Radioactive Contamination and Animal Production and Health

The recent nuclear crisis in Japan, which took place in the aftermath of a serious earthquake and tsunami, has focused the attention of the world on the problems that arise if there is a major release of radionuclides into the atmosphere. Of first concern is the human population that is exposed to contamination in the immediate vicinity of the nuclear power plant, and the need for rapid action to prevent their suffering ill-effects. However, there are potentially longer term problems due to the ecological impact from contamination with radionuclides, on pastures and water courses that are used for rearing livestock. These problems are of concern to the animal health professional, firstly because of the possible ill-effects to animals that have been raised on contaminated land and secondly because of the risk to humans from consumption of meat and milk products from livestock that have eaten contaminated feed.

Reports from the Government of Japan indicate that several radionuclides of consequence to human health have been found in the soil, vegetation and in animals, or their products. These include Iodine-131 and Caesium-137 that have both been found in the soil, in milk and in leaf vegetables such as spring onions and spinach. Some of the samples have been reported to be above the levels allowed by the Japanese food hygiene law for emergency monitoring criteria for intake of vegetables. Where these radionuclides have contaminated grazing land, milk from livestock is affected, so it is possible that any beef cattle will begin to show radionuclides in the muscle tissues. No data are yet available on contamination in standing water such as lakes, reservoirs and fish ponds.

Investigations that were conducted in the aftermath of the Chernobyl accident have shown that radiation doses to livestock that became contaminated with radionuclides of iodine or caesium were significantly below the levels that causes clinical damage, and it was unlikely that there would be any detrimental effect on their health. This is because the risk to their welfare from genetic defects or cancer caused by the accumulative somatic damage from radiation over a long period was unlikely to occur, given their short life span. Nonetheless, products from the animals still present a risk to humans, and in the interest of food safety, monitoring for radioactive contamination is essential. For instance, in the UK, following the Chernobyl accident in 1986, restrictions were placed on the marketing of sheep on 10,000 farms owing to contamination with caesium-137. Twenty years later those restrictions were still in place on 400 farms and 220,000 sheep were being monitored. In Scotland, these measures were finally relaxed on the last farm still undergoing monitoring in June 2010. Similar restrictions were put in place in other countries affected.

What are radionuclides and why are they hazardous to animal and human health?

Radioactive Contamination and Animal Production and Health Radionuclides are radioactive atoms either man-made or naturally occurring. All elements have radioactive forms so there are many radionuclides. At Chernobyl, some 60 radionuclides were emitted from the reactor, but only a few were considered to present serious health hazards to humans and animals, namely Iodine-131, Caesium-137, Caesium-134, Strontium-89, Strontium-90 and Plutonium-239. Iodine-131 is a volatile radionuclide that emits beta and gamma rays and combines easily with organic materials and soil minerals. Water, grass, vegetables and animal fodder become contaminated. The half-life is 8 days, but in the thyroid it can last for 100 days potentially causing malignant tumors. Caesium-137 spreads readily in the environment in soil, water and in the air. It can be ingested or inhaled and locates in muscle tissue, bones and fat. It has a half-life of 30 years and is extremely toxic. Strontium-89 (half-life 50 days) and Strontium-90 (half-life approximately 30 years) occur in the soil, food and water. These elements can be deposited in bones and remain in the body for long periods. Plutonium-239 is an alpha ray emitter with an extremely long half-life. It can enter the body by ingestion or inhalation, and although some is eliminated it remains in bones and the liver for years, where it can cause tumors development.

Environmental impacts of radionuclide contamination

The Chernobyl nuclear accident caused ecological problems in the Ukraine and Belarus as well as further afield in Europe, in the higher northern latitudes. Contamination over this long distance was primarily by caesium and iodine. The transfer of radionuclides in the environment depends on the particular ecosystem, thus for the most important element, caesium, transfer is higher in the natural environment than in agricultural ecosystems. This is due to the physicochemical behaviour of the soils; in natural systems where there is a lack of nutrients there is no competition between caesium and potassium, leading to higher transfer rates of caesium. Transfer is low where there has been intensive agriculture and the soils have a high nutrient status and a high proportion of clay materials. In forest there is a multilayered structure consisting of a mineral layer low in clay and a layer rich in organic matter. Radionuclides migrate down through the soil so that eventually they are no longer present in the root-containing zone. Migration is lower in peaty soils than in highly organic soils. In forests, there is initially a filtering of contaminants by the tree canopy then, following leaf/needle fall and rain run-off, the soil in forest floor becomes the main repository for contamination with radionuclides. However, trees and plants continue to become contaminated through root uptake. Radiocaesium can be recycled in in trees through uptake and regular leaf/needle fall, and stored in the long-term in the trunks of the tree. Fruits and fungi present in the forest become contaminated, with very high levels of caesium-137 being found in mushrooms. Surface water systems are also directly affected by nuclear fallout but persistence of radionuclides in catchment soils and river and lake sediments is important in determining their distribution. In rivers, due to the constant flow of water there is less contamination in the longer term, since bottom sediments tend to be replaced, particularly in flood conditions. In contrast, in lakes where there is little or no water exchange, contamination in bottom sediments can be high.

In the immediate vicinity of Chernobyl, 23,000 km2 of land was heavily contaminated and this area, known as the Exclusion Zone, was subject to restriction of agricultural activities. Animals living in this area were exposed to high levels of radionuclides via food, water and air and levels in some were many hundreds of times higher than in unaffected populations - many animals that remained in this zone died from radiation induced illnesses. Today, mammals, birds, fish and amphibians show morphological deformities, and genetic disorders. The greatest impact from radioactive contamination was in Ukraine, Belarus and Russia, but radionuclides from Chernobyl were carried in the atmosphere into other countries in Europe and Scandinavia including Austria, Bulgaria, Croatia, Czech Republic, Finland, Germany, Greece, Hungary, Italy, Moldova, Norway, Poland, Romania, Slovenia, Sweden, Switzerland and the United Kingdom. Other affected territories were in Asia (including Turkey, Georgia, Armenia, United Arab Emirates and China), northern Africa, and North America. The major issue in many of these countries was contamination of food products (milk and meat) from domesticated livestock that had ingested radionuclides that were then introduced into the human food chain. The most common source of this contamination came from ruminants, including wild animals that grazed in natural or semi-natural ecosystems that were minimally managed by man. These were in areas such as mountain pastures, marshlands and tundra.

Transfer of radionuclides to livestock grazing on contaminated pastures

Animals grazing in natural, semi-natural, or forest habitats are more prone to acquire high levels of radionuclides than those on agricultural land. In Austria, the alpine regions were among the most heavily contaminated areas. Cattle are moved to mountain pastures in the summer and within 10 days their levels of radiocaesium begins to rise. Levels can reach two orders of magnitude greater than when they were grazed on agricultural land. Sheep in Wales, England and Scotland are often reared on unimproved land, and levels of radiocaesium reached 4000 Bq/kg in the immediate aftermath of Chernobyl. In forest regions, the species involved are likely to be wild ruminants such as deer or wild boar. Caesium-137 levels are high in these animals because they ingest fungi that are known to take up large quantities of the radionuclide. In contrast, wild ruminants grazing on agricultural land have lower levels of radiocaesium. In Croatia in 2002, radiocaesium levels were high, but not sufficient to cause concern to human health, except in cases where there might be high consumption such as hunters. In Southern Germany, Caesium-137 levels in meat often exceed several thousand Bq/kg; again ingestion of fungi is the reason for this. Since radiocaesium remains in the top 10-15cm of soil in these forest zones where fungal hyphae grow, it is likely that the wild boar meat will continue to be contaminated for the foreseeable future. There is a financial penalty for this, as the German government compensates hunters who cannot eat meat that is too highly contamined. Fish in enclosed lakes or ponds often have high levels of radiocaesium; fish in Finnish lakes had levels varying from 16 - 6400 Bq/kg in 2003.

Sampling for measurement of radioactivity

Various procedures can be used for monitoring levels of radionuclides in milk and meat, and although there are no standardized methods it is essential that surveys take into account all aspects of contamination in relation to the environment, likely exposure, the animal species and their foraging habits. The following list indicates some of the procedures used to monitor animals exposed to radiation.

Live animals - cattle, sheep, goat, poultry

Meat:

Milk:

Mitigating the effects of radionuclide contamination

Radioactive Contamination and Animal Production and Health Contamination can be mitigated by taking measures to the transfer of radioactive pollutants. It is important to reduce exposure wherever possible, especially in the immediate aftermath of contamination, i.e. by bringing livestock in from pasture and confining them to pens to prevent their grazing on contaminated pasture. Animals should be fed with uncontaminated feed as soon as possible. Changing land use is effective in reducing transfer to man. A switch from milk production to beef or pigs can reduce radionuclide transfer by 5-fold. To reduce radiocaesium in milk cattle can be supplied with a caesium-binding compound such as ammonium ferric cyanoferrate (or AFCF, "Prussian Blue") as a bolus into the rumen, in compounded concentrate feed, in salt licks, or simply sprinkled on the diet. AFCF reacts with consumed radiocaesium in the intestine to form a complex that is eliminated in the faeces. In the case of meat-producing animals, moving to uncontaminated pastures and feeding uncontaminated feed may only be necessary close to the time of slaughter since the biological half-life of radiocaesium, for example, is of the order of two to four weeks depending on the species. In the case of wild boar meat, brining in sodium chloride and potassium nitrate can reduce caesium-137 levels by >70%.

Radioactive Contamination and Animal Production and Health The most salutary lesson learned in the past 25 years has been the need for the regulatory authorities in countries affected by contamination to take a much broader view of the environmental consequences and adopt a more holistic approach in addressing the situation. Thus, the international scientific community has a more fundamental understanding and greater insight into the way in which different ecosystems are affected by nuclear contamination, which will provide the basis for predicting the risk to, and likely impact on, agriculture in the Fukushima incident.

For more information please visit: http://www-naweb.iaea.org/nafa/emergency/agricultural/index.html