Cadmium is a toxic heavy metal that exists naturally but in very low concentrations. It has been classified by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) as one of the top food contaminants, following aflatoxin and arsenic. Once ingested, cadmium can cause serious harm to the body. The traditional method for determining cadmium in feed is the extraction method (GB/T 13082-1991), which is widely used due to its accuracy, but it involves lengthy sample preparation. This article reviews the sources of cadmium in feed, its harmful effects on livestock and poultry, and the various analytical methods used for detection.
Cadmium belongs to Group IIB of the fifth period in the periodic table and was first discovered in 1878. It is considered one of the most hazardous heavy metals in the environment. Since 1972, FAO and WHO have ranked it among the primary food contaminants. Cadmium is highly toxic and poses a significant risk to both animals and humans. Long-term exposure to cadmium through contaminated feed can lead to chronic poisoning, affecting animal growth performance and overall health. Even small amounts of cadmium can negatively impact animal productivity, and it may accumulate in meat, eggs, and milk, eventually reaching humans through the food chain.
The presence of cadmium in feed has become more prominent due to environmental pollution and the extensive use of mineral additives. This contamination not only affects animal health but also threatens human well-being. Therefore, monitoring cadmium levels in feed has become a critical concern for animal nutritionists.
Sources of cadmium in feed are diverse. Naturally, cadmium is found in the Earth's crust at low concentrations (0.15–0.20 mg/kg), seawater (0.11 μg/kg), and surface water (1–130 μg/kg). In the air, it is present at 0.002–0.005 μg/m³, and in soil, it exceeds 1 mg/kg. While plants typically contain low levels of cadmium, aquatic organisms like algae and fish have a strong ability to bioaccumulate it. For example, algae can concentrate cadmium up to 11–20 times, while fish can accumulate it up to 10,000–100,000 times. Fishmeal, commonly used in feed, often contains higher levels of cadmium, with an average of 1.2 mg/kg and up to 25 mg/kg in polluted areas.
Feed hygiene standards in China (GB 13078-2001) set a maximum limit of 2 mg/kg for cadmium in fishmeal. However, during metal refining processes, cadmium often coexists with other elements like zinc, lead, and copper, leading to environmental contamination. Poorly processed mineral feed additives, such as zinc sulfate, may also contain high levels of cadmium. These materials are among the main sources of cadmium in animal feed. Additionally, raw materials like calcium hydrogen phosphate and bacitracin zinc should be monitored for cadmium content. Although zeolite powder has low cadmium levels, its large usage makes it a potential source of contamination.
Studies conducted in Hunan Province revealed that many feed samples exceeded national standards for cadmium, especially in industrialized areas. In contrast, a survey in Jinhua City showed that most feed samples met the required limits, with cadmium levels ranging from 0.006 to 0.104 mg/kg. These findings highlight the importance of monitoring cadmium levels in feed to ensure the safety of both animals and consumers.
Cadmium toxicity in livestock and poultry primarily affects the kidneys and bones. After entering the body through the digestive tract or respiratory system, it is mainly absorbed in the duodenum and distributed in the liver and kidneys. Prolonged exposure leads to bone decalcification, kidney damage, and other serious health issues. In pigs, cadmium poisoning can cause spleen enlargement, gastric ulcers, heart hypertrophy, and lung congestion. It also causes anemia, renal damage, and reproductive problems in animals.
Research has shown that even low levels of cadmium can reduce the performance and antioxidant capacity of laying hens over time. This effect becomes more pronounced with prolonged exposure, highlighting the need for strict cadmium control in feed.
Several analytical methods are used to detect cadmium in feed, including colorimetry, flame atomic absorption spectrometry, graphite furnace atomic absorption, inductively coupled plasma optical emission spectrometry (ICP-AES), and inductively coupled plasma mass spectrometry (ICP-MS). The GB/T 13082-1991 method, though reliable, is time-consuming. Recent improvements, such as hydride generation-atomic fluorescence spectrometry (HG-AFS), microwave digestion, and dry ash methods, have enhanced detection efficiency, sensitivity, and accuracy, making them more suitable for routine analysis in feed testing.
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