Metals of concern

What is selenium?

Selenium is widely but unevenly distributed in the earth's crust. It is most often associated with copper ores but may also be found with silver, lead and zinc ores. Organic compounds of selenium may form in plants, fish and animals.

Selenium is used in electronics and photocopiers due to its semiconductive and photoelectric properties. Glass, pigments, rubber, metal alloys, textiles, plastics, photographic emulsions, nutritional supplements, antidandruff shampoo, sheep and cattle feed additives, medical therapeutic agents and petroleum are products that may contain selenium. Broccoli, onions, whole wheat, tomatoes, tuna, bran and wheat germ are natural whole foods containing selenium.

How does selenium enter the environment?

Selenium can be released into the soil through leaching and weathering of bedrock. In the Yukon, the shale rock in the Selwyn area is high in selenium, and some lakes that sit in this host-rock have higher levels of natural selenium. Ground and surface water can transport selenium through the environment. Plants can absorb water-soluble selenium compounds from the soil and groundwater and transform them into organic compounds. Milk-vetch is a flowering plant in the Yukon that thrives in high selenium soils; selenium accumulates in animals that forage on the plant.

Some selenium may also be released to the environment by human activity, primarily coal combustion, metal ore refinement (particularly copper), and leaching from waste containers.

Is selenium toxic?

At low levels, selenium is an essential element in the diet. It acts as an antioxidant in the body, helping to prevent damage to tissues by oxygen. Both inorganic (from minerals) and organic (from plants) selenium can be metabolized, however, organic selenium is metabolized more efficiently than inorganic selenium. Selenium can be flushed out of the body to a limited extent through urine, feces and breath.

Because selenium is a micronutrient, a deficiency in the diet may have harmful effects. The reverse is also true: if you ingest, inhale or absorb too much selenium, it can have negative health effects. Short-term low-dose exposure may result in hair loss, muscle discomfort, skin rashes, swelling, nausea and fatigue. Higher short-term doses can lead to fingernail loss, changes in the nervous and circulatory systems and/or possible damage to the liver and kidneys. Long-term chronic high doses of selenium can trigger the build-up of fluid in the lungs and lead to severe bronchitis.

High levels of selenium are known to be toxic to animals, this has been a problem in the Western United States and Canada. Moose in the Yukon have levels of selenium in their organs that would be considered toxic in cattle; this may indicate that moose have adapted to these higher levels. However, selenium levels of concern to humans have not been found in Yukon country foods, including moose.

Selenium is thought to have mitigating effects on the toxic action of mercury, so mercury monitoring of Yukon foods has been combined with studies about selenium levels.

Facts about selenium

• selenium is found naturally in the earth's crust
• selenium is used mostly in electronic and photocopier components
• although selenium is thought to mitigate the toxic action of mercury, high concentrations of selenium have negative health effects
• as an antioxidant, selenium helps to prevent damage caused by oxygen to the body's tissues
• foods that contain selenium include broccoli, onions and whole wheat
• selenium is not found in any Yukon country foods at levels of concern

What is cadmium?

Pure cadmium is a bluish-white soft metal that occurs naturally in Yukon lead-zinc minerals.

Cadmium is conductive, bright in appearance and does not corrode easily. Most of the cadmium produced globally is used in nickel-cadmium batteries. Cadmium is also used in plastic stabilizers to prevent polyvinyl chloride (PVC) from decomposing through heat and light. Plastics, ceramics, glasses and enamels may be tinted with cadmium-based pigments.

Some metal products are electroplated with a cadmium protective coating to slow down rusting. Solder, dental amalgams, alloys, electronic devices, television picture tubes, mirrors and solar cells all use cadmium.

How does cadmium enter the environment?

The primary source of cadmium in the North is from natural erosion and weathering of the land. When cadmium enters the environment, plants can absorb it. Concentrations vary by species and the absorption rate may be encouraged by certain environmental conditions. For example, willows are known cadmium accumulators. Animal foraging brings cadmium into the food chain and, as a result, cadmium accumulates in caribou, moose, beaver and other animals

There is a consumption limit guideline in the Yukon for specific animal organ meats.

Is cadmium toxic?

Cadmium is absorbed in the gastrointestinal tract and is transported through the bloodstream and deposited in the liver and the kidneys, where proteins bind with the metal. This may help to protect the animal from toxic effects. Most cadmium is excreted by animals and does not biomagnify in the food chain.

Consumption of large quantities of organ meats may present a risk to humans. This is because an animal may ingest more cadmium than it is able to flush out of its system. As a result, cadmium accumulates in the body, which can lead to toxic health effects when humans consume a large amount of kidney or liver meat from these animals. It should be noted, however, that exposure to cadmium through diet and environment are minor compared to the cadmium inhaled from cigarette smoking.

Although cadmium does accumulate in the liver and kidney of both animals and humans, it does not accumulate in the muscle tissue or meat. There is no consumption limit for the meat of Yukon wild game.

Long-term chronic exposure to cadmium has been linked to kidney disease, lung damage and the development of less dense, fragile bones. Animal studies completed in the U.S. have shown that more cadmium is absorbed into the body if the diet is low in calcium, protein and iron and high in fat. A balanced diet can reduce the amount of cadmium absorbed by the body from food and drink.

Facts about cadmium

• erosion and weathering of the local geology are the primary sources of cadmium in the Yukon environment
• cadmium is used in batteries, protective metal coatings, pigments and stabilizers
• willow (salix artica) is known as a cadmium-accumulating plant
• a consumption guideline exists for cadmium in organ meats in Yukon game, and a guide is provided in this fact sheet. Caribou and moose continue to be monitored
• a balanced diet can reduce the amount of cadmium absorbed by the body from food and drink. Diets that are low in calcium, iron and protein and high in fat allow for higher absorption of cadmium
• cigarette smoking is the most significant source of cadmium in humans
• cadmium is not found in Yukon country foods at levels of concern

What is arsenic?

Arsenic is the 20th most abundant element in the earth's crust and is found in copper, lead, silver and gold. When combined with oxygen, sulphur and chlorine, inorganic arsenic salts are formed. These include the sulphide minerals arsenopyrite and realgar. Arsenic is also found naturally in the environment in organic compounds. These compounds are generally formed by bacteria in a process called methylation. Metallic or elemental arsenic is steel grey, brittle and rarely found naturally.

How does arsenic enter the environment?

Arsenic has several industrial applications. The most important is its use in chemically preserved wood. Ninety percent of arsenic in Canada is made into the wood preservative chromated copper arsenate. Wood that has been treated with this chemical is referred to as pressure-treated wood. Arsenic is also used in batteries, ammunition, light-emitting diodes and electronics. Historically, Arsenic was used in fungicidal seed and crop insecticide but these uses are no longer legal.

Some of the arsenic mineralization in the Yukon is associated with gold ore deposits including those at Mount Freegold, Montana Mountain and Mount Nansen. While natural erosion and weathering releases arsenic into the environment in these areas, mining activity may increase the natural levels. The Crown-Indigenous Relations Northern Affairs Canada Waste Management Program has remediated certain sites by capping the mine tailings. Ongoing studies are underway to measure the effectiveness of the caps in reducing arsenic release into the environment.

Is arsenic toxic?

At very high concentrations, arsenic can be toxic or lethal to a wide range of organisms. Once treated with arsenic fungicides, crop yields decrease. Malformations have been found in amphibians in the areas around such crops.

Arsenic may be inhaled, ingested or, to a small extent, absorbed through the skin. When inorganic arsenic is taken into the human body, much of it (approximately 80%) is changed to organic arsenic and excreted in the urine. Inorganic arsenic that is not transformed tends to concentrate in the hair, skin and nails during the first 2 weeks of exposure, then elevated levels may appear in the liver, spleen, kidney and muscle tissue. Fish undergo a similar detoxification process through which the inorganic arsenic is changed to organic arsenic and excreted in urine. Organic arsenic is considered to be less toxic than inorganic arsenic because it is excreted at a much faster rate.

Arsenic is considered a carcinogen but is also presently used in some medicines to treat leukemia, a form of cancer. If, over an extended period of time, arsenic is absorbed at a faster rate than the body can clear it, the metal can accumulate in the body. People who have been chronically exposed to arsenic have suffered skin damage, problems with their circulatory system and have an increased risk of cancer.

Facts about arsenic

• arsenic occurs naturally in rocks and minerals such as arsenopyrite
• natural erosion, volcanoes and mining activities are potential sources of arsenic in the environment
• micro-organisms are able to transform inorganic arsenic into organic arsenic compounds
• arsenic has been used both medicinally and as a poison for many years
• arsenic can be ingested, inhaled or absorbed through the skin
• both inorganic and organic arsenic can be excreted through urine, organic arsenic is considered less toxic because the body excretes it at a faster rate
• arsenic is not found in Yukon country foods at levels of concern

What is lead?

Lead is a naturally occurring element and a component of more than 200 minerals. The Yukon is host to various ore deposits that contain lead in their mineral composition. Lead has had many uses in human history but its danger to human health has only recently been widely recognized.

Lead can be a formidable contaminant as it is persistent, toxic and can be stored in the tissues of plants and animals. The Romans used lead to line city waterways and in glazes on food and wine containers. The Romans' chronic consumption of lead through contaminated drinking water, other beverages and food may have resulted in widespread lead poisoning and contributed to the fall of the Roman Empire. Members of the ill-fated Franklin Expedition to the Northwest Passage in 1845 may have suffered from lead poisoning from solder that was used to seal tin cans of preserved food.

Metallic lead is a bluish-grey soft metal that has a low melting point. Its high density and ability to block radiation, coupled with its resistance to corrosion and its readiness to form alloys and chemical compounds, have made lead a useful element for industrial products. Lead is used in:

• solder
• leaded glass and crystal
• ammunition
• radiation shields in computer monitors and other medical equipment
• batteries
• radar
• jet engine blades
• fishing weights

Lead is also very easy to recycle, approximately 55% of the lead products made in Canada contain recycled lead.

Many products that contained lead have been phased out globally in the past 3 decades through new regulations in Canada and elsewhere. Lead solder for plumbing is no longer legal in new construction but may still be present in buildings older than 20 years. In 1978, Canadian regulations discontinued the use of lead-based paint. Most Western countries eliminated anti-knock agents in gasoline by the mid-1980s, but traces of lead still remain in roadside vegetation.

How does lead enter the environment?

Natural processes such as rock weathering and erosion, volcanoes and forest fires contribute to significant releases of lead globally. Lead mining, smelting and refining operations, along with industrial and municipal effluents, are major human-made sources of lead.

Natural rock weathering and mine waste rock leaching are the common ways that lead is released into the Yukon environment. In the 1980s, human activity releasing lead into the global environment was estimated to be 28 times greater than that of natural emissions. Since that time, global levels have decreased dramatically due to international agreements eliminating lead from products such as gasoline.

Like other metals, lead dissolves more readily in acidic waters. Sulphide in rocks or mine tailings can react with oxygen and water to produce sulphuric acid. This can increase the acidity of the water surrounding the rock or tailings and dissolving lead and other metals. Drainage flowing downstream from these areas may harm aquatic systems.

In the atmosphere, lead can travel for considerable distances from its source by sticking to particles in air currents. It is deposited on soil, surface waters and plants through rain and snow. Movement of lead from soil into groundwater will depend on the type of lead compound and the characteristics of the soil. Plants may absorb lead from groundwater, and animals may consume lead when eating plants containing lead residue. The lead may be stored in animal tissue.

Lead has been used in pure form and as an alloy in lead shot and fishing tackle. If these recreational pieces are left in nature it can harm waterfowl and other wildlife that may ingest it. However, studies completed in the Yukon have not found elevated levels of lead from global sources in country foods.

Is lead Toxic?

Lead is a non-essential element in the human diet; we do not need to eat it to be healthy. Lead is not considered to be a carcinogen, and other toxic effects can be attributed to the excess intake of lead. Short-term effects include:

• anaemia
• a decrease in the attention span and learning ability of children
• increased blood pressure in adults
• long-term exposure can increase the risk of heart and kidney disease

Most lead leaves the adult body a short time after shortterm exposure. Children, however, are far more susceptible than adults to lead poisoning. It is important for everyone, especially children and pregnant women, to have proper nutrition. A balanced diet consisting of vitamins and minerals, especially calcium and iron, can lower the amount of ingested lead that enters the bloodstream. Good nutrition can effectively reduce the toxic effects of lead.

Facts about lead

• lead is a naturally occurring element and a component of more than 200 minerals
• combustion of fossil fuels, smelting and natural weathering of rock are the major sources of lead in the environment
• radiation shields in computer monitors and medical equipment, solder, pewter objects and lead/zinc batteries are a few products that contain lead
• lead is a non-essential element and does not have any health benefits
• lead is persistent, toxic, and can be absorbed from food or through the skin. Many lead products have been phased out since the 1980s
• children are more susceptible than adults to the toxic effects of lead
• a balanced diet of vitamins and minerals can reduce the toxic effects of lead
• lead is not found in Yukon country foods at levels of concern

What is mercury?

Metallic mercury is a shiny silver-white element and the only metal that is liquid at room temperature. Mercury minerals are often found near copper deposits in rocks. Metallic mercury is used in:

• thermometers
• barometers
• batteries
• electrical switches
• fluorescent bulbs
• dental amalgams

Mercury is also released by the industrial production of caustic soda and chlorine. Mercury compounds were once widely used as pesticides in agriculture, and as fungicides in paint.

How does mercury enter the environment?

Mercury may be released into the environment by natural weathering of rocks, forest fires, evaporation from soils and surface waters, and volcanic activity.

Human activity is adding to the release of mercury. Waste disposal and incinerators, smelting of mercury-containing ore and the operation of coal-fired plants are the major human-caused sources. Global air currents transport mercury into the Yukon environment.

It has been estimated that elemental mercury can stay in the atmosphere from 2 months to 2 years. It is unique among the metals because it is a liquid, and can evaporate from surface water and soil. Once mercury can be carried by air currents to cooler locations. Upon condensation and subsequent precipitation, mercury enters the surface environment. It can enter the atmosphere again through evaporation and continue to travel. This repeating cycle of evaporation, transportation and condensation is known as the grasshopper effect, which allows the transport of mercury over long distances. In the Yukon, rain and snow are the source of all mercury content found in lakes that do not receive it from geological sources.

Inorganic mercury is transformed into organic mercury by micro-organisms in the soil and water through a process called methylation. Methyl mercury can accumulate and biomagnify in the terrestrial and aquatic food chains. Generally, aquatic food chains are longer than terrestrial food chains, and as a result, levels of organic mercury in older predatory fish such as lake trout can reach levels dangerous for consumption. However, no consumption advisories have been issued for mercury in Yukon traditional foods. The monitoring of mercury levels in lake trout from Lake Kusawa and Lake Laberge is conducted under the Northern Contaminants Program.

Is mercury toxic?

Methyl mercury or organic mercury is much more toxic than inorganic mercury because it is absorbed into the bloodstream more quickly. Levels of inorganic mercury must be higher than organic mercury levels to cause toxic effects, because much of the inorganic mercury is cleared from the body through the kidneys and urinary tract. Inorganic mercury is a liquid, it may be absorbed through the skin, and when it is a vapour, it is absorbed easily through the lungs.

Mercury is considered a neurotoxicant. If toxic levels are reached, nerve tissue may be damaged or destroyed. Symptoms of mercury poisoning may include shyness, tremors, memory problems, changes in vision and hearing, mental retardation and liver and kidney damage.

Facts about mercury

• mercury is a natural element in the earth's crust
• forest fires, weathering, erosion and volcanic activity are the major natural sources of mercury in the Yukon environment
• coal and waste incineration are the major human-caused sources of mercury in the global environment
• mercury can evaporate from soils and surface water. Once in the atmosphere, mercury can travel to another location where it condenses in rain or snow. When conditions warm, mercury can once again evaporate. This repeating cycle of evaporation, transportation and condensation is called the grasshopper effect
• lower temperatures in the North cause mercury compounds to evaporate less from soils and surface water
• methyl mercury (an organic mercury compound) can build up in fish tissue, which is why the Northern Contaminants Program monitors the fish in Yukon lakes
• mercury is not found in Yukon country foods at levels of concern