1. Maternal Methylmercury Exposure Through Rice Ingestion in Rural China
1 1Department of Environmental Health Sciences, University of South Carolina Arnold School of Public Health, South Carolina, USA; Shanghai Key Laboratory for Children's Environmental Health, Xinhua Hospital, Shanghai, China; 3Department of
Epidemiology and Biostatistics, University of South Carolina Arnold School of Public Health, South Carolina, USA
Email: chuan@email.sc.edu, xdyu1108@163.com, jliu@msilbox.sc.edu, rothenbs@mailbox.sc.edu
• Mercury is a global pollutant and potent neurotoxin; methylmercury is one of the most toxic form of mercury, which most severely
afflicts the developing fetus (Clarkson and Magos, 2003). Intake of seafood is regarded as the primary methylmercury exposure
pathway (NRC, 2000).
• Flooded rice paddies are important mercury methylation sites, where methylmercury is bioaccumulated in rice grain (Rothenberg et al.,
2014). Although currently reported methylmercury concentrations in rice are lower than the concentrations in seafood, the rice
consumption is still another significant methylmercury exposure pathway among rice-eating population. Yet there are few studies
concerning dietary MeHg inkake through rice among pregnant women. There is only one pilot study conducted among 17 pregnant
women in Guizhou Province, China (Rothenberg et al., 2013).
• The major aim of this study is to evaluate maternal dietary methylmercury exposure through rice and fish consumption within a
population of pregnant women living in rural China where rice is a primary food.
Chuan Hong1, Xiaodan Yu2, Jihong Liu3, Sarah E. Rothenberg1
1. BACKGROUND & SIGNIFICANCE
3. RESULTS & DISCUSSION
4. CONCLUSIONS
• We are working in a rural area of Guangxi Zhuang Autonomous Region,
China, where rice is a staple food (Fig. 1).
• Between May 2013 and March 2014, a total of 398 healthy pregnant women
were recruited at parturition. After providing informed consent, mothers
donated hair and blood samples, a rice sample from their home, and filled out a
4-part questionnaire and a semi-quantitative food frequency questionnaire.
• Fish tissue (n=13) was collected from local markets in May 2014, and included
common freshwater fish species consumed by residents. For other aquatic food
varieties, total mercury concentrations were determined from a comprehensive
literature review (n=8 published papers).
• Laboratory analyses:
(1) Freshwater fish tissue total mercury concentrations and rice methylmercury
levels.
(2) Maternal biomarkers measures included maternal hair (trimester 3) total
mercury and methylmercury concentrations, and maternal blood total mercury
levels.
2. METHODS
Figure 1. Guangxi Zhuang Autonomous Region, China ( red
region)
Table 1. Summary statistics for parameters, including concentrations of total mercury (THg) and methylmercury (MeHg) in rice and fish tissue, and
maternal hair and blood, and the calculated daily dietary MeHg intake from rice and fish. The cohort sample size (N) is 398 mothers. For column sample
sizes are < 398 due to missing data.
Parameters N Mean (Range) or N(%) Median Source Parameters N Mean (Range) Median
Rice MeHg
(ng/g)
398
2.7
(0.32-15)
2.2 This study
Daily Total MeHg intake
(ug/day)
398
1.2
(0-20)
0.77
Freshwater fish THg
(ng/g)
13
31
(1.5-98)
23 This study
%Daily MeHg intake from rice
(ug/day)
396
71
(0-100)
87
Marine fish THg
(ng/g)
838 64*
Liu et al., 2014a, 2014b;
Pan et al., 2014; Chen et
al., 2013
%Daily MeHg intake from fish
(ug/day)
396
29
(0-100)
13
Eel THg
(ng/g)
21 50* Yamashita et al. 2006
Hair THg
(μg/g )
398
0.48
(0.077-1.7)
0.40
Shellfish THg
(ng/g)
96 24*
Lei et al., 2013;
Li et al., 2013
Hair MeHg
(μg/g )
398
0.32
(0.011-1.4)
0.28
Shrimp THg
(ng/g)
10 10* Tong et al., 2015
Hair %MeHg
(of THg)
398
67
(14-110)
67
Crab THg
(ng/g)
10 74* Tong et al., 2015
Blood THg
(ug/L)
397
1.5
(0.29-8.6)
1.2
Spiral Shell THg
(ng/g)
11 28*
Tong et al., 2015;
Lei et al., 2013
DailyTotalMeHgintake
(µg/day)
Non-farmers
Figure 2. For non-farmers and farmers, (a) comparison between the daily total methylmercury intake (Wilcoxon test, z=3.3, p<0.01); (b)
comparison between the proportion of daily methylmercury intake from fish (Wilcoxon test, z=4.7, p<0.0001); (c) comparison between the
proportion of daily methylmercury intake from rice (Wilcoxon test, z=-4.9, p<0.0001)
Figure 3. Log mercury levels in maternal biomarkers versus log daily total MeHg intake plus a categorical variable for the mother’s job (non-
farmers / farmers), including regression trends for mothers who were non-farmers (blue line) and mothers who were farmers (red line). (a) Hair
total mercury (THg): r2=0.039, p<0.01 (b) Hair methylmercury (MeHg): r2=0.032, p<0.01 (c) Blood total mercury (THg): r2=0.037, p<0.01
• Results indicated that this cohort was exposed to low-level methylmercury via daily rice and/or fish consumption. Mercury levels in
maternal biomarkers was comparable to some U.S. cohorts for pregnant women.
• Although the fish/shrimp ingestion contributed to the maternal methylmercury exposure, the daily rice consumption was also a significant
methylmercury exposure pathway among this cohort, especially for those who were farmers. The MeHg exposure pathway between non-
farmers and farmers was different.
• These present results will be applicable to other cohorts where the prenatal methylmercury exposure via rice and fish consumption.
• The mean of rice methylmercury levels was 2.7 ng/g (geometric mean = 2.1 ng/g) (Table 1.), which was close to the global rice
methylmercury concentration (2.5 ng/g, from Rothenberg et al., 2014). Among all mothers, nearly 90% ingested rice every day, while a
subset (58%) reported consuming ingested fish at least one time per month. The primary type of consumed fish was the freshwater fish.
• Hair total mercury levels averaged 0.48 ug/g (geometric mean = 0.41 ug/g) (Table 1.), which was similar or lower compared to some
U.S. pregnant women cohorts, where fish ingestion was the primary exposure pathway (mean range: 0.29-0.55 ug/g, from Stewart et al.,
2003; Oken et al., 2005; Xue et al., 2007). Hair methylmercury and total mercury concentrations were highly correlated (Spearman’s
correlation: r=0.92, p<0.001, n=398).
• Among mothers, 78% (n=309) were famers, and 23% (n=89) held other occupations. The average total mercury and methylmercury
levels in maternal hair and blood were slightly highly for farmers compared to non-farmers (Wilcoxon test, p range: 012-0.29).
Compared to farmers, non-farmers had a higher average daily total methylmercury intake (1.5 ug/day vs. 1.1 ug/day, Fig. 2a). And for
non-farmers, the proportion of daily methylmercury intake from fish was higher than farmers (43% vs. 25%, Fig. 2b), while the
proportion of daily methylmercury intake from rice was lower (57% vs. 75%, Fig. 2c). The results reflect that mercury levels in rice
were lower than that in fish.
• Daily total dietary methylmercury intake was positively related with all mercury levels in maternal hair and blood, but the trends were
different between non-farmers and farmers.
Log Daily Total MeHg Intake
5. ACKNOWLEDGEMENTS
This research was funded by a grant to S. Rothenberg by the National Institute of Environmental Health Sciences (R15ES022409). The
content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of
Health.
Farmers Non-farmersNon-farmers FarmersFarmers
%DailyTotalMeHgintake
fromfish
%DailyTotalMeHgintake
fromrice
a. Comparison of Total MeHg intake
LogBloodTHg
LogHairTHg
LogHairMeHg
Log Daily Total MeHg IntakeLog Daily Total MeHg Intake
The study site
* Weighted mean
a. b. c.
6. REFERENCES
See the supplementary sheet.
c. Comparison of %MeHg intake from riceb. Comparison of %MeHg intake from fish
Wilcoxon
P<0.01
Wilcoxon
P<0.0001
Wilcoxon
P<0.0001