V 4.1 (2013)

Ministry of the Environment

National Institute for Minamata Disease
Minamata Disease Archives
55-10 Myojin, Minamata, Kumamoto 867-0055
Phone : +81-966-69-2400/ Fax: +81-966-62-8010
E-mail: mail@nimd.go.jp(All rights reserved)

REFERENCE FOR
HAIR MERCURY CONCENTRATION
1 ppm mercury means that 0.001 g mercury is contained in 1,000 g(1/1, 000, 000 ).

Total mercury concentration in hair (ppm)

50

50 ppm: No neurological adverse effect has
beenfound among adults below this level(WHO,1976; 1990)
14 ppm: The concentration in maternal hairreflects methylmercury exposures that would
have
no appreciable adverse effect on theoffspring in two study populations ofFaroes Islands and Seychelles (JECFA, 2004)

105 ppm: A former safe exposure level ofmethylmercury for adults (3.3μg/kg/week)(WHO, 1973)
2.8 ppm: Provisional tolerable weekly intake levelof
methylmercury in Japan (2.0μg/kg/week)(JECFA, 2004) **2.5 ppm: Mean level of males in Japan*

5

2.2 ppm: Provisional tolerable weekly intake
level of methylmercury (1.6 μg/kg/week)(JECFA, 2004) ***1.6 ppm:

0Mean level of females in Japan*

1.0 ppm:
Reference Dose level ofmethylmercury (0.1 μg/kg/day) without anappreciable risk of deleterious effects during alifetime (USEPA, 2001) ***** Multi-site survey in Japan (NIMD, 2000-2004)** The domestic provisional tolerable weekly intake (PTWI) is 2.0 µg/kg bodyweight/week, and was derived from the non-observable-adverse-effect (NOAEL)/benchmark dose (BMDL) level, 11 ppm in maternal hair on the fetus development anduncertainty factor 4 (Food Safety Committee of Japan, 2005).
*** The provisional tolerable weekly intake (PTWI) is 1.6 µg/kg body weight/week, andwas derived from the non-observable-adverse-effect (NOAEL) /benchmark dose (BMDL)
level, 14 ppm in maternal hair on the fetus development and uncertainty factor 6.4(JECFA, 2004).
**** The Reference Dose (RfD) is 0.1 µg/kg body weight/day, and was derived frombenchmark dose (BMDL) level, 46-79 ppb in maternal blood and uncertainty factor 10(NRC, 2000, US-EPA, 2001)

WHAT IS `MERCURY` ?
Mercury has been widely used in our life. Mercury is roughly divided
into three chemical forms: metallic mercury, inorganic mercury, andorganic mercury (R-Hg+). Methylmercury (MeHg) is considered to be
an exclusive organic mercury generated in the natural environment. The
three chemical forms are inter-converted in the natural environment.

Hg0

MeHg+

Metallic mercury

Methylmercury

Metallic mercury is liquid, andeasy to vaporize. It has beenused for clinical equipment andfluorescent lamps, etc. It isalso used in artisanal smallscale gold mining operation.

Methylmercury is naturallygenerated from inorganic
mercury by certain bacteria in
the water environment, andaccumulates in fish andmammals through the food web.

Hg2+
Inorganic mercury

Inorganic mercury includes
mercuric oxide, mercuric sulfide,etc. Mercuric sulfide had beenused as a pigment cinnabar andas a germicide since ancienttimes.

－ 2 －MERCURY IN THE NATURAL ENVIRONMENT
Mercury has been coming out from under the earth crust to the surface
by volcanic explosion throughout the long history of the earth.
Mercury currently is widely distributed in the environment; air, water,and soils. Mercury compounds circulate throughout the environment
including vaporization from the surface of land and sea into the air,and precipitation from the atmosphere to the sea and land. The
predominant chemical forms of mercury are inorganic and metallic
mercury in the environment.

Mercury circulation in the environment
5,600 tAtmosphere500 - 2,000 t
Geogenic
1,600 tEarthsurface

1,000,000 t
Surface soil

5,000
t2,300 - 3,400 t
Human大地
activities(Earth)5,400 - 8,400 t
Rain, snow

2,000 - 4,000 tSea surface
432,000 t
Ocean
water

Source: Technical background report to the global atmospheric mercury assessment(UNEP, 2008)

International efforts for the reduction of mercury discharge
Recently, mercury emission and release into the environment have been increasing
by human activities including coal combustion and artisanal small-scale gold mining.
An international convention of mercury is now being prepared to reduce mercury
usage and load to the environment and to prevent the pollution and health damage.

HOW CAN MERCURY ENTER
THE HUMAN BODY?
Among mercury species, methylmercury (MeHg) and metallic mercury
vapor easily enter the human body from the intestinal tract and lung,respectively. MeHg binds to cysteine (a kind of amino acid) to form acomplex whose structure is similar to methionine, an essential aminoacid, and then incorporated into tissues including brain and fetus via anamino acid transporter.
Dental amalgams are thought to produce metallic mercury vapor, but thebody burden of the metallic mercury generated from the amalgams may
be relatively low.

Methylmercury(MeHg)

Cysteine

MeHg-cysteine

Methionine(Essential amino acid)

Mercury（Hg）

Carbon（C）

Oxygen（O）

Sulfur（S）

Nitrogen（N）

Hygrogen（H）

FATE OF METHYLMERCURY IN THE BODY
Methylmercury (MeHg) is distributed among various organs in the bodyafter the absorption through gastrointestinal tract, and high accumulation isfound in liver and kidney. Although the blood-brain barrier protects thebrain against xenobiotic toxic substances, the MeHg-cysteine complex easily
passes through the barrier. On the other hand, MeHg is excreted from thehuman body with an averaged daily excretion rate of 1.4% resulting abiological half-life of 50 to 70 days. Since a part of MeHg is taken up in thehair protein, hair mercury can be conventionally used to estimate MeHg
exposure levels.

hairMeHg

brainblood-brain barrier

blood plasma

bloodplacenta
fetus

red blood cellliver

kidneybile secretionsmall
intestine

fecesurine

TAKE SPECIAL CARE CONCERNING MERCURYEXPOSURE FOR PREGNANT WOMEN
The placenta functions to filter toxic substances in the mother’s blood toprevent them entering the baby. However, MeHg easily passes through theplacenta as cysteine-conjugate (see p.3), and accumulates in the fetus. Since
developing nervous tissue of fetus is most susceptible to MeHg, Japanese
Food Safety Commission determined, in 2005, that a safe exposure level(PTWI, provisional tolerable weekly intake) for pregnant woman was 2µg/kg/week. It is correspond to hair mercury level about 2.8 ppm (see p.1).
PTWI was calculated using the maternal hair level 11 ppm, that is supposed tothe highest level without adverse effect on the fetus, and uncertainty factor 4.
Research on the fetal effects of low levels MeHg is still in progress.

Placenta membrane
Mother’s bodyFetus
WASTES
CO2, Urea, etc.

Nutrients (amino acids,glucose, fatty acids, etc.),
antibodies, vitamins,oxygen, water, etc.

Toxic substances

INTAKE OF SEAFOOD
MeHg is generated by microorganisms from inorganic mercury in theaquatic environment, then accumulated in marine organisms via the foodweb. Accordingly, the major route of human exposure to MeHg is theordinary consumption of fish and shellfish. However, there is a wide
variation in mercury levels among species. Large carnivorous fishes,including tuna, swordfish and shark, often contain MeHg at highconcentrations. Marine mammals including tooth whales and dolphins
also show high levels. Pregnant women are recommended to avoid
excessive consumption of such fishes, because the developing nervous
system of the fetus is highly susceptible to MeHg. Since fish and shellfish
are also rich in valuable nutrients, the appropriate consumption of seafoodis useful to encourage child growth and to maintain good health.

Black tuna （0.97 ppm）

Red sea-beam （0.06 ppm）

Horse mackerel, Sardine, Spottedsardine, Chub mackerel (0.02 ppm)

Ribbon fish （0.05ppm）
Black rockfish, Silverwhiting （0.03 ppm）
Cuttlefish （0.01 ppm）

Swordfish （0.81 ppm）

Rockfish

Yellowtail （0. 13 ppm)

(0.05 ppm)
Common octopus(0.05 ppm)

Alfonsino （0.49 ppm）

Hake （0.18 ppm）

Japanese littleneck(0.01 ppm)

The concentration is average of total mercury level and was taken from reports of Tokyo
Metropolitan Government Bureau of Public Health and National Institute for Minamata Disease.
Values may vary with fish size and habitat.
Red values are above Japanese provisional regulatory standards of total mercury (0.4 ppm) infish and shellfish..
Japanese government announced, in 2005, a revised advisory for pregnant and may be pregnant
women on the intake of certain fishes and shellfishes including swordfish, black tuna, andwalleyed tuna.