Mercury Contamination in Rice: Sources, Impacts and
Solutions
Tan Mei PengID: 012235School of BioscienceUniversity of
Nottingham, Malaysia Campus43500, Jalan Broga, Semenyih
Malaysia.
Many researchers have found rice is another pathway of MeHg
exposure. Most of this rice contamination occurs in China since
China is the largest source of mercury consumption (VCM industries)
and producer in the world. Such contamination is spreading to other
parts of the world as well which include Indonesia, Philippines and
with the concern of Sub-Saharan Africa due to the increase of
artisanal small-scale mining sectors (ASGM) which gold prices and
demand are increasing. In UNEP Global Mercury Assessment 2013
report, ASGM has the highest level of atmospheric mercury
emissions. This review paper contained the Hg contamination of rice
in certain countries which leads to the question of the
biogeochemistry of rice. Research on health impacts from mercury
speciation exposure found that methylmercury is the most neurotoxic
species to human and it has been reported to have severely damaged
the IQ of the new-borns. Mercury use and gold consumption were
compared and discussed as well as the rice and mercury production.
Several mitigations has been suggested and applied. Hg
contamination in rice has brought negative impacts to the human and
the environment which should be continuously monitored to gain a
better picture in solving the problem.
Keywords: Methylmercury, Rice, Gold, ASGM, health
impactsIntroductionMany researchers have found several traces of
heavy metals like arsenic (As), lead (Pb), cadmium (Cd), copper
(Cu), Chromium (Cr) and zinc (Zn) are common contaminations in
paddy rice around the world due to anthropogenic and industrial
activities(YS et al. 2010; Meharg and Rahman, 2003; Liu 2011; Park
2011). Yet, heavy metal like mercury (Hg) is not uncommon
contamination in paddy rice; however it is not been reported as
much as As, Pb and Cd until recent years. All these heavy metals
contamination are toxic to the environment and humans health.
Mercury contamination especially methylmercury (MeHg) is a
potent toxicant which has been widely spread into the aquatic
system as well as paddy rice. The first reported outbreak of MeHg
contamination and poisoning was in Minamata in 1950s and Niigata in
1960s (Harada, 1995). It was found that the bioaccumulation of MeHg
in fish and shellfish samples has caused severe negative health
impact (Harada, 1995; Li, Feng and Qiu, 2010). Later on, it became
a world issue which has been reported in Iraq, Canada and US in
1969 (Harada, 2011) and other parts of the world. In the recent
research from IPEN and Biodiversity Research Institute (BRI), Japan
and Uruguay fish samples contained more than 1.0ppm of mercury
which is not recommended to consume according to USEPA guidelines
(IPEN and BRI, 2013).
One of the earliest researches on mercury contamination in paddy
rice was conducted by Morishita, Kishino and Idaka (1982) in Nifu
Mine in Seiwa Village, Japan whereby they collected samples of
soil, rice plant and human hair to measure the mercury level. It
was found that soil sample near the pits and mine of Nifu contained
higher mercury level (5.05ppm 98.6ppm) compared to soil samples
distant from Nifu (below 1.0ppm). The mercury level in brown rice
is higher near the mine compared to soil free from
contamination.
Fish is usually the dominant source of Hg compared to rice. The
issue of mercury contamination in paddy rice became a global issue
when Hg was found in several countries paddy rice. In Guizhou
Province, China; rice is the major pathway for meHg exposure rather
than fish (Zhang et al. 2010). Severe Hg pollution was found in
Guizhou Province due to Hg mining and smelting (Wanshan), zinc
smelting (Weining), and heavy coal-based industry (Qingzhen). Other
than China, paddy field in Naboc area, Philippines also
contaminated with Hg due to irrigation using Hg contaminated river
water nearby artisanal gold mining and 38% of the local inhabitants
were classified as Hg intoxicated. (Appleton et al. 2005). In
Indonesia, GunungPongkor, rice straw and rice grain contain high
mercury due to traditional gold mining and smelting. Values were
higher than the maximum permitted level of mercury in soils (0.5
ppm). The concentration of mercury in soil near the mining was
higher than in more distant soils. (Setyorini, Prihatini and
Kurnia, 2002)
Several studies have been done on the effects of mercury
exposure and human health. Usually hair and blood samples were used
for detecting methylmercury in the body. Research show that to
measure recent exposure, mercury in blood (B-Hg) is a good
biological indicator and hair is good measurement for the average
exposure over the growth period especially on pregnant woman and
infants (Apostoli et al., 2003; Cernichiari,1995 as cited in Li et
al. 2010).
According to EPA (1999), mercury exists in three chemical forms,
methylmercury (Organic mercury), elemental mercury and inorganic
mercury. Exposure of elemental mercury through inhaling the vapour
will cause toxicity in lungs, gingival, skin and eyes. It also
causes insomnia; weaken central nervous systems, kidney and lower
immune system. High exposure of inorganic mercury (released from
industries, eg. Mercuric chloride) may experience skin rashes,
dermatitis, mental disturbances, and central nervous breakdown and
weaken muscles.
Li, Feng and Qiu (2010) stated MeHg (organic mercury) was formed
through the methylation of inorganic Hg by microorganisms present
in sediments which are bioavailable and biomagnifies in the aquatic
food chain. MeHg also formed in water-saturated soils like paddy
field whereby MeHg will be bioaccumulated in the paddy rice.
Ingestion of MeHg food has caused negative impacts on cognitive
thinking, memory, attention, language, and fine motor and visual
spatial in fetal (1999). 95% of the ingested MeHg will be absorbed
in the gastrointestinal tract where it will be distributed readily
in all tissues (Harada, 1995). MeHg has the ability to cross
diffuse the barriers and penetrate all membranes easily (Mangal,
2001). 5% of adults contained 200 g/L of Hg in the blood would
experience neurological effects (WHO, 1990).
Rice does not contain a lot of beneficial micronutrients (eg.
n-3 LCPUFA, selenium and essential amino acids) like fish. Rice
contains less protein than fish that can prolong the survival after
ingestion of MeHg (Adachi and Hirayama, 2005). This concludes more
health risks with the consumption of MeHg contaminated rice than
fish if both were to be taken at the same rate.
Sources and Biogeochemistry of Mercury in Rice
Many researchers have found the sources of mercury contamination
in paddy rice were released from Hg mining, non-ferrous metal
smelting, coal combustion industries and artisanal and small-scale
gold mining (ASGM) and most of the contaminated paddy rice were
reported in Wanshan mining areas, China (Anderson et al. 2012;
Appleton et al. 2005; CCICED, 2011; Li et al. 2010; Zhang and Wong,
2006; Zhang et al. 2010).
Currently, China is the worlds biggest Hg emitter with the Hg
emission increasing rapidly in Asia (Lin, 2011). UNEP global
mercury assessment (UNEP, 2013) indicated East and Southeast Asia
have contributed 40% of the global Hg emission seen in Figure 1.
The demand for Hg in China is increasing due to usage of Hg as
catalyst for PVC production (CCICED, 2011). The emission of Hg in
China has caused China to be one of country with highest Hg
pollution.
In general, mercury can be released through natural sources
(volcanoes), anthropogenic activities and re-emission. In figure 2,
it showed the simplified version of anthropogenic activities and
the mercury cycle. The biogeochemistry of mercury has received
attention from many researchers because the methylmercury (MeHg) is
a neurotoxic component to human and wildlife; moreover it is easily
accumulated in biota and biomagnified in the food chains (Horvat et
al., 2002).
Figure 1: Global Distribution of Atmoshperic Hg Emission
(2010)
Feng, Qiu, Shang and Wang (2011) did research on mercury
contamination in Large Scale mercury mining (LSMM) and Artisanal
Mercury Mining (ASMM) in Guizhou. The results indicated there were
heavy Hg contaminations from LSMM and AMM. The Hg released from
LSMM were mainly concentrated in the historical mining and smelting
facilities, while Hg pollution resulted from AMM was found to be
distributed everywhere in the mining area. Moreover, newly
deposited Hg (mostly IHg) on Paddy field from AMM was more ready
for methylation than the bulk of old Hg in soil. This suggested the
significant impact of AMM on MeHg accumulation in rice, which can
pose a health risk to human.
Several paddy fields were contaminated with Hg from mine
tailings and irrigation with mercury contaminated water (Appleton
et al., 2005; Zhang et al., 2009). Even though mercury level in
paddy soil has positive relationship with the mercury level in the
river/water being used for irrigation but that only apply to total
mercury (THg) and not MeHg. Zhang et al. (2009) research showed
weak correlation (P>.05) between MeHg concentrations in river
and paddy soil and suggested Hg methylation is more important in
the paddy soil than transport of MeHg from river to the soil. There
was also weak correlation between THg concentration and MeHg
concentration in paddy soil which showed that there are more
factors to be considered. For instance, Frohne et al. (2012)
studies found that incresed Hgt (total dissolved mercury content)
concentration has an inhibitory effect on Hg net methylation
Another research suggested agricultural wetland like rice field
is one of the potential sources for bioaccumulation of
methylmercury. Ackerman and Smith (2010) introduced caged
mosquitofishes into the agricultural wetlands; white rice fields,
wild rice fields and permanent wetlands. After 2 months, it was
found that mercury was increased tremendously in all the caged
fishes. The total concentrations of mercury increased tremendously
from 135% to 1,197% while mercury body burdens rose from 29% to
1,566%. Fish mercury concentrations are the highest in white rice
fields (12 times higher than the initial concentrations), wild rice
fish mercury concentrations were 6 times greater and permanent
wetlands were 3 times greater. 82% of caged fish and 59% of wild
fish have mercury concentrations exceeded 0.2 g/g, a common fish
toxicity threshold.
Boening (2000) and Rinklebe (2010) found that many floodplains
soils contain high Hg content are due to atmospheric deposition and
transport from the watershed. In paddy field, Meng et al. (2010)
reported Hg in ambient air is the source for the accumulation of
Inorganic Mercury (IHG) on the above ground parts while IHG
concentrations in the root were related to Hg concentrations in the
paddy soil. Positive correlation of THg and MeHg in rice does not
concluded MeHg in rice was due to methylation of IHg in the paddy
soil. Zhang et al. (2009) stated the high concentration of THg and
MeHg in rice plants may be due to external factors whereby THg
might be absorbed from the ambient air through leaf surface while
MeHg was due to the uptake from the soil via roots. Machiwa (2010)
research also found the rice husks contained higher concentration
of Hg which may due to significance of atmospheric transport of
Hg.
In order to determine if rice is the bioaccumulator for
methylmercury in paddy soil, Zhang and his team (Zhang et al. 2009)
went and collect the samples of Qiu et al. (2008) research showed
the rice grown at abandoned mercury mining areas in China contained
methylmercury of > 100 g/kg in its edible portion which were
10-100 times higher than other crops. This showed that
methylmercury is easily bio-accumulated in paddy rice and there is
a positive relationship of MeHg in paddy soil and rice plants.
There are a few biogeochemical cycles that have large effect on
MeHg production. Maryland Department of Natural Resources (2008)
concluded Hg and S cycles are closely linked together and the key
to control Hg methylation rate is the balancing of sulphate and
sulfide. According to Frohne et al. (2012) research, sulfate
reducing bacteria (SRB) such as Desulfobactor species or
Desulfovibrio species helps to promote Hg methylation. The bacteria
process the sulfate in the contaminated floodplain soils to take up
inorganic mercury and convert it to methylmercury through metabolic
process. Toxicity became greater when inorganic mercury been
converted to methylmercury thus biota require longer time to
eliminate the methylmercury (USGS, 2000). On the other hand,
sulphide creates mercury complexes that are not bioavailable for Hg
methylation. Frohne et al. (2012) have also found that high
concentration of dissolved organic carbon (DOC) may promote Hg
methylation by enhancing the activity of SRB. DOC served as an
essential carbon source for bacteria. The positive relationship of
DOC/Hgt plays an important role for methylation.
Liu et al. (2012) stated the exchange of MeHg between paddy soil
and rice plants mainly occurs in pore water and it was found there
was a significant correlation of MeHg uptake flux from soil to the
roots to the top of the rice plants using the diffusive gradient in
thin films (DGT) technique. Hg cycling of flooded rice paddy in
Wanshan Hg mining region was investigated by Rothenberg and Feng
(2012) in 2008 and 2009. The rice-planted section pore water
contained higher concentrations of MeHg compared to the fallow
section of the same paddy. Pore water in rice-planted section was
more acidic which indicated that the low pH value has some effect
on the mobility and methylation of Hg (Boening, 2000).
Nevertheless, Rothenberg and Feng (2012) research showed that the
fallow section of paddy field act as a sink for FeS(s) and no
presence of FeS(s) in rice-planted section and both sections
contain low sulphide concentrations. It was suggested FeS decreased
the bioavailability of Hg by interacting with inorganic sulphur
ligands. Fe (III) reduction has increased electron acceptors for
SRB which indirectly enhanced Hg(II)-methylation. Frohne et al.
(2012) also reported Fe reduction through Fe reducing bacteria like
Geobacter, able to decrease demethylation.
The distribution pattern and content of methylmercury (MeHg) and
inorganic mercury (IHG) in rice plants tissues (Oryza sativa L.)
became the interest and focus for researchers (Meng et al., 2010).
The research concluded rice plants cultivated in Hg mining sites
have higher concentrations of IHg and MeHg than the control sites
and rice seed (brown rice) has the highest MeHg being accumulated
compared to the other parts of the plants (hull, root, stalk and
leaf.) Meng et al. (2011) research suggested newly deposited Hg is
more easily transformed to MeHg and accumulated in the tissues of
rice plants compared to Hg which has been deposited for a long
time. Orihel et al. (2006) research also suggested aging Hg in
sediments and soils decreases the bioavailability of Hg for
methylation. Meng et al. (2011) research confirmed soil is the
potential source of bioaccumulation of MeHg whereby MeHg was first
absorbed by the roots and then translocate to the leaf and stalk.
During ripening period (harvest season), most of the MeHg was
transferred to the rice seed and very small amount was being
retained in the root section. Except for premature plants, most of
the MeHg will retain in the leaf and stalk.
Main Geographic Trend in Rice production, Mercury Production and
Emissions
In 2012/2013 forecast from FAO (2013), rice was third highest
ranking cereal being produced with the annual production of 486
million tonnes (m/t). It is a staple food for nearly half of the
current world population. Adapted from 2011 FAO statistical data,
China (202.6 m/t), India (155.7 m/t), Indonesia (65.7 m/t), Vietnam
(42.3 m/t) and Bangladesh (50.6 m/t) are the top five global rice
producers countries since 1961.
Nonetheless, Asia consumed 90 % of the rice especially for the
low income population as they spent 50% of their income on rice
(Zeigler and Barclay, 2008). According to IRRI (2013), about one
billion including 640 million in Asia were living in poverty where
rice is their main food source. FAO (2004) reported rice provided
27% of energy supply, 20% of protein and its a good source of
niacin, thiamine and riboflavin in the developing countries. It was
noted that rice is one of the basic food that provide nutrients yet
places like Wanshan in Guizhou China, people are getting
intoxicated from the rice consumption.
Figure 3: Rice Production from 1961-2011 (tonnes). FAO Stat.
Rice is also linked to poverty when rice prices have tripled in
2008; about 100 million people were being forced to live in
poverty. When rice prices rose to 71% from 2007 to 2010, about 2
millions of people were impoverished in Indonesia (Dartanto, 2010).
It was thus concluded the increase/decrease rate of poverty was
highly affected by the fluctuations of the world price.
The global rice consumption since 1990s per capita is 65kg due
to stronger economic in many Asian countries. IRRI (2013) reported
rice consumption in China, India and Indonesia have declined as
higher income opted for larger variety of food choices. Based on
FAO statistics, global rice consumption does not decreased for
there was a rising demand in other parts of Asia, Latin America and
Sub-Saharan Africa (Rejesus et al. 2012). Since 2011, rice
production in Sub-Saharan Africa has risen by 4.4% (FAO, 2013). The
newly developed rice variety New Rice for Africa (NERICA);
collaboration and funding from NGOs, Africa Rice Center and IRRI
has successfully sustained 2.28% population growth per year (Wailes
and Chavez, 2012). Rejesus et al. (2012) made a forecast suggested
global rice consumption will continue to rise from 450 (m/t) in
2011 to about 650 (m/t) by 2050.
Western countries like Spain, Slovenia, California USA and Italy
used to be the major Hg mining areas responsible for over 70% of
the total global production. Nevertheless in 2000, Hg decreases to
1800 tons from these mines. However, the trend of Hg mining
appeared to be shifting focus to the east, the Asia countries with
the estimated total production of 1930 tons in 2011 (Hylander and
Meili, 2003; USGS, 2012). China being the major staple of rice
production is also one of the countries with highest Hg production;
1,400 metric tons in 2011 (USGS, 2012).
As there will be increasing trend for global rice production and
consumption, the mercury production and the graph of the global
rice production has been compared with global mercury production
shown as below in Figure 4. The mercury production only covers Hg
mining and by-products from smelting activities (USGS, 2012). There
may not be drastic mercury mining due to less expensive Hg sources
could be gained from recycling; eg. Hg from closed chlor-alkali
plants and by-product from zinc, copper could replace if new
regulations restrict Hg emissions from ore refining (Swain et al.
2007).
According to Lin (2011) and Maxson (2009), the demand of Hg in
China was predicted to increase as PVC/VCM production is expanding
with the intentional use of Hg as catalyst. Thus, Hg mining in
China might increase but only for domestic use.
Figure 4: Global Mercury (USGS) and Rice Production (FAO Stat)
1961-2011 (tonnes)
The trend of anthropogenic mercury emissions to air also shifted
from Europe and North America to East and Southeast Asia and China
is the largest contributor (CCICED, 2011; UNEP, 2013). In CCICED
(2011) report, China has released 643 tonnes of mercury into the
air in 2007 whereas in UNEP (2013) report, China is responsible for
three-quarters of atmospheric mercury released of East and
Southeast Asia (average of about 583 tonnes). Thus, high mercury
production and emission have caused concern of Hg contamination in
paddy rice.
It was known that atmospheric mercury is easily dispersed,
travel and deposit on soil or water bodies within the range of
100-1000km. With such increasing production of rice, it has been a
concern to the rice consumer (UNEP, 2013).
Artisanal Mining Gold Production
UNEP global mercury assessment (2013) showed the atmospheric Hg
emission has slightly increased by 30 tonnes since 2005 (1930 tons)
to 2010 (1960 tons), Figure 5. Comparing 2005 and 2010 atmospheric
mercury emission, artisanal small-scale gold mining (ASGM) has
doubled from 350 tons to 727 tons. This may due to the increment of
gold prices in the market, rising rate of rural poverty, and better
data was obtained for the mercury emissions level. China was
considered as one of a significant contributor in ASGM even though
the recent information was limited due to China had banned such
activities in 1996. Nevertheless, East and Southeast Asia, South
America and Sub-Saharan Africa are the main contributors in this
sector (Table 1).
Table 1: Hg emissions from ASGM sectorRegionCountriesASGM Hg
Emissions (Tonnes)East and Southeast
AsiaChina652Indonesia200Philippines 90South
AmericaColombia200Bolivia150Peru100Sub-Saharan
AfricaGhana120Tanzania 60
Figure 5: Global Atmospheric Hg Emission in 2010 (tons)
London-based International Institute for Environment Development
(IIED) new report suggested Artisanal Small-Scale mining (ASM) is
one of the sectors where 20 to 30 million of the worlds poorest
people are depending on it to support the livelihood more than five
times of that number (IIED, 2013). The International Labour
Organisation (ILO) statistics showed ASGM supports livelihood of
more than 13 million people in the developing world (Phiri, 2011).
ASM employment rate is 10 times higher than large-scale mining and
people involved in this sector include women and children as
labourers too. ASM brings contribution to the society yet it does
not sustain the environment and it is illegal in the society. The
labourers are usually unskilled and not knowledgeable especially on
the danger of using mercury for amalgamation method for purifying
the gold. ASGM has produces 20% gold to the market every year
(IIED, 2013). However most of their contributions were informal and
not being taken account from the government. ASGM miners wages
could only be $2 - $5 dollars a day depending on the countries and
geographic area (Siegel and Veiga, 2010 as cited in IIED, 2013)
In Ghana, artisanal miners have shifted their attention from
diamond mining to gold mining (Nyame and Grant, 2012). This may be
due to the banning of most of the export of diamonds in 2006 under
Kimberley Process Certification Scheme with more strict production
and export regulations. This regulation has caused the increased
price of small-scale diamond mining. The diamond artisanal
small-scale miners unable to find alternative employment were
forced to shift attention other mining sector. Such changing
patterns have contributed to an increase use of mercury and
increase ASGM mercury emissions.
Many ASGM sectors use mercury for amalgamation due to it is
fast, inexpensive and effective where it is easy to be used by
unskilled artisanal miners (Phiri, 2011). Amalgamation method has
caused Hg released into the environment in several ways which
causes negative health impacts to those who live within the mining
area. For example, elemental mercury vaporizes when blow-torching
the amalgam in an open vessels or through burning. Direct
amalgamation of ground ore without the practice of gravity
concentration and over usage of mercury have caused the Hg residues
(Inorganic mercury) together with other wastes to be discharged
into the waterways and tailings (Beinhoff and Calvez, 2001). When
mercury was being used together with cyanide to extract gold,
cyanide dissolves mercury to form cyano-mercuric complexes which
are more bioavailable causes higher rate of methylation (Telmer and
Veiga, 2008 as cited in Pirrone and Mason, 2009). UNIDO (2006 as
cited in Pirrone and Mason, 2009) found fishes which contaminated
with cyanide and mercury contain higher level of MeHg than mercury
alone.
It was noted soils around gold mining areas in general are
naturally rich in mercury and the formation of soil naturally
concentrates and sequesters mercury (Jonasson and Boyle, 1972 as
cited in Pirrone and Mason, 2009). Furthermore, soil erosion from
mining releases mercury from the soil into the water bodies in an
accelerated rates will be more ready to be methylated and
bioaccumulated where it likely becomes available to be methylated
and bioaccumulated in floodplains. Vaporizes mercury would be
inhaled by the people living in mining area while and ingest MeHg
contaminated rice and fishes. Both ways of emissions cause serious
issues to the health.
The increase demand of gold especially for jewellery about 43%
in 2012 was demanded (World Gold Council, 2013). The demand and
soaring gold prices has caused ASGM to use more mercury to produce
gold. Swain et al. (2007) stated Hg is an actively traded commodity
whereby in year 2000 about 9000t of metallic Hg were bought and
sold. In 2008, about 1000 tonnes/year of mercury being released
into the air while in 2011, it has increased to 1465 tonnes/year
(Telmer, 2011). It was suggested about 1.3:1 (Hg:Au) being used to
produce 27 tonnes of gold through concrete amalgamation. Obtained
data from USGS for gold and mercury prices comparison (Figure 6)
showed both mercury and gold prices increases simultaneously. This
is one of the factors why atmospheric mercury emissions are
increasing.
Figure 6: Global Mercury and Gold Prices 1900-2011.
Australias Bureau of Resources and Energy Economics (2013) has
forecast world gold mine production in 2013 to be increased by 4
per cent, compared to 2012 (2836 tonnes), to total 2956 tonnes but
the gold prices would most likely decrease due to economic downturn
and reducing demand from main consumer (India).This forecast does
not include ASGM.
The increase of gold demands, ASGM activities, increasing Hg
consumption, rice production booming in Sub-Saharan Africa and
other parts of the world has summed up to possible increasing Hg
contaminated rice in the world.
Mitigation
In 10th January 2013 (UNEP, 2013), 140 nations have signed a
legally binding treaty known as Minamata Convention to reduce
mercury. Some notable actions were discussed and will be taken into
account. For example, The UNEP Mercury Products Partnership has
decided to totally cut off of long line products which contained
mercury by 2020. 70% of mercury thermometers and blood pressure
devices will be reduced by 2017. 20 tonnes of mercury emissions
should be reduced by 2016 according to Mercury and Air Toxics
Standard. Since 2011, European Union has banned mercury exports and
on 1st Jan 2013, USA has set the rule of banning mercury exports as
well. This is to reduce mercury being transferred to developing
countries for activities like ASGM.
A few methods have been discussed in UNEP (2008) report on using
alternative in replacing the mercury. Since ASGM is the biggest
mercury emissions sector, more efforts should be made. New treaty
Minamata Convention stated they do not plan to ban the usage of
mercury but there will be stricter regulations on supply and demand
of mercury. (UNEP, 2013). UNEP has provided the guidelines to
reduce mercury use for ASGM.
As such, method like gravity separation which includes all
processes that separate gold from ore based on density. One of the
method known as Gravity separation process which does not require
the use of mercury and it can be applied to whole ore and ore
concentrate. The separation processes comes in four methods
including sluices, vibrating tables, hand screening and
centrifuges.
Another way to replace mercury in ASGM is using the iGoli
process which was developed by Mintek, a mineral technologist
working with government of South Africa. iGoli process can produce
99% pure gold, a better method of extracting gold compared to
amalgamation process which contained 5% residual mercury in the
extracted gold. This process can be applied to free-gold ore and
refractory ore. This method has been applied in Peru, Tanzania and
Mozambique.
Chinas VCM industries consume and released most mercury in the
world. Alternatives like using ethylene-based VCM process which
uses ethylene as the primary feedstock. Ethylene-based process need
only 3,500 kw/hours to produce 1 tonnes of PVC compared to use
acetylene-based process which required 6,500 7,000 kw/h (ICIS,
2003; as cited in UNEP, 2008). On the other hand, Foreign Economic
Cooperation Office of China (FECO) has proposed by 2015 the use of
low-mercury accelerants will be applied to all calcium carbide
process-based PVC industries (UNEP, 2011).
In terms of reducing methylmercury concentration in rice, Peng
et al. (2012) reported rice grown aerobically had reduced THg and
MeHg concentrations remarkably and it also reduced the MeHg content
in the grain. Different rice cultivars have different level of THg
and MeHg. Rothenberg and Feng (2012) research showed that among the
50 indica rice cultivars in three different sites
(highly-contaminated, moderately-contaminated and background
sites), moderately-contaminated sites contained higher THg and MeHg
level. This is due to alkaline conditions in highly-contaminated
site has reduces the uptake of Hg species by decreasing the
micronutrients solubility which required for plant growth. Perhaps
cultivating low Hg accumulating rice would be the key to cultivate
in high mercury contaminated sites.
Certain measures of reducing methylmercury in terms of healths
perspective have been taken into account. European Food Safety
Authority (2012) has set a new standard for methyl mercury intake
per week to 1.3 g/kg bw (lower than previous JECFA safes level
1.6g/kg) due to the new findings considered long chain omega 3
fatty acids present in fish may have previously led to an
underestimation of the potential adverse effects of methylmercury
in fish. The consumption of inorganic mercury is 4 g/kg bw.
However, no tolerable safe level for consumption of methylmercury
contaminated rice. Rice does not contain the omega 3 fatty acids
benefits which play an important role in growth, development and
the function of the brain. Transande et al. (2005) and Bellanger et
al. (2013) reported pregnant women exposed to MeHg, will reduce the
IQ of new-borns that may last for a lifetime. Using cost analysis
studies, it showed the loss of intelligence will cause lower
economic productivity to the countries.
Ballatori et al. (1998) and Aremu et al. (2008) research found
N-acetylcysteine (NAC, a non-toxic amino derivative) could be the
antidote in reducing MeHg level in body through urinary excretion.
It is effective when taken orally or intravenously and about 5%
MeHg doses eliminated through urine within 2 hr using 1 mmol/kg of
NAC. Furthermore, NAC significantly reduced the body burden of MeHg
in pregnant rats. However, more research has to be done.
Economic analysis should be used in making policies. For
example, evaluation of health using benefit-cost analysis (BCA)
method based on monetary values or cost effectiveness analysis
(CEA) - comparative cost and consequences of alternative decisions
would be taken into account (Swain et al. 2007; Levin, 1995).
Public sector policies are important but it was suggested
private sector and NGOs should make policies too as a guidelines in
curbing mercury (IIED, 2013). Especially ASGM, it is important to
get involve in local communities to make a better policies based on
their lifestyle, usage of mercury, incentives, challenges and more.
Integrated cross-scale governance like could be one of the way to
tackle mercury issue. In conclusion, policies making should be
integrated with multiple levels of governance, an integration of
local, regional and global (Selin and Selin, 2006).
AcknowledgementsI thanked Dr. Lawal Billa and Dr. Paul Williams
for their patience and guidance. It was a tedious work that I would
not be able to complete it without any aids. This paper has gave me
more insight on the impacts of mercury contamination in paddy rice
and a bigger picture of how environmental scientists do.
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