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Trace Elements in Abiotic and Biotic Environments
In streams and lakes, its content may be up to about 1.20  pg/L (Reimann and
de Caritat 1998). Rainwater collected in Sweden, during 1999, contained Ir at the
mean value of <100 pg/L (Eriksson 2001a).
22.3 HUMANS
The total amount of Ir in human body has not been reported; however, the total
amount in the tissues is 20 ng/kg (Emsley 2011). Its concentrations in human fluids
are 7.4 ng/L in the blood and 18 ng/L in the urine (Hoppstock and Sures 2004).
Ir is clinically inert, but Ir chloride is moderately toxic when ingested. It does not
normally cause problems, as it is relatively unreactive, but all Ir compounds should
be regarded as highly toxic. Most Ir compounds are insoluble and so, if taken,
would not be absorbed by the body. The radioactive isotope 192 Ir is a γ-ray emitter,
and is used in the radiation therapy (Emsley 2011).
Iridium concentrations is relatively high in miscellaneous cereals, 2 μg/kg fresh
weight (FW). Its contents in several foods, bread, carcass meat, offal, milk, and
nuts is about 1 μg/kg FW. Other products contain Ir <1 μg/kg FW. Mean dietary
exposure for adults in the United Kingdom have been estimated at 2 μg/day (Ysart
et al. 1999).