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Residual levels of Rare Earth Elements in Cereal and Their Health Risk Assessment from Mining Area in Jiangxi, South China

Yanmin Wang, Hong Zhou, Li Xiong, Chengwei Liu, Xingyong You
Journal of Food and Nutrition Research. 2020, 8(1), 58-62. DOI: 10.12691/jfnr-8-1-8
Received November 09, 2019; Revised January 06, 2020; Accepted January 24, 2020

Abstract

The content of rare earth elements (REEs) in cereal were investigated, the risks of REEs exposure to human health were assessed. 428 cereal samples were collected from rare earth mining area and control area in Jiangxi, South China. The contents of 14 rare earth elements were determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The average concentrations of total rare earth elements in cereal from mining and control areas were 99.03 μg/kg and 34.21 μg/kg, and the difference was statistically significant (t=4.81, P=0.001). The Rice had the highest rare earth elements concentrations (102.79 μg/kg and 35.28 μg/kg for mining and control areas, respectively) and Maize had the lowest rare earth elements concentrations (76.98 μg/kg and 26.95 μg/kg for mining and control areas, respectively). The rare earth elements distribution patterns for both areas were characterized by enrichment of light rare earth elements. The health risk assessment demonstrated that the estimated daily intakes of rare earth elements through cereal consumption were considerably lower than the acceptable daily intake (70 μg/kg bw). The human health risks of REEs associated with cereal are low, but more attention should be paid to the effects of continuous exposure to rare earth elements on children.

1. Introduction

Rare Earth Elements (REEs) are members of the group IIIB in the periodic table. The International Union of Pure and Applied Chemistry (IUPAC) defines the rare earth metals as a group of 17 elements consisting of the 15 lanthanoids [La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu] plus Sc and Y 1. Commonly, La, Ce, Pr, Nd, Sm, Eu are indicated as light REE because of their atomic mass lower than 153 while Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu are indicated as heavy REE because of their atomic mass greater than 153.

REE was used in many applications in the past and it is becoming more popular in high-techindustry nowadays. REE is widely distributed in the biosphere. REEs can be accumulated in different areas of the environment following anthropogenic inputs because of the low mobility of these elements. Life processes (physiological and biochemical) of plants, soil, and living organisms are effected by rare earth elements [2-5] 2. REE effect enzyme activity, production, and intensity of photosynthesis, content of phytohormones, water regime of plants, and water deficiency resistance, and put effects on seed germination 6. REE-based fertilizers increased the yield and quality of crops mostly used in China since the 1990’s. Every year, about 50-100 million tons of REE-based salvolatile and phosphate fertilizers enter the agriculture system causing adverse health effects and detrimental environmental issues through bioaccumulation through the food chain 7. In China, REE-accumulated plants enter the human food chain through different pathways causing danger to public health 8. Small concentration ratio (CR) shows low transfer of REE from soil to plants. For humans, sample’s acceptable daily intake (ADI) of rare earth nitrates is 0.2-2 mg/kg 9, a safety standard range of 12-120 mg/person/day 10. Low level of REE in human tissues and fluids supports low transfer level of REE through food chain.

China has produced over 90% of the world’s rare earth supply with the only 23% of the world total reserves and has become to a leading producer of REEs 11. However, in recent years, with the increased exploitation of REEs in China, mining activities have led to intensive accumulation of REEs and enhanced the level of REEs in the environment high enough to cause harmful effects on human beings 12. Although there is no report on incidents of human poisoning through food chain, like other heavy metals, high concentrations of rare earth elements are likely to be harmful to plants and human health [13-16] 13, and it has already been proven that long-term exposure of REE dust may cause pneumoconiosis in humans 17. Besides these, people are increasingly interested in the impact of REE on children’s neurodevelopment. Researches for children showed that REE might be related to decreased IQ and memory loss 18, 19. It is therefore necessary to investigate their concentration levels in major daily food of vegetable, cereal and meat to assess the potential risk of REE to human health.

The rare earth ore in present study is located in Dingnan County in the south of Jiangxi province and is one of the 11 national planned rare earth production areas, the rare earth reserves are approximately 1.10 million tonnes 20.

This is the first study dealing with REE in cereal of local households in close proximity to a large-scale rare earth mining site in Jiangxi, China. The main objectives were: (1) to investigate the levels of REE in cereal of mining and control areas in Dingnan County; (2) to evaluate the health risk of dietary REE exposure through cereal consumption.

2. Materials and Methods

2.1. Sampling and Pretreatment

The samples were collected from 10 sampling sites (5 from mining area and 5 from control area during September and November in 2016. The mining area is located in the vicinity of Dingnan rare earth ore and the control area was chosen from the site located 60 km away from the mining area. The living conditions, economic backgrounds and cultural and living habits are similar between the mining area and the control area. The natural environment is not affected by the rare earth mining area. The cereals were grown by the local residents and stored at house. Each sample was asked whether it was grown or bought in the market. The samples bought in the market were excluded. A total of 428 samples (edible part) including Rice, Maize and Legume were collected. Samples were washed with tap water and further washed three times with deionized water. Then, the samples were ground into powder in an agate mortar, passed through 0.149 mm nylon sieve, and stored at −20 °C until analysis was made.

2.2. Analytical Methods

The REEs concentration of all samples was determined by inductively coupled plasma mass spectrometry (ICP-MS, 7500CE, Agilent, Palo Alto, California, USA). The microwave digestion system was used for analysis where approximately 0.50g of the sample was weighed and digested with 8 ml of concentrated nitric acid (65%) in a PTFE digestion vessel. The solution was then poured into a volumetric flask and diluted to 10 ml with ultra-high purity water after cooling for about 40 min. The detailed measurement condition of ICP-MS was described by GB 5009.94-2012. REE concentration was expressed as μg/kg. External calibration was performed by measuring standard solutions obtained from national center of analysis and testing for nonferrous metals and electronic materials, China (NCATN). The standard solutions contained these 14 REE at 0, 0.05, 0.1, 0.5, 1, and 10 μg/L levels. Mixed solutions containing In, Rh, and Re obtained from NCATN were used as on-line internal standard at 1 μg/L level. The limits of detection (LOD) of these 14 REE for this method were 0.03-1.01μg/kg, which were determined as three times of standard deviation from seven blank solutions.

The accuracy and precision of the cereal analysis were assessed using Rice (GBW10010, national certifed reference materials of China). Standard solutions were inserted into the sample sequence every 8 samples to verify sensitivity and repeatability. The recoveries of REE were 88.2-98.6%.

2.3. Health Risk Assessment

The estimated daily intake of REE through cereal consumption was calculated according to Equation 1 21.

(1)

Here, EDI (μg/kg bw per day) represents the estimated daily intake of REE, Cv is level of REE in cereal (μg/kg), CR is consumption rate (kg/day), BW is body weight (kg). For analytical results below the LOD, 1/2LOD was used to produce estimates. Zhu et al., 22 have proposed a daily allowable intake of 70 μg/kg bw for rare earth oxides, which was certificated from human health survey in REE mining areas and animal experimental results.

2.4. Statistical Analyses

Statistical analyses for comparing the average results of different cereal samplings were performed using Student's t-test. P<0.05 was considered statistically significant. Statistical analysis was conducted using SPSS software package 16.0 (SPSS Inc., Chicago, IL, USA).

3. Results and Discussion

3.1. REE Levels in Cereal

The average concentration of REE for all 428 samples was 66.93 μg/kg. For cereal collected from mining and control areas, the average concentrations were 99.03 μg/kg and 34.21 μg/kg, respectively, and the difference was statistically significant (t=4.81,P=0.001). La, Ce, Pr and Sm were major elements and accounted for over 84% of total REE for mining area (Table 1). The total REE, light REE and heavy REE were statistically significant different between cereal from mining and control areas (P < 0.05). The results are consistent with previous studies, but the REE levels in the present study are relatively lower 23, 24, The reasons for the differences in REE levels between different studies include the type of rare earth ore, REE levels in soils, and plant species. High concentration level of REE in soil can lead to more absorption and accumulation of REE 25. Plant uptake of REE also depends on mobility and bioavailability of REE in soil 26, 27. Different type of rare earth ore has different mobility and bioavailability of REE influencing the absorption of REE.

3.2. REE Levels in Different Categories of Cereal

We divided the samples into three categories: Rice, Maize and Legume. For both mining and control areas, The REE concentrations of Rice were 130% higher than that of Maize. The Rice and Maize from mining area had significant higher REE concentrations than control area (P=0.01, P=0.004). Legume was no statistically significant difference in REE concentrations between mining and control area (Table 2). For both mining and control areas, the REE concentrations in cereal declined in the order of Rice > Legume > Maize. Previous studies had demonstrated the similar result 26, 27. Results of a study on REE absorption and distribution showed that the Rice had higher REE concentrations than Maize due to higher accumulation ability, but both plants show high concentration in roots 28, 29. Further analysis demonstrated that root tips of Rice and pea plants significantly show La and Yb in the xylem and endoderm 25. This may be the reason that Maize has the lowest REE levels compared to Rice and Legume.

3.3. REE Distribution Pattern

The REE geochemistry of cereals from mining area and control are characterized by a relatively uniform chondrit-enormalized REE-pattern, with variable L/H (ΣLREE/ΣHREE= 6.38 to 8.59), significant LREE enrichment((La/Yb)N= 18.50 to 22.05 ) (Table 3). The values of δEu and δCe of mining area and value of δEu of control area were close to 1, but the value of δCe of control area indicated that there was a pronounced Ce-anomaly, (La/Sm)N and (Gd/Yb)N indicated that the internal differentiation status of light REE and heavy REE was moderate.

Mining area contains higher REE concentrations in comparison with control area. Although the REE abundances were different, the REE distribution patterns were similar for the two areas Figure 1. There was an obvious Nd anomaly in the distribution patterns. The reason might be the low Nd abundance in samples which is less than that in chondrites, resulting in a low ratio of sample/chondrite.

  • Figure 1. Chondrite-normalized REE distribution patterns for cereals. The REE abundances were normalized to those in chondrite, and then the pattern was achieved by plotting the ratios on a logarithmic scale against the atomic number. The REE in chondrite were assumed to be no fractionation. This could eliminate the abundant changes between odd and even atomic numbers.
3.4. REE Distribution Pattern

For different gender/age groups, the estimated daily intakes (EDI) of the total rare earth oxides were considerably lower than the established allowable daily intake (70 μg/kg bw), even calculated with 95% quantile of rare earth oxides in cereal, but children aged 2-12 years had higher EDI than the other group, especially the group of 2-7 years. The EDI of people over 13 years were substantially the same and had little variation (Table 4). Based on these results, the harm of REE exposure to adults through the consumption of these cereal is negligible. But more attention should be paid to the effects of continuous exposure to low levels of REE on human, especially on children 2-12 years old. In Jiangxi Province of China, rare earths mining activities are highly done and show strong correlation between the hairs of the mothers and their young children. Pair-comparison analysis for the means showed that the average hair level of five kinds of REEs in the young children was two times high as their mothers. Results indicate children living in nearby area found with maximum mean La concentration of 2202.9 ng/g that decreases with increase in distance from the mining sites. The levels of REEs in the hairs can be used as a biomarker to reflect body’s level of exposure to REEs 31. A study conducted in Fujian province also demonstrated that vegetable consumption would not result in exceeding the safe value of REE EDI for adults 32. However, it is worth noting that children’s neurodevelopment is more susceptible to REE that is related to decreased IQ and memory loss.

It should be noted that the health risk assessment results might be influenced by other factors such as other food (vegetables, meats, and fruits) ingestion and bioavailabi- lity of REE. The REE intake through dermal absorption and breath inhalation was not estimated. In addition, the data of consumption rate was obtained in 2007 and may have been changed after these years of economic development. Therefore, a more systematic risk assessm- ent is needed.

4. Conclusion

The concentration of total REE in cereals from mining area is higher than that of control area. For both areas, REE concentration decreases in the order of Rice > Legume > Maize. The REE distribution patterns for both mining and control areas exhibit LREE enrichment trends. The health risk assessment demonstrated that the estimated daily intakes of rare earth elements through cereal consumption were significantly lower than the acceptable daily intake (70 μg/kg bw). The human health risks of REEs associated with cereal are low, but more attention should be paid to the effects of continuous exposure to rare earth elements on children.

Acknowledgements

This study was sponsored by the Key Laboratory Project of Jiangxi Province (20171BCD40021).

References

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[15]  Wang Z, Liu D, Lu P, Wang C. 2001. Accumulation of rare earth elements in corn after agricultural application. J. Environ. Qual. 30: 37-45.
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[18]  Fan G Q, Zheng H L, Yuan Z K. 2005. Effects of thulium exposure on IQ of children. J Environ Health. 22: 256-257.
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[24]  Lu G C, Gao Z H, Meng Y X, Chen H, Ren S Y. 1995. Hygienic investigation of different rare earth (RE) mining areas in China: RE levels of farmer’s natural living environment and head hair. CHINESE JOURNAL OF ENVIROMENTAL SCIENCE. 16: 78-82.
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In article      View Article
 
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Published with license by Science and Education Publishing, Copyright © 2020 Yanmin Wang, Hong Zhou, Li Xiong, Chengwei Liu and Xingyong You

Creative CommonsThis work is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

Cite this article:

Normal Style
Yanmin Wang, Hong Zhou, Li Xiong, Chengwei Liu, Xingyong You. Residual levels of Rare Earth Elements in Cereal and Their Health Risk Assessment from Mining Area in Jiangxi, South China. Journal of Food and Nutrition Research. Vol. 8, No. 1, 2020, pp 58-62. http://pubs.sciepub.com/jfnr/8/1/8
MLA Style
Wang, Yanmin, et al. "Residual levels of Rare Earth Elements in Cereal and Their Health Risk Assessment from Mining Area in Jiangxi, South China." Journal of Food and Nutrition Research 8.1 (2020): 58-62.
APA Style
Wang, Y. , Zhou, H. , Xiong, L. , Liu, C. , & You, X. (2020). Residual levels of Rare Earth Elements in Cereal and Their Health Risk Assessment from Mining Area in Jiangxi, South China. Journal of Food and Nutrition Research, 8(1), 58-62.
Chicago Style
Wang, Yanmin, Hong Zhou, Li Xiong, Chengwei Liu, and Xingyong You. "Residual levels of Rare Earth Elements in Cereal and Their Health Risk Assessment from Mining Area in Jiangxi, South China." Journal of Food and Nutrition Research 8, no. 1 (2020): 58-62.
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  • Figure 1. Chondrite-normalized REE distribution patterns for cereals. The REE abundances were normalized to those in chondrite, and then the pattern was achieved by plotting the ratios on a logarithmic scale against the atomic number. The REE in chondrite were assumed to be no fractionation. This could eliminate the abundant changes between odd and even atomic numbers.
  • Table 4. Estimated daily intake (μg/kg bw) of total rare earth oxides via cereal consumption in mining and control areas by different gender/age groups
[1]  Connelly N G, Damhus T, Hartshorn R M, Hutton A T. 2005. In Nomenclature of Inorganic Chemistry IUPAC Recommendations. http://old.iupac.org/publications/ books/author/connelly.html.
In article      
 
[2]  Liu Y, Peng Z, Wei G, Chen T, Sun W D, He J F, Liu G J, Chou C L, Shen C C. 2011. Interannual variation of rare earth element abundances in corals from northern coast of the south china sea and its relation with sea-level change and human activities. Mar Environ Res. 71: 62-69.
In article      View Article  PubMed
 
[3]  Laveuf C, Cornu S, Juillot F. 2008. Rare earth elements as tracers of pedogenetic processes. Compt Rendus Geosci.340: 523-532.
In article      View Article
 
[4]  Balabanova B, Stafilov T, Sajn R. 2015. Lithological distribution of rare earth elements in automorphic and alluvial soils in the Bregalnica river basin. Maced J Chem Chem Eng. 34: 201-212.
In article      View Article
 
[5]  Rollinson H R. 1993. Using Geochemical Data: Evaluation, Presentation, and Interpretation. Longman Scientific and Technical, Essex; Wiley and Sons, New York.
In article      
 
[6]  Liu Y, Diwu C, Zhao Y, Liu X, Yuan H, Wang J. 2013. Determination of trace and rare earth elements in Chinese soil and clay reference materials by ICP-MS. Chin J Geochem. 33:95-102.
In article      View Article
 
[7]  Xiong B K, Zhang S R, Guo B S, Zheng W. 2001. Reviews of the use of REEs-based fertilizer in the past of three decades. Symposium of the use of REEs in agricultural of China. Baotou, P.R. China.
In article      
 
[8]  Naczynski D J, Tan M C, Zevon M, Wall B, Kohl J, Kulesa A, Chen S, Roth C M, Riman R E, Moghe P V. 2013. Rare-earth-doped biological composites as in vivo shortwave infrared reporters. Nat Commun. 4: 2190-2199.
In article      View Article  PubMed
 
[9]  Hutchison A J, Albaaj F. 2005. Lanthanum carbonate for the treatment of hyperphosphatemia in renal failure and dialysis patients. Expert Opin Pharmacother. 6: 319-328.
In article      View Article  PubMed
 
[10]  Zhu J G, Chu H Y, Xie Z B, Yagi K. 2002. Effects of lanthanum on nitrification and ammonification in three Chinese soils. Nutr Cycl Agroecosys. 63: 309-314.
In article      View Article
 
[11]  SCIO(The State Council Information Office of the People’s Republic of China). 2012. Situation and Policy of China’s Rare Earth Industry, White Paper (English Version). http://www.scio.gov.cn/zfbps/ndhf/2012/Document/1175419/1175419.htm.
In article      
 
[12]  Feng L X, Xiao H Q, He X, Li Z J, Li F L, Liu N Q. 2005. Long term effects of lanthanum intake on the neurobehavioral development of the rat. Neurotoxicology and Teratology. 28: 119-124.
In article      View Article  PubMed
 
[13]  Fu F, Akagi T, Yabuki S, Iwaki M. 2001. The variation of REE (rare earth elements) patterns in soil-grown plants: A new proxy for the source of rare earth elements and silicon in plants. Plant Soil. 235: 53-64.
In article      View Article
 
[14]  Zhu F, Fan W, Wang X, Qu L, Yao S. 2011. Health risk assessment of eight heavy metals in nine varieties of edible vegetable oils consumed in China. Food Chem Toxicol. 49: 3081-3085.
In article      View Article  PubMed
 
[15]  Wang Z, Liu D, Lu P, Wang C. 2001. Accumulation of rare earth elements in corn after agricultural application. J. Environ. Qual. 30: 37-45.
In article      View Article  PubMed
 
[16]  Verma S, adav S Y, Singh I. 2010. Trace metal concentration in different Indian tobacco products and related health implications. Food Chem Toxicol. 48: 2291-2297.
In article      View Article  PubMed
 
[17]  Hirano S, Suzuki K T.1996. Exposure, metabolism, and toxicity of rare earths and related compounds. Environ Health Per.104: 85-95.
In article      View Article  PubMed
 
[18]  Fan G Q, Zheng H L, Yuan Z K. 2005. Effects of thulium exposure on IQ of children. J Environ Health. 22: 256-257.
In article      
 
[19]  Zhu W F, Xu S Q. 1996. Investigation on children’s IQ in rare earth area. Chin Sci Bul.l 41: 914-916.
In article      
 
[20]  DIIT (Department of Industry and Information Technology in Jiangxi province), 2018. A Comprehensive Report on the Rare earth and tungsten industry in Dingnan County. http://www.jiangxi.gov.cn/art/2009/7/30/art_5000_274871.html
In article      
 
[21]  USEPA(United States Environmental Protection Agency). 2000. Guidance for Assessing Chemical Contaminant, Data for Use in Fish Advisories, Washington, DC. https://tamug-ir.tdl.org/handle/1969.3/27939.
In article      
 
[22]  Zhu W F, Xu S Q, Shao P P, Zhang H, Feng J. 1997. Investigation on intake allowance of rare earth a study on bio-effect of rare earth in South Jiangxi. Chin Environ Sci. 17: 63-66.
In article      
 
[23]  Zhang H, Feng J, Zhu W F. 1999. Characteristic of rare earth distribution in biologic chains of rare earth rich background regions. Journal of Chinese Rare Earth Society. 17: 365-368.
In article      
 
[24]  Lu G C, Gao Z H, Meng Y X, Chen H, Ren S Y. 1995. Hygienic investigation of different rare earth (RE) mining areas in China: RE levels of farmer’s natural living environment and head hair. CHINESE JOURNAL OF ENVIROMENTAL SCIENCE. 16: 78-82.
In article      
 
[25]  Tyler G. 2004. Rare earth elements in soil and plant systems-A review. Plant and Soil. 267: 191-206.
In article      View Article
 
[26]  Loell M, Albrecht C, Felix H P. 2011. Rare earth elements and relation between their potential bioavailability and soil properties, Nidda catchment (Central Germany). Plant Soil. 349: 303-317.
In article      View Article
 
[27]  Tyler G, Olsson T. 2001. Plant uptake of major and minor mineral elements as influenced by soil acidity and liming. Plant Soil. 230: 307-321.
In article      View Article
 
[28]  Wei Z, Yin M, Zhang X, Hong F, Li B, Tao Y, Zhao G, Yan C. 2001. Rare earth elements in naturally grown fern Dicranopteris linearis in relation to their variation in soils in South-Jiangxi region (southern China). Environ Pollut .114: 345-355.
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[29]  Xu X, Zhu W, Wang Z, Witkamp G. 2002. Distribution of rare earths and heavy metals in field-grown Maize after application of rare earthcontaining fertilizer. Sci Total Environ. 293: 97-105.
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