Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:6:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 6 (pt 1/5)
Character Range: 2169035–2171983

6                   Cobalt

6.1              General
Several comprehensive reviews of cobalt in the environment and its toxicity to humans are available and should be consulted for more detailed information (ATSDR 2004; WHO 2006). The following provides a summary of the key aspects of cobalt that are relevant to the derivation of a soil HIL.

Cobalt (Co) is a silvery grey solid at room temperature. Naturally occurring cobalt is most commonly found in association with nickel, silver, lead, copper, and iron ores. Common cobalt minerals include linnaeite (Co3S4), carrolite (CuCo2S4), safflorite (CoAs2), skutterudite (CoAs3) and glaucodot (CoAsS). In the natural environment, cobalt may be found in two oxidation states, Co2+ and Co3+, dependent upon Redox potential and pH of the environment (WHO 2006).

Cobalt comprises approximately 0.0025% of the weight of the Earth's crust, making it the 33rd most abundant element. Cobalt is a key constituent in several alloys including alnico, an alloy with powerful permanent magnetic properties that is used for high-speed, heavy-duty, high-temperature cutting tools. Cobalt has also been used as a colourant in glass, ceramics, and paints, is of catalytic use to the petrochemical and plastic industries, and is applied to soils as a fertiliser to increase plant yields or to increase the cobalt concentration in forage crops and prevent the symptoms of cobalt deficiency in livestock (ATSDR 2004; WHO 2006).

Cobalt is a dietary essential element as it is a key component of Vitamin B12 (ATSDR 2004). As such, adverse effects can occur as a result of deficiency as well as contamination. Without sufficient levels of dietary cobalt, red blood cell production may be severely inhibited, leading to anaemia, heart disease, reduced growth and the breakdown of both the nervous and the immune systems in humans (IARC 1991). Excess amounts of cobalt may also have harmful effects in humans. Inhaled cobalt primarily targets the respiratory tract. From the respiratory tract, cobalt particles may be absorbed into the blood via dissolution or transported to the gastrointestinal tract with mucous when swallowing. Gastrointestinal cobalt absorption rates are reported to vary greatly in humans, with some studies associating iron deficiencies with increased cobalt absorption rates (ATSDR 2004). Cobalt in the body partakes in reactions that generate oxidants and free radicals capable of deoxyribonucleic acid (DNA) damage and other deleterious effects (ATSDR 2004).

6.2              Previous HIL
The derivation of the previous HIL (HIL A = 100 mg/kg) for cobalt is presented by Buckett & Di Marco (1998). In summary, the HIL was derived on the basis of the following:
    * Intakes of cobalt from other sources were estimated with dietary intakes considered most significant for the general population. Intakes calculated were based on limited data where total background intakes were estimated to be