Human relationshipwith mercury
Eﬀects of Dietary Methylmercury
on Human HealthType of Mercury
Mercury has been used in our lives in various applications. Mercury is roughly
divided into 3 chemical forms: metallic mercury, inorganic mercury (inorganic
mercury compounds), and organic mercury. Methylmercury is the only
organic mercury that is generated in the natural environment.
*Mercurochrome, a disinfectant, and mercury-based pesticides are also produced from man-made organic mercury, butmercury-based pesticides are no longer used.

In natural, mercury is transformed
as shown by the arrow.
Metallic
mercury

Methylmercury

Metallic mercury is an easily vaporized
liquid. It has been used forthermometers and ﬂuorescent lamps.
It has properties of dissolving gold andsilver, and has also been used in dental
amalgam (silver teeth using mercury),
and artisanal and small-scale goldmining.

Methylmercury is produced little bylittle in the natural environment andaccumulates in ﬁshes, shellﬁshes, etc.
It is the most toxic, and caused
Minamata disease when it wasdischarged from a chemical factory ina large amount in the past.

Hg0

CH3Hg+

Inorganic
mercury
Hg2+

Inorganic mercury
compounds include mercuricoxide and mercuric sulﬁde.
Among them, mercuric
sulﬁde has been used sinceancient times as a germicide.
It also has been used as
cinnabar pigment for paintingof lacquers and shrine gates.

1

Mercury in the Natural Environment
Since the birth of the earth, mercury has been coming out from the earthʼs crustto the surface by volcanic eruption, etc. Recently, the amount of humanemission of mercury has been increased due to industrial activities such as
artisanal and small-scale gold mining, coal combustion by thermal power
generation, etc., cement production, and production of metals. Mercury circulates
between the atmosphere, oceans, fresh waters, and soils, and exists mainly in 3
chemical forms: metallic mercury, inorganic mercury, and methylmercury. Inorganic
mercury is the most abundant among them.

● Circulation of mercury in the natural environment(Annual estimated amount)

500 t

Volcanoes,etc.

600 t

Forest ﬁres,
Combustion ofplants

1,000 t2,500 tSoil and （2,000-3,000 t）
vegetation
Anthropogenic

3,600 t To Lands/fresh waters
3,800 t To Oceans
3,400 t（2,900-4,000 t）
Ocean surface

300 t

100 t

Rivers

Ocean bed

*UNEP, Global Mercury Assessment 2018

The Minamata Convention on Mercury

The Minamata Convention on Mercury was adopted in Kumamoto City andMinamata City in 2013, and went into eﬀect on August 16, 2017. The objective ofthe convention is to reduce the artiﬁcial release of mercury from products using
mercury, factories, and mines into the environment to prevent environmental
pollution and health hazards caused by mercury. This convention also claims toreduce the supply, use, and release of mercury and to limit its international trade.

2Intake of Methylmercury from Seafood
A tiny amount of inorganic mercury is dissolved in natural waters such as theoceans and lakes. A part of inorganic mercury transforms to methylmercury bymicrobial action in water.
In the ecosystem, methylmercury accumulates in organisms such as ﬁsh andshellﬁsh via the food chain. This means that large carnivorous ﬁsh and deep
marine ﬁsh, as well as carnivorous marine mammals such as dolphins, have higher
levels of methylmercury concentration, compared to small herbivorous oromnivorous organisms.
The consumption of seafood allows the methylmercury to enter the body,even though it is trace amounts. The amount of methylmercury in the body varies
depending on how individuals eat ﬁsh (type and amount). However, in countries such
as Japan, where people eat more seafood than in Western countries, they tend toingest relatively large amounts of methylmercury. Also, cooking, such as grilling,simmering, and frying, does not remove the methylmercury in seafood.

Most of mercury
in water isinorganic mercury

Inorganicmercury

Dolphin/Whale

Food chainLargecarnivorous ﬁsh

Hg2+

Bacteria

Plankton

Small ﬁsh

CH3Hg+
Methylmercury

Methylmercury

The food chain stands for the relationship of ʻEating ‒ Eatenʼ in natural. Here,small ﬁsh eat plankton, and large carnivorous ﬁsh, dolphins, etc. eat small ﬁsh.
In association with this process, methylmercury is bioconcentrated.

3Seafood Types and Methylmercury
The methylmercury concentration in ﬁsh and shellﬁsh varies greatly among
species. Other than large carnivorous ﬁsh such as blueﬁn tuna, bigeye tuna,
southern blueﬁn tuna, and swordﬁsh, the methylmercury concentration tends to behigh in red bream and hilgendorf saucord. In addition, it is even higher in toothed
whales such as bottlenose dolphin. Be careful not to overeat these ﬁshes andshellﬁshes, etc. during pregnancy. On the other hand, the mercury
concentration in canned tuna is not so high, despite medium-sized yellowﬁn andwhite tuna, and small tuna being used as ingredients.
Seafood, however, also contains many great nutrients. A balanced diet, including
seafood, etc., is very important for the promotion of our health and the growth offetuses.

Blueﬁn tuna

Mackerel

Bigeye tuna

Saury

SalmonSardine0.99 ppm

0.14 ppm

0.96 ppm

0.05 ppm

0.03 ppm

0.03 ppm● Seafood Commonly consumed in Japan and Their Mean
Mercury Concentrations
Fish species

Mercury concentration(ppm)

Fish species

Mercury concentration(ppm)

Mackerel

0.14

Octopus

0.03Salmon

0.03

Flatﬁsh0.04

Horse mackerel

0.05

Hard clam and Littleneck clam

0.01

Saury

0.05

Bonito0.15

Squid0.04

Yellowtail

0.15

Tuna(all species including marlin)

0.68

Sea bream

0.10

Canned tuna (ﬁsh ﬂake, etc.)

0.14

Eel0.06

Shrimp

0.03

Crab

0.10

Sardine0.03

Sweetﬁsh

0.06

The table was based on the ranking of “Fishes and Shellﬁshes commonly consumed”
in the national survey conducted by National Institute for Minamata Disease. Fishes andshellﬁshes that are not included in the table but have a high total mercury concentration
include red bream (0.65 ppm) and hilgendorf saucord (0.36 ppm). In addition, themethylmercury concentration in bottlenose dolphin is 6.6 ppm.

4

Intake of Methylmercury into the Body
The ingested methylmercury is mainly absorbed from the intestinal tract into thebody. Vaporized metallic mercury is absorbed from the lungs into the body, while
inorganic mercury is poorly absorbed.
The protein that makes up our body consists of many amino acids, and one ofthem is cysteine. When methylmercury binds to this cysteine, it forms a complex
which is similar structure to methionine, another amino acid. Methionine is a very
essential amino acid, indispensable for brain function and fetal growth, andmethylmercury enters the brain and fetus in the same pathway as that ofmethionine.
Hair and nails are also made of protein, and methylmercury is taken up in the hairand nails.
Unlike methylmercury, metallic or inorganic mercury does not have the property of
being taken into hair.

Methylmercury（CH３Hg+）Cysteine(amino acid)5

MethylmercuryCysteine
ComplexMethionine(Essential amino acid)

Mercury (Hg)

Carbon (C)Oxygen (O)Sulfur (S)Nitrogen (N)Hydrogen (H)Methylmercury in the Body
When methylmercury enters the body, it is absorbed mainly from the intestinal
tract and accumulates particularly in the liver and kidneys. The brain and fetus areprotected by the blood vessel barrier called the blood-brain barrier and theplacenta, respectively, so that harmful substances absorbed from the outside of
the body do not get into them, but methylmercury easily passes through them.
The methylmercury concentration in the blood becomes higher in fetuses than inmothers.
Minamata disease is a serious methylmercury intoxication caused by eating large
amounts of ﬁsh contaminated with high levels of methylmercury. Typical symptoms
include sensory disturbance and cerebellar impairments, and the patients still
suﬀers from residual disabilities.
On the other hand, methylmercury is constantly excreted from the human body,
mainly via feces, after degradation. On average, 1 to 1.4% of methylmercury inthe body is daily excreted from the body, and the mean time required to excretehalf the amount in the body (biological half-time) is 50 to 70 days.

Brain

Methylmercury isabsorbed from the intestinal tract andcarried by the blood to ...

HairFetus

Bloodbrain barrier

LiverBloodPlacenta

Absorption
KidneyA part of methylmercury isbiotransformed to inorganic mercury
by tissues and intestinal bacteria
and is excreted mainly via the feces.

Intestinal
tract

Excretion
Feces/Urine
6

Special Care for Pregnant Women
It is known that fetuses are particularly susceptible to theeﬀects of methylmercury. Intake of methylmercury during
pregnancy may aﬀect the growth of fetus, and it is said
that the eﬀects of methylmercury are relatively likely toappear on language ability, and attention, etc.
Note that since ﬁsh also contains nutrients such as
polyunsaturated fatty acids (DHA and EPA) that promote
the growth of babies and suppress the harmful eﬀects ofmethylmercury, a balanced diet is important.

Familiar Mercury and
Health Effects

The preservative thimerosal (atype of organic mercury) containedin vaccines and the mercury indental amalgam have been shownto have no association with autism.
Dental amalgam hardly causes
neurological symptoms or fetaleﬀects.
There is no genetic inﬂuencecaused by mercury, and themercury in a fatherʼs body does
not aﬀect the baby.

Recommened Intakeof Methylmercury

The safety standard (tolerableintake) for methylmercury is
2.0 μg/kg body weight/week
during pregnancy, and 3.4 μg/kg
body weight/week for the general
population. According to the hairmercury survey conducted by
National Institute for Minamata
Disease, the mean intake in Japanis estimated to be about 1.6 μg/kg
body weight/week.

See the website of the Ministry of Health, Labour and Welfare for how toeat ﬁsh during pregnancy.
Please search with “For you who will be a mom,” etc

For you
who willbe a mom,search7

Would You Like to Measure
the Mercury Concentrationin Your Hair?
Do you know that your hair contains trace amounts of mercury? A part ofmethylmercury absorbed in the body is taken into the hair, and the concentrationof methylmercury in the body can therefore be estimated using hair.
Why is methylmercury taken into hair? It is because the hair mainly composed ofproteins, and methylmercury is taken up with other nutrients during the process ofmaking these proteins. It is more than 200 times more concentrated comparedto the concentration in blood.
As described above, methylmercury is concentrated in hair and easy to handle.
Therefore, it is used as an index for methylmercury intake.

Minamata Disease Archives accepts
mercury analysis by hair sampling forvisitors.
If you wish, please contact the staﬀ in the 1st
ﬂoor oﬃce. We will inform you the measurement
results by mail in approximately 1 to 2 months.

8Concentration of Mercury Taken
into Hair (Hair Mercury Concentration)
The mercury in hair is derived from the methylmercury that has naturallyaccumulated in seafood, and its concentration varies from person to person
depending on how the person eats seafood. It should be noted thatmethylmercury is constantly excreted from the human body and does notkeep accumulating. Methylmercury levels in your body can be varied bychanging your diet.

● Indication of Hair Mercury Concentration

50 ppm

A level at which neurologicalsymptoms may be caused*１

11 ppm

A level at which would no appreciable
adverse eﬀect on the fetal development*２

Exceeding this level is rare*3

Few participants exceed this level when limited to pregnant mothers*3

2.5 ppm

Mean level for males (Japan)

1.6 ppm

Mean level for females (Japan)

Mean of about 3,500 people in Japan*3

Mean of about 5,600 people in Japan*3

No major eﬀect on the health is observed at less than 50 ppm,except during pregnancy*Permed hair may show lower mercury concentration than the actual value

1 ppm is a unit representing 1/10,000 of 1%.

*1) Maximum
non-eﬀect level in thegeneral population(WHO, 1990)
１ppm（ピーピーエム）とは１％（パーセント）の１万分の１を表す単位です*2) Maximum non-eﬀect level for eﬀects on fetus (Food Safety Commission of Japan, 2005)*3) According to a survey conducted by National Institute for Minamata Disease

Unlike methylmercury, metallic or inorganic mercury

does not have the property to be taken into hair.

9There Is No Normal Value for Hair Mercury
Concentration
The Hair mercury concentration varies depending on how you eat seafood(type and amount).
Regional diﬀerences are also observed in hair mercury concentration. In general,
areas with large tuna consumption such as Eastern Japan tend to show higher
concentrations than in Western Japan. On the other hand, the coastal area does
not necessarily show higher concentration than the inland area.

50%

Male
40%

90% of men have hairmercury concentrations
within the range of

0.8 to 7.2 ppm

30%

Rate of population

Rate of population● Distribution of Hair Mercury Concentration50%

Female40%

0.6 to 4.5 ppm

30%

20%

20%

10%

10%

0%

90% of women have hairmercury concentrations
within the range0%0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20〜
Hair mercury concentration（ ppm ）0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20〜
Hair mercury concentration（ ppm ）Hair Mercury Concentration Varies by Age
The diﬀerence by age occurs because the way people eat seafood changes withage. Growing children may have high mercury concentration by eating a lot ofseafood, but there usually is no need to worry about it.

5 ppm

Male

4 ppm

3 ppm

2 ppm

1 ppm

0 ppm

Mean of hair mercury
concentration

Mean of hair mercury
concentration● Mean of Hair Mercury Concentration (ppm)
5 ppm

Female

4 ppm

3 ppm

2 ppm

1 ppm

0510 15 20 25 30 35 40 45 50 55 60 65 70 75 80〜
Generation

0 ppm

0

5

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80〜
Generation

104058-18 Hama, Minamata City, Kumamoto, 867-0008
TEL 0966-63-3111