livestock and Forage. North Carolina State University Cooperative Extension Publication AG #523. 21 pages
http://www.ces.ncsu.edu/disaster/drought/Understanding_mycotoxins.pdf
CAST. 2003. Mycotoxins: Risks in Plant, Animal and Human Systems. Task Force Report No. 139, Ames, IA.
Hammond, B., Campbell, K., Pilcher, C., Degooyer, T., Robinson, A., McMillen, B. et al. 2004. Lower Fumonisin Mycotoxin Levels in the Grain of Bt Corn Grown in the US in 2000-2002. Journal of Agricultural and Food Chemistry. 52: 1390-1397.
Kendra, D., Dyer, R. 2007. Opportunities for Biotechnology and Policy Regarding Mycotoxin Issues in International Trade. 119: 147-151.
Murphy, P., Hendrich, S., Landgren, C., Bryant, C. 2006. Food Mycotoxins: An Update. Journal of Food Science. 71(5): R51-R65.
Wu, F. 2007. Bt Corn and Impact on Mycotoxins. CAB Reviews. 2(60): 8 pages.
Wu, F., Miller, J., Cassman, E. 2004. Bt Corn and Mycotoxin Reduction: Economic Impacts in the US and the Developing World. Journal of Toxicology, Toxin Reviews. 23(2-3): 711-716
