Zinc


Disclaimer

Introduction

Zinc is a naturally-occurring element. Pure zinc is a metal, and in combination with other elements is a widespread and common part of the earth's crust.

Zinc is important to various industries. Uses for metallic zinc include dry cell batteries, alloys like brass and bronze, and protective coatings for rust-prone metals like iron. Zinc compounds find use in paints, wood preservation, smoke bombs, ceramics, anti-dandruff shampoo, deodorants, and other products and industrial processes.

Zinc is a minor but essential nutrient: too little can lead to reproductive, immune, and other health problems. On the other hand, too much zinc can be poisonous.



Environmental Fate and Transport of Zinc

Zinc enters the air, water, and soil as a result of both natural processes and human activities. Most zinc enters the environment as the result of human activities, such as mining, purifying of zinc, lead, and cadmium ores, steel production, coal burning, and burning of wastes. These releases can increase zinc levels in the atmosphere. Waste streams from zinc and other metal manufacturing and zinc chemical industries, domestic waste water, and run-off from soil containing zinc can discharge zinc into waterways. The level of zinc in soil increases mainly from disposal of zinc wastes rom metal manufacturing industries and coal ash from electric utilities. In air, zinc is present mostly as fine dust particles. This dust eventually settles over land and water. Rain and snow aid in removing zinc from air. Most of the zinc in bodies of water, such as lakes or rivers, settles on the bottom. However, a small amount may remain either dissolved in water or as fine suspended particles. The level of dissolved zinc in water may increase as the acidity of water increases. Some fish can collect zinc in their bodies if they live in water containing zinc. Most of the zinc in soil is bound to the soil and does not dissolve in water. However, depending on the characteristics of the soil, some zinc may reach groundwater. Contamination of groundwater from hazardous waste sites has been noticed. Zinc may be taken up by animals eating soil or drinking water containing zinc. If other animals eat these animals, they will also have increased amounts of zinc in their bodies.

Zinc enters the air, water, and soil as a result of both natural processes and human activities. Most zinc enters the environment as the result of mining, purifying of zinc, lead, and cadmium ores, steel production, coal burning, and burning of wastes. These activities can increase zinc levels in the atmosphere. Waste streams from zinc and other metal manufacturing and zinc chemical industries, domestic waste water, and run-off from soil containing zinc can discharge zinc into waterways. The level of zinc in soil increases mainly from disposal of zinc wastes from metal manufacturing industries and coal ash from electric utilities. Sludge and fertilizer also contribute to increased levels of zinc in the soil. In air, zinc is present mostly as fine dust particles. This dust eventually settles over land and water. Rain and snow aid in removing zinc from air. Most of the zinc in lakes or rivers settles on the bottom. However, a small amount may remain either dissolved in water or as fine suspended particles. The level of dissolved zinc in water may increase as the acidity of water increases. Fish can collect zinc in their bodies from the water they swim in and from the food they eat. Most of the zinc in soil is bound to the soil and does not dissolve in water. However, depending on the type of soil, some zinc may reach groundwater, and contamination of groundwater has occurred from hazardous waste sites. Zinc may be taken up by animals eating soil or drinking water containing zinc. Zinc is also a trace mineral nutrient and as such, small amounts of zinc are needed in all animals.

Exposure to Zinc

Zinc occurs in many foods, at concentrations ranging from 2 parts per million in leafy vegetables to nearly 30 parts per million in some meats. Zinc also occurs in most drinking water, with levels that vary according to the source of the water and the means of delivering it. Zinc coated water pipes or containers may increase zinc exposure.

Zinc concentrations in air are generally low, though concentrations may increase in, and sometimes near, facilities that use zinc in certain industrial processes. Examples of the latter include mining, smelting, welding, and manufacture of metals, alloys, metal parts, and other products that contain zinc. Construction workers, auto mechanics, and painters may also experience greater than average exposures to zinc.

Zinc Metabolism

Zinc is an essential nutrient and under normal conditions our bodies store a certain amount of it. Zinc typically leaves our bodies in urine and feces.

Health Effects of Zinc

According to US EPA's IRIS database (checked in August, 2014), it is not currently possible to tell whether zinc exposure causes cancer in humans. Reasons cited include inadequate or inconclusive occupational exposure studies of humans, lack of adequate animal studies, and equivocal results of genotoxicity tests.

According to a 2005 report issued by the Agency for Toxic Substances and Disease Registry, inhaling large amounts of zinc (as zinc dust or fumes from smelting or welding) can cause metal fume fever, a generally reversible disease. We know little about the long-term human health effects of breathing zinc dust or fumes.

Large doses of zinc (10 to 15 times higher than the recommended daily allowance) taken by mouth, even for a short time, can cause stomach cramps, nausea, and vomiting. Ingesting high levels of zinc for several months may cause anemia, damage the pancreas, and decrease levels of high-density lipoprotein (HDL) cholesterol.

Experiments on animals fed very large amounts of zinc (1,000 times higher than the recommended daily allowance) for several months caused many health effects, including anemia and injury to the pancreas and kidney. Rats became infertile or, if dosed after becoming pregnant, had smaller babies. Certain zinc compounds (for example, zinc acetate and zinc chloride) placed on the skin of animals caused irritation, suggesting that the same effect may occur in humans.

Because zinc is an essential nutrient, consuming too little can also cause health problems. Symptoms of zinc deficiency may include loss of appetite, decreased sense of taste and smell, decreased immune function, slow wound healing, and skin sores. Zinc deficiency in males may cause poorly developed sex organs and retarded growth. Zinc deficiency in pregnant women may lead to birth defects in their children.

References and Excerpt Sources

U.S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry. Toxicological Profile for Zinc, August 2005

U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS)