The general population is exposed to anthropogenic and natural sources of cobalt through the air, water and diet (greatest exposure).
Exposure to cobalt in the diet
The greatest exposure to cobalt for the general population is through food in their diet. Cobalt is essential to human life as part of Vitamin B12, in which the reference nutrient intake (RNI) value is 2.5 µg of Vitamin B12/day for adults, including pregnant women (COMA 1991). Inorganic cobalt is essential for many plants and ruminant animals, and is therefore often found in a variety of food sources such as meat, dairy products, fish, green leafy vegetables, fresh cereals and nuts.
For the general population the greatest exposure to cobalt is from the diet
On average, the daily exposure estimation of adults to inorganic cobalt is 12 µg cobalt from food sources (excluding supplements)7. The European Food Safety Authority has suggested an acceptable safe amount of cobalt of 120 µg Co/day while the UK Expert Group on Vitamins and Minerals has stated that up to 1400 µg Co/day7 (in a 60 kg adult) was unlikely to lead to adverse health effects.
Exposure to cobalt in the atmosphere
The majority of cobalt typically found in the air is attached to anthropogenic pollutant particles, whilst a much smaller fraction of the cobalt present is from natural dust sources. The average background level of cobalt in the air is approximately 1 x 10-9 mg/m3 (Friberg et al., 1996). In remote areas the Co value is lower, at approximately 1 x 10-10 mg/m3 (Friberg et al., 19961) and in industrialised areas this value can be higher, exceeding 1 x 10-5 mg/m3 (Friberg et al., 19961). Cobalt in air can eventually settle out of the atmosphere onto land or into water.
Exposure to cobalt in water
All natural waters contain trace concentrations, ‘background’ levels, of cobalt. This concentration varies within the same body of water as well as between bodies of water around the world. The background concentration of cobalt in water can differ due to flow conditions, water pH, temperature, plants, animals and composition of sediments. The average amount of cobalt found in oceans ranges from 0.002 µg/L (North Central Pacific Ocean) to 0.39 µg/L (Indian Ocean). The average background level of cobalt in European surface waters is approximately 0.33 µg/L in comparison to 0.02 to 53 µg/L in North American freshwaters.
Exposure to cobalt in soil
The natural background of cobalt in European soils can range from between 1 to 20 mg Co/kg dry weight, with the amount of cobalt increasing in areas which are geologically rich in cobalt (e.g. North Wales, United Kingdom). The amount of cobalt in soil is dependent on a multitude of factors such as local geology, atmospheric deposition of cobalt-containing dust, soil age and climactic factors. It should be noted that the majority of cobalt in soil is not in a form that is available for uptake by plants or animals – this is due to the formation of carbonate and hydroxide minerals.
This summary is intended to provide general information about the topic under consideration. It does not constitute a complete or comprehensive analysis, and reflects the state of knowledge and information at the time of its preparation. This summary should not be relied upon to treat or address health, environmental, or other conditions.
 Committee on Medical Aspects of Food and Nutrition Policy. 1991. Report on Health and Social Subjects No.41, 1991. Dietary Reference values for Food Energy and Nutrients for the United Kingdom. HMSO, London.  Expert Group on Vitamins and Minerals. Safe upper levels for vitamins and minerals. London: Food Standards Agency. 2003.  European Food Safety Authority. Scientific Opinion on safety and efficacy of cobalt compounds (E3) as feed additives for all animal species: Cobaltous acetate tetrahydrate, basic cobaltous carbonate monohydrate and cobaltous sulphate heptahydrate, based on a dossier submitted by TREAC EEIG1. EFSA J 10(7):1-27. 2012.  Friberg et al., 1986. Handbook of the Toxicology of Metals. Second Edition, Vols I, II. Amsterdam: Elsevier Science Publishers B.V. pV2 214.  Nagpal, 2004. Water Quality Guideline for Cobalt. Technical Report. British Columbia: Water Protection Section: Water, Air and Climate Change Branch; Ministry of Water, Land and Air Protection.  Parametrix. 2009. Cobalt Concentrations in Drinking, Ground, and Surface Waters of the United States and Canada. Prepared for CI by Parametrix, Albany, Oregon. July 2009.  FOREGS database. weppi.gtk.fi/publ/foregsatlas  Wendling LA, Ma Y, Kirby JK, McLaughlin MJ. (2009). A predictive model of the effects of aging on cobalt fate and behavior in soil. Environ Sci Technol 43, 135-141.  Perez-Espinosa et al. 20104.