Heavy Metal Concentrations in Rice from Guangzhou and Associated Health Risks

Transcription

1 January, 2018 Journal of Resources and Ecology Vol. 9 No.1 J. Resour. Ecol (1) DOI: /j.issn x Heavy Metal Concentrations in Rice from Guangzhou and Associated Health Risks CHEN Nengchang *, ZHANG Xiaoxia, ZHENG Yuji Guangdong Institute of Eco-Environmental Science& Technology/Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Guangzhou , China Abstract: In recent years, excessive levels of cadmium (Cd) in rice have been a focus of attention of the government, the public and scientists. In Guangzhou rice is a staple food for most citizens and understanding the level of Cd and other heavy metals in rice is important for food safety and health. Consumers in different income groups purchase rice from various sources at different prices but we know little about the relationship between price and safety. At the same time, the presence of zinc (Zn) can also affect the level of risk from Cd in rice and so affect food safety. This study offers a preliminary exploration of interactions between price, safety and nutritional quality. 125 rice samples were collected from markets and from the homes of high-income, middle-income and low-income groups in Guangzhou city, and were tested for the content of Cd and Zn. The results showed that 25.6% of the rice samples contained Cd in excess of the national standard, with higher levels of Cd in Indica rice than in Japonica. At the same time, we designed a questionnaire survey for groups with different incomes to assess their exposure to risks from rice with Cd and their perceptions and sources of information about risks. The survey showed that, as a whole, the low-income group faces higher risks from rice with Cd, and that there is strong public demand for scientific information about Cd in rice. Key words: rice; cadmium; Guangzhou; risk; groups with different income 1 Introduction Cadmium (Cd) is not an essential element for plants, animals or humans. In the human body, intake of food with high levels of cadmium can lead to fever, renal dysfunction (proteinuria), lung injury (pulmonary emphysema), rhinitis and chronic bronchitis, as well as affecting the bones, resulting in a painful disease known as itai-itai, or tongtongbing in Chinese (Tucker 2011; Nogawa et al., 1996). Hence, increases in cadmium concentrations in soil and crops in recent decades (Jones et al., 1987) have become a focus of attention. Since rice is a staple food in Asia, the effects of cadmium levels in rice on public health have received considerable attention. Japan, where the first known case of itai-itai disease occurred, has been at the forefront of this research, with several studies examining the relationship between cadmium and disease and seeking to assess maximum tolerable intake levels (Nogawa et al., 2017, 2015, 2004; Watanabe et al., 2002; Osawa et al., 2001; Nakashima et al., 1997) These investigations have produced slightly different conclusions regarding maximum acceptable levels of Cd in rice and a number of different standards are in effect in different countries. For example, the current WHO standard is 400 μg Cd kg 1 and this is also the standard currently used in Japan and Taiwan. However, some studies from Vietnam indicate that the 400 μg Cd kg 1 standard may not be protective where people consume large amounts of rice or have relatively low body weight (Minh et al., 2012). Other factors, including the way in which rice is processed and overall Received: Accepted: Foundation: FORHEAD with funding from the Rockefeller Brothers Fund (RBF) *Corresponding author: CHEN Nengchang, ncchen@soil.gd.cn Citation: CHEN Nengchang, ZHANG Xiaoxia, ZHENG Yuji Heavy Metal Concentrations in Rice from Guangzhou and Associated Health Risks. Journal of Resources and Ecology, 9(1):

2 86 Journal of Resources and Ecology Vol. 9 No. 1, 2018 health and nutritional status will also affect levels of cadmium intake and its effects on health (Chaney et al., 1999; Holdaway and Wang, 2018). In order to protect populations with high levels of rice consumption, China has maintained the stricter standard of 200 μg Cd kg 1. An investigation by the Chinese Center for Disease Control and Prevention of the cadmium-polluted area in Maba, Shaoguan, suggested that cadmium in rice should be controlled at the even lower maximum level of 160 μg kg 1 (personal communication). Yet, despite the ongoing debate about standards, it is clear that in light of the high toxicity of cadmium and the close correlation between its levels in rice and a number of severe health effects, it is crucial to keep levels of Cd in rice very low in order to protect public health. Since the beginning of the 21 st century, cadmium rice has become a problem in China with social, economic and health ramifications. In 2002, cadmium concentrations in about 10% of the Chinese rice examined exceeded the national standard, according to an investigation by the Ministry of Agriculture (MOA). In 2006, market research by Nanjing Agricultural University produced similar findings. Yet the results of these studies were not well publicized (Zhen Yanhong et al., 2008). In 2009, the problem of cadmium rice began to catch the attention of newspapers run by the Nanfang Media Group. In 2011, an article entitled Deadly Cadmium Tainted Rice (Gemi Shaji in Chinese) appeared on the popular website, caixin.com, and finally managed to focus the attention of the government and the society on excessive cadmium levels in rice and the associated health risks. In February of 2013, a year that might be called The Year of Cadmium Rice, an article entitled Hunan's Problematic Rice Goes to Guangdong's Dining Tables caused public alarm (Nanfang Daily, nfdaily/html/ /27/ content_ htm). In April the Guangdong Food and Drug Administration announced that among 18 batches of rice investigated, 44.7% had cadmium levels that were above the national standard ( htm). Against a backdrop of intense pressure from the public, a thorough investigation of the cadmium content of rice and the safety situation regarding rice in Guangdong markets was conducted. It found that cadmium rice was coming mainly from Hunan province; and that about 35% of rice from the province contained cadmium levels in excess of the national standard. However, we still know little about current levels of cadmium in rice on the market and the severity of the health risks to different groups remains unknown. Understanding these differences is important because some of the factors that affect the impact of cadmium on health are likely to be affected by income and by other dimensions of living conditions and lifestyle, for example the composition of the diet, nutritional status, smoking habits, etc. These differences may be very pronounced in China, where economic inequality is high and people of different income levels have access to very different sources of food. Since the presence or absence of other substances protective to health, such as Zn affect the way in which cadmium is metabolized by the body (Chaney et al., 1999), it is also important to understand variation in these in relation to levels of Cd. Our research sought to make a preliminary exploration of some of the factors that may affect the severity of risks from cadmium in rice and the distribution of risk within the population through a study of rice on sale in markets in Guangzhou. Because, there is reason to suspect that they might be most severely affected, we were particularly concerned to assess the risks to low-income groups. 2 Methods This study used two sampling methods: (1) We collected samples from the homes of residents from three communities in Guangzhou city that represented low-income (migrant population), middle-income, and high-income groups. Each community contributed approximately one third of the total sample. To ensure effective sampling, we obtained 62 rice samples. Considering that zinc can inhibit risks from heavy metals in rice, we tested the samples for cadmium and zinc. In addition, we used a questionnaire to gather information about rice consumption, rice brands and other issues from local residents in these three communities. Based on these data, we made a preliminary assessment of the risks to health for different population groups from cadmium in rice in Guangzhou in (2) We studied the distribution of Guangzhou-based supermarkets and markets for agricultural products where rice is available. On the basis of this, we acquired 63 rice samples from supermarkets, markets for agricultural products and other purchase locations, noting the prices, possible production places, purchase channels and other information. We then analyzed the levels of cadmium and zinc and other elements in these different rice samples. We used this data to more clearly understand the places where different resident groups purchased rice, and to determine if there were correlations between the income and level of education of residents and food safety risks. Rice samples were ground to <0.15 mm for analysis. Rice powder samples (0.25 g) were then digested with 4 ml HNO 3 and 1 ml HClO 4, and the concentrations of Cd and Zn were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES, Perkin Elmer DV3300). 3 Results 3.1 Levels of cadmium in rice and resulting risks The China National Food Safety Standard: Maximum Limit of Contaminants in Food (GB ) stipulates that the level of cadmium in rice cannot exceed 200 μg kg 1. Standards set by WHO (CODEX STAN , Rev ),

3 CHEN Nengchang, et al.: Heavy Metal Concentrations in Rice from Guangzhou and Associated Health Risks 87 Japan (Notification No. 183, Japanese Ministry of Health, Labor and Welfare, 2010), and Chinese Taiwan (Wei Shu Shi Zi Announcement No ) stipulate that cadmium levels are not to exceed 400 μg kg 1. Fig.1 shows the levels of cadmium in the rice samples collected for this study. The minimum content was zero and the maximum content was 1041 μg kg 1. About one third of the samples contained extremely low levels of cadmium. However, 25.6% of the samples exceeded Chinese national standard of 200 μg kg 1 for Cd in rice, and 5.6% of the samples exceeded the WHO standard of 400 μg kg 1. This indicates that excessive levels Cd in the rice in Guangzhou markets is a problem that must not be ignored. Research has shown that different rice varietals have different propensities to absorb heavy metals. Our research bears this out. Fig.1 shows the levels of cadmium in the rice samples of different types. Rice in Guangzhou markets is either Indica rice produced mainly in southern China, or Japonica rice produced in central and northern China. Of the 125 rice samples, 28 were Japonica and 97 were Indica; there were 3.46 times more Indica samples than Japonica samples. This shows that Indica rice is the staple food in Guangzhou (Tab.1), which is not surprising given that the city is located in southern China. Fig. 1 shows that although one Japonica sample had cadmium level in excess of the national standard, most had very low cadmium content. In contrast, even if they did not exceed the standard, the Indica samples generally contained a certain amount of cadmium. Japonica and Indica rice were found to contain, on average, 30 μg kg 1 and 180 μg kg 1 of cadmium, respectively. The average for Indica rice was therefore just below the current Chinese GB standard. However, 32% of the Indica samples contained cadmium in excess of the standard, and due to the dominance of Indica in Guangzhou this meant that 25.6% of all the rice samples contained cadmium in excess of the standard. Although there was one exception, due to the fact that Japonica rice was mixed with some Indica rice for sale in the supermarket, our results confirm the findings of previous research that Japonica rice is generally safer and that Indica rice is more likely to be hazardous to health. 3.2 Sources of rice samples collected from private homes In order to shed light on the distribution of risks from cadmium in rice, our questionnaire survey explored patterns of rice consumption and the sources of rice among Guangzhou residents of different socioeconomic groups including low income migrants, and middle and high income residents. We found that rice was the staple food for 77.8% of respondents and that 81.7% consumed Indica rice (Tab. 1). Although we do not have precise consumption levels, given the relatively high levels of cadmium in Indica, this dependence on it as a staple food suggests that many people in the city are potentially being exposed to excessive levels of cadmium. Of the 62 samples collected from homes of residents from the three communities, we were able to document the source for 56 of them and these are shown in Table 2. We found considerable differences in the levels of cadmium in rice sourced from different channels. Although these represented a very small percentage of the sample, rice received as a gift was the safest and rice samples from online shopping and home-delivery services contained the most cadmium. The majority of respondents (64.3%) purchased their rice from supermarkets and it is encouraging that, on average, rice from this source contained cadmium levels below half of the national standard; and rice from the second major supply source, agricultural product markets, only slightly exceeded it. However, the highest levels of cadmium detected in rice from these sources were in excess of the Chinese national standard and some rice from the agricultural product store also exceeded the laxer WHO standard. This shows that even in these more highly regulated contexts, some unsafe rice is being sold. Fig. 1 Levels of cadmium in Indica and Japonica rice Table 1 Staple food of the residents in Guangzhou Rice Staple food Indica rice Japonica rice 18.3 Wheat flour 0 Rice & wheat flour Level of Zn in the Rice Samples Research has established that levels of dietary zinc, to a lesser extent, influence the absorption of cadmium and its distribution in organs and tissues (Chaney et al., 2001; Fox et al., 1979; Reeves and Chaney, 2001; Reeves and Vanderpool, 1998). We therefore tested the 125 rice samples from residential homes and rice markets for zinc. Although we cannot offer a detailed analysis here, we briefly discuss some of the implications of this variation. Research has shown that if the ratio of cadmium to zinc (Cd/Zn) is less than in rice grains, the risk of cadmium to human health is much lower (Chaney et al., 2005). Fig.2 illustrates the implications of this variation in levels

4 88 Journal of Resources and Ecology Vol. 9 No. 1, 2018 Table 2 Levels of cadmium in rice samples from different sources Supermarket Rice store Market for agricultural products Wholesale market Delivery Online shopping Gift Average Value (μg kg 1 ) Maximum (μg kg 1 ) Minimum (μg kg 1 ) Amount of Samples in excess of Chinese standard of total sample of zinc by examining the Cd/Zn ratio in the samples. It shows that rice with low zinc content will not be safe even if its cadmium content is less than 200 μg kg 1 (e.g. the rice sample in Fig. 1 which contained 185 μg kg 1 of Cd). Rice containing high zinc content, however, will be comparably safe even if its cadmium content exceeds the sample (e.g. the rice sample in Fig. 1 which contained 240 μg kg 1 of Cd). Another major goal of our study was to explore the distribution of risks from cadmium in rice across people in different socioeconomic groups and with different levels of education. We divided the 62 respondents to our questionnaire into the following six groups by educational level: elementary school, junior middle school, senior middle school/secondary vocational school, undergraduate/other postsecondary education, Master's degree, and PhD. Fig. 3 shows the average level of cadmium in the rice consumed by respondents of different educational groups. Although the number in this group was small (n=4), the rice eaten by respondents with a PhD was the safest. However, the relationship between safety and education level was not linear. The rice consumed by the group with elementary school education was safer than that consumed by the group with junior middle school education and also safer than that consumed by the group with Master's degrees. Rice consumed by the group with senior middle school or secondary vocational school and those with undergraduate or other postsecondary education was also safer than that consumed by those with Master's degrees, but still less safe than that consumed by the group with elementary school education. Fig. 2 Ratio of cadmium to zinc and levels of cadmium in rice 3.4 Risks from Cadmium in Rice for Different Groups Fig. 3 Relationship between education and levels of cadmium in rice The number of respondents in each category is too small for us to draw firm conclusions from these findings, and the reasons for these differences are also likely to be complex and need to be further explored. However, we can suggest some possible explanations relating to the financial circumstances and supply channels available to different groups. Respondents with junior middle school education are mostly blue-collar and/or workers, and those with Master's degrees are at a time in their lives when they are busy with marriage arrangements and seeking to purchase a house after graduation, so both groups may have relatively tight financial situations and be more likely to buy inexpensive rice with a higher risk of contamination. Rice consumed by the group with elementary school education is often home-grown or obtained from friends, and likely to be safer. Respondents with PhDs would often be more settled in their careers and have greater financial resources as well as better access to information about food safety. We also divided respondents into three income groups: low income (annual income of less than CNY ); mid-

5 CHEN Nengchang, et al.: Heavy Metal Concentrations in Rice from Guangzhou and Associated Health Risks 89 dle income (annual income of CNY ); and high income (annual income greater than CNY ). Here again, the results show that the picture is not entirely straightforward, with some high cadmium samples appearing in the homes of high income residents (see Fig.4). However, on the whole, low-income groups probably still suffer higher risks from cadmium intake, because they generally have a less varied diet and eat more rice. Fig.5 shows that, overall, expensive rice is safe, and unsafe rice is cheap. However, although the most expensive rice was the safest, there was wide variation in cadmium levels in inexpensive rice. Fig. 4 Relationship between income and levels of cadmium in rice Fig. 5 Relationship between the price of rice and cadmium levels 3.5 Demand for rice safety information Our survey also sought to understand where people obtained information about the safety of rice, and what they knew. Tab.3 shows that 77% of respondents got their information Table 3 Perceptions of heavy metal pollution Ways of getting cadmium rice information Fear that they are consuming cadmium rice Causes of cadmium rice TV 25.3 Industrial Yes 77.6 pollution 44.4 Newspaper 21.5 Water pollution No Internet reports 30.4 Over fertilization 6.9 Mobile phone 6.3 Other reasons 11.1 Friends 7.6 Other ways 8.7 from TV, newspaper and internet reports. Among those 77% of the questionnaire respondents, 77.6% feared that they are consuming cadmium rice, and about 81.9% thought that cadmium rice comes from places with high levels of water or industrial pollution. This shows that, at least for our sample, public fear about cadmium rice is considerably greater than the actual risk to which they are exposed. Our survey found strong demand for more information about the problem of cadmium in rice and risks to health. As shown in Table 4, 98.1% of the respondents were eager to obtain information about safety guidelines for cadmium in rice, and 84.6% wanted to attend informational lectures about cadmium in rice or other food safety problems. Table 4 Scientific information demands To obtain information about safety guidelines for Cd in rice To attend informational lectures about Cd in rice or other food safety problems Yes 98.1 Yes 84.6 No 1.9 No Conclusions In light of concern about the prevalence of cadmium rice on sale in markets in China, this study has offered a preliminary exploration of levels of cadmium in rice from a number of different sources of supply in Guangzhou. It also examined patterns of risk from cadmium in rice across population groups of different socioeconomic and educational status. We found that a quarter (25.6%) of the 125 rice samples we collected from Guangzhou residents and rice suppliers contained levels of cadmium which exceeded the national standard for cadmium and the percentage of samples of Indica rice exceeding the standard (35%) was considerably higher than that of Japonica rice. Given that 77.8% of respondents to our survey said that rice was their staple food, and 81.7% said that they consumed Indica rice, this means that many Guangzhou residents are potentially exposed to excessively high levels of cadmium. However, their actual level of exposure will depend upon how much rice they consume, as well as whether or not they are exposed to cadmium through other foods, through smoking or in their work environment. The impact of cadmium on health is also mediated by other factors including general health status and nutrition which this study did not investigate. To the extent that it is possible, however, it would be advisable for people who eat a lot of rice to vary the type of rice they consume, and, in particular, not restrict themselves to Indica rice from one source. We also found variation in levels of cadmium from different sources of supply. Most respondents (64.3%) purchased rice from supermarkets and agricultural product markets which were relatively safe sources of supply. However, even in these quite highly regulated contexts, some

6 90 Journal of Resources and Ecology Vol. 9 No. 1, 2018 rice samples contained excessively high levels of cadmium, indicating that tighter supervision is necessary. We did not find a linear relationship between levels of cadmium in rice consumed by population groups with different levels of education or income, or between price and cadmium levels. In fact, we found that individuals with middle school education and Masters degrees had a higher risk than other groups, and although the most expensive rice was the safest, there was wide variation in cadmium levels in inexpensive rice. This suggests that financial circumstances and available sources of supply interact to shape levels of risk in complex ways. Overall, lower income groups probably face the highest risk of exposure to cadmium through rice because their consumption levels are higher and their overall nutritional status is likely to be worse. However, these relationships require more detailed research in order to provide targeted protection and advice to vulnerable groups. Our study also explored the relationship of levels of Zn protective to health. When zinc levels in rice are taken into consideration in the cadmium risk assessment, we see that rice with higher levels of zinc can be safe even when it somewhat exceeds the 200 μg kg 1 threshold value for cadmium, while rice with lower levels of zinc may be risky even when it is within the standard for cadmium. Our survey showed that public awareness of the problem of cadmium rice in Guangzhou is high, with the media the major source of information. The percentage of respondents who feared that they were consuming cadmium rice was considerably higher than the percentage who are likely to be at risk. In addition to better regulation to ensure the safety of rice on sale in China s cities, there is also clearly a great need for better public education about the problem and ways in which consumers can protect themselves until such time as all rice on the market meets safety standards. This concern was reflected in strong demand among our respondents for more reliable scientific information about food safety. References Chaney R L, J S Angle, M S Mcintosh, et al Using hyperaccumulator plants to phytoextract soil Ni and Cd. Zeitschrift Fur Naturforschung Section C-a Journal of Biosciences, 60(4): Chaney R L, P G Reeves, and J S Angle Rice plant nutritional and human nutritional characteristics role in human Cd toxicity. In: Horst WJ (Ed.), In Plant Nutrition: Food Security and Sustainability of Agro- Ecosystems Through Basic and Applied Research, The Netherlands, Kluwer Academic Publishers/Dordrecht, Chaney R L, J A Ryan, Y M Li, et al Soil Cadmium as a Threat to Human Health. In: McLaughlin MJ and Singh BR eds. Cadmium in Soils and Plants. Kluwer Academic Publishers. 85: Department of Health, Executive Yuan, Limit Standard for Heavy metals in Edible Rice. Wei Shu Shi Zi Announcement No (in Chinese) Fox MRS, R M Jacobs, AOL Jones, et al Effects of nutritional factors on metabolism of dietary cadmium at levels similar to those of man. Environmental Health Perspectives, 28(28): Jones K C, C J Symon, and A E Johnston Retrospective analysis of an archived soil collection II Cadmium. Science of The Total Environment, 67(1): Holdaway J, and W Y Wang From soil pollution to cadmium rice to public health impacts: An interdisciplinary analysis of influencing factors and possible responses. Journal of Ecology and Resources, 9(1): Minh N D, R Hough, L T Thuy, et al Assessing dietary exposure to cadmium in a metal recycling community in Vietnam: Age and gender aspects. Science of the Total Environment, 416(2): Nogawa K, and M Kido Itai-itai disease and health effects of cadmium. In: Chang, L.W. (Ed.), Toxicology of Metals, CRC Lewis Publishers, NY, pp Nogawa K, T Kido, M Nishijo, et al Benchmark dose of cadmium concentration in rice for renal effects in a cadmium-polluted area in Japan. Journal of Applied Toxicology, 35(1): Nogawa K, E Kobayashi, Y Okubo, et al Environmental cadmium exposure, adverse effects and preventive measures in Japan. BioMetals, 17(5): Nogawa K, M Sakurai, and M Ishizaki Threshold limit values of the cadmium concentration in rice in the development of itai-itai disease using benchmark dose analysis. Journal of Applied Toxicology, 37: Nakashima K, E Kobayashi, K Nogawa, et al Concentration of cadmium in rice and urinary indicators of renal dysfunction. Occupational and Environmental Medicine, 54(10): National Health and Family Planning Commission of the People's Republic of China, China Food and Drug Administration, National food safety standard. Maximum levels of contaminants in foods GB (in Chinese) Osawa K, E Kobayashi, Y Okubo, et al A retrospective study on the relation between renal dysfunction and cadmium concentration in rice in individual hamlets in the Jinzu River basin. Toyama Prefecture, Japan. Environmental Research, 86(1): Reeves P G, and R L Chaney Mineral nutrient status of female rats affects the absorption and organ distribution of cadmium from sunflower kernels (Helianthus annuus L.). Environmental Research, 85(3): Reeves P G, and R A Vanderpool Organ content and fecal excretion of cadmium in male and female rats consuming variable amounts of naturally occurring cadmium in confectionery sunflower kernels (Helianthus annuus L.). 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7 CHEN Nengchang, et al.: Heavy Metal Concentrations in Rice from Guangzhou and Associated Health Risks 91 陈能场, 张晓霞, 郑煜基 广东省生态环境技术研究所 / 广东省农业环境综合治理重点实验室, 广州 摘要 : 镉不是人体的必需元素, 镉的摄入对人体健康带来威胁 近年来, 大米中镉含量超标问题引起了政府 公众和科学家的高度重视 在中国南方的广州, 大米是大多数市民的主食, 了解大米中镉和其他重金属的含量对食品安全和健康至关重要 不同收入群体的消费者以不同的价格购买不同来源的大米, 但对价格与安全的关系知之甚少 同时, 锌的存在也会影响水稻 cd 的风险水平, 从而影响食品安全 本研究对价格 安全和营养品质之间的相互作用进行了初步探讨 本文以广州为调查地点, 通过从市场商店采购和高 中和低收入群体搜集获得了 125 大米样本, 分析了这些样品中的 Cd 和 Zn 及其健康风险 结果表明, 在调查的样本中,25.6% 大米含 Cd 超标, 籼米含镉量较高 另一方面, 我们对不同收入群体进行了问卷调查, 以评估其在大米中镉风险的暴露情况及其规避风险的途径, 以及他们对风险信息的看法和来源 根据调查结果, 从总体上看, 低收入群体面临着较高的 Cd 风险, 公众迫切需要获得关于稻米中 Cd 的科普知识 关键词 : 水稻 ; 镉 ; 广州 ; 风险 ; 不同收入群体