Zearalenone is a naturally occurring toxic compound produced by certain types of mold. This widespread contaminant is commonly found on various agricultural crops. Its presence in food and feed can pose concerns for both animal and human health. Understanding its origins, effects, and monitoring is important for food supply safety.
Sources and Contamination of Zearalenone
Zearalenone is primarily produced by Fusarium species, including Fusarium graminearum and Fusarium culmorum. These fungi infect various cereal crops like maize (corn), wheat, barley, oats, rye, and sorghum. Contamination occurs during pre-harvest crop development and improper storage after harvest.
Toxin formation depends on environmental factors. Cool, humid weather during the growing season, especially during flowering and grain filling, promotes fungal growth and toxin production. Ideal conditions for zearalenone synthesis include temperatures from 20 to 30°C, high moisture content (above 15%), and relative humidity exceeding 70%.
Health Implications in Animals
Swine are particularly sensitive to zearalenone due to its estrogenic effects, making them the most affected livestock species. Exposure can lead to hyperestrogenism, manifesting as swollen and reddened vulvas, enlarged mammary glands, and abdominal straining in young gilts. In severe cases, prolapse of the vulva, uterus, or rectum may occur.
The toxin significantly impacts reproductive performance in female pigs, causing infertility, constant estrus, or pseudopregnancy. Affected sows may experience diminished fertility, reduced litter sizes, and smaller offspring. Nursing piglets can exhibit hyperestrogenic symptoms through milk transfer. Male boars can also suffer from reduced serum testosterone levels, decreased testicle weight, impaired spermatogenesis, feminization, and suppressed libido.
Cattle are less sensitive to zearalenone than pigs but show adverse effects with prolonged exposure. Reproductive issues in dairy heifers and cows include reduced fertility, abnormal estrous cycles, ovarian cysts, spontaneous abortions, and reduced milk production. Young male cattle may experience infertility and testicular atrophy.
Poultry exhibit higher tolerance to zearalenone, partly due to their naturally elevated estrogen levels. However, at higher concentrations, effects such as reduced feed intake, decreased egg production, and changes in egg quality, including specific gravity and shell thickness, can be observed.
Human Health Risks
Zearalenone functions as an endocrine disruptor because its chemical structure mimics that of the natural hormone estrogen, 17β-estradiol. This allows the toxin to bind to estrogen receptors, disrupting normal hormonal balance. Such interference can affect various physiological processes regulated by hormones.
Exposure to zearalenone has been linked to several health concerns in humans. It can cause hormonal imbalances, influencing levels of estradiol, progesterone, testosterone, and cortisol. These imbalances may contribute to reproductive issues, including reduced fertility in both women and men.
Studies have also suggested a connection between zearalenone exposure and premature puberty in girls. The toxin can affect male reproductive cells, potentially reducing spermatogenesis by decreasing testosterone levels. It has also been implicated in conditions such as polycystic ovary syndrome (PCOS), premature ovarian function (POF), and endometriosis.
The International Agency for Research on Cancer (IARC) has classified zearalenone as a Group 3 agent. This classification means there is insufficient evidence to determine its carcinogenic potential in humans.
Detection and Regulatory Limits
Reliable analytical methods detect and quantify zearalenone levels in food and feed commodities. High-Performance Liquid Chromatography (HPLC), often coupled with fluorescence detection or mass spectrometry, provides precise and sensitive measurements. Enzyme-Linked Immunosorbent Assay (ELISA) offers a rapid screening method for initial detection.
Government agencies worldwide, such as the Food and Drug Administration (FDA) in the U.S. and the European Food Safety Authority (EFSA) in Europe, have established guidance or maximum limits for zearalenone. These regulatory limits protect both animal and human health, varying based on the specific commodity and intended use.
The European Commission provides guidance levels for zearalenone in complete feed, with different thresholds for various animal categories:
- Piglets and gilts: 100 µg/kg
- Sows and fattening pigs: 250 µg/kg
- Calves and dairy cattle: 500 µg/kg
- Poultry: 2000 µg/kg
The EFSA has set a tolerable daily intake (TDI) for zearalenone in humans at 0.25 µg/kg body weight per day. Regulatory bodies continuously review and update these limits based on new scientific data to ensure ongoing food and feed safety.