Thesis for the Degree of Doctor of Philosophy - DTU Orbit

using oxygen as reaction gas in a dynamic reaction cell (DRC) ICP-MS (Izmer et al., 2003). Using 1% of
tertiary amine solution as sample matrix, memory effects are minimized (Brown et al., 2007). Due to the
poor detection limit for 129 I/ 127 I of 10 −7 , even when using DRC ICP-MS, this technique is only suitable for
measurement of high level 129 I environmental samples (Izmer et al., 2003).
1.3 Chemical speciation analysis concept
In the environment an element can occur in different isotopic composition, oxidation states, and
chemical forms as for example inorganic and organic compounds.
According to Templeton et al., (2000) the chemical speciation analysis of one element/isotope is
defined as the separation and quantification of different chemical species of one element/isotope in a sample
without altering the chemical forms of the element/isotope in question in the original sample.
The toxicity, bioavailability, mobility and fate of different elements/radioactive isotopes depend
primarily on the chemical form in which the element in question is present and to a lesser extent on its total
concentration. For example, of all arsenic compounds, the most poisonous is the inorganic As (III) which is
known as a carcinogenic agent (Lamble and Hill, 1996). The arsenic toxicity decreases in the order: As (III)
> As (V) > MMAA (Monomethylarsonic acid) > DMAA (dimethylarsenic acid) > other arsenic-organic
compounds (Lamble and Hill, 1996). Hexavalent chromium compounds are much more toxic than those of
trivalent chromium (Nriagu, 1988, Katz and Salem, 1994). An illustrative example on the importance of
speciation was the well known case of drinking water contamination with hexavalent chromium which
occurred in the southern Californian town of Hinkley, causing a high number of cancers
(http://static.ewg.org/reports/2010/chrome6/chrome6_report_2.pdf). Iodine is considered to be a key element
involved in human health (iodine toxicity and deficiency disorders). Iodide and iodate, are less toxic than
elemental iodine and some organically bound iodine compounds (Hou et al., 1997). The important role of
iodine in the synthesis of the thyroid hormones 3,5,3
22
’ -triiodothyronine (T3) and of 3,5,3 ’ ,5 ’ -
tetraiodothyronine (T4) or thyroxine is widely known (Glowa and Mezyk, 1998). These hormones are
essential for normal growth and physical as well as mental development. Iodine deficiency gives rise to
hypothyroidism, symptoms of which are extreme fatigue, goiter, mental slowing, depression, weight gain,
and low basal body temperatures. Iodine deficiency is also the main cause of preventable mental retardation,
primarily occurring when babies or small children are rendered hypothyroidism by a lack of the element.
Iodine toxicity can result from an intake of 2.0 mg of iodide per day. Exposure to excessive iodine levels
may occur through consumption of foods and or dietary supplements. The thyroid gland enlarges as a
consequence, and goiter is produced. This enlargement is also called hyperthyroidism. In addition to goiter,
iodine toxicity produces ulcers on the skin. This condition has been called "kelp acne," since it can also arise
from eating kelp, an ocean plant, which contains high levels of iodine.