Here, we have taken the aquatic environment to include freshwater systems such as lakes, streams and rivers and salt water or marine systems including estuaries and oceans.
What concentration of cobalt is found in natural waters?
As cobalt is naturally occurring and a widely dispersed element, all natural waters contain trace concentrations of this element, sometimes called “background”, i.e. the naturally occurring concentration present in waters due to geologic rather than anthropogenic influence. This “background” concentration varies widely around the world and can even vary within the same water body. Concentrations of cobalt in water can change depending on flow conditions (Neal et al. 1996).
The concentrations of cobalt in water changes due to varying flow conditions.
Variations can be due to water quality characteristics such as acidity or alkalinity (pH), temperature, and salinity, as well as the plants and animals present and the composition of the sediments. For example, if manganese or iron oxide is present in the sediment, it can attract and adsorb almost all of the cobalt out of the water column and onto the mineral grains within the sediment (Dong et al. 2007). As a result, “nodules” form naturally in some areas of the ocean. One day cobalt may be recovered or extracted from these sediments as an alternative to terrestrial mining (i.e. mining on land).
The concentrations of cobalt found in oceans are low, between 0.002μg/L in north central Pacific Ocean and 0.39μg/L in Indian Ocean (Nagpal 2004). According to the Forum of European Geological Surveys (FOREGS) database, the average dissolved background concentration of cobalt in EU surface waters is 0.33μg/L, with a median value of 0.16μg/L (min: 0.01μg/L, max: 15.7μg/L). In North America, the average dissolved cobalt concentration in surface waters is 0.79μg/L and the median is 0.50μg/L (min: 0.02μg/L, max: 53.2μg/L) (Parametrix 2009). Local aquatic organisms are typically adapted to background range concentrations of cobalt. It should also be remembered that cobalt, in the form of vitamin B12, is regarded as essential to most forms of biological life.
How does cobalt enter the aquatic environment?
Cobalt can enter the aquatic environment from a number of sources, both natural and anthropogenic. Natural sources include volcanic emissions, the weathering of rocks by the action of water, and decomposition of plant waste. Human releases of cobalt into the aquatic environment are very limited and include: Cobalt mining and processing activities, the production of alloys and chemicals, sewage effluents, urban run-off and agricultural run-off (Nagpal 2004; Kim et al. 2006).
Sediment, the ultimate repository for waterborne cobalt
Factors affecting the speciation and fate of cobalt in water, soil and sediment include organic ligands such as humic acids, anions, pH, and redox potential (Kim et al. 2006). Cobalt, regardless of its source, i.e. natural or anthropogenic, has the same transport pathways within the aquatic environment. Once in the water column, the principal pathway involves binding of cobalt to suspended solids, and with time these particles settle to the bottom of the water body and become part of the bed sediments (Nagpal 2004). Depending on the depositional environment, cobalt may remain on the sea/lake floor, become buried under further deposition or be transported into an ocean where it will be deposited as sediment, potentially permanently. This is a natural geological process which, millions of years ago, created some of the ore bodies that are mined today. Some cobalt, however, will remain in the water column (i.e. the water above the sediment). Cobalt, if it is in the form of vitamin B12, is utilised by fauna in the environment. If this low level of cobalt in water was unavailable, a number of the aquatic organisms in these waters would show signs of vitamin B12 deficiency such as not achieving optimal growth or development.
References and further reading
Dong D, Liu L, Hua X, Lu Y. 2007. Comparison of lead, cadmium, copper and cobalt adsorption onto metal oxides and organic materials in natural surface coatings. Microchem J. 85, 270-275. FOREGS. Forum of European Geological Surveys. Available at: http://www.gsf.fi/publ/foregsatlas/index.php Kim JH, Gibb JH, Howe PD. 2006. Concise International Chemical Assessment Document 69. Geneva: World Health Organization. Nagpal NA. 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. Neal C, Smith CJ, Jeffery HA, Jarvie HP, Robson AJ. 1996. Trace element concentrations in the major rivers entering the Humber estuary, NE England. J Hydrol 182, 37 – 64. Parametrix. 2009. Cobalt Concentrations in Drinking, Ground, and Surface Waters of the United States and Canada. Prepared by Parametrix, Albany, Oregon. July 2009. CI study 50.
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.