Abstract:
Mercury is a non-essential mineral for human body. Its small amounts can cause toxicity in
human body. Mercury intake more than 1g is injurious to health. Studies show that oral LD10 is
approx. 100g for a 70kg man. More than recommended amounts can cause several problems in
human body like cardiovascular diseases, Central nervous system impairment, lungs diseases and
various metabolic issues.
Mercury toxins occur in three forms; Organic mercury, Inorganic mercury and metallic or
elemental mercury. Organic mercury is the form of mercury which is soluble in organic solvents
and it can be absorbed up to 95% in human body, whereas, Inorganic mercury is a water soluble
form and it is accumulated in and released from kidney through urination. Metallic mercury is
lipid soluble form of mercury and it can reach brain crossing the blood brain barrier. It also
occurs in the form of vapors and can be inhaled.
Major sources of mercury are dental amalgam for elemental mercury, fish for organic mercury
and many preservatives for inorganic mercury. Mercuric toxicity can be treated with selenium
and other antioxidants rich foods and intake of sulfur containing amino acids (cysteine and
methionine). Besides these nutrition therapies some drugs are also created to treat toxicity of
mercury.
Introduction:
Toxicity is defined as the quality of being toxic or poisonous. In terms of nutrition it is excess of
any nutrient or mineral. Where, Toxicology is defined as a branch of science concerned with
nature, effects and detection of poisons. In toxicology the physical and chemical properties of
toxins are studied along with the state it results in and treatment.
Mercury is a non-essential and toxic mineral for human body. It is ranked 3rd in the list of most
toxic substances by United States Government Agency for Toxic Substances and Disease
Registry (Clifton, 2007; Kevin et al., 2014). Mercury is considered to be major environmental
pollutant and is widely used in agriculture, medicines and industries. Mercury is not destroyed
and it circulates in ecosystems (Jung & Zheng, 2012). Mercury is present in different sources in
three forms i.e. Organic, Inorganic and metallic mercury.
Toxicology Of Mercury
Organic mercury is present in the forms of Ethyl Mercury and Methyl Mercury. Inorganic form
of mercury occurs as mercuric (Hg++) and mercurous (Hg+
) salts and other compounds with
sulfur chlorine or oxygen in solid state. Metallic mercury also known as elemental mercury is
liquid at room temperature and vaporizes easily (Jung & Zheng, 2012; Kevin Et Al., 2012).
Mercury can enter human body via ingestion, inhalation or absorbed through skin. Its intake can
cause toxicity and results depend on the form of mercury taken in. Organic forms of mercury
(Me-Hg and Eth-Hg) interferes with replication, translation and transcription, haeme synthesis
and cause CNS disorders. Inorganic forms due to their water soluble nature cause renal problems
and also chest pain. Elemental mercury is mainly responsible for major CNS disorders like
Alzheimer’s disease, skin infections and lung diseases (Kevin Et Al., 2012; Jung & Zheng, 2012;
Syverson & kaul 2014). The toxicity is treated by both MNT and drugs.
States of Mercury:
Mercury is present in the environment in three forms
1. Organic Mercury: Organic mercury includes compounds of mercury with organic
functional groups like methyl (CH3), ethyl (C2H5) or phenyl (C6H5). Phenyl Mercury is
present in different medicines as preservative (Syverson & Kaur, 2014). Ethyl Mercury
is in the form of thimerosal present in vaccines, and is the recent most concerned form of
mercury (Clarkson & Magos, 2008; Guzzi & La Porta, 2008; Kevin Et. Al. 2014).
Methyl Mercury is, due to its lipid soluble nature, easily taken up by lower organisms. It
is therefore, present in edible tissues of such animals (Clarkson & Magos, 2008; Kevis
Et. Al., 2014). Half-life of methyl mercury is approx. 39-70 days. (Kevin et. Al., 2014).
2. Inorganic Mercury: Inorganic form of mercury occurs as Mercuric (Hg++) Salts,
Mercurous (Hg+
) Salts and Mercuric chloride (calomel). Calomel is quite insoluble in
water and is considered less harmful (Syverson & Kaur, 2014). Mercuric and Mercurous
Salts are more water soluble and more toxic. These are easily absorbed in Gastrointestinal
Tract System (Byrns & Penning, 2010; Kevin Et. Al., 2014). Half-life of Inorganic
Mercury is around 40 days (Kevin Et. Al., 2014)
3. Metallic Mercury: Metallic mercury is commonly known as Elemental Mercury.
Elemental Mercury has a low vapor pressure (2µm Hg) but also low latent heat of
Toxicology Of Mercury
evaporation (295kJ/kg). Due to this property it is vaporized easily (Byrns & Penning,
2010; Kevin Et. Al., 2014; Jung & Zheng, 2012). Mercury vapor is a monoatomic gas
(Clarkson, 1998). It is transported to brain either by dissolving in serum or adhering to
cell membranes (Bernhoft, 2011). Exposures to elemental or metallic mercury occur at
workplaces or at homes (Syverson & Kaur, 2014).