Food chain
Relation of rice intake and biomarkers of cadmium for general population in Korea

https://doi.org/10.1016/j.jtemb.2017.04.010Get rights and content

Abstract

Environmental exposure to cadmium can cause renal damage. Foods containing cadmium are generally regarded as the main environmental sources of human exposure to cadmium. In this study, foods that are ingested in large amounts, including rice and other types of food with a high concentration of cadmium, were investigated to determine the correlation between the foods’ cadmium content and biomarkers. The datasets required for this study, including blood cadmium concentration, biomarker concentration, and data on the amount of consumption by food item, were obtained from KNHNES. Furthermore, data on food groups with high daily exposure to hazardous amounts of cadmium were obtained by monitoring raw food sources from 2010 to 2012.

The investigation was then followed by correlation analysis, which was performed to assess the relationship between the amount of rice consumption and cadmium concentration. The Pearson coefficient analysis on the relationship between the amount of food consumption and the biomarker showed that the correlation between foods’ cadmium content and blood cadmium and that of between foods’ cadmium content and other biomarkers were confirmed as statistically significant in the case of the cadmium content of white rice, while, in the case of brown rice, it was confirmed by a few biomarkers.

Introduction

Cadmium is found in most natural foods, particularly in grains and seaweed among vegetables, and in fishes and shellfishes among animals. Generally, in Asian countries like South Korea and Japan, where rice is the staple food, exposure to cadmium through rice is known as the major cause of non-occupational exposure to cadmium. Human exposure to cadmium is mostly through foods (90%). Cadmium exposure levels of 30–50 μg/day have been estimated among adults, and these levels have been linked to increased risk of bone fracture, cancer, kidney dysfunction, and hypertension [1], [2]. Diet is considered the main source of Cd intake among non-smokers [3], especially since food cultured in Cd-rich soil constitutes a major source of Cd [4]. The process by which cadmium is absorbed in the gastrointestinal tract depends on one’s intake and nutritional status [5]. The exposure rate through smoking is also somewhat high, while exposure through water or air is not significant [6]. The cadmium absorbed by the body travels through the blood, and approximately 50% will be found in the liver and in the kidneys. Its biological half-life is reported to be between 10 and 30 years in the kidneys [7]. Cadmium does not only have a long half-life, but is also considered a metal accumulated in the body that is hardly excreted or metabolized [6]. Thus, it is a matter of serious concern as the elderly may be more sensitive to Cd damage compared to younger people. Previous studies also revealed that bone damage caused by Cd was more common among elderly women [8], [9], [10]. The cadmium in the body stabilizes as metallothionein, a low molecular derived protein complex, in the liver, kidneys, intestines, and muscles; then, it moves to the kidneys and is excreted with urine, thus leaving no toxic symptoms. A large amount of cadmium, however, cannot form metallothionein and causes toxic symptoms [11].

Changes in the kidney marker beta-2 microglobulin was regarded as a critical endpoint in the risk assessment of cadmium [12], [13], but there are ongoing discussions in the scientific literature concerning other potential critical effects, including bone damage and cancer [14], [15]. Investigations indicate that a critical concentration in urine similar to that established by the EFSA for beta-2 microglobulin also apply to cadmium-induced osteoporosis [16]. Cadmium hinders generative functions, raises the risk of preeclampsia, and causes blood vessel disorders in the testicles in the long term [11]. The absorbed cadmium spreads around the entire body through the blood, but it is mostly accumulated in the liver and in the kidneys [17]. Right after cadmium is absorbed, cadmium concentration in the liver rises dramatically, but it is then slowly redistributed to the kidneys. As absorption continues, the concentrations of cadmium in the liver and in the kidneys also increase [18]. The lethal dose of cadmium is 20–30 g [17]. In the case of acute poisoning, pain in the throat epithelial cells and digestive disorders similar to the symptoms of food poisoning (e.g., nausea, diarrhea, stomach ache, chills, and headache) occur within a few hours after exposure to cadmium. Furthermore, chest pain, coughing, and dyspnea can occur due to the lung disorders caused by excessive cadmium absorption [6], [11]. Chronic exposure to cadmium leads to various kidney disorders, including damage to and atrophy of the epithelial cells. Chronic exposure can also cause hypertension, diabetes, and urinary stones. Hyposthenia, cell fiber formation, glomerular obsolescence, and necrosis can also occur as morphological changes [6]. Chronic toxic effects of cadmium through ingestion can cause gradual histopathologic change in the kidneys, including damage to the proximal tubule epithelial cells, interstitial fibrosis, and damage to the glomerulus basal cells [19]. As signs of biochemical damage to the kidneys, low-molecular proteinuria, diabetes, and aminoaciduria can occur. Cadmium excretion through the urine can increase due to renal tubule impairment [11]. Exposure to cadmium decreases the calcium content of the bones, and cadmium excretion increases through the urine. If the filtering function of the kidneys is damaged, the creatinine level in the blood rises, and the concentration of cadmium in the urine decreases due to the lowered excretion of creatinine.

The IARC classified cadmium into group 1 (carcinogenic to humans) after deeming that there was enough evidence that cadmium can cause cancer in both animals and humans [20], [21]. The EC (European Commission) classified only a few cadmium compounds as potentially carcinogenic (Carcinogen category 2, Annex 1 to the directive 67/548/EEC18) [22].

The EPA specified the carcinogenic degree of cadmium as group B1 (probable human carcinogen) [23]. The cadmium absorbed by the body is mostly discharged through urination and bowel movement. Only a very small portion of the absorbed cadmium is excreted through the urine, however, due to its high accumulation rate in the body. Generally, the excretion rate is no more than 2 μg/day. It can also be excreted through breast milk, amounting to 5–10% of the cadmium concentration in the blood [18].

The cadmium concentration in the blood and the rate of domestic rice consumption were compared in this study to evaluate the correlation between rice consumption and the level of cadmium in the body. As the most consumed type of food daily in South Korea is rice (white rice), and as the main path of cadmium absorption in the country is through ingestion, these factors were considered in the analysis.

Section snippets

Selection and sampling of food products

In the selection of surveyed food products, this study was based on the data obtained from the Korea National Health and Nutrition Examination Survey (KNHANES 2010–2012) on the consumption of marine, agricultural and meat and egg products. The study focused on foods that were commonly consumed in Korea. The levels of cadmium were measured in marine foods (about 120 species), agricultural foods (about 140 species), and meat and egg products (about 20 species) collected from local markets in

Selection of target food items by considering their cadmium concentration, daily exposure, and amount of consumption

The levels of cadmium were measured in the marine (about 120 species), agricultural (about 140 species), and meat and egg (about 20 species) product samples collected in South Korea. Since mollusks tend to contain a high amount of cadmium compared to other food items, the fat innkeeper worm, squid, octopus minor, beka squid, and webfoot octopus were selected as part of the assessment on cadmium concentration. Mollusks tended to show higher levels of average daily dosage (ADD) and risk compared

Discussion

This study was conducted to assess the trend in increasing cadmium exposure due to rice consumption. The contamination levels of the food items sold in South Korea were compared first, before singling out the food groups with higher contamination levels than other groups. Also, the consumption amounts of the target food items were calculated by using the datasets extracted from the Korean National Health and Nutrition Examination Survey, while foods that are consumed in large amounts across the

Conclusion

In this study, the unique characteristics of the body’s heavy-metal exposure based on rice consumption were analyzed. As people in the East primarily eat rice, they tend to ingest a higher amount of rice compared to populations in the West. Also, the impact of cadmium exposure arising from such tendency was investigated. Foods ingested in large amounts and with high cadmium contamination levels were compared as the control group in this study, and the correlation between the amount of food

Acknowledgement

This study was supported by the Institute for Environmental Research, college of medicine, Yonsei University.

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